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Molten wax spray treatment makes oriented strandboard (OSB) more water repellent and reduces thickness… Lotter, Barend Theron 2014

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    MOLTEN WAX SPRAY TREATMENT MAKES ORIENTED STRANDBOARD (OSB) MORE WATER REPELLENT AND REDUCES THICKNESS SWELLING   by BAREND THERON LOTTER B.Sc., The University of Stellenbosch, 2007  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF  THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTRAL STUDIES  (Forestry)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)  April 2014 © Barend Theron Lotter, 2014   ii  Abstract When oriented strandboard (OSB) absorbs moisture its compressed wood strands swell up and recover strains that were induced during hot pressing.  Adhesive bonds that hold the strands together rupture and permanent thickness swelling occur.  Few post-treatments are able to effectively reduce the thickness swelling of OSB.  OSB is porous, with inter-strand voids up to 1.5 mm in diameter.  Surface coatings are less effective at restricting moisture ingress into OSB than into solid wood, because of the irregular surface of OSB.   Molten wax has a low viscosity and may be able to flow into and block the inter-strand voids of OSB.  In this thesis I hypothesize that the water repellency and dimensional stability of OSB may be improved by spraying molten wax onto the hot surface of the board.    Furthermore, I hypothesize that polar and low melting point waxes will form more effective water repellent barriers than nonpolar or high melting point waxes.  The properties of 13 different waxes and five custom made wax blends were characterized with emphasis on properties likely to influence the water repellency of OSB.  Molten waxes were sprayed onto the surface of hot OSB and the water absorption and thickness swelling of the samples were measured.  Wax treatments were able to reduce the rate of water absorption and the rate of thickness swelling, but not the extent thickness swelling.  I conclude that wax treatments are able to increase the water repellency of OSB and reduce the thickness swelling during short-term periods of exposure to water. Waxes with high melting point temperatures tended to form more effective water-repellent barriers, especially for short-term exposure periods, contrary to my hypothesis.  Blends of pure beeswax, which contains polar functional groups, and strongly hydrophobic waxes, such as paraffin wax, formed excellent water-repellent barriers. The results suggest that a combination of polar and nonpolar wax is more effective at reducing the thickness swelling of wax-treated OSB than waxes that contain only hydrophobic components.     iii  Preface This thesis is original and unpublished work of Barend Theron Lötter.  Support and technical assistance from my supervisor, supervisory committee members and colleagues is gratefully acknowledged (pp. xix).       iv  Table of contents  Abstract ............................................................................................................................................ ii Preface ............................................................................................................................................ iii Table of contents  ........................................................................................................................... iv List of tables .................................................................................................................................. viii List of figures ................................................................................................................................... ix List of abbreviations ................................................................................................................... xviii Acknowledgements ...................................................................................................................... xix Dedication  .................................................................................................................................... xx Chapter 1.  Introduction .................................................................................................................. 1 1.1.  General introduction ........................................................................................................... 1 1.2.  General hypothesis ............................................................................................................. 4 1.3.  Outline of thesis .................................................................................................................. 5 Chapter 2.  Literature review ........................................................................................................... 7 2.1.  History and current markets ............................................................................................... 7 2.1.1.  A brief history of oriented strandboard ...................................................................... 7 2.1.2.  Current markets ........................................................................................................... 8 2.2.  Water absorption and thickness swelling ......................................................................... 11 2.2.1.  Water absorption ....................................................................................................... 11 2.2.2.  Thickness swelling ...................................................................................................... 12 2.2.3.  Industry standards for measuring thickness swelling ............................................... 14 2.3.  Factors that affect thickness swelling ............................................................................... 14 2.3.1.  Raw materials ............................................................................................................ 15 2.3.1.1.  Wood species ........................................................................................................ 15 2.3.1.2.  Strand geometry and orientation ......................................................................... 16 2.3.1.3.  Resin content ........................................................................................................ 17 2.3.1.4.  Wax sizing ............................................................................................................. 18 2.3.2.  Board density ............................................................................................................. 18 2.3.3.  Porosity ...................................................................................................................... 19 2.4.  Treatments that reduce thickness swelling ...................................................................... 21 2.4.1.  Thermal modification ................................................................................................ 22  v  2.4.2.  Chemical treatments ................................................................................................. 25 2.4.3.  Film-forming surface coatings ................................................................................... 27 2.4.4.  Penetrating water-repellent treatments ................................................................... 29 2.5.  Waxes and their properties .............................................................................................. 30 2.5.1.  Origin ......................................................................................................................... 31 2.5.2.  Chemical composition ............................................................................................... 31 2.5.3.  Water repellency ....................................................................................................... 32 2.5.4.  Melting point temperature ........................................................................................ 35 2.6.  Summary ........................................................................................................................... 37 Chapter 3.  Wax properties that affect the water repellency of wax-treated OSB ....................... 39 3.1.  Introduction ...................................................................................................................... 39 3.2.  Materials and methods ..................................................................................................... 40 3.2.1.  Waxes ......................................................................................................................... 40 3.2.2.  Contact angle measurements .................................................................................... 42 3.2.2.1.  Experimental design ............................................................................................. 42 3.2.2.2.  Sample preparation .............................................................................................. 43 3.2.2.3.  Contact angle measurements ............................................................................... 44 3.2.3.  Surface confocal profilometry ................................................................................... 46 3.2.3.1.  Surface roughness measurements on pure wax surfaces .................................... 46 3.2.3.2.  Profilometry image rendering .............................................................................. 47 3.2.4.  Scanning electron microscopy ................................................................................... 47 3.2.5.  Melting point temperatures ...................................................................................... 49 3.2.5.1.  Congealing point: ASTM D938 – 12 ...................................................................... 49 3.2.5.2.  Drop melting point: ASTM D127 – 08. .................................................................. 50 3.2.6.  Viscosity ..................................................................................................................... 51 3.2.7.  Acid number titration ................................................................................................ 51 3.2.8.  Fourier transform infrared (FTIR) spectroscopy ........................................................ 52 3.2.9.  Statistical methods .................................................................................................... 52 3.3.  Results ............................................................................................................................... 53 3.3.1.  Contact angles ........................................................................................................... 53 3.3.1.1.  Glass slides coated with different wax types ....................................................... 53 3.3.1.2.  OSB samples treated with different wax types .................................................... 55  vi  3.3.2.  Surface confocal profilometry ................................................................................... 57 3.3.2.1.  Surface roughness measurements of wax-coated glass slides ............................ 57 3.3.2.2.  Profilometry images ............................................................................................. 58 3.3.3.  Scanning electron microscopy ................................................................................... 61 3.3.4.  Melting point temperature ........................................................................................ 64 3.3.5.  Viscosity ..................................................................................................................... 65 3.3.6.  Acid number titration ................................................................................................ 66 3.3.7.  Relationships between contact angles on pure wax and on wax-treated OSB surfaces  .................................................................................................................... 67 3.3.8.  Relationships between contact angles and melting point temperatures ................. 69 3.4.  Discussion .......................................................................................................................... 71 3.5.  Conclusion ......................................................................................................................... 75 Chapter 4. Effects of wax treatments on thickness swelling........................................................ 77 4.1.  Introduction ...................................................................................................................... 77 4.2.  Materials and methods ..................................................................................................... 79 4.2.1.  Experimental design .................................................................................................. 79 4.2.2.  Waxes ......................................................................................................................... 80 4.2.3.  Oriented strandboard ................................................................................................ 81 4.2.4.  Sample preparation ................................................................................................... 81 4.2.5.  Wax application ......................................................................................................... 83 4.2.6.  Thickness swelling measurement .............................................................................. 85 4.3.  Results ............................................................................................................................... 86 4.3.1.  Wax application and physical appearance of wax-treated samples ......................... 88 4.3.2.  Effect of wax type on total thickness swelling .......................................................... 89 4.3.3.  Effect of wax treatment and wax type on the rate of thickness swelling ................. 90 4.3.4.  Effect of wax treatment and wax type on thickness swelling ................................... 95 4.3.5.  Relationship between wax melting point and thickness swelling ............................. 98 4.4.  Discussion .......................................................................................................................... 98 4.5.  Conclusion ....................................................................................................................... 103 Chapter 5.  Effects of wax polarity and melting point temperature on water absorption and thickness swelling ................................................................................................... 104 5.1.  Introduction .................................................................................................................... 104  vii  5.2.  Materials and methods ................................................................................................... 106 5.2.1.  Experimental design ................................................................................................ 106 5.2.2.  Waxes ....................................................................................................................... 107 5.2.3.  Oriented strandboard .............................................................................................. 107 5.2.4.  Sample preparation ................................................................................................. 108 5.2.5.  Wax application ....................................................................................................... 109 5.2.6.  Water absorption and thickness swelling measurement ........................................ 110 5.3.  Results ............................................................................................................................. 111 5.3.1.  Relationship between water absorption and thickness swelling ............................ 114 5.3.2.  Wax application and physical appearance of wax-treated samples ....................... 115 5.3.3.  Effect of wax treatments and wax type on water absorption................................. 116 5.3.4.  Effect of wax treatments and wax type on thickness swelling ............................... 123 5.3.5.  Effects of initial moisture content on water repellency, water absorption and thickness swelling ................................................................................................... 134 5.3.6.  Effects of water repellency of wax-treated surfaces on water absorption and thickness swelling ................................................................................................... 137 5.3.7.  Effects of melting point temperatures on water absorption and thickness swelling            ................................................................................................................................ 139 5.4.  Discussion ........................................................................................................................ 142 5.5.  Conclusion ....................................................................................................................... 147 Chapter 6.  General discussion, suggestions for further research and conclusions ................... 149 6.1.  General discussion .......................................................................................................... 149 6.2.  General conclusions ........................................................................................................ 152 6.3.  Suggestions for further research .................................................................................... 153 Bibliography ................................................................................................................................. 156 Appendices .................................................................................................................................. 170 Appendix 1 - Chapter 3 ........................................................................................................... 170 Appendix 2 - Chapter 4 ........................................................................................................... 185 Appendix 3 - Chapter 5 ........................................................................................................... 191    viii  List of tables Table 3.1. The 13 waxes and five wax blends used to treat OSB ................................................. 42 Table 3.2. Summary of the ANOVA for the initial contact angles of 5 µL water droplets and the time it took droplets to form contact angles of less than 90° (t<90°) on wax-coated slides and wax-treated OSB surfaces (averaged across all wax types) ......................................................... 53 Table 3.3. Melting point temperatures of different waxes measured according to ASTM D938-12 and ASTM D127 08 .................................................................................................................. 65 Table 3.4. Apparent viscosity of different waxes according to ASTM D2669-06 ......................... 66 Table 3.5. Empirical acid number of waxes according to ASTM D1386-10 ................................. 67 Table 4.1. The origin, melting point tempeatures, and viscosities of seven waxes .................... 80 Table 4.2. Amounts of wax applied to individual samples ........................................................... 85 Table 4.3. The effect of wax treatments on the thickness swelling of OSB samples immersed in water (α = 0.05) ............................................................................................................................ 87 Table 4.4. The effect of wax on the thickness swelling of OSB samples immersed in water (α = 0.05) .............................................................................................................................................. 88 Table 5.1. The names, abbreviations, origin, melting point, and viscosity of 16 waxes ............ 107 Table 5.2. Summary of the amount of each wax type applied to seven samples ..................... 109 Table 5.3. The effects of wax treatments on the water absorption and thickness swelling of OSB samples, and a comparison between wax-treated samples and “moisture resistant” samples.  All samples were floated face down on water for 72 h and measured at 2 h, 24 h, 48 h and 72 h (α = 0.05) ..................................................................................................................................... 112 Table 5.4. The effect of individual wax on the water absorption and thickness swelling of OSB samples that were floated face down on water for 2 h, 24 h, 48 h and 72 h, as well as a comparison between wax-treated samples and “moisture resistant” samples ........................ 113 Table 5.5. Average water absorption of all OSB samples .......................................................... 116 Table 5.6. Average thickness swelling of all OSB samples ......................................................... 123    ix  List of figures Figure 2.1. A typical two-story single family home under construction in West Point Grey, Vancouver, Canada.  Note the large amount of OSB for wall sheathing ........................................ 9 Figure 2.2. A multi-storey building under construction on Marine Drive, North Vancouver, Canada. OSB was used for wall sheathing.  The ground floor is typically used for commercial real estate and the upper levels are for medium density residential accommodation ....................... 10 Figure 2.3. A single-family home under construction in West Point Grey, Vancouver, Canada (left).  The mud and water in the foreground suggests that the building was exposed to rain water.  A close up (right) of OSB wall sheathing that was left unprotected in a rain shower, while the building was under construction ................................................................................... 10 Figure 2.4. Oven dried OSB (left) and the same OSB sample immersed in water for 18 h (right).  Note that the panel edge swelled by almost 4 mm (± 20%) after 18 h ........................................ 13 Figure 2.5. Three types of inter-strand voids in flakeboard, as classified by Furuno et al. (1983)19 Figure 2.6.  Initial contact angle of a 5µL water droplet on a hydrophilic surface (left) and a hydrophobic surface (right).  A solid is considered to be hydrophobic when θ > 90° .................. 33 Figure 3.1. Fischer-Tropsch and paraffin waxes as they were received from Sasol Wax, South Africa .............................................................................................................................................. 42 Figure 3.2. Goniometer equipped with a camera and syringe (left) and  CAM 200 software (right), which was able to calculate the geometry of water droplets using a Young-Laplace algorithm........................................................................................................................................ 45 Figure 3.3. The white-light non-contact confocal profilometer (Altisurf 500 ®, ALTIMET, France) used to scan the surface profiles of pure wax surfaces ................................................................ 46 Figure 3.4. The 12 mm diameter SEM stub with the five wax-treated OSB samples that were examined using scanning electron microscopy: (A) beeswax; (B) carnuaba wax; (C) Merkur 300; (D) Tekniwax 600; (E) Vaseline. ..................................................................................................... 49 Figure 3.5. Initial contact angle of 5µL water droplets placed on glass slides coated with different wax types (n = 11).  Note the large mean initial contact angle of water droplets on stearic acid.  Differences larger than the least significant difference (LSD = 3.02°) are statistically significant at a 5% level.  Clear data points are not significantly different to the data point for a blend for Sasolwax M3M and ethylene maleic anhydride (M3M+EMA). Refer to Appendix 1 for precise numerical values ............................................................................................................... 54    x  Figure 3.6. The time it took for 5µL water droplets to form contact angles of less than 90° on glass slides coated with different wax types (n = 11).  Differences larger than the least significant difference (LSD = 4.73 min) are statistically significant at a 5% level.  Clear data points are not significantly different to the data point for Tekniwax 801 (T801). Refer to Appendix 1 for precise numerical values ...................................................................................... 55 Figure 3.7. Initial contact angle of 5µL water droplets placed on OSB surfaces treated with different wax types (n = 6). Differences larger than the least significant difference (LSD = 9.4°)  are statistically significant at a 5% level.  Clear data points are not significantly (p > 0.05) different to the data point for Merkur 300.  Refer to Appendix 1 for precise numerical values         ....................................................................................................................................................... 56 Figure 3.8. The time it took for 5µL water droplets to form contact angles of less than 90° on OSB surfaces treated with different wax types (n = 6).  Differences larger than the least significant difference (LSD = 9.22 min) are statistically significant at a 5% level.  Clear data points are not significantly different to the data point for a blend of beeswax and Sasolwax C (Bee+Sc). Refer to Appendix 1 for precise numerical values ........................................................ 57 Figure 3.9. Average surface roughness (Ra) of glass slides coated with different wax types (n = 3).  Differences larger than the least significant difference (LSD = 2.61 µm) are statistically significant at a 5% level.   Clear data points are not significantly different to the data point for lanolin (Lan). Refer to Appendix 1 for precise numerical values................................................... 58 Figure 3.10. Profilometry image of the surface of a glass slide coated with stearic acid. The 10 x 10 mm2 image consists of 1177 profile scans, scanned with x-axis spacing of 8.5 µm and y-axis spacing of 8.5 µm.  The gauge resolution for the z-axis was 0.333 nm (Head No.3).  The white and brown areas represent large wax crystals, while the black areas represent unmeasured points that were beyond the 3 mm focal plane of the profilometer head ................................... 59 Figure 3.11. Profilometry images of the surface of a glass slide coated with carnauba wax. The original 5 x 5 mm2 image (left) consists of 1251 profile scans with x-axis spacing of 3.5 µm and y-axis spacing of 4 µm. The area within the dashed white square on the original image is magnified on the right. The gauge resolution for the z-axis was 3.333 nm (Head No.2) ............. 60 Figure 3.12. Profilometry images of the surface of a glass slide coated with microcrystalline wax.  The original 5 x 5 mm2 image (left) consists of 1112 profile scans, scanned with x-axis spacing of 3.5 µm and y-axis spacing of 4.5 µm.  The gauge resolution for the z-axis was 3.333 nm (Head No.2). The magnified image of the area within the dashed white square (right) shows that the surface of microcrystalline wax formed microscopic peaks (white) and valleys (black), similar to those found on the super-hydrophobic surfaces of the leaves of some plant species (Barthlott and Neinhuis 1997) ....................................................................................................... 60    xi  Figure 3.13. Profilometry images of the surface of a glass slide coated with two different petroleum jellies, Vaseline (left)  and  Merkur 300 (right). The 1 x 1 mm2 images consists of 287 profile scans, scanned with x-axis spacing of 3.5 µm and y-axis spacing of 3.5 µm.  The gauge resolution for the z-axis was 3.333 nm (Head No.2) ..................................................................... 61 Figure 3.14. SEM photomicrographs of an OSB surface coated with beeswax.  The lower magnification image (left) shows that wax covered the OSB surface, but that tiny holes were present in the coating. The image on the right showes the area within the dashed white rectangle at a higher magnification ............................................................................................... 62 Figure 3.15. SEM photomicrographs of an OSB surface coated with carnauba wax. The lower magnification image (left) shows that the wax totally covered the OSB surface and formed a smooth coating  with large and small micro cracks at the surface.  The image on the right shows the area within the dashed white rectangle at a higher magnification ........................................ 62 Figure 3.16.  SEM photomicrographs of an OSB surface coated with a Fisher-Tropsch wax (Merkur 300).  The lower magnification image (left) shows that the surface of Merkur 300 is not as smooth as those of beeswax or carnauba wax. The image on the right shows the area within the dashed white rectangle at a higher magnification.  Merkur 300 tended to agglomorate around certain areas ...................................................................................................................... 63 Figure 3.17. SEM photomicrographs of an OSB surface coated with a paraffin wax (Tekniwax 600).  The lower magnification image (left) shows that the surface of Tekniwax 600 appeared to be relatively rough. The image on the right shows the area within the dashed white rectangle at a higher magnification. Crater-like formations were visible on the surface ................................. 63 Figure 3.18. SEM photomicrographs of an OSB surface coated with a Vaseline.  The lower magnification image (left) suggests that some Vaseline was absorbed into the hot OSB surface.  The image on the right shows the area within the dashed white rectangle at a higher magnification. The surface topography of an area coated with Vaseline was very smooth ........ 64 Figure 3.19.  Relationship between (1) the initial contact angle of 5µL water droplets placed on glass slides coated with different wax types and (2) the time it took those droplets to spread and form contact angles of less than 90° on a pure wax surface (α = 0.05) ................................. 68 Figure 3.20. Relationship between (1) the initial contact angle of 5µL water droplets placed on glass slides coated with different wax types and (2) the time it took water droplets placed on wax-treated OSB surfaces to spread and form contact angles of less than 90° (α = 0.05) ........... 69     xii  Figure 3.21. Relationship between (1) the melting point temperatures of the different wax types and (2) the initial contact angles of 5µL water droplets placed on pure wax surfaces (α = 0.05) ............................................................................................................................................... 70 Figure 3.22.  Relationship between (1) the melting point temperatures of the different wax types and (2) the times it took 5µL water droplets to spread and form contact angles of less than 90° on OSB surfaces treated with different wax types (α = 0.05) ......................................... 71 Figure 4.1.  The seven waxes used in this chapter (and one wax that was not included) after dynamic viscosities were measured using a stress-controlled rheometer (Anton Paar MCR 501).  (A) Sasolwax M3M;  (B) Vaseline; (C) carnauba wax; (D) lanolin; (E) Sasolwax C; (F) Tekniwax 600; (G) beeswax ........................................................................................................................... 81 Figure 4.2. An OSB sample prior to application of molten wax .................................................... 83 Figure 4.3. The Champ 10s pneumatic spray gun used to spray molten wax onto the OSB samples. Solid wax is inserted into the temperature controlled heating chamber at the back of the spray gun (left). The contol panel (right) is used to set the pressure inside the heating chamber and spray pressure at the nozzle tip .............................................................................. 84 Figure 4.4.  A schematic drawing of the Champ 10s spray gun’s nozzle assembly.  The spring, the ball and the stopper is housed inside the spray nozzle. The ball and spring is held in place by the stopper, which is screwed into the back of the nozzle. The spray nozzle, with the three parts inside it, is screwed onto the head of the spray gun body. The spray cap is also screwed onto the spray gun body, and it covers the spray-nozzle assembly. Molten wax is forced out of the spray gun when the chamber pressure is high enough to force the ball to compress the spring. A second pneumatic line, at the top of the spray gun body, helps to atomize the molten wax that escapes ................................................................................................................................... 84 Figure 4.5. Eight OSB samples mounted in the swellometer tank and immersed in water (left).  Each sample had one linear variable differential transducer (LVDT) mounted above it, which measured thickness swelling over time. A close up (right) of a LVDT with its footpad zeroed onto the surface of an OSB sample treated with molten Vaseline ............................................... 86 Figure 4.6.  Close up of the surface of OSB sprayed with approximately 270 g /m2  of molten carnauba (left) wax and  Vaseline (right).  Note that the high application rate caused surface coatings to form, even though the OSB samples were hot (170°C) when the waxes were sprayed onto them.  Carnauba wax coatings cracked and flaked off when touched, while Vaseline formed a defect-free coating that filled the surface voids ........................................................... 89    xiii  Figure 4.7.  Effect of wax type on the total thickness swelling of wax-treated OSB samples after 21 days of immersion in water  Non-overlap of error bars indicates that means are significantly different at the 5% level.  The least signficant difference (LSD)  is 0.45 mm ................................ 90 Figure 4.8.  The average thickness swelling of untreated and wax-treated OSB samples that were immersed in water for 24 h (n = 7).  Refer to attached CD for numerical values ................ 91 Figure 4.9.  The average thickness swelling of untreated and wax-treated OSB samples that were immersed in water for 21 days (n = 7).  Refer to attached CD for numerical values ........... 92 Figure 4.10.  Effect of wax treatments on the time it took OSB to reach 25% and 50% total thickness swelling (TTS). Non-overlap of error bars indicates that means are significantly different at the 5% level.  The least signficant difference (LSD) for 25% TTS is 35.7 h and the LSD for 50% TTS is 47.5 h ...................................................................................................................... 93 Figure 4.11.  Effect of wax type on the time it took wax-treated OSB samples to reach 25% and 50% of total thickness swelling (TTS). Non-overlap of error bars indicates that means are significantly different at the 5% level.  The least significant difference (LSD) for 25% TTS is 47.3 h and the LSD for 50% TTS is 62.8 h ................................................................................................. 94 Figure 4.12.  Effect of wax treatments on the thickness swelling of OSB after 2 h, 24 h, 72 h, and 240 h.  Non-overlap of error bars indicates that means are significantly different at the 5% level.  The least signficant differences (LSD) for 2 h, 24 h, 72 h and 240 h are 0.02 mm, 0.13 mm, 0.22 mm, and 0.42 mm, respectively.  Note the different y-axis scales for each plot, always starting at zero ............................................................................................................................................ 96 Figure 4.13.  Effect of individual wax types on the thickness swelling of OSB samples after 24 h, 72 h, and 240 h of immersion in water.  Also included (bottom right) are the melting point temperatures of the different waxes.  Non-overlap of error bars indicates that means are significantly different at a 5% level.  The least significant differences (LSD) for 24 h, 48 h, and 240 h are 0.17 mm, 0.29 mm, and 0.56 mm, respectively ............................................................ 97 Figure 5.1. Samples were floated face down on water for 72 h.  The weight and the thickness of each sample was measured after 2 h, 24 h, 48 h, and 72 h ........................................................ 111 Figure 5.2. The relationship between water absorption and thickness swelling of untreated and wax-treated OSB samples that were floated face down on water for 72 h.  Moisture resistant samples not included ................................................................................................................... 114 Figure 5.3. Relationships between water absorption and thickness swelling of untreated and wax-treated OSB samples that were floated face down on water for 72 h.  Measurements were made after 2 h (top left), 24 h (top right), 48 h (bottom left) and 72 h (bottom right) .............. 115    xiv  Figure 5.4. Average water absorption of: (1) untreated OSB (n = 7); (2) all wax-treated samples (n = 112); (3) OSB samples treated with a blend of beeswax and synthetic beeswax (n = 7); and (4) “moisture resistant” OSB (n = 7).  All samples were floated on water for 72 h and measurements were taken after 2 h, 24 h, 48 h, and 72 h ......................................................... 116 Figure 5.5. Average effect of wax treatments on the water absorption of OSB samples that were floated face down on water for 2 h (left) and 24 h (right), as well as comparison between the water absorption of these samples and those of “moisture resistant” (MR) OSB samples.  Two independent statistical analyses were conducted for each water exposure period (2 h and 24 h), each time comparing the wax treatments to a different control.  The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level.  The least significant difference (LSD) between untreated samples and wax-treated samples after 2 h and 24 h was 0.66 mL and 2.57 mL, respectively (error bars drawn).  The LSD between untreated samples and MR samples after 2 h and 24 h was 0.69 mL and 2.46 mL, respectively (not drawn) ................................................................... 117 Figure 5.6. Average effect of wax treatments on the water absorption of OSB samples that were floated face down on water for 48 h (left) and 72 h (right), as well as comparison between the water absorption of these samples and those of “moisture resistant” (MR) OSB samples.  Two independent statistical analyses were conducted for each water exposure period (48 h and 72 h), each time comparing the wax treatments to a different control.  The two controls (Untreated and MR) have clear data points.   Non-overlap of error bars indicates that means are significantly different at a 5% level.  The least significant difference (LSD) between untreated samples and wax-treated samples after 48 h and 72 h was 4.63 mL and 7.32 mL, respectively (error bars drawn).  The LSD between untreated samples and MR samples  after 48 h and 72 h was 4.61 mL and 7.4 mL, respectively (not drawn) ..................................................................... 118 Figure 5.7. Effect of wax type on the water absorption of wax-treated OSB samples that were floated face down on water for 2 h, as well as a comparison between the water absorption of these samples and “moisture resistant” (MR) OSB samples.  Two independent statstical analyses were conducted, each time comparing the wax treaments to a different control.  The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) between untreated samples and wax-treated samples is 0.91 mL (error bars drawn), while the LSD between MR samples and wax-treated samples is 0.94 mL (not drawn) ............................ 120 Figure 5.8. Effect of wax type on the water absorption of wax-treated OSB samples that were floated face down on water for 24 h, as well as a comparison between the water absorption of these samples and “moisture resistant” (MR) OSB samples.  Two independent statistical analyses were conducted, each time comparing the wax treatments to a different control.  The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) between untreated samples and wax-treated samples is 3.53 mL (error bars drawn), while the LSD between MR samples and wax-treated samples is 3.37 mL (not drawn) ............................ 121   xv  Figure 5.9. Effect of wax type on the water absorption of wax-treated OSB samples that were floated face down on water for 48 h, as well as a comparison between the water absorption of these samples and “moisture resistant” (MR) OSB samples. Two independent statstical analyses were conducted, each time comparing the wax treaments to a different control.  The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) between untreated samples and wax-treated samples is 6.35 mL (error bars drawn), while the LSD between MR samples and wax-treated samples is 6.32 mL (not drawn) ................................... 122 Figure 5.10. Effect of wax type on the water absorption of wax-treated OSB samples that were floated face down on water for 72 h.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) between untreated samples and wax-treated samples is 10 mL ................................................................................ 123 Figure 5.11. Average thickness swelling of: (1) untreated OSB (n = 7); (2) all wax-treated samples (n = 112); (3) OSB samples treated with a blend of beeswax and synthetic beeswax (n = 7): and (4) “moisture resistant” OSB (n = 7).  All samples were floated on water for 72 h and measurements were taken after 2 h, 24 h, 48h, and 72 h .......................................................... 124 Figure 5.12. Average effect of wax treatments on the thickness swelling of OSB samples that were floated face down on water for 2 h (left) and 24 h (right), as well as a comparison between the water absorption of these samples and those of “moisture resistant” (MR) OSB samples.  Two independent statistical analyses were conducted for each water exposure period (2 h and 24 h), each time comparing the wax treatments to a different control. The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) between untreated samples and wax-treated samples after 2 h and 24 h was 0.04 mm and 0.11 mm, respectively (error bars drawn).  The LSD between untreated samples and MR samples after 2 h and 24 h was 0.04 mm and 0.12 mm, respectively (not drawn) ................................................................ 125 Figure 5.13. Average effect of wax treatments on the thickness swelling of OSB samples that were floated face down on water for 48 h (left) and 72 h (right), as well as a comparison between the water absorption of these samples and those of “moisture resistant” (MR) OSB samples. Two independent statistical analyses were conducted for each water exposure period (2 h and 24h), each time comparing the wax treatments to a different control. The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level.  The least significant difference (LSD) between untreated samples and wax-treated samples after 48 h and 72 h was 0.16 mm and 0.19 mm, respectively (error bars drawn).  The LSD between untreated samples and MR samples after 2 h and 24 h was 0.17 mm and 0.2 mm, respectively (not drawn) .................................................................. 126    xvi  Figure 5.14.  Effect of wax type on the thickness swelling of wax-treated OSB samples that were floated face down on water for 2 h, as well as a comparison between the thickness swelling of these samples and “moisture resistant” (MR) OSB samples. Two independent statstical analyses were conducted, each time comparing the wax treaments to a different control. The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) for both statistical analyses is 0.06 mm (error bars drawn) ...................................................................... 128 Figure 5.15. Effect of wax type on the thickness swelling of wax-treated OSB samples that were floated face down on water for 24 h, as well as a comparison between the thickness swelling of these samples and “moisture resistant” (MR) OSB samples. Two independent statistical analyses were conducted, each time comparing the wax treatments to a different control.  The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) between untreated samples and wax-treated samples is 0.15 mm (error bars drawn), while the LSD between MR samples and wax-treated samples is 0.16 mm (not drawn) ........................... 129 Figure 5.16. Effect of wax type on the thickness swelling of wax-treated OSB samples that were floated face down on water for 48 h, as well as a comparison between the thickness swelling of these samples and “moisture resistant” (MR) OSB samples. Two independent statstical analyses were conducted, each time comparing the wax treaments to a different control.  The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) between untreated samples and wax-treated samples is 0.22 mm (error bars drawn), while the LSD between MR samples and wax-treated samples is 0.23 mm (not drawn).................................. 130 Figure 5.17. Effect of wax type on the thickness swelling of wax-treated OSB samples that were floated face down on water for 72 h, as well as a comparison between the thickness swelling of these samples and “moisture resistant” (MR) OSB samples. Two independent statistical analyses were conducted, each time comparing the wax treatments to a different control.  The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) between untreated samples and wax-treated samples is 0.27 mm (error bars drawn), while the LSD between MR samples and wax-treated samples is 0.28 mm (not drawn) ........................... 131 Figure 5.18. The time-delayed thickness swelling of OSB samples treated with different wax types.  Measurements were taken after the samples were floated face down on water for 72 h and then conditioned at 20 ± 1°C and 65 ± 5% r.h. for a minimum of two weeks  and a maximum of four weeks.  Non-overlap of error bars indicates that means are significantly different at a 5% level.  All samples from each individual experimental replication were measured at the same time, irrelevant of their conditioning period ......................................... 133    xvii  Figure 5.19.  Total thickness swelling of untreated and wax-treated OSB samples after they were floated face down on water for 72 h and then conditioned at 20 ± 1°C and 65 ± 5% r.h. for a minimum of two and a maximum of four weeks.  Non-overlap of error bars indicates that means are significantly different at a 5% level.  All samples from each individual experimental replication were measured at the same time, irrelevant of their conditioning period .............. 134 Figure 5.20.  Relationship between (1) the initial moisture content of wax-treated samples that were  oven dried, wax treated and then conditioned at 20 ± 1°C and 65 ± 5% r.h. for a minimum of seven days, and (2) the time it took for 5 µL water droplets to spread over wax-treated OSB surfaces and form contact angles of less than 90° ...................................................................... 135 Figure 5.21.  Relationships between (1) the initial moisture content of wax-treated samples that were oven dried, wax treated and conditioned at 20 ± 1°C and 65 ± 5% r.h. for a minimum of seven days, and (2) the water absorption of the samples after they were floated  face down on water for 2 h (left) and 24 h (right) ............................................................................................. 136 Figure 5.22. Relationships between (1) the initial moisture content of wax-treated samples that were oven dried, wax-treated and conditioned at 20 ± 1°C and 65 ± 5% r.h. for a minimum of seven days, and (2) the thickness swelling of the samples after they were floated  face down on water for 2 h (top left), 24 h (top right), 48 h (bottom left), and 72 h (bottom right) ................ 137 Figure 5.23. Relationships between (1) the times it took for 5 µL water droplets to spread over wax-treated surfaces and form a contact angles of less than 90° (t<90°), and (2) the water absorption of wax-treated OSB samples that were floated face down on water for 2 h (top left), 24 h (top right), 48 h (bottom left), and 72 h (bottom right) ...................................................... 138 Figure 5.24. Relationships between (1) the times it took for 5µL water droplets to spread over wax-treated surfaces and form a contact angles of less than 90° (t<90°) and (2) the thickness swelling of wax-treated OSB samples that were floated face down on water for 2 h (top left), 24 h (top right), 48 h (bottom left), and 72 h (bottom right) ........................................................... 139 Figure 5.25. Relationships between the melting point temperatures of the waxes sprayed onto OSB surfaces and the water absorption of wax-treated samples that were floated face down on water for 2 h (left) and 24 h (right) ............................................................................................. 140 Figure 5.26. Relationships between the melting point temperatures of the waxes sprayed onto the surface of OSB and the thickness swelling of wax-treated samples that were floated face down on water for 2 h (top left), 24 h (top right), 48 h (bottom left), and 72 h (bottom right)          .................................................................................................................................................... 141 Figure 5.27. Relationship between the melting point temperatures of different wax types and the total thickness swelling of wax-treated OSB samples that were floated face down on water for 72 h and then conditioned at 20 ± 1°C and 65 ± 5% r.h. for a minimum of two and a maximum of four weeks .............................................................................................................. 142   xviii  List of abbreviations EMC  Equilibrium moisture content HM  High melting point temperature (> 65°C) IB  Internal bond strength LM  Low melting point temperature (< 65°C) MC  Moisture content MDF  Medium density fibreboard MOE  Modulus of elasticity  MOR  Modulus of rupture  MR  Premium-grade “moisture resistant” OSB OSB  Oriented strandboard PTS  Permanent thickness swelling (springback) r.h.   Relative humidity RTS  Reversible thickness swelling  TS  Thickness swelling TTS   Total thickness swelling measured (i.e. the last measurement of each experiment)  t<90°  Time it took for water droplets to form contact angles of less than 90° WA  Water absorption   xix  Acknowledgements I would like to thank Professor Philip D. Evans for providing me with the opportunity to come to Canada and to pursue innovative research at one of the world’s leading forestry research centers.  Without his support and guidance this thesis would not have materialized. I will always be grateful for the freedom I was given to explore my hypotheses and to learn from my mistakes, and for his infinite patience.  The technical writing skills that Professor Evans taught me will forever be an asset in my life.  Finally, I would like to thank Professor Evans for his courage in pursuing scientific research in its truest sense.  I would like to thank Dr. Simon C. Ellis and Professor Reinhard Jetter for being part of my supervisory committee and for providing me with their expert advice and guidance. I am thankful for the support and friendship of all the members of the Dr. Evans’ research group.  It was an honour to work with and learn from such an internationally diverse group of people.  Special thanks goes to Siti Hazneza for her benevolence and for being our unofficial “lab mummy”.  George Chan, Wenchang He, and Kenny Cheng also deserve a big thank you for their technical assistance. I would like to thank the Faculty of Graduate and Postdoctoral Studies at The University of British Columbia for awarding me the Mary and David Macaree Fellowship Award, and for the people in the Graduate student office of the Faculty of Forestry who recommended me for this award and who provided support during my time at the Faculty (Cindy Prescott , Gayle Kosh,  Dan Naidu, and Robin Poirier-Vasic).  I would also like to thank the technical and administrative staff at the Center for Advanced Wood Processing for their support (Neeta Hundle, Ivy Fung, Genny Go, Lawrence Gunther, Vincent Leung, Diana Hastings, and Winfield Liu) I would like to acknowledge Kevin Blau of Tolko Industries Ltd. for supplying me with OSB panels and Sidney Subramony of Sasolwax (South Africa) for supplying some of the waxes.   My warmest thanks go to Lorien Nesbitt for her encouragement, advice and, most of all, her faith in me. Finally, I would like to thank all my family members for keeping me at home while I was far away.    xx  Dedication To my parents, who’s unwavering love and support is the greatest blessing in my life.  1  Chapter 1. Introduction  1.1 General introduction Oriented strand board (OSB) is a low-cost wood composite, extensively used as a structural panel for residential and commercial construction (Howard and McKeever 2012).  In 2010, OSB accounted for 60% of the U.S. structural panel market (Howard and McKeever 2012).  In 2012, production of OSB in North America reached 15.5 million m3 and European production exceeded 4.9 million m3 (UNECE/FAO 2013).    Structural wood-based composites may represent over 50% of the building materials for residential housing in North America (Moya et al. 2008), with an average-sized single-family home consuming about 1,060 m2 of OSB (Anonymous 2012). OSB is composed of approximately 95% wood, 4% resin and 1% wax sizing (Kline 2005).  Wood accounts for approximately 68% of the raw material cost of OSB, while resin accounts for 25% and wax for 7% (Spelter et al. 2006).  To make OSB, thin, rectangular strands of wood, typically 75 - 150 mm long, 15 - 25 mm wide, and 0.3 - 0.7 mm thick, are blended with thermosetting resin and paraffin wax (Irle and Barbu 2010).  The strands are then arranged into a mat with layers of varying grain direction.  The layer closest to the face of the mat is generally oriented parallel to its length, while the sub-surface layer (or core) is randomly or cross-oriented.  The mat is consolidated in a hot press at platten temperatures of up to 200°C or more (Shmulsky and Jones 2011).  A large amount of pressure (4 – 6 MPa) is required to achieve good contact between the strands (Paridah et al. 2006).  The high pressure compresses and strains the strands, while the thermosetting resin cures.  Hot pressing therefore causes a certain amount of compression strains to set inside the board.     When OSB is exposed to liquid water or high humidity conditions the compressed strands swell and recover some of their original dimensions.  This may cause the adhesive bonds to break which leads to further permanent thickness swelling and losses of mechanical strength (Kelly 1977; Hsu and Bender 1988; Wu and Suchsland 1997; Wu and Piao 1999).  When in service OSB   2  can be exposed to rain and high levels of relative humidity, especially during the early stages of building construction (Winterowd et al. 2003).  The wood strands of OSB are hygroscopic and naturally adsorb and desorb moisture, depending on the relative humidity of their environment.  Boards that undergo large fluctuations in moisture content can swell, shrink and buckle.  Such boards often need to be replaced or sanded level, before construction can continue (Taylor et al. 2008).  Increases in moisture content may also lead to undesirable changes in the appearance of OSB (Biblis 1990) and higher susceptibility to biological attack (Zabel and Morrell 1992).   Moisture ingress into OSB occurs through a series of voids that exist as a result of strands that overlap each other (Suchsland 1962; Maloney 1993; van Houts et al. 2004).  These inter-strand voids are relatively large compared to the natural capillary system in wood (Zhang and Smith 2010b).  Their presence, on the outer surfaces of the panels, makes it difficult to control the water uptake and dimensional stability of the panels, since they provide an easy passage for moisture ingress (Bolton and Humphrey 1994; van Houts et al. 2006; Zhang and Smith 2010b).  The panel edges, for example, have numerous voids (van Houts et al. 2004) that are often coated to prevent excessive edge swelling (Winterowd et al. 2003).   Various different technologies can reduce the thickness swelling of OSB.  These include: (1) modification to production processes, such as changes to the board composition and press parameters; (2) chemical treatments of the strands before pressing (pre-treatment); (3) thermal modification of either the strands (pre-treatment) or the consolidated boards (post-treatment); or (4) the application of surface coatings and water repellents (post-treatment).  These technologies and their shortcomings will briefly be discussed here.   Increasing the resin content of OSB can improve its dimensional stability, but this increases the cost of the product (Forintek Canada Corp. 1998; Shmulsky and Jones 2011).  High performance OSB, with high resin content, is commercially available, but at premium prices.  Another method used to improve the dimensional stability of OSB is to spray wax onto the strands before the boards are pressed.  The wax acts as a water repellent and reduces thickness   3  swelling when boards in service are exposed to water (Winistorfer et al. 1992).  There is, however, an effective limit, of about 2-3%, that can be added to the internal structure of OSB, after which point the water repellency of the board does not significantly increase as wax content increases (Hsu et al. 1990, Winistorfer et al. 1992).  Moreover, the mechanical properties of OSB deteriorate as wax content increases above this limit (Lehmann 1978; Winistorfer et al. 1992; Forintek Canada Corp. 1998)  Chemical treatments can be used to reduce the hygroscopicity of the wood strands before the board is pressed, but such treatments are usually expensive and may reduce the mechanical properties of boards.  The process of acetylation, for example, is able to bulk the cell wall of wood and limit water adsorption, but this process makes the wood strands less wettable and reduces their bonding ability (Rowell et al. 1987; Papadopoulos and Traboulay 2002; Papadopoulos and Gkaraveli 2003).  Another bulking treatment is to impregnate the wood strands with low molecular weight phenol formaldehyde resin before conventional pressing.  This treatment is able to improve the dimensional stability of OSB (Paridah et al. 2006; Wan and Kim 2006), but the cost of extra resin and additional blending and drying equipment restricts the technology to speciality products (Haygreen and Gertjejansen 1971). Thermal modification aims to reduce the hydrophilic nature of OSB.  In general, the literature shows that thermal modification of wood strands prior to pressing can reduce the thickness swelling of OSB, but that mechanical properties are often impaired (Goroyias and Hale 2002; Paul et al. 2006; Ohlmeyer 2007; Mendes et al. 2013).  Thermal post-treatment of OSB has less severe effects on mechanical properties, but it is also less effective at reducing thickness swelling (Ohlmeyer 2007; Mendes et al. 2013).   Surface coatings and water repellents are by far the most common treatments used to reduce water absorption and improve the dimensional stability of solid wood.  Both systems can reduce swelling by preventing water from being absorbed by wood cell walls.  Wood coatings retard the ingress of water by creating a low-permeability barrier film at the wood surface (Orman 1955; Huldén and Hansen 1985; Thomas 1991; Derbyshire and Miller 1996; Derbyshire   4  and Robson 1999), but in order for a coating to be effective the coatings must be complete and free of defects (Stamm and Hansen 1935; Stamm and Seborg 1936; Borgin 1965).  Any cracks or openings that allow the ingress of moisture will reduce the effectiveness of the system, accelerate its degradation, and result in swelling of the underlying wood.  Unfortunately, film-forming coatings are not as effective on OSB as they are on wood.  The large voids in the panel surface may remain uncoated and open for water penetration (Feist 1982; Evans and Cullis 2008). The irregular surface of OSB also makes it difficult to achieve a continuous film, unless large quantities of coating material are used (Grossman 1992; Semple et al. 2009).  Water repellents, however, can be applied to irregular surfaces, such as those of OSB, and may slow the rate of water ingress by creating a sub-surface moisture-resistant barrier.  Wax, for example, can be applied to solid wood to block water pathways and increase the capillary pressure required for spontaneous water absorbtion (Gibson 1965; Borgin and Corbett 1970).  In particleboards, wax sizing is able to form an internal water-repellent barrier that reduces the rate of water absorption (Maloney 1993).  Semple et al. (2009) showed that certain wax emulsions can be sprayed onto OSB to create a water resistant surface, but their results show that the water-based solutions may also cause pre-swelling of the surface strands. Mantanis and Papadopoulos (2010) dipped OSB samples into a water-repellent solution containing paraffin wax and found that this step could reduce the water absorption and thickness swelling of OSB.  1.2 General hypothesis Waxes have melting points as low as 40°C and very low viscosities when they are molten.  At 10°C above their drop melting point temperature, the viscosities of wax are always lower than 10 Pa·s (Wolfmeier et al. 2000).  These properties make it possible to spray wax when it is molten.  In fact, up until the late 1990s waxes incorporated into the body of OSB were sprayed directly onto the flakes before pressing, and were not blended with the resin (Shen 1980; Eckert and Edwardson 1998).  When molten wax is applied to a hot surface, the wax in contact with the surface will remain liquid until the wax cools below its congealing point temperature.    5  The surface temperature of freshly pressed OSB can be as high as 250°C, well beyond the congealing point of most waxes (Wolfmeier et al. 2000).  Hence, when molten wax is sprayed onto the surface of freshly pressed OSB, it may remain liquid for long enough to flow into the voids between the wood strands, at the surface, where it could act as a water repellent barrier once it solidifies.  Accordingly, I hypothesize that moisture resistance and dimensionally stability of OSB will improve when molten wax is sprayed directly onto its surface, while it is hot.  I further hypothesize that low melting point waxes will form more effective water repellent barriers than high melting point waxes, because they will have the ability to flow into inter-strand voids more easily and block moisture ingress into OSB.  1.3 Outline of thesis Following this introduction, Chapter 2 reviews relevant literature focusing on: (1) the history and current markets for OSB; (2) water absorption and thickness swelling of OSB; (3) the factors that influence the thickness swelling of OSB; (4) treatments that have been used to reduce the thickness swelling of OSB; and (5) wax properties that that are likely to influence their performance as a molten, water-repellent treatment for OSB. Chapter 3 covers experimental techniques that were used to characterize the properties of 13 different waxes and five custom-made wax blends; focusing on relevant properties identified in the literature review (Chapter 2).   Glass slides were coated and OSB surfaces were treated with the waxes.  Contact angle measurements were used to examine relationships between the wax properties and the hydrophobicity of wax-coated glass and wax-treated OSB surfaces. Chapter 4 is a preliminary experimental chapter that compares the ability of seven different waxes to stabilize the dimensions of OSB.  Waxes were sprayed onto OSB at a fixed temperature (100°C) and treated samples were immersed in water.  Continuous thickness swelling measurements were made over a period of 21 days.    6  Chapter 5 compares the ability of eleven different waxes and five wax blends to dimensionally stabilize OSB.  Untreated commercially available, “moisture resistant” OSB samples, with high resin content, were also included as a benchmark.  The waxes that were tested included polar and nonpolar waxes with a wide range of melting point temperatures.  Waxes were sprayed at 25°C above their melting point temperatures.  Samples were floated face down on water for 72 h and water absorption and thickness swelling measurements were made after 2 h, 24 h, 48 h and 72 h.  Samples were then conditioned at 20 ± 1°C and 65 ± 5% relative humidity for a minimum of two weeks before measurements taken again.  In combination with the results from Chapter 3 relationships were established between the water repellency of wax-treated OSB surfaces and the water absorption and thickness swelling behaviour of wax-treated OSB samples.  Conclusions were drawn on effects of wax polarity and the ability of waxes to restrict the thickness swelling of treated OSB. Finally, Chapter 6 discusses the results of all three experimental chapters, makes suggestions for further research, and draws overall conclusions.     7  Chapter 2. Literature review 2.1 History and current markets 2.1.1 A brief history of oriented strandboard Oriented strandboard (OSB) is technically a type of particleboard that is composed of thin, rectangular strands of wood that are oriented and bonded together with a waterproof adhesive, as mentioned in Chapter 1 (Elmendorf 1965).  The literature sometimes refers to OSB as flakeboard, a term which also includes waferboard (Berglund and Rowell 2005).  In contrast to OSB, the squarish flakes of waferboard are not usually aligned or oriented in a specific direction.  One of the earliest references to a wood composite that resembles OSB is a patent by Watson (1905).  He describes a composite board consisting of “thin pieces of wood that are secured together by means of a suitable bonding agent, so that the particles will overlap and interlock.”  He refers to the use of many different particle shapes and sizes, but does not emphasize how particle geometry and particle orientation can improve board properties.  The influence of particle geometry on the mechanical properties of particleboard was described as early as 1954 (Turner 1954), followed by a series of studies on its effects on board properties (Post 1958; Burmabaugh 1960; Jorngensen and Odell 1961; Jorgensen and Murphey 1961; Post 1961; Lehmann 1974).  The advantages of particle alignment were also recognized as early as 1952 (Geimer 1976; Snodgrass et al. 1974), but were not capitalized on until practical methods of orienting wood flakes were developed (Vajda 1974; Impellizzeri et al. 1976).  Modern OSB, with its slender and oriented strands evolved from waferboard by using these improvements to create a better structural panel. The commercialization of OSB can be traced back to early work by Armin Elmendorf, who started to develop cement bonded composite boards using oriented strands and shavings in the 1930s (Impellizzeri et al. 1976).  He first described OSB in 1949, as a way to use veneer waste (Elmendorf 1950).  However, it was not until 1965 that he filed a patent for the product (Elmendorf 1965). Three years later in 1968 Elmendorf and the Potlatch Corporation   8  established the first North American pilot plant to manufacture OSB on a large scale (Snodgrass et al. 1974; Impellizzeri et al. 1976). Today OSB rivals plywood in the structural panel market (Howard and McKeever 2012).  It makes more efficient use of timber resources than plywood and it has better mechanical properties than waferboard, its predecessor.  Plywood and OSB have comparable mechanical properties (Cai and Ross 2010), but the manufacturing costs for OSB can be up to 25% lower (Spelter et al. 2006). This is mainly because OSB is able to use lower quality and cheaper logs that are unsuitable for lumber or veneer (Green and Hernandez 1998), and because up to 90% of each log can be used (APA 2009).  Plywood, however, is still considered a superior product in terms of dimensional stability, especially thickness swelling (Spelter et al. 2006; Coulson 2012; Mendes et al. 2013).   2.1.2 Current markets In 2010, OSB production in North America reached 13.5 million m3 (UNECE/FAO 2012).  The U.S. produced about 9.1 million m3 of this total, which accounted for 60% of its own structural panel market (Howard and McKeever 2012).  In the same year European production exceeded 4.8 million m3 (UNECE/FAO 2012; UNECE/FAO 2013).   By 2012, North American production had increased to 15.5 million m3 (+ 14.6%) and European production had increased to almost 5 million m3 (+ 2.7%) (UNECE/FAO 2013).  The top five producing countries in Europe were Germany, Romania, Czech Republic, Poland and Latvia (UNECE/FAO 2013).  Howard and McKeever (2013) estimated that in 2013 the U.S. consumed 8.9 million m3 on OSB; 26% more than it produced.  In Russia, increases in the construction of timber frame buildings have led to an increase in imports of OSB.  Russia has just built its first two OSB plants and future demand for OSB may be met in part from domestic production (UNECE/FAO 2013).  Most OSB panels are manufactured to a standard 1220 x 2440 mm size, with thicknesses ranging from 6.3 - 19 mm (Shmulsky and Jones 2011).  These panels are mostly used for structural applications such as sheathing for roofs, walls, and subfloors (APA 2009) (Figures 2.1 – 2.1).  Other applications include use as insulation panels, I-joist webbing, packaging, and   9  furniture (APA 2009).  OSB is also suitable for engineered wood flooring (Barbuta et al. 2012).  Together OSB and plywood represent over 50% of the building materials for residential housing in North America (Moya et al. 2008).  In 2010, 82% of the OSB consumed in the U.S. was used for structural purposes and this application alone consumed about 9.32 million m3 of OSB (Howard and McKeever 2012). OSB panels that are left unprotected against rain and is exposed to high levels of relative humidity absorbs moisture and swells in thickness, particularly at the edges ( Figure 2.3).  Once this occurs panels often need to be sanded, to make them flat, or replaced at extra cost (Winterowd et al. 2003; Taylor and Wang 2007; Shmulsky and Jones 2011).  Figure 2.1. A typical two-story single family home under construction in West Point Grey, Vancouver, Canada.  Note the large amount of OSB for wall sheathing    10   Figure 2.2. A multi-storey building under construction on Marine Drive, North Vancouver, Canada. OSB was used for wall sheathing.  The ground floor is typically used for commercial real estate and the upper levels are for medium density residential accommodation   Figure 2.3. A single-family home under construction in West Point Grey, Vancouver, Canada (left).  The mud and water in the foreground suggests that the building was exposed to rain water.  A close up (right) of OSB wall sheathing that was left unprotected in a rain shower, while the building was under construction    11  2.2 Water absorption and thickness swelling 2.2.1 Water absorption  OSB is composed of approximately 95% solid wood (Kline 2005).  Wood is a hygroscopic material that changes in moisture content depending on the relative humidity of its environment (Skaar 1972).  Dry wood adsorbs water when placed in a humid or wet environment, while wood with a high moisture content loses water when placed in a dry environment.  The moisture content of OSB increases by absorption and adsorption and decreases it by desorption.  Absorption is the physical take-up of liquid water (e.g. capillary action), whereas adsorption is the attraction of water molecules to hydrogen bonding sites, such as free hydroxyl group in wood cell walls (Orman 1955, Shmulsky and Jones 2011, Stamm 1964).  Water in wood fibres may be present inside the cell walls, as bound water, or in the cell cavities, as free water (water vapour) (Tiemann 1906). Bound water is held within the polymer matrix of wood by hydrogen bonds (Skaar 1972). The polymer matrix of wood consists of three major components: (1) cellulose (40 – 50%); (2) hemicellulose (25 – 35%); and (3) lignin (18 – 35%) (Pettersen 1984).  Bound water is primarily bonded to the free hydroxyl groups of hemicellulose (Browning 1963; Burmester 1970; Burmester and Wille 1975; Burmester 1975; Rowell and Banks 1985).  Bound water is also bonded to cellulose, but the crystalline structure of the polymer makes its hydroxyl groups less accessible (Stamm 1964).  Water adsorption by cellulose thus occurs mostly in its less crystalline, amorphous, regions (Zeronian et al. 1983; Pizzi 1993).  Lignin, which is the aromatic structural component of wood, is the least hydrophilic of the three compounds.  Wood only changes in dimensions when bound water is gained or lost (with the exception of collapse of wood cells that can occur above fibre saturation point).  The fibres shrink when cell walls lose water and swell when water is gained.  The maximum amount of water bound in the cell wall usually ranges from 25 - 30% of the oven dry weight of wood (Skaar 1972).  This maximum is known as the fibre saturation point (FSP) (Tiemann 1906).  Below FSP, nearly all water is bonded within the cell wall.  Above FSP, wood is dimensionally stable, because the   12  addition of free water does not cause fibres to swell.  The mechanical strength of wood is also strongly dependent on its moisture content below FSP, and improves significantly as bound water is lost (Tiemann 1906). Water (liquid and vapour) absorption by OSB is influenced by the structure of the board, particularly the presence of large voids between strands (inter-strand voids) and smaller voids found within strands (intra-strand voids) (Suchsland 1959; Dai et al. 2005).  Liquid water is absorbed into these voids by capillary action and then adsorbed into the walls of the wood cells by diffusion.  When dry OSB is immersed in water, initial absorption is rapid and occurs primarily through inter-strand voids (Wu and Piao 1999; van Houts et al. 2004; Semple et al. 2009).  The amount of water in OSB (or wood) is expressed as a percentage of its oven dry weight (ASTM 2007).  OSB undergoes significant changes in both thickness and linear dimensions with an increase in moisture content. According to Wu and Piao (1999) the short-term (24 h) thickness swelling of OSB is directly proportional to the amount of water it absorbs.   Thickness swelling can cause substantial losses in panel strength and many other undesirable effects.  For example, linear expansion due to water adsorption can create moisture traps and out-of-plane distortion (Coulson 2012). 2.2.2 Thickness swelling A considerable amount of research has been done in an attempt to understand and reduce the thickness swelling (TS) of OSB.  TS can lead to variations in thickness between different boards, as well as variation within boards.  Horizontal density differences, across the plane of an individual board, may lead to variable TS (Suchsland 1962), which can be telegraphed through coatings (Williams and Winandy 2008) or resin impregnated overlays (Biblis 1990).  TS is pronounced at the panel edges (Carll and Wiedenhoeft 2009) (Figure 2.4.) and several North American companies have developed ways of restricting the edge swelling of OSB exposed to water (Evans et al. 2013).  Thickness swelling variations between boards may also lead to out-of-level floors or out-of-plumb walls, which can be time-consuming and expensive to fix (Shmulsky and Jones 2011).   13  The total thickness swelling (TTS) of OSB is the net result of two components: reversible thickness swelling (RTS) due to natural hygroscopic swelling of wood, and permanent thickness swelling (PTS) due: (1) the release of compressive strains that were imparted to flakes during  hot-pressing (Neusser et al. 1965; Halligan 1970; Kelly 1977; Wu and Suchsland 1997); (2) delamination of glue-line between flakes and cracking of wood, both of which create voids within the board (Kelly 1977; Hsu et al. 1988); and (3) the deformation of flakes.  PTS is also sometimes referred to as springback.  Figure 2.4. Oven dried OSB (left) and the same OSB sample immersed in water for 18 h (right).  Note that the panel edge swelled by almost 4 mm (± 20%) after 18 h  The rupture of adhesive bonds when OSB swells, permanently reduces the strength of boards.  Hence, mechanical strength properties of OSB are inversely proportional to TS (Suchsland 1973; Suchsland and Xu 1991; Wu and Suchsland 1997; Wu and Piao 1999; Linville and Wolcott 2001).   Wu and Piao (1999) reported an average loss of 0.014 MPa internal bond strength for every 1% increase of PTS.    Accordingly, if PTS can be reduced then strength losses will be avoided. PTS can account for 60% to 75% of the TTS of OSB, depending on exposure conditions (Wu and Suchsland 1997; Wu and Piao 1999).  The majority of PTS occurs above 80% relative humidity (Gatchell et al. 1966; Wu and Suchsland 1997; Wu and Piao 1999), or above moisture contents of 10% to 15% (Wu and Suchsland 1997; Hartley et al. 2007).  PTS has a nonlinear relationship with moisture content: below 5%, barely any PTS occurs, but as moisture content increases above 10% PTS significantly increases (Wu and Suchsland 1997).     14  It is clear that PTS is associated with strength losses of OSB, as mentioned above.  Most PTS occurs rapidly during initial exposure to water and then diminishes over time, until compressive strains are relieved (Post 1961; Johnson 1964; Kelly 1977; Wu and Lee 2002; Moya et al. 2009).  It is therefore important to protect OSB building panels during the early stages of construction, when they are vulnerable to rain and high relative humidity.  Once construction is complete, panels are not exposed to rain.  Furthermore, the relative humidity inside completed buildings is usually lower than that at which significant PTS occurs (Arena et al. 2010; Rudd and Henderson 2007). 2.2.3 Industry standards for measuring thickness swelling The dimensional stability of structural wood based panels is most often measured in terms of water absorption (WA), thickness swelling (TS), and linear expansion (LE), although other dimensional measurements, such as creep and warp, may also be of interest.  According to the standard, ASTM D1037 – 12, WA and TS is measured using a 24 h water submersion test (American Society for Testing and Materials 2012).  WA and TS are expressed as a percentage change from values of the sample conditioned at 65 ± 5% relative humidity and 20°C.  Linear expansion, on the other hand, is reported as the percentage change in length between 50% and 90% relative humidity, at a constant temperature of 20°C.  Although it is not standard practice, longer water submersion tests of 72 h or more are also commonly used by industry.  According to the Voluntary Performance Standard PS 2-04, which most North American OSB manufactures comply to, the average TS of OSB must be limited to 25% (NIST 2004).  In Europe, the EN 300 standard limits TS to between 12% and 25%, depending on board type and end-use (EN 2006). 2.3 Factors that affect thickness swelling The material processing variables that affect the TS of OSB have been well established and include: wood species, strand geometry, board density, resin content, blending efficiency,   15  hydrophobic additives, and pressing conditions (Halligan 1970; Kelly 1977; Maloney 1993).   The following three factors will be discussed here in more detail: (1) raw materials; (2) board density; and (3) board porosity. 2.3.1 Raw materials 2.3.1.1 Wood species The dimensional stability of OSB can be altered by changing the species or mix of species used to make the boards.  Species related variables that influence the dimensional stability of OSB include wood density, acidity, and extractives content (Maloney 1993).  Of these factors wood density has the largest effect (Halligan 1970; Maloney 1993).   Low density wood is usually used to make OSB, because the strands can be pressed together more easily during manufacture, thus ensuring better inter-strand bonding (Maloney 1993).  Such compression of strands, however, comes at a price, because compressive strains that are set in the wood strands when they are pressed and bonded together can increase the permanent thickness swelling that occurs when OSB is subsequently exposed to moisture.   The most common hardwood species used to manufacture OSB is trembling aspen (Populus tremuloides Michx.) (Wang and Winistorfer 2000; Cai 2012).  In fact, the first waferboards produced in Canada consisted of 95% trembling aspen and 5% black poplar (Populus balsamifera L.) (Shen 1980).  The most common softwood species used to manufacture OSB in North America are southern yellow pine species, such as longleaf pine (Pinus palustris Mill.), shortleaf pine (Pinus echinata Mill.), loblolly pine (Pinus taeda L.), and slash pine (Pinus elliottii Engelm.) (Wang and Winistorfer 2000).  In Europe, Scots pine (Pinus sylvestris L.) is used as raw material for OSB, while in Southern Hemisphere countries, such as Brazil, Chile, South Africa and Australia, there is potential for the use of eucalyptus species (Eucalyptus spp.) as raw material (Iwakiri et al. 2004).  Grant (1995) provided a comprehensive literature review on the effects of alternate wood species on OSB properties.  Many studies have also investigated the potential of bamboo as raw material for OSB and have found that the   16  dimensional stabilities of the bamboo boards are sufficient to pass the standards for wood-based OSB (Lee et al. 1996; Sumardi et al. 2006; Malanit et al. 2011).  2.3.1.2 Strand geometry and orientation It is well known that strand geometry affects the dimensional stability of OSB (Mottet 1967; Turner 1954).  Both Halligan (1970) and Kelly (1977) wrote comprehensive reviews of the effects of flake geometry on the TS of flakeboards and other particleboards.  They noted that the thickness stability of flakeboard increases as strand thickness decreases and strand length increases.  More recently, Brochmann et al. (2004) examined the effect of flake thickness on the TS of OSB.  They found that the TS of OSB after 24 h immersion in water was significantly lower for boards that had thin strands at the face of the board and thicker strands in the core.  The reduced thickness swelling of boards with thinner strands occurs as a result of reduced densification during pressing (Brochmann et al. 2004).  Dai (2004) also reported that TS of OSB decreases as flake width increases and strand thickness decreases.   Zhang et al. (1998) showed that high performance OSB composites can be manufactured by using very thin strands for the face layer.  Avramidis and Smith (1989) examined the effects of face-to-core ratios on TS of OSB, and did not observe any significant differences for boards made with different layer ratios.  Geimer et al. (1975) made flakeboard with different combinations of core material (19 mm pulp chips cut to 0.5 mm with a ring flaker) and  face material (50 x 12.7 x 0.5 mm3 with a disk flaker).  They observed that 3-layer flakeboard swells less than boards manufactured from only core strands.  As mentioned in Chapter 1, flake alignment can influence the dimensional stability of flakeboard and OSB.  These effects, however, primarily influence linear expansion and flake alignment has little effect on the TS of flakeboard composites (Geimer 1982; Sekino and Suzuki 1984; Shupe et al. 2001).      17  2.3.1.3 Resin content The most common resins used to bond OSB are: (1) phenol formaldehyde (PF), (2) methylene diphenyl diisocyanate (pMDI); and (3) urea formaldehyde (UF) resins (Gomez-Bueso and Haupt 2010; Kloeser et al. 2007).   These resins are added as a liquid or a powder to the wood flakes before they are pressed together (Gomez-Bueso and Haupt 2010 Ellis 1993; Forintek Canada Corp. 1998; Chapman 2006).  Resin type has a significant influence on the TS of OSB (Gillespie 1984; Brochmann et al 2004).  Using isocyanate resins instead of phenolic resins, for example, can reduce TS of OSB (Taylor et al. 2008). The use of iscocyanate resins, however, is often restricted due to their higher cost compared to PF or UF resins (Forintek Canada Corp. 1998; Chapman 2006).  Increasing the resin content of OSB can also improve the dimensional stability of boards (Linville and Wolcott 2001), but there is an optimal level, after which additional resin no longer reduces TS (Kelly 1977). The optimal resin content for OSB has been reported to be between 6 – 12 %, depending on resin type (Kelly 1977; Generalla et al. 1989; Biblis 1990;).  Other factors that affect the optimal resin content include resin distribution (Ellis 1993) and the extent to which the resin fully cures (Halligan 1970; Brochmann et al. 2004).  Since adhesives can represent between 15 - 20% of the production costs of OSB, resin content is usually kept to a minimum (Forintek Canada Corp. 1998), with average resin contents being in the range of 2 – 4% of dry board weight (Forintek Canada Corp. 1998; Kline 2005).  Premium-grade OSB panels containing up to 10% isocyanate resin are used commercially for I-beams webs, flooring panels,  and other applications that require enhanced dimensional stability (Forintek Canada Corp. 1998, Spelter et al. 2006). In a report by Taylor and Wang (2007), which was later published in a peer-reviewed journal (Taylor et al. 2008), the properties of high performance “moisture resistant” OSB panels were measured.  Although the report did not provide information on the resin content of the boards, it did imply that the different manufacturers used high loadings of pMDI resins. The TS of some “moisture resistant” panels after 24 h of immersion in water, was reported to be approximately 70% less than regular OSB.  After 72 h the TS of the same boards was approximately 50% less than regular OSB.   18  2.3.1.4 Wax sizing  About 0.5 – 1.5% paraffin wax is added to OSB to improve its short-term water repellency (Kline 2005; Maloney 1993).  The rate of WA and TS of OSB is slowed by the addition of wax sizing (O'Halloran 1989; Roffael and May 1983), but the extent of TS at high humidity conditions is not reduced according to Hsu et al. (1990).  Before OSB is pressed, paraffin wax is added to its strands as a molten slack wax or as a water-based wax emulsion (Eckert and Edwardson 1998).   Some studies have suggested that emulsion wax is more effective at reducing the rate of WA and TS than neat, molten wax, as a result of differences in wax distribution (Hsu et al. 1990; Eckert and Edwardson 1998).  The rate of WA and TS of OSB decreases as its wax content increases (Winistorfer et al. 1996; Winistorfer et al. 1992; Zhang et al. 2007), however, there is a limit to the amount of wax sizing that can be added, after which point additional increases have little effect on thickness stability (Hsu et al. 1990; Maloney 1993).  Maloney (1993) provides excellent theory on how wax sizing reduces the rate of WA and TS of particleboards.   According to Hsu et al. (1990) the swelling of waferboards manufactured without wax sizing was unacceptable.  The literature often emphasizes that wax sizing does not prevent water vapour absorption (Heebink 1967; Maloney 1993). Neimsuwan et al. (2008), however, reported that wax sizing does reduce the rate of water vapour absorption of individual strands, but that this effect is likely to be small in relation to WA by the entire board. 2.3.2 Board density According to Maloney (1993) the ingress of free water into particleboard is inversely related to board density, is because boards with higher densities are usually less porous; with less space for the ingress of free water via capillaries between the particles.  Thickness swelling of OSB and flakeboard increases as board density increases (Linville and Wolcott 2001; Rice and Carey 1978).  Linville and Wolcott (2001) reported that the relationship is proportional for OSB, while Rice and Carey (1978) reported a similar but not proportional relationship for flakeboard.   Differential swelling between the high density face and lower density core layers of OSB is well documented (Suchsland 1962).  It has been shown that TS increases as density increases and   19  that the rate of TS is highest in the surface layers (Winistorfer and Xu 1996; Wang and Winistorfer 2003; Gu et al. 2005; Tackie et al. 2008).  Thus, efforts to improve the dimensional stability of OSB often focus on stabilizing surface layers.   2.3.3 Porosity  Water absorption into OSB is influenced by the permeability, and thus the porosity of the boards (Zhang and Smith 2010a). OSB is highly porous, mainly because of the presence of large inter-strand voids, as mentioned above (Suchsland 1959, Dai et al. 2005).   Furuno et al.  (1983) described three types of inter-strand voids in flakeboard and named them: Type-I, Type-II and Type-III voids (Figure 2.5).  Type-I voids occur between two flakes as a result of their delamination; Type-II occur between the tips of two flakes which are not in contact, but are held in place by two other flakes; and Type-III voids are formed at the tip of a single flake that is squeezed between two other flakes.     Figure 2.5. Three types of inter-strand voids in flakeboard, as classified by Furuno et al. (1983)  Dai et al. (2005), who also classified inter-strand voids in OSB, referred to Type-II voids as non-contact voids and Type-III as partially filled edge voids. Perhaps more descriptively, Zhang et al. (2010a) referred to Type-II voids as rectangular voids and Type-III as triangular voids.   The size and shape of inter-strand voids are affected by board density and strand geometry (Dai et al. 2005; Li et al. 2008;  Li et al. 2009; Li et al. 2010; Standfest et al. 2009), as well as strand orientation (Lenth and Kamke 1996; Standfest et al. 2009; van Houts et al. 2003). Void sizes decrease when board density increases or when strand thickness decreases.  According to van Houts et al. (2003), as well as Lenth and Kamke (1996), boards that are made with long strands that are oriented in a specific direction, produce voids that are also long and thin.  As strand Type I Type II Type III   20  length decreases or when orientation is randomized, the voids become shorter and more spherical in shape.  According to Li et al. (2009) voids reach a maximum size when strand length is around 110 mm and decrease as the strands become longer or shorter.  The average void diameter in OSB normally varies between 100 µm and 300 µm (Li et al. 2009; Li et al. 2010), however, larger voids of 1.5 mm or more in diameter are not uncommon (Standfest et al. 2009).   In terms of volume; voids represent one of the three main components of OSB (Dai et al. 2005).  Wu et al. (2006) used X-ray tomography to characterize the void structure of OSB.  For a threshold level of 100, they reported that boards with a density of 650 kg / m3 contained about 4% void space, while boards with a density of 750 kg / m3 contained about 2% void space.   The voids were not distributed evenly throughout the boards.  Core layers contained up to 8% void space, while surface layers contained about 1% void space.  Standfest et al. (2009), who also used X-ray technology to examine void volumes, reported that voids in surface layers are on average smaller than those in the core.  Wu et al. (2006) noted that the ratio of void volume to total board volume increases substantially when higher threshold levels are used during image analysis.  Void analysis by X-ray tomography techniques may therefore be biased. Shaler (Shaler 1986; Shaler and Blankenhorn 1990 ) used mercury porosimetery to measure the total void volume for flakeboard made of either aspen or maple (Acer spp).  He developed equations that can be used to determine the inter-strand void volume, based on board density.  According to his equations, aspen flakeboard, with a density of 700 kg/m3, contains of approximately 7.3% inter-strand voids.    Although these descriptions of voids in OSB are helpful, they do little to describe how inter-strand voids are connected and how they affect liquid water flow.  In fact, there is very little literature available on this subject.  Bolton and Humphrey (1994) argued that the moisture flow paths in flakeboard are heterogeneous, consisting of different types of pores geometries in series.  According to them, inter-strand voids may or may not be “connected via low, long and wide slit pores between the flat faces of the flakes.”  Their hypothesis is supported by two   21  observational studies that used nuclear magnetic resonance (NMR) imaging to examine the flow of water into OSB (van Houts et al. 2004, van Houts et al. 2006).  These studies observed that once inside the board, water consistently traveled in thin corridors, along the length and width of the panel.  Another interesting observation was that, in some cases, water penetrated the surface and the edge of OSB at a similar rate (van Houts et al. 2004). This observation was surprising, since the edges of OSB are considered to offer easier access for water ingress than the surface of the board.  Indeed, as mentioned before, the edges of OSB boards are usually coated with edge seals to slow WA.  Lastly, van Houts et al. (2006) also reported that large strands on the surface of OSB were able to inhibit water ingress into the interior of the board, by blocking access to sub-surface inter-strand voids (van Houts et al. 2006).  2.4 Treatments that reduce thickness swelling As mentioned above, OSB undergoes reversible thickness swelling (RTS) when moisture is absorbed by wood strands, while permanent thickness swelling (PTS) occurs when compressive stresses are relieved and adhesive bonds fail.  Most technologies to control the TS of OSB focus on limiting the amount of moisture that the wood elements absorb, although there are some, such as steam injection pressing, that try to reduce internal strains.  According to Rowell and Banks (1985) there are three types of treatments that can improve the dimensional stability of solid wood:  (1) water repellent treatments (Type-I); (2) dimensional stabilization treatments (Type-II); and (3) treatments that are both water repellent and dimension-stabilizing (Type-III).  Water repellent treatments, such as film-forming surface coatings or penetrating wax solutions, retard the rate of water absorption, but not the extent of swelling.  Dimensional stabilizing treatments do not change the rate of water absorption, but decrease the extent of swelling.  According to Hill (2007), the properties of solid wood can be modified through thermal, chemical, and biological processes, or by impregnating wood with polymers.  These methods of modification can be used to improve the dimensional stability of solid wood.  Three such treatments include: (1) the reduction of hygroscopicity (e.g. thermal   22  modification); (2) bulking treatments (e.g. acetylation and polymer impregnation); and (3) chemical cross-linking (e.g. formaldehyde reaction) (Rowell and Banks 1985). Many of the same treatments that improve the dimensional stability of solid wood can also be used to improve the dimensional stability of OSB.  Technologies available to reduce the TS of OSB can be divided into three main groups: (1) pre-treatment of strands; (2) post-treatment of consolidated boards; and (3) production processes (Del Menezzi and Tomaselli 2006; Mantanis and Papadopoulos 2010).   Pre- and post-treatment include thermal and chemical modification, similar to the dimensional stabilizing techniques for solid wood, while “production processes” may include changes in resin content, wax sizing, particle geometry, or steam injection pressing.  The following dimensional stabilizing and water repellent treatments for OSB will be discussed here: (1) thermal modification; (2) chemical modification; (3) film-forming surface coatings; and (4) penetrating water repellent treatments.   2.4.1 Thermal modification  When wood is subjected to temperatures over 100°C for extended periods it becomes more dimensionally stable due to thermal degradation of its three major chemical constituents (cellulose, hemicellulose, and lignin) (Beall and Eickner 1970; Esteves and Pereira 2008).   As mentioned before, most bound water in wood is bonded to the hydroxyl groups of hemicellulose.  Hemicellulose is the least thermally stable of wood’s major components and decomposes at temperatures ranging from 130°C to 200°C (Runkel and Wilke 1951; Kudo and Yoshida 1957).  Cellulose starts to degrade at temperatures above 200°C (Fengel and Wegener 1989).  Lignin is the most stable and the least hydrophilic of the three components.  Significant thermal degradation of lignin is reported to begin around 280°C (Kudo and Yoshida 1957; Paul et al. 2006); although some degradation is also reported at temperatures below 200°C (Esteves and Pereira 2008; Fengel and Wegener 1989). The capacity of the cell wall to hold water decreases markedly as the hydroxyl groups on hemicelluloses are degraded.  At the same time the proportion of crystalline cellulose in wood increases when it is exposed to high temperatures (Bhuiyan et al. 2001; Pétrissans et al. 2003;   23  Wikberg and Maunu 2004; Bhuiyan and Hirai 2005; Boonstra and Tjeerdsma 2006).  Thus heat treatment makes wood less hygroscopic.  Further reasons for the loss of hygroscopicity during thermal degradation can be attributed to increased cross-linking of lignin and the formation of water insoluble chemicals, such as furfural and acetic acid (Rowell and Youngs 1981; Tjeerdsma et al. 1998; Esteves and Pereira 2008). The use of thermal modification techniques to improve the dimensional stability of OSB and related products, such as flakeboard, has received considerable attention.  Most work aims at removing or degrading the hemicellulose component of the wood, while keeping cellulose and the lignin matrix intact.  Theoretically this approach will maintain the structural integrity of the wood elements, while making them less hygroscopic.  In general, the literature shows that thermal treatments can reduce the TS of OSB, but at the same time mechanical properties, such as internal bond strength (IB), modulus of rupture (MOR), and modulus of elasticity (MOE), are often significantly compromised (Mendes et al. 2013; Ohlmeyer 2007).  Peleaz-Samaniego et al. (2013) divided thermal treatments of wood composites into two groups: (1) dry processes, such as torrefaction, which occurs in an environment with limited moisture; and (2) moist or wet processes, such as hot water extraction or steam treatment.  The authors emphasized that the classification is unofficial and should only be used for discussion purposes.  The same classification will be used here to discuss first pre- and then post-treatments that reduce the TS of OSB using thermal modification.     Thermally pre-treating OSB strands in a dry environment (i.e. torrefaction) decreases the wettablilty of wood strands, which reduces their bonding ability (Suchsland and Xu 1991; Šernek et al. 2004).  The IB strength of OSB made with thermally modified strands is, therefore, lower than boards made with untreated strands (Goroyias and Hale 2002; Paul et al. 2006; Ohlmeyer 2007; Mendes et al. 2013).  Furthermore, the MOR and MOE of such thermally pre-treated boards is also reduced, because exposure to high temperature in a dry environment embrittles wood strands (Goroyias and Hale 2002; Paul et al. 2006; Ohlmeyer 2007; Mendes et al. 2013).    24  Thermal pre-treating of OSB strands in wet environments includes processes such as hot water extraction of hemicellulose or pre-steaming of wood strands.  Hsu et al. (1988) pre-treated wood flakes (Populus ssp.) with saturated steam and founds that the TS of flakeboards made with these flakes decreased as steam pre-treatment time increased.  A short treatment time (3 min) did not markedly affect the mechanical properties of the boards, but MOR and IR reduced as treatment time increased.  A treatment time of 4.5 min reduced MOR by about 10% and IB strength by about 17%.  The authors suggested that partial hydrolysis of hemicellulose reduced the development of stresses during hot pressing.   Recently, there has been greater focus on hot water extraction of hemicellulose, since the additional advantage of this technology is that the sugar by-products may be used to produce biofuels (Sattler et al. 2008).  Paredes et al. (2008) reported that OSB panels made with hemicellulose-extracted red maple (Acer rubrum L.) strands absorbed more water than untreated boards, while TS was only slightly reduced.   The authors attributed this surprising finding to increased cell porosity and lower initial equilibrium moisture content (EMC) of hot water extracted strands.  Conversely, Hosseinaei et al. (2011a) reported a substantial reduction in WA for OSB made with hemicellulose-extracted southern yellow pine (Pinus spp.) strands.  These boards were less susceptible to TS than untreated boards and maintained most of their mechanical properties when exposed to water.  An increase in bending properties was attributed to the increased cellulose crystallinity of treated wood flakes, while lower IB strength was attributed to a number of factors, including poor adhesion due to low wettability.  These findings were later confirmed by Paredes et al. (2010), who also examined the properties OSB made with hemicellulose-extracted pine strands. Unlike thermal pre-treatments, post-treatments do not improve TS simply by removing or degrading hemicellulose.  Instead, it has been suggested that one of the main effects of thermal post treatment is the relaxation of internal strains which normally lead to permanent TS (Suchsland and Enlow 1968; Del Menezzi et al. 2009).   Thermal post-treatment in a dry environment is usually done by keeping the boards in a hot press, under low, contact pressure, for short periods of time; or by hot stacking the boards at high temperatures (> 150°C) for extended periods of time.  The literature shows that thermal post-treatments can significantly decrease the TS of OSB (Del Menezzi and Tomaselli 2006); however, there are conflicting   25  reports about how the treatments alter mechanical properties.  Some results show that mechanical properties, particularly IB strength and MOR, are significantly reduced (Ohlmeyer 2007; Del Menezzi et al. 2009), while others have found that they are unaffected or slightly improved (Hsu 1987, Hsu et al. 1989, Okino et al. 2007, Mendes et al. 2013).  According to Ohlmeyer (2007), the mechanical properties of OSB bonded with pMDI resins are less affected by thermal treatments than other types of resin. Fewer studies have investigated the effects that thermal post-treatment in wet environments have on the properties of OSB.  Most of the research in this field has focused on steam injection, during hot pressing (Geimer and Kwon 1999), rather than post-production treatment.  Heebink and Hefty (1969) demonstrated that a steam post-treatment quickly releases the internal strains in flakeboard, by allowing the board to swell without restriction.  Unrestrained boards decreased in density and mechanical strength upon steam post-treatment.  Boards that were restrained during treatment were less dimensionally stable than unrestrained boards, but had better initial strength properties.  A patent by Go et al. (2000) describes how steam post-treatment, under vacuum, can significantly reduce the TS of OSB.  Steam post-treatment, however, does not seem to be commercially viable, due to the need for additional steaming equipment and the  extra sanding that is required to achieve a uniform final thickness after steaming (Hujanen 1973; Kelly 1977).  Furthermore, steam post-treatment is also known to degrade the adhesive bonds of UF bonded OSB (Kelly 1977).    Of all the thermal treatments, hot water extraction and dry contact pressing appear to be the ones that are most suited to industrial applications. Hot water extraction, however, is very sensitive to variation in wood stock, temperature, and treatment time.  Dry contact pressing offers only limited reductions in TS and the additional treatment time can significantly increase production costs.  2.4.2 Chemical treatments The two most promising chemical treatments for reducing the TS of OSB include acetylating and pre-treating wood strands with low molecular weight PF resin.  Lehmann (1964) evaluated   26  various methods to improve the dimensional stability of particleboard, including the following chemical treatments: (1) impregnating particles with PF resin; (2) adding polyethylene glycol; (3) and cross-linking with formaldehyde vapour.  None of these treatments produced boards that were significantly more stable than untreated boards.  Other studies, however, have found that impregnating wood particles with low molecular weight PF resin, prior to spraying  the particles with conventional adhesive, significantly improves the dimensional stability of particleboards.  Early work on PF impregnation of flakeboard particles includes studies by Talbott (1959), Maxwell et al. (1959), and Brown et al. (1966).   Low molecular weight PF resin is able to bulk the capillary system inside wood flakes, without chemical bonding, thus restricting moisture ingress (Rowell and Banks 1985).  Haygreen and Gertjejansen (1971) found that impregnation of wood flakes with 5 – 10% low molecular weight PF resin significantly reduced the TS of flakeboards.  Increased resin content improved the strength properties of flakeboard, regardless of whether flakes were impregnated or sprayed with resin before hot pressing.  These results are supported by other studies (Hujanen 1973; Kajita and Imamura 1991).  More recently it was reported that impregnating wood strands with as little as 1 - 2% low molecular weight PF resin, in addition to 4 - 5% conventional adhesive, significantly reduced the TS of OSB (Paridah et al. 2006; Wan and Kim 2006).  PF impregnation can, therefore, be commercially used to dimensionally stabilize OSB, however, the additional resin blending and drying equipment restricts the technology to speciality products (Haygreen and Gertjejansen 1971). Another chemical treatment that is able to significantly reduce the TS of OSB is acetylation.  Acetylation substitutes hydroxyl groups in wood with less hygroscopic acetyl groups, thus bulking the wood and leaving it in a swollen state.  OSB produced with acetylated strands, therefore, absorbs much less water and boards undergo significantly less TS (Papadopoulos and Traboulay 2002).  One drawback of acetylation is that water soluble PF and UF resins are less able to bond the acetylated strands together (Papadopoulos and Traboulay 2002; Papadopoulos and Gkaraveli 2003).  The acetylated strands are more hydrophobic and water soluble resins are unable to effectively penetrate them (Rowell et al. 1987).  Furthermore, the low moisture content of acetylated strands during hot pressing makes them less compressible and thus increased pressures are required for good adhesion (Youngquist et al. 1986).  For   27  these reasons, OSB panels produced with acetylated strands and water-soluble resins have poor mechanical properties.  Papadopoulos and Traboulay (2002) reported that, depending on the percentage weight gain during acetylation, the IB strength of PF bonded OSB made from acetylated strands was 17.5 - 30 % less than boards made from unmodified strands.  Others reported similar reductions in mechanical properties for acetylated and PF bonded flakeboard and particleboard (Rowell et al. 1987; Youngquist et al. 1986).  Alternative resins, such as a pMDI  (Vick et al. 1991; Youngquist and Rowell 1990)  or methylmelamines (Wagner et al. 2007)  can be used to bond acetylated flakes without significant losses in strength properties, but these adhesives are usually more expensive than PF resin.  Other drawbacks to the use acetylation for the production of dimensionally stable OSB include: (1) the need for large amounts of chemicals; (2) the long reaction times required to acetylate wood particles (Rowell et al. 1986); and (3) the unpleasant vinegar-like smell of acetylated wood (Wagner et al. 2007).  Rowell et al. (1986) described a “simplified” acetylation procedure for flakeboard production, which required a reaction time of 3 h to achieve 15% weight gain. An interesting study by Baştürk (2007) showed that the short-term WA and TS of OSB can be reduced by pre-treating wood strands with chitosan.  Chitosan is a modified carbohydrate polymer derived from chitin, the main component of many natural materials, such as insect exoskeletons, crustacean shells and fungal cell walls.  According Baştürk water-soluble chitosan acetate is converted back to chitin during hot pressing and acts as a water-repellent film around OSB strands. 2.4.3 Film-forming surface coatings Little research has been done on the use of film-forming surface coatings to reduce the WA and TS of OSB.  He et al. (2000) coated the surfaces or edges of OSB samples using five different types of paint. Such coatings significantly reduced the WA and TS of OSB immersed in water for 24 h.  Evans and Cullis (2008) examined the dimensional stability of OSB samples that were coated with UV-cured finishes.  They noted that UV radiation is unable to cure coatings that penetrate below the surface of OSB and also that the surface topography of OSB makes it a less   28  than ideal material when using roller coater.  Garay et al. (2009) coated OSB samples with either paint or a non-film forming coating called Lasur, and measured the dimensional stability of the samples when they were exposed to 95% relative humidity and a temperature of 40°C for 800 h.  They reported that both treatments significantly reduced thickness swelling, but that the penetrating stain, Lasur, was the most effective treatment for the samples that were exposed to high humidity conditions for longer than 200 h.  According to Grossman (1992), very thick surface coatings are needed to totally prevent moisture from being absorbed by OSB.  He describes acrylic elastomeric coatings that are capable of producing very thick and highly elastic protective films, which can be used to make OSB suitable for exterior applications.   He goes further to describe the specific building techniques required to make such a coating system work in practice.  A number of studies have evaluated the long term performance of coatings applied to OSB (Hann et al. 1962; Feist 1982; Grozdits and Bibal 1983; Williams and Winandy 2008).  Feist (1982) coated waferboard surfaces with various film-forming finishes and exposed them to natural weathering for 21 – 43 months.  He observed that fungal growth occurred in many of the samples and suggested that coatings with defects allowed moisture to penetrate the waferboards, but that the coatings then prevented the moisture from escaping. Williams and Winandy (2008) painted OSB with one or two coats of latex paint and mounted the samples vertically on an outdoor fence.  After three years of natural weathering the one-coat system failed, with delamination of surface flakes, while the two-coat system clearly showed the contours of the flakes beneath the paint.  They reported that latex paint was only effective at reducing TS when two coats were applied and when the sample edges were sealed with a commercial OSB edge seal.  No short-term water soak tests were conducted.    Biblis (1990) examined the physical and mechanical properties of OSB overlaid with resin impregnated paper.  He found that when water was sprayed onto the surface, the flakes underneath the overlay would swell up and telegraph through the overlay.  According to Biblis applying coats of paints or primers underneath the overlay did not prevent the telegraphing effect of the swollen flakes. A patent by Hetzler and Martin (1983) describes the addition of a   29  porous paper layer onto the surface of waferboard, which might provide limited water resistance.  2.4.4 Penetrating water-repellent treatments Wax is possibly the most common water repellent used to increase the water resistance of wood products, such as millwork (Feist and Mrax 1978, Williams 2000), decking, and wood based composites (Maloney 1993).  When paraffin wax is applied to solid wood, it is normally blended with resin, solvent and fungicides (Feist and Mraz 1978; Banks and Voulgaridis 1980).  Solvents allow wax to penetrate the capillary system of wood and block voids, thus forming an internal water-repellent barrier (Borgin 1965).  Very little literature is available on the subject of penetrating water repellents for OSB.  Two relevant studies and one patent will be discussed here. Borgin and Corbertt (1970) used various waxes as water repellents for radiata pine wood (Pinus radiata D.Don).  The water repellents consisted of 2.5%, 10%, 25% or 50% of wax in mineral turpentine.  The waxes in their study included paraffin waxes, petroleum jelly, beeswax, and carnauba wax.  They found that all waxes were effective at preventing water uptake by and swelling of solid wood, but the best performing waxes were paraffin waxes.  They also showed that beeswax’s ability to prevent swelling improved over time and that it was consistently better at dimensionally stabilizing wood than carnauba wax and petroleum jelly.  They concluded that paraffin waxes could perform even better if they contained hydrophilic groups that would increase their affinity to wood. A patent by Racota (2007) describes a latex-free wax emulsion that can be sprayed onto the surface of OSB before or after hot pressing.  The process she developed is claimed to make the panel more water resistant.  The patent, however, does not provide any details on the physical properties of panels sprayed with the emulsion, nor does it mention the use of neat molten wax.     30  Semple et al. (2009) sprayed water-based wax emulsions and linseed oil-wax solutions onto the surface of hot (120°C) OSB samples. The waxes in their study included soy wax, beeswax, carnauba wax, and paraffin wax.  The solid wax spread rates for the water-based emulsions and oil-wax solutions were approximately 9 g / m2 and 87 g / m2, respectively. Some of the water-based emulsions were able to reduce the short-term TS of OSB, but many of them caused pre-swelling of the surface strands, which increased the rate of WA and TS.  Based on the linear relationship they found for WA and TS, they concluded that the water-based wax emulsions did not significantly reduce water ingress into the intra-strand voids of OSB.  Linseed oil and wax solutions were more effective at reducing the short term WA and TS of OSB than water-based emulsions, however, oil-based solutions also failed to block surface voids.  The authors mentioned that the best results were obtained when linseed oil dried to form a uniform and continuous film over the surface voids of OSB.  Linseed oil solutions that contained beeswax rarely performed better than those containing paraffin or soy wax, and almost never performed better than those containing carnauba wax.  The findings by Semple et al. (2009) indicate that spraying wax onto the surface of OSB may be an effective and reliable method of improving the water repellency of OSB; if wax is able to penetrate the OSB and block inter-strand voids.  Spraying neat, molten wax onto the surface of hot OSB will not cause pre-wetting of the surface strands.  Such a treatment might be able to form an effective internal water-repellent barrier, without the need for a defect-free surface coating. 2.5 Waxes and their properties Waxes are notoriously difficult to define.  A definition by the German Association for Fat Science (Deutsche Gesellschaft für Fettwissenschaft) include the following criteria: (1) drop melting point temperatures above 40°C; (2) melt viscosities below 10 Pa·s when molten; (3) at 20°C they must be kneadable or hard to brittle, coarse to finely crystalline, transparent to opaque, but not glassy, or highly viscous or liquid (Wolfmeier et al. 2000).   31  The properties of wax can be engineered according to the needs of an application. According to Neimsuwan et al. (2008) the water repellency of OSB is closely related to wax properties such as chemical composition, melting point, viscosity, and oil content.  The following paragraphs will discuss the origin of wax and the following three properties: (1) its chemical composition; (2) water repellency; and (3) melting point temperature. 2.5.1 Origin Wax can be sourced directly from nature or it can be synthesized from coal, oil, or gas.  “Natural waxes are formed through biochemical processes and are products of plant and animal metabolism” (Wolfmeier et al. 2000).  Natural wax can be subdivided into three main groups, namely: (1) animal waxes; (2) vegetable waxes; and (3) mineral waxes.  Mineral waxes, which include paraffin waxes, such as lignite (montan) and peat waxes, are sometimes referred to as fossil waxes, because they were formed through biological processes during earlier geological periods (Wolfmeier et al. 2000).  Synthetic waxes, on the other hand, are manufactured by bonding hydrocarbons to form n-alkane and alkene bonded polymer chains.  There are two main types of synthetic wax, namely: (1) Fischer-Tropsch waxes; and (2) polyolefin waxes.   2.5.2 Chemical composition The chemical structure of any wax is dominated by hydrocarbon chains.  These chains are also why wax is strongly hydrophobic (Adam 1963; Wolfmeier et al. 2000). The carbon chains can be straight or branched, and their length can range from several thousand carbon atoms to as few as 16 (Wolfmeier et al. 2000). The chemical composition of different waxes can vary considerably, as functional groups, such as aromatic, carboxyl, ester, and amide groups, are often bonded to their carbon chains.  Beeswax and carnauba wax, for example, consist mostly of complex esters, as well as fatty acids and fatty alcohols (Kolattukudy et al. 1976; Greener-Donhowe and Fennema 1993).  Paraffin wax and microcrystalline waxes, on the other hand, consist entirely of saturated hydrocarbons (Bennett 1963; Hilditch 1965; Greener-Donhowe and   32  Fennema 1993).  Paraffin wax consists primarily of straight chains, while microcrystalline wax contains straight, branched or cyclic components (Hsu and Bender 1988).  All waxes are, therefore, blends of various hydrocarbon chains that are either straight or branched, and may or may not contain aromatic and polar components.  Waxes can also contain additional compounds.  Beeswax, for example, may contain propolis, a resin that is produced by bees (Apis spp.) to protect and seal the honeycomb (Budija et al. 2008).  Wax properties depend on the length of the carbon chains and the degree of branching, as well as the presence of functional groups.  For example, wax emulsions that consist of long chain n-alkanes are more effective at reducing WA and TS of medium density fibreboard (MDF) and particleboard than those consisting of short chain n-alkanes (Roffael and May 1983; Schriever and Roffael 1984; Hague 1995; Roffael et al. 2005).  Hsu and Bender (1988) used contact angle measurements to show that the water repellency of paraffin wax and microcrystalline wax generally increases as the length of the carbon chains increased, while water repellency decreased as the degree of branching increased.  The carbon number distribution of the wax and the ratio of straight versus branched carbon chains can be determined by gas chromatography or mass spectrometry (Levy et al. 1961).  Another technique used to characterize the chemical structure of wax is infra-red (IR) spectroscopy.  IR spectroscopy can be used to identify the functional groups and the bond types that are present, while the degree of branching can be inferred (Coates 2000).  2.5.3 Water repellency  The following paragraphs review: (1) the principles of water repellency; (2) the water-repellency of wood and thermally modified wood; (3) the water repellency of pure wax; and (4) the water repellency of wax-treated wood. When a liquid droplet is placed on a solid surface, there are adhesive forces between the liquid and the solid, as well as cohesive forces within the liquid (Young 1805).  At the edge of the droplet, where the liquid and solid interfaces simultaneously meet the surrounding air, the contact angle (θ) can be measured (Figure 2.6).  The angle (θ), which is conventionally   33  measured within the liquid, can be used to assess the wettability of the solid surface according to Young’s equation (Young 1805):                        (Equation 2.1) where:      =  surface energy of solid     =  surface energy of solid/liquid interface      =  surface tension of liquid       =  contact angle (that liquid makes with solid)   Figure 2.6.  Initial contact angle of a 5µL water droplet on a hydrophilic surface (left) and a hydrophobic surface (right).  A solid is considered to be hydrophobic when θ > 90° If the cohesive force within the liquid is larger than the adhesive force between the liquid and the solid, the droplet will bead on the solid surface, and the contact angle will be between 0 and 180 degrees.  On the other hand, if the adhesive force is larger than the cohesive force, the droplet will spread over the surface and the contact angle will be zero (Adam 1963). A common method used to determine the water repellency of materials, including porous materials, such as wood and OSB, is to determine whether the initial contact angle of a water droplet placed on the surface of the material is larger or smaller than 90° (Borgin 1965).  If the angle is smaller than 90°, spontaneous capillary action will occur, and the water droplet will quickly be absorbed into the porous medium (Borgin 1965; Richardson 1993; Rowell and Banks 1985). The material is then defined as hydrophilic.  Conversely, if the initial contact angle is larger than 90°, the material is hydrophobic, and the water droplet is absorbed into the material at a much slower rate.  In this case, most of the water droplet may even be lost due to   34  evaporation, rather than absorption.  Thus, a second measure, commonly used to evaluate the water repellency of wood, is to examine the rate of change of contact angle over time (Rak 1975). The longer it takes for the contact angle of a water droplet to reduce to less than 90°, the more hydrophobic the wood surface is.  Water droplets sitting on strongly hydrophobic surfaces tend to have contact angles that remain above 90° until the droplet almost completely evaporates.  Semple et al. (2009) sprayed heated OSB surfaces with water-based wax emulsions and linseed oil-wax solutions.  They found reported that initial contact angles of water droplets on wax-treated OSB surfaces were similar to those on untreated OSB surfaces, but that the droplets remained on wax-treated surfaces for much longer.  It also should be noted that the surface roughness of the solid can have a significant effect on contact angle (Wenzel 1949). The leaves of the lotus plant (Nelumbo nucifera, Adams), for example, are extremely hydrophobic as a result of the leaf’s rough surface texture, in addition to the presence of wax (Barthlott and Neinhuis 1997).  The contact angles of water droplets on wood surfaces can vary considerably, although they are almost exclusively below 90°.   In a study by de Meijer et al. (2000), the static contact angles of water droplets on various wood species were measured along the grain.  They measured contact angles on unmodified wood surfaces to be between 54° and 78°.  These results agree with those of others who measured static contact angles of water droplets on the surfaces of wood samples cut from various wood species (Gindl et al. 2001; Mantanis and Young 1997; Mohammed-Ziegler et al. 2004).  Interestingly, de Meijer et al. (2000) measured contact angles on thermally treated wood to be as low as 61°.  Gérardin et al. (2007) reported advancing wood-water contact angles on heat-treated European beech (Fagus sylvatica L.) to be 69.4°, and those on heat treated Scots pine to be to be 81.3°; while Pétrissans et al. (2003) reported advancing contact angles of 42.2° on heat treated European beech and 88.9° on Scots pine.  Contrary to these findings, Hakkou et al. (2005) reported the contact angles on heat treated European beech to be much higher, with values close to or equal to 90°.  Nonetheless, all of these studies observed that the contact angles of water droplets were higher on heat treated   35  surfaces than on unmodified wood surfaces. Hosseinaei et al. (2011b) also found that hot water extraction of wood resulted in larger wood-water contact angles.  As mentioned above, wood can also be made hydrophobic by using water repellents (Borgin and Corbett 1970; Voulgaridis and Banks 1983).  Initial contact angles for water droplets on pure paraffin wax surfaces typically range from 105° to 114° (Adam 1963).  Meiron et al. (2004) measured the advancing contact angle of water droplets on a smooth beeswax surface to be 111°.  Bartell et al.  (1936) found the contact angles of water droplets on carnauba wax to be 107°.  Holloway (1969) reported the contact angles of water droplets on leaf waxes (i.e. vegetable waxes) to be between 94° and 109°. Holloway (1969) also reported that waxes with polar functional groups, such as esters and ketones, are less hydrophobic than waxes without these groups.  He concluded that the orientation of functional groups affects the hydrophobic properties of wax.  Adam and Jessop (1925), for example, reported the contact angles of water droplets on stearic acid to be anywhere between 50° and 105°, depending on the orientation of the polar groups.  The literature suggests that waxes with polar functional groups tend to be more effective at increasing the water repellency of wood than waxes without these groups (Adam 1963; Borgin 1965; Rowell and Banks 1985).  Polar groups increase the attraction of wax to the wood, while methyl groups and other saturated hydrocarbons repel water.  A common method to determine the polarity of wax is to measure the number of carboxylic acids.  This is done by measuring the amount of potassium hydroxide necessary to neutralize a sample of known weight (ASTM 2010).  2.5.4 Melting point temperature The melting point or congealing point of a material is the temperature at which the material changes between liquid and solid phase and is usually reported as a single temperature. For waxes, however, there is no distinct temperature at which it changes between solid and liquid phases; instead wax changes phase over a range of temperatures (Bennett 1963).  Greener-Donhowe and Fennema (1993) presented melting curves that accurately plot the melting (or   36  congealing) temperatures for beeswax, microcrystalline wax, and carnauba wax.  Most waxes melt at temperatures somewhere between 40°C and 100°C, although some remain solid at temperatures above this range. The melting point temperature of wax increases as the length of the carbon chain and the number of polar functional groups increase, and it decreases as the degree of branching of the wax increases (Wolfmeier et al. 2000).  A wax with a high melting point, therefore, generally, has a larger molecular mass and possesses stronger intermolecular forces, than a wax with a low melting point.   Voulgaridis (1986) suggested that stronger intermolecular bonding forces within wax may increase the water resistance of wax-treated wood.  He treated Scots pine and European beech samples with solvent-based resin/wax solutions and immersed the samples in water at different temperatures (20°C, 40°C, 60°C, and 80°C).  The different water repellent solutions contained paraffin waxes (including microcrystalline wax) with different melting point temperatures (56°C, 85°C, and 115°C).  Voulgaridis (1986) found that at low water temperatures (20°C), water-repellent solutions that contained wax with low melting point temperatures performed better than those containing higher melting point waxes, while at higher water temperatures, he found the opposite. At water temperatures of 40°C, 60°C, and 80°C, water repellent solutions that contained the highest melting point wax (115°C) performed the best.  These results suggest that wood treated with high melting point waxes might be more effective than those treated with low melting point waxes, because they are better able to resist the effects of warm water.   Eckert and Edwardson (1998) used six different slack waxes, with a wide range of melting point temperatures, to test the effects of melting point temperature on the water repellent properties of OSB.  They blended between 0.6 - 1.2% of neat wax with wood strands before boards were pressed, but found no clear relationship between the melting point temperatures of the waxes and WA of test samples after 24 h of immersion in water.     37  Hsu and Bender (1988) used differential scanning calorimetry and contact angle measurements to examine the effect of melting point temperatures on the water repellency of paraffin wax and microcrystalline wax, but they did not find a relationship between the two properties.  2.6 Summary Oriented strandboard is a relatively inexpensive building material that is extensively used for residential and commercial construction (Spelter et al. 2006).  One shortcoming that limits the use of OSB is the excessive thickness swelling (TS) that occurs when it is exposed to moisture (Spelter et al. 2006, Coulson 2012, Mendes et al. 2013).  The porous structure of OSB allows water (liquid and vapour) to easily penetrate it (Suchsland 1959, Dai et al. 2005).  According to the literature, initial water absorption by OSB is fairly rapid and occurs primarily through the void network between overlapping strands (Wu and Piao 1999, van Houts et al. 2004, Semple et al. 2009). TS of OSB often causes problems during building construction, when the panels are unprotected and exposed to rain (Winterowd et al. 2003).  Uneven surfaces, created by differential swelling, often need to be sanded level before construction can continue (Shmulsky and Jones 2011).  In some cases the affected boards may even need to be replaced (Taylor et al. 2008).  TS may also cause boards to lose mechanical strength (Wu and Piao 1999).  The standard method to test the TS of OSB is to immerse samples in water for 24 h and to measure their thickness increase, relative to their original dimensions.  The most widely used industry standard requires the TS of OSB to be less than 25% after 24 h of immersion in water (NIST 2004).  There are many technologies available that can reduce the rate or extent of OSB thickness swelling; few of these, however, are used in practice.  Those that are used are limited to speciality products that are sold at premium prices.  For example, high performance OSB products, which are bonded with large amounts of superior, but expensive isocyanate-based resins, are commercially available (Forintek Canada Corp. 1998).  Such premium-grade OSB   38  products, however, can cost up to three times more than regular OSB (Evans, P.D., personal communication, March 5, 2014).  Film-forming surface coatings, such as paint, can be used as a post-treatment to improve the thickness stability of OSB, but they are ineffective, unless thick coatings are applied (Grossman 1992). Post-treating OSB with water repellents, particularly wax, may be more effective than film-forming surface coatings at improving the thickness stability of OSB.  Waxes are effective water repellents for solid wood (Gibson 1965, Borgin and Corbett 1970, Feist and Mraz 1978), but almost no research has investigated their use as a post-treatment for OSB; except for the work of Semple et al. (2009) and Mantanis and Papadopoulos (2010).  Waxes are already blended with OSB strands before pressing to make the panels more water resistant (Maloney 1993).  These waxes are able to increase the capillary pressure required for spontaneous water absorption by OSB (Gibson 1965; Borgin and Corbett 1970).  There is, however, a limit to the amount of wax that can be blended with the strands before pressing, after which point additional increases in wax content have little effect on thickness stability (Hsu et al. 1990, Winistorfer et al. 1992).  This thesis explores whether it is possible to increase the water repellency and improve the dimensional stability of OSB by spraying molten wax onto the surface of hot OSB.  Waxes have melting point temperatures as low as 40°C and they have very low viscosities when they are liquids (Wolfmeier et al. 2000).  It is, therefore, possible to spray molten wax onto the surface of OSB as a post-treatment.  When OSB exits the hot press its surface temperature may be as high as 250°C.  If molten wax is sprayed onto such hot OSB surfaces it may be able to flow into and block the inter-strand voids of OSB, before solidifying to form a water repellent barrier.  I hypothesize that such wax-treatments may reduce the rate of water absorption and thickness swelling of OSB, as hypothesized in Chapter 1.    39  Chapter 3. Wax properties that affect the water repellency of wax-treated OSB 3.1 Introduction The aim of this chapter is to characterize the waxes that I sprayed onto OSB surfaces in Chapters 4 and 5.  Some of the properties that are likely to affect the performance of wax as a molten water-repellent treatment for OSB were identified and discussed in the previous chapter.  The properties that are measured in this chapter are: (1) chemical composition; (2) water repellency; (3) melting point temperature; and (4) viscosity. Thirteen waxes were sourced based on their expected melting point temperatures and chemical composition.  Three wax blends, each consisting of equal proportions of two waxes with notably different properties, were prepared to determine the combined effect of their properties on the water repellency of wax-treated OSB.  Two more wax blends were prepared by mixing one part ethylene maleic anhydride (EMA) with three parts wax.  This was done to created wax blends with expected melting point temperatures and polarity of the wax blends (Grauman 2013).  All wax blends were prepared by melting the individual waxes or additives together.   The water repellency of pure wax surfaces and molten wax-treated OSB surfaces were determined by measuring the contact angles that water droplets made on treated surfaces.  Two response variables were measured: (1) initial contact angle; and (2) the time it took for water droplets to spread and form a contact angles of less than 90° (abbrev. as t<90°).  Regression analysis was used to examine the relationship between the water repellency of pure wax and molten wax-treated OSB surfaces.  I hypothesize that there will be a positive correlation between the variables measured on each of the two surface types.  Because surface roughness affects apparent contact angle (Wenzel 1949), a profilometer was used to measure the roughness of the pure wax surfaces.  The roughness data was statistically analysed and the results were used to help explain the contact angles of water droplets on pure wax surfaces.   40  There are also factors that may affect the contact angles that form on wax-treated OSB surfaces.  The wood strands in OSB, for example, are thermally modified and partially coated with resin and wax when the board is manufactured.  Unsal et al. (2010) measured contact angles on thermally post-treated OSB panels and reported the initial contact angle to be as large as 100°, while contact angles on untreated OSB were approximately 75°.  Semple et al. (2009) reported the initial contact angles of water droplets on untreated OSB surfaces to be 108°.  They also reported that water droplets placed on untreated OSB surfaces remained there for a shorter time than when placed on OSB surfaces sprayed with water-based wax emulsions or linseed oil-wax solutions.  Thus, I hypothesize that the initial contact angles of water droplets placed on molten wax-treated OSB surfaces will be higher than those on untreated OSB surfaces, and that the  t<90° times on wax-treated surfaces will be longer than those on untreated surfaces. Lastly, based on suggestion that waxes with polar functional groups are better water repellents for solid wood (Borgin 1970), I examine the relationship between the acid number of wax, a proxy measure for polarity, and the contact angles that water droplets make on wax-treated OSB surfaces.   3.2 Materials and methods 3.2.1 Waxes The thirteen individual waxes and the five wax blends are listed in Table 3.1.  Animal waxes included beeswax and lanolin, while vegetable waxes included carnauba wax, soy wax, and stearic acid (sourced from palm wax).  Mineral waxes included microcrystalline wax, Vaseline, Merkur 300, Tekniwax 600, and a paraffin wax commercially called “synthetic beeswax”.  Synthetic beeswax is used as a cheap alternative to beeswax when making candles.  The original patent for Vaseline states that it is: “the residuum of petroleum that is left after the greater part of petroleum has been distilled off” (Chesebrough 1872).   Merkur 300, which was donated by Sasol Wax (South Africa), is also a petroleum jelly, similar to Vaseline.  Original,   41  unscented Vaseline was sourced from a local pharmacy in Vancouver, Canada.  The raw, unfiltered lanolin was donated by Cape Mohair and Wool (South Africa), while carnauba wax (grade T1), filtered beeswax, stearic acid, synthetic beeswax, and microcrystalline wax were purchased from Wicks and Wax, in Burnaby, Canada.  Soy wax was purchased from Maiwa Supply, on Granville Island in Vancouver, Canada.  Synthetic waxes included three Fischer-Tropsch waxes that were donated by Sasol Wax (South Africa) (Figure 3.1).  Sasol Wax also donated Tekniwax 600. The wax blends that were custom-made for the study were melted together at a 1:1 or a 3:1 weight ratio (Table 3.1).  Proportional amounts of each wax were weighed and the solids were placed together in a single glass beaker.  The glass beaker was then placed in an oven, set at    approximately 10°C above the melting point temperature of the wax with the highest melting point.  Once the wax in the glass beaker was liquid, the blend was stirred together using a glass rod.  The required amount of wax for each experimental replication, of each experiment, was independently blended, shortly beforehand, using new parent stock.  Therefore, only small quantities of the wax blends, typically between 15 to 50 g, were freshly prepared whenever needed.  Two of the blends that were prepared contained ethylene maleic anhydride (EMA).  These blends were included because of their expected high melting point temperatures and polarity.      42  Table 3.1. The 13 waxes and five wax blends used to treat OSB Wax Origin Beeswax Animal Lanolin Animal Soy wax Vegetable  Stearic acid Vegetable  Carnauba wax Vegetable  Sasolwax C Fischer-Tropsch Tekniwax 801 Fischer-Tropsch Tekniwax 600 Petroleum Sasolwax M3M Fischer-Tropsch Merkur 300 Petroleum jelly  Vaseline Petroleum jelly Microcrystalline wax Petroleum Synthetic Beeswax Petroleum Beeswax + Sasolwax C (1:1) Blend Beeswax + Vaseline (1:1) Blend Beeswax + Synthetic Beeswax (1:1) Blend Beeswax+ Ethylene Maleic Anhydride (3:1) Blend Sasolwax M3M + Ethylene Maleic Anhydride (3:1) Blend    Figure 3.1. Fischer-Tropsch and paraffin waxes as they were received from Sasol Wax, South Africa 3.2.2 Contact angle measurements 3.2.2.1 Experimental design The sessile drop method was used to measure the contact angle of water droplets on two types of surfaces: (1) wax-coated glass slides; and (2) wax-treated OSB surfaces.  Wax-coated glass slides are sometimes referred to as “pure wax surfaces” in the text below.   A randomized block   43  design was used to examine the effect of the different waxes on the contact angles that water droplets made on each of the two surface types (pure wax or OSB).  Measurements on wax slides were replicated eleven times and measurements on OSB were replicated six times.  OSB panels were donated by Tolko Industries, Canada (more information on the OSB panels can be found in Section 4.2.3).   An independent OSB panel was used for each experimental replication (block), and panels were sampled from Tolko’s production line at different times to account for random variation in board properties caused by variation in raw materials and the manufacturing process.   A 5 µL droplet of distilled water was placed onto the surface in question (pure wax or OSB) and images of the droplets were recorded over time.  Water droplet volume had a standard deviation of 0.3 µL.  Contact angles were calculated using software programed with a Young-Laplace algorithm (CAM 200 software, KSV Instruments, 2007. CAM 200, 3rd edition, Espoo, Finland).   Analysis of variance, for a randomized block design, was used to determine how the wax-treated surfaces differed with regard to: (1) initial contact angle; and (2) the time it took water droplets to spread and form contact angles less than 90°.   The statistical program Genstat 12.1 (VSN International 2009) was used to analyze data with a 95% confidence interval (α = 0.05) and to check the assumptions of ANOVA (i.e. independent observations, normality, and equal variance).  Results are presented in graphs and error bars on each graph (± standard error of difference, p < 0.05) can be used to estimate whether differences between individual means are statistically significant.  3.2.2.2 Sample preparation A table saw (Altendorf F45 ELMO) was used to cut a square piece of OSB (150 x 150 x 18 mm3) from a random location on an independent OSB panel.  A band saw (Ryobi BS 902) was then used to divide the square into 20 strips (75 x 15 x 18 mm3); so that the surface strands of each strip were oriented perpendicular to its length.  A wax treatment was randomly assigned to 18 of the strips and one strip was left untreated.  The remaining (20th) strip was discarded.  The 19 selected samples were then oven dried at 100 ± 2°C for 24 h, and once dried they were placed in a vacuum oven at 90 ± 1°C.   44  OSB samples, including untreated control samples, were then individually placed in a second oven (170°C), between two heated metal plates (1kg each), for 10 min.  This was done to mimic the temperatures reached when OSB is pressed and to ensure that the surface was hot enough to prevent molten wax, which was subsequently applied, from solidifying too quickly on the surface of the sample.  Approximately 20 g of each wax type was placed in a 125 mL glass beaker and heated to 100 ± 2°C.  A disposable pipette was used to apply a 1 µL drop of molten wax close to the center of each sample.  Voids on the surface of the sample were avoided when placing the wax droplet on the OSB and care was taken to ensure the wood grain of the treated area ran perpendicular to the length of the OSB strip.  The molten droplet was left to absorb into the OSB surface for ten seconds, before the remaining wax, on top of the surface, was wiped off using a clean cotton cloth.  This was done to prevent the excess wax forming a thick coating over the wood surface.   The treated OSB samples were conditioned at 20 ± 1 °C and 65 ± 5% relative humidity for a minimum of five days before contact angle measurements were made.    Similarly, wax-coated glass slides were also prepared for each wax type.  Approximately 20 g of each wax was individually placed in a 125 mL glass beaker, which was then placed in an oven (100 ± 2°C) until the wax was molten.  Individual glass slide were vertically dipped into the molten wax for 1 min, before being removed and horizontally placed on a flat surface; where the wax was left to solidify. Coated slides were placed in a desiccator for a minimum of 1 hour before contact angle measurements were taken.  Care was taken to keep the prepared samples free of any surface contamination, which could have affected contact angle measurements.   3.2.2.3 Contact angle measurements The sessile drop method was used to measure contact angles.  All measurements were made in a climate controlled room (20 ± 1 °C and 65 ± 5% r.h.), using a goniometer (KSV CAM 101).   The goniometer consisted of a digital camera, a height-adjustable stage, and a syringe filled with distilled water (Figure 3.2).  The digital camera was connected to a personal computer, so that its image could be viewed on-screen, in real time.  The height-adjustable stage was positioned   45  directly in front of the camera, and the syringe was fixed in a vertical position above the stage.  Samples (pure wax or OSB) were placed on the stage and it was adjusted so the surface of interest appeared on the lower portion of the computer screen.  OSB surfaces were positioned so that the wood’s grain directly below the syringe ran parallel to the image plane, i.e. perpendicular to the location of the camera.  This was done to record how water droplets spread along the grain.  A 5 µL drop of distilled water was placed on the positioned surface and images were recorded every 1 s for 480 frames and every 15 s for 360 frames thereafter. The left and right contact angle of each image was calculated using software programed with a Young-Laplace algorithm (CAM 200 software, KSV Instruments, 2007. CAM 200, 3rd edition, Espoo, Finland).  From each measurement, the initial contact angle (Ci) and the time it took for the contact angle to spread and form an angle of less than 90 degrees (t<90°) was recorded.  Figure 3.2. Goniometer equipped with a camera and syringe (left) and  CAM 200 software (right), which was able to calculate the geometry of water droplets using a Young-Laplace algorithm Syringe Height-adjustable stage Sample Camera Software displaying video footage    46  3.2.3 Surface confocal profilometry  3.2.3.1 Surface roughness measurements on pure wax surfaces A white-light non-contact confocal profilometer (Altisurf 500 ®, ALTIMET, France) was used to measure the roughness of wax-coated glass slides (Figure 3.3).  Wax-coated glass slides were prepared as described above (Section 3.2.2.2).    A randomized block design, with a single factor (wax type) was used to determine whether the surface roughness of wax-coated glass slides differed.  The experiment was replicated three times and new samples were prepared for each replication (block). Statistical analysis was performed using Genstat 12.1 (VSN International 2009) (α = 0.05), as described above (Section 3.2.2.1).  Figure 3.3. The white-light non-contact confocal profilometer (Altisurf 500 ®, ALTIMET, France) used to scan the surface profiles of pure wax surfaces The profilometer was used to scan a 10 x 10 mm2 area on each sample surface. The gauge resolution was set at 0.333 nm (Head No.3) and the sampling rate was 30 Hz.  Profiles were scanned from west to east with an x-axis spacing of 8.5 µm and y-axis spacing of 1111 µm.  Ten White light source  Sample stage   47  profiles, each consisting of 1179 measured points, were scanned per specimen.  Measurement speed was 250 µm / s and each scan took 8 min 4 s.  The image analysis software package, AltiMap Premium (Version 6.2.6142), was used to analyse the profiles and extract the roughness data for each scanned sample.  First, the ten profiles were uploaded into the program and any non-measured points were filled using data from neighbouring points.  The average surface roughness (Ra) of each profile was then calculated, using a 0.8 mm roughness cutoff (λc).  The Ra value of a profile is the arithmetic mean deviation of its peaks and valleys from its center line (Ashori et al. 2008).  The Ra values of the ten profiles were averaged to estimate the mean roughness of the entire 10 x 10 mm2 area. 3.2.3.2 Profilometry image rendering Topographical images of five of the different types of wax-coated glass slides were rendered by combining high resolution profile scans for each surface.  The following five pure wax surfaces were scanned: (1) stearic acid; (2) carnauba wax; (3) microcrystalline wax; (4) Vaseline; and (5) Merkur 300.  The methods used were similar to those described Section 3.2.3.1, however, the profiles were scanned at much higher resolutions.  The sampling rate was set at 30 Hz and the gauge resolution was set at either 3.333 nm (Head No.2) or 0.333 nm (Head No.3).  Scan areas were either 10 x 10 mm2, or 5 x 5 mm2, or 1 x 1 mm2.  The areas were scanned from west to east, with an x-axis spacing of 3.5 µm and y-axis spacing varying between 3.5 µm and 4.5 µm.  The measurement speed was 100 µm / s.  The image analysis software, AltiMap Premium (Version 6.2.6142), was used to render the images.  Each individual profile was levelled by subtracting the points from a 3rd degree least squared polynomial.  A thresholding function was then used to reduce the heights of peaks and the depths of valleys that fell outside the 99.5th percentile.  Rendered images are presented in Section 3.3.2.2. 3.2.4 Scanning electron microscopy  Five OSB surfaces, each coated with a different wax type, were examined using scanning electron microscopy (SEM).  The waxes were: (1) beeswax; (2) carnauba wax; (3) Merkur 300;   48  (4) Tekniwax 600; and (5) Vaseline.  A table saw (Altendorf F45 ELMO) was used to cut a square piece of OSB (150 x 150 x 18 mm3) from a random location on an independent OSB panel (more information on the OSB panel can be found in Section 4.2.3).  A small resaw was then used to isolate 5 mm of the face layer by splitting each block across its horizontal plane.  The isolated surface layer, therefore, measured 150 x 150 x 5 mm3 after resawing.  A bandsaw (Ryobi BS 902) was then used to cut five small equilateral triangles, with side lengths of 10 mm, from areas on the face layer that were free of voids.  The side lengths of the triangular samples were then reduced to approximately 5 mm by holding the samples between thumb and forefinger and sanding the sides down with 220 grit abrasive paper.  The triangular shaped samples were then placed in an oven at 100 ± 2°C for a minimum of 1 h.  Approximately 20 g of each of the five waxes mentioned above were individually placed in separate 125 mL glass beakers.  The five beakers were then placed in an oven (100 ± 2°C) until the waxes were molten.  Each of the five small triangular OSB samples was picked up using clean tweezers and was dipped into one of the molten waxes for three seconds.  The hot, wax-coated samples were then placed in a Petri dish and left in a vacuum desiccator for 1 h at 22°C, before being attached to a 12 mm diameter aluminum SEM stub using epoxy resin as an adhesive.  All samples were mounted on the same stub, hence the need for samples to be triangular.  A digital photograph of the mounted samples was taken and individual samples were labelled on the picture for future identification (Figure 3.4).   A sputter coater (Nanotech SEMPrep II) was used to coat the samples with an 8 nm layer of gold, before they were examined using a field emission scanning electron microscope (Hitachi S-4700, FESEM), with an accelerating voltage of 5 kV. Secondary electron images of the wax coated OSB surfaces were obtained and saved as TIFF files.   49   Figure 3.4. The 12 mm diameter SEM stub with the five wax-treated OSB samples that were examined using scanning electron microscopy: (A) beeswax; (B) carnuaba wax; (C) Merkur 300; (D) Tekniwax 600; (E) Vaseline  3.2.5 Melting point temperatures Melting point temperatures of waxes were characterized by measuring their congealing points (ASTM D938 – 12) and their drop melting points (ASTM D127 – 08)).  Together these two measurements provide an estimate of the melting point range of each wax.  3.2.5.1 Congealing point: ASTM D938 – 12  A drill press was used to drill a 5 mm hole through the length of a small cone-shaped cork stopper.  A thermometer was pushed through the hole, so that the bulb of the thermometer extended 20 mm from the narrow side of the cork.  Approximately 50 g of wax was placed in a 125 mL glass beaker.  The glass beaker, containing the wax, and an empty Erlenmeyer flask (125 mL) were both heated to 100 ± 2°C.  Once the wax was molten, the beaker was removed from the oven and the bulb of the thermometer was dipped into the wax.  The thermometer was used to gently stir the wax until the thermometer reading stabilized.  The thermometer was then quickly removed from the beaker and turned horizontally, so that a liquid wax droplet remained attached to its end.  The thermometer was continuously rolled between thumb and A B C D E   50  forefinger to ensure that the droplet remained hanging on the end of the bulb.  While doing this, the hot Erlenmeyer flask was removed from the oven and the thermometer bulb was secured inside the flask by fitting the cork stopper. The hot Erlenmeyer flask slowed the rate of cooling of the molten wax droplet.  The entire assembly was slowly rotated about its horizontal axis until the hanging wax droplet congealed enough to rotate up with the bulb.  The temperature at which this occurred was recorded as the congealing point temperature of the wax in question.  The procedure was repeated three times for each wax and the average (mean) temperature is reported (Table 3.3).      3.2.5.2 Drop melting point: ASTM D127 – 08. Two small cone-shaped cork stoppers were collected.  A number of small grooves (3 mm deep) were then cut along the sides of both corks using a hand saw.  A drill press was then used to drill a 5 mm diameter hole through the length of each cork.  A thermometer was pushed through each hole, so that the bulb of the thermometers extended 100 mm from the narrow side of the corks.  Both thermometers were then placed in a refrigerator and chilled to approximately 4°C. Approximately 50 g of wax was placed in a 125 mL flask and heated to 100 ± 2°C. One of the chilled thermometers was removed from the refrigerator.  Its tip was wiped clean of any moisture and it was very briefly dipped into the molten wax.  The thermometer bulb, with its wax-covered tip, was then immersed in water (16 ± 2°C) for a minimum of 5 min.  This procedure was repeated for the second thermometer.  Each thermometer was then fitted to an empty test tube (25 mm in diameter and 150 mm long).  A 1500 mL flask was filled with water and placed on a heating plate.  The two test tubes were vertically suspended in the water bath so that the water level was just below their rims.  The hot plate was switched onto “medium heat” (approximately 160°C) and the water was heated.  The two temperatures, when the wax at the tip of each of the two thermometers melted and dropped off, were recorded.  The drop melting point of the wax is reported as the average of these two temperature measurements.    51  3.2.6 Viscosity The apparent viscosity of each wax was measured using the standard test method, ASTM D2669 – 06, however, the amount of wax used for each measurement was reduced from 800 g to 200 g, because insufficient amounts of each wax were available to use the standard test amount.    Approximately 200 mL of molten wax was poured into a 250 mL glass beaker (Griffin standard form).  The glass beaker was placed on a hot plate and a thermometer was suspended, with its bulb immersed just below the surface of the molten wax.  A Brookfield synchro-electric viscometer (model L T,  0 rpm, No. 2 spindle) was positioned above the glass beaker, so that its spindle was immersed up until the indicated immersion mark.  The wax was heated to    0°C above its melting point and then slowly cooled.  The dynamic viscosity of the wax was measured at 100°C, as well as at temperatures 25°C, 15°C, and 5°C above the melting point of the wax.  Measurements were repeated three times and the average for each wax is reported in Table 3.4.    3.2.7 Acid number titration The empirical acid number was calculated according to the standard test procedure ASTM D1386-10.  A 0.1 N solution of ethanolic potassium hydroxide was made by slowly dissolving 6.6 g of potassium hydroxide (KOH) (Sigma-Aldrich, ACS reagent, ≥85%, pellets) in 5.6 g of distilled water and then diluting the solution to 1000 mL with ethanol (reagent grade, anhydrous, denatured, Sigma-Aldrich). The ethanolic potassium hydroxide solution was then standardized with a 0.1 N solution of hydrochloric acid (HCl) (hydrochloric acid concentrate, standard solution, Sigma-Aldrich).  As an indicator, 1 g of phenolphthalein was dissolved in 100 mL of ethanol.  Between 1 - 2 g of the wax in question was weighed and placed in a 250 mL glass beaker.  The beaker was placed on a warm hot plate and 40 mL of xylene (reagent grade, Sigma-Aldrich) was added to dissolve the wax.  Five drops of phenolphthalein was added to the xylene solution.  The solution was then titrated with ethanolic potassium hydroxide until it turned pink for at least 10 s.  The volume of ethanolic potassium hydroxide necessary to neutralize the solution was used to calculate the acid number. The acid number represents “the   52  number of milligrams of potassium hydroxide necessary to neutralize 1 g of the sample” (ASTM 2010).  The following equation was used to calculate the acid number:              (   )(    )(    )         (Equation 3.1) Where:  A = millilitres of alkali solution required for titration of the sample B = millilitres of alkali solution required for titration of a blank sample N = normality of the alkali solution C = grams of sample used 3.2.8 Fourier transform infrared (FTIR) spectroscopy Wax slides were prepared by individually placing 10 g of each wax in 125 mL glass beakers, heating the waxes in an oven (100 ± 2°C), and then vertically dipping a glass slide into each wax.  The coated slides were placed on a horizontal surface to allow the waxes to cool and solidify to form an even surface.  The slides were then placed in a desiccator for a minimum of 1 h, before infra-red spectra were obtained using an FTIR spectrometer (Perkin Elmer Spectrum One, Waltham, MA, USA)  equipped with a single bounce attenuated total reflectance accessory (PikeMiracle, PIKE Technologies, WI, USA).  Before each measurement a background spectrum was obtained. Each infra-red spectrum consisted of 24 scans taken over a range from 4,000 – 700 cm−1 at a resolution of 4 cm−1. The recorded FTIR spectra can be found in Appendix 1. 3.2.9 Statistical methods  Regression analysis was used to examine the relationships between selected wax properties and the water repellency of wax-treated OSB.  The statistical program, “R Studio”, was used to analyze the data with a 95% confidence interval (α = 0.05) and to check the assumptions of ANOVA (RStudio2014).  Results for the regression analysis are reported in Section 3.3.7 -3.3.8.   53  3.3 Results 3.3.1 Contact angles  Analysis of variance revealed significant (p < 0.05) differences between the initial contact angles of water droplets on different types of wax-coated glass slides (p < 0.001), as well as on different types of wax-treated OSB surfaces (p = 0.01) (Table 3.2).  Furthermore, there were also significant differences (p < 0.001) in the time it took for water droplets to form contact angles of less than 90°, on both wax-coated glass slides and wax-treated OSB surfaces.  The analyses of variance and relevant data is appended to this thesis (Appendix 1). Table 3.2. Summary of the ANOVA for the initial contact angles of 5 µL water droplets and the time it took droplets to form contact angles of less than 90° (t<90°) on wax-coated slides and wax-treated OSB surfaces (averaged across all wax types)    Surface type p -value Initial contact angle (°) t<90° (min) Wax-coated glass slides < 0.001 < 0.001 Wax-treated OSB surface 0.01 < 0.001 3.3.1.1 Glass slides coated with different wax types Water droplets that were placed on glass slides coated with stearic acid formed initial contact angles of 128°, significantly larger than those of droplets on any of the other wax types (Figure 3.5).  Slides coated with a blend of Sasolwax M3M and ethylene maleic anhydride had the second largest initial contact angles, measuring 109.7°, significantly larger than most other wax types; except for slides coated with the six wax types that have clear data points in Figure 3.5.  The smallest contact angle formed on slides coated with lanolin (100.6°), however, there were no significant (p > 0.05) differences  in the contact angles of water droplets on lanolin coated slides and slides coated with: (1) carnauba wax (100.8°); (2) Sasolwax C (101.6°); (3) synthetic beeswax (103.6°); or (4) Vaseline (102.1°).   54     Figure 3.5. Initial contact angle of 5µL water droplets placed on glass slides coated with different wax types (n = 11).  Note the large mean initial contact angle of water droplets on stearic acid.  Differences larger than the least significant difference (LSD = 3.02°) are statistically significant at a 5% level.  Clear data points are not significantly different to the data point for a blend for Sasolwax M3M and ethylene maleic anhydride (M3M+EMA). Refer to Appendix 1 for precise numerical values The t<90° on microcrystalline wax surfaces was 42.7 min, significantly longer than those on any of the other wax coated slides (Figure 3.6).  The 2nd longest t<90° was for glass slides coated with Tekniwax 600 (37.3 min) and the 3rd longest time was for slides coated with stearic acid (31.8 min).  The t<90° times for these three waxes were significantly (p < 0.05) different from each other, as well as those of all other wax types.  The 4th longest t<90° was for slides coated with Tekniwax 801 (22 min), however, there was no significant (p < 0.05) difference in this time and the t<90° times of the four wax-coated slides that have clear data points in Figure 3.6. The t<90° on lanolin coated slides was 21.6 seconds, smaller than those of any of the other wax-coated slides, but not significantly different from those of slides coated with Merkur 300 (1.35 min) or Sasolwax C (2.3 min).    55   Figure 3.6. The time it took for 5µL water droplets to form contact angles of less than 90° on glass slides coated with different wax types (n = 11).  Differences larger than the least significant difference (LSD = 4.73 min) are statistically significant at a 5% level.  Clear data points are not significantly different to the data point for Tekniwax 801 (T801). Refer to Appendix 1 for precise numerical values 3.3.1.2 OSB samples treated with different wax types On untreated OSB surfaces, water droplets formed an initial contact angle (118.6°) significantly larger (p < 0.001) than on OSB surfaces treated with soy wax (105°) (Figure 3.7).  OSB surfaces treated with soy wax had the smallest initial contact angles, significantly smaller than those of most of the other wax types, but not significantly smaller than those of surfaces treated with: (1) carnauba wax (114.3°); (2) lanolin (113.6°); (3) microcrystalline (114.2°); or (4) synthetic beeswax (113.7°).  The largest initial contact angles were formed on surfaces treated with Merkur 300 (124.8°), however, there were no significant (p > 0.05) differences between these contact angles and those formed on untreated OSB surfaces, nor were there any differences between them and those formed on OSB surfaces treated with any of the eleven wax-treated surfaces that have clear data points in Figure 3.7.      56    Figure 3.7. Initial contact angle of 5µL water droplets placed on OSB surfaces treated with different wax types (n = 6). Differences larger than the least significant difference (LSD = 9.4°)  are statistically significant at a 5% level.  Clear data points are not significantly (p > 0.05) different to the data point for Merkur 300.  Refer to Appendix 1 for precise numerical values The average t<90° time for water droplets that were placed on untreated OSB surfaces was 8.3 min (Figure 3.8).  There were no significant differences between this t<90° time and those of droplets on surfaces treated with any of the following five wax types: (1) lanolin (0.49 min); (2) Sasolwax C (5.3 min); (3) soy wax (13.1 min); (4) Tekniwax 801 (14.8 min); or (5) Vaseline (14.9 min).  The shortest t<90° time was for water droplets placed on OSB surfaces treated with lanolin, however, there were no significant (p > 0.05) differences between these times and those of droplets placed on either untreated OSB surfaces or surfaces treated with Sasolwax C.  The longest t<90° time was for droplets placed on surfaces treated with a blend of beeswax and Sasolwax C (31.5 min), however, there were no significant differences between the t<90° times of these droplets and those of droplets placed on surfaces treated with any of the nine wax types that have clear data points in Figure 3.8.   57   Figure 3.8. The time it took for 5µL water droplets to form contact angles of less than 90° on OSB surfaces treated with different wax types (n = 6).  Differences larger than the least significant difference (LSD = 9.22 min) are statistically significant at a 5% level.  Clear data points are not significantly different to the data point for a blend of beeswax and Sasolwax C (Bee+Sc). Refer to Appendix 1 for precise numerical values 3.3.2 Surface confocal profilometry  3.3.2.1 Surface roughness measurements of wax-coated glass slides The average surface roughness (Ra) of glass slides coated with stearic acid was 64.8 µm, higher than those of any of the other wax-coated slides (Figure 3.9).  Tekniwax 600 coated slides had the 2nd roughest surface (18.2 µm), followed by Sasolwax C (14.2 µm).  These three waxes had surfaces roughness values that were significantly (p < 0.05) different from each other as well as from those of surfaces created by the other waxes.  The 4th roughest surfaces were those of glass slides coated with a blend of beeswax and Sasolwax C (7.7 µm).  These surfaces , however, were not significantly (p > 0.05) rougher than those of wax slides coated with any of the following five wax types: (1) soy wax (6.8 µm); (2) Sasolwax M3M (6 µm); (3) beeswax (5.8 µm); (4) Vaseline (5.8 µm); and (5) a blend of beeswax and ethylene maleic anhydride (5.2 µm).  The   58  smoothest surfaces were those of glass slides coated with lanolin (1.6 µm).  The surface roughness of lanolin coated surfaces, however, was not significantly (p > 0.05) different than those of the five waxes that have clear data points in Figure 3.9.  Figure 3.9. Average surface roughness (Ra) of glass slides coated with different wax types (n = 3).  Differences larger than the least significant difference (LSD = 2.61 µm) are statistically significant at a 5% level.   Clear data points are not significantly different to the data point for lanolin (Lan). Refer to Appendix 1 for precise numerical values   3.3.2.2 Profilometry images Topographical images of five of different types of wax-coated glass slides are shown in Figures 3.10 to 3.13.  Notice that the z-axis scale for Figure 3.10 is reported in millimetres while those in the other figures are reported in micrometers.  Stearic acid crystals were large enough to be visible to the naked eye. The height differences between the top and bottom of the stearic acid crystals were so large that the valley regions fell beyond the 3 mm focal plane of the profilometer (Figure 3.10).    59   Figure 3.10. Profilometry image of the surface of a glass slide coated with stearic acid. The 10 x 10 mm2 image consists of 1177 profile scans, scanned with x-axis spacing of 8.5 µm and y-axis spacing of 8.5 µm.  The gauge resolution for the z-axis was 0.333 nm (Head No.3).  The white and brown areas represent large wax crystals, while the black areas represent unmeasured points that were beyond the 3 mm focal plane of the profilometer head The surfaces of glass slides coated with carnauba wax (Figure 3.11) and Vaseline (Figure 3.13) appeared to be relatively smooth, while the surfaces of the slides coated with microcrystalline wax (Figure 3.12) had microscopic peaks (colored white) and valleys (colored black).   60   Figure 3.11. Profilometry images of the surface of a glass slide coated with carnauba wax. The original 5 x 5 mm2 image (left) consists of 1251 profile scans with x-axis spacing of 3.5 µm and y-axis spacing of 4 µm. The area within the dashed white square on the original image is magnified on the right. The gauge resolution for the z-axis was 3.333 nm (Head No.2)   Figure 3.12. Profilometry images of the surface of a glass slide coated with microcrystalline wax.  The original 5 x 5 mm2 image (left) consists of 1112 profile scans, scanned with x-axis spacing of 3.5 µm and y-axis spacing of 4.5 µm.  The gauge resolution for the z-axis was 3.333 nm (Head No.2). The magnified image of the area within the dashed white square (right) shows that the surface of microcrystalline wax formed microscopic peaks (white) and valleys (black), similar to those found on the super-hydrophobic surfaces of the leaves of some plant species (Barthlott and Neinhuis 1997)     61   Figure 3.13. Profilometry images of the surface of a glass slide coated with two different petroleum jellies, Vaseline (left)  and  Merkur 300 (right). The 1 x 1 mm2 images consists of 287 profile scans, scanned with x-axis spacing of 3.5 µm and y-axis spacing of 3.5 µm.  The gauge resolution for the z-axis was 3.333 nm (Head No.2) 3.3.3 Scanning electron microscopy SEM photomicrographs of (1) beeswax; (2) carnauba wax; (3) Merkur 300; (4) Tekniwax 600; and (5) Vaseline on OSB are shown in Figures 3.14 – 3.18.  The surfaces of all wax-treated samples were totally covered (coated) with wax and there were considerable differences in the morphology of the surfaces.  OSB surfaces coated with beeswax had tiny holes present on the surface (Figure 3.14).  Whether these holes were merely superficial, or whether they penetrated the OSB surface, was not clear.  OSB surfaces coated with carnauba wax were smooth, but large cracks were present (Figure 3.15).  Merkur 300 tended to agglomerate on certain areas on OSB surfaces and its surface morphology was not as smooth as those of beeswax and carnauba wax (Figure 3.16).  OSB coated with Tekniwax 600 had small crater-like formations on the surface (Figure 3.17).  Vaseline coated OSB surfaces were very smooth and the morphology suggests that a certain amount of Vaseline was absorbed into the hot OSB surface (Figure 3.18).   62   Figure 3.14. SEM photomicrographs of an OSB surface coated with beeswax.  The lower magnification image (left) shows that wax covered the OSB surface, but that tiny holes were present in the coating. The image on the right showes the area within the dashed white rectangle at a higher magnification   Figure 3.15. SEM photomicrographs of an OSB surface coated with carnauba wax. The lower magnification image (left) shows that the wax totally covered the OSB surface and formed a smooth coating  with large and small micro cracks at the surface.  The image on the right shows the area within the dashed white rectangle at a higher magnification      63   Figure 3.16.  SEM photomicrographs of an OSB surface coated with a Fisher-Tropsch wax (Merkur 300).  The lower magnification image (left) shows that the surface of Merkur 300 is not as smooth as those of beeswax or carnauba wax. The image on the right shows the area within the dashed white rectangle at a higher magnification.  Merkur 300 tended to agglomorate around certain areas  Figure 3.17. SEM photomicrographs of an OSB surface coated with a paraffin wax (Tekniwax 600).  The lower magnification image (left) shows that the surface of Tekniwax 600 appeared to be relatively rough. The image on the right shows the area within the dashed white rectangle at a higher magnification. Crater-like formations were visible on the surface     64   Figure 3.18. SEM photomicrographs of an OSB surface coated with a Vaseline.  The lower magnification image (left) suggests that some Vaseline was absorbed into the hot OSB surface.  The image on the right shows the area within the dashed white rectangle at a higher magnification. The surface topography of an area coated with Vaseline was very smooth 3.3.4 Melting point temperature The drop melting and congealing point temperatures of the 18 different waxes are reported in Table 3.3.  The congealing point temperatures were on average 2.6°C lower than the drop melting point temperatures.  Together these two temperatures can be used to estimate the melting point temperature range of a wax. The highest two drop melting point temperatures (87°C and 85°C) were recorded for wax blends that contained ethylene maleic anhydride.  Carnauba wax had the 3rd highest drop melting point temperature (81°C).  Both microcrystalline wax (73°C) and synthetic beeswax (77°C) also had relatively high drop melting point temperatures.  Sasolwax M3M (63°C) had the highest drop melting point temperature of all the Fischer-Tropsch waxes, while Sasolwax C  (31°C)  had the lowest drop melting point temperature of this group of synthetic waxes.        65  Table 3.3. Melting point temperatures of different waxes measured according to ASTM D938-12 and ASTM D127 08 Wax Origin ASTM D938-12: Congealing point (°C) ASTM D127 08: Drop melting point  (°C) Sasolwax C Fischer-Tropsch 29 31 Lanolin Animal 35 - Tekniwax 801 Fischer-Tropsch 42 44 Soy wax Vegetable  51 54 Merkur 300 Petroleum Jelly 54 55 Vaseline Petroleum Jelly 53 59 Beeswax + Sasolwax C (1:1) Blend 54 59 Beeswax + Vaseline (1:1) Blend 58 62 Tekniwax 600 Petroleum 62 63 Stearic acid Vegetable  61 63 Beeswax Animal 64 65 Sasolwax M3M Fischer-Tropsch 63 68 Beeswax + Synthetic beeswax (1:1) Blend 69 73 Microcrystalline wax Petroleum 72 73 Synthetic beeswax Petroleum 75 77 Carnauba wax Vegetable  81 81 Sasolwax M3M + EMA* (3:1) Blend - 85 Beeswax + EMA* (3:1) Blend - 87 *EMA = Ethylene maleic anhydride     3.3.5 Viscosity The apparent viscosities of the 18 waxes are reported in Table 3.4.  The wax with the highest viscosity at 25°C above its melting point was raw, unfiltered lanolin.  This was much higher than those of any of the other waxes, and was most likely affected by the presence of wool fibres in the lanolin.  The blend of beeswax and ethylene maleic anhydride also had a viscosity that was noticeably higher than those of most of the other waxes.  The viscosity of microcrystalline wax increased dramatically as it approached its congealing point.  The three waxes that consistently had the lowest viscosities were Sasolwax C, Merkur 300, and Tekniwax 801.       66  Table 3.4. Apparent viscosity of different waxes according to ASTM D2669-06   Viscosity (mPa·s)   100°C MP†+5°C MP+15°C MP+25°C Sasolwax C 4.4 6.9 6.3 5.3 Merkur 300 4.8 9.4 6.8 6.0 Tekniwax 801 5.5 11 8.8 7.5 Stearic acid 6.6 10.5 8.3 7.7 Sasolwax M3M 6.6 9.6 8.4 8.1 Beeswax + Sasolwax C (1:1) 7.5 12.8 10.3 10.2 Beeswax + Vaseline (1:1) 9.2 15.8 13.3 11.4 Vaseline 9.4 15.8 12.0 9.5 Tekniwax 600 10.3 18.3 15.0 12.8 Synthetic Beeswax 11.2 15.6 13.1 8.4 Soy wax 12.1 25.0 19.6 15.8 Beeswax 13.1 20.4 17.5 14.5 Beeswax + Synthetic Beeswax (1:1) 16.4 20.7 17.6 16.2 Microcrystalline wax 17.0 139.3 19.6 17.5 Carnauba wax 24.8 50.8 26.9 22.2 Lanolin 28.5 400 295 134.1 Sasolwax M3M + EMA* (3:1) 36.5 46.0 36.5 29.5 Beeswax + EMA* (3:1) 68.8 83.9 63.5 51.3 †MP = Wax melting point temperature (°C) *EMA = Ethylene maleic anhydride      3.3.6 Acid number titration The empirical acid numbers of the 18 different waxes are reported in Table 3.5.  Stearic acid had the highest acid number (215.3 mg KOH / g), followed by soy wax (31.5 mg KOH / g).  Beeswax had an acid number of 18.5 mg KOH / g and pure ethylene maleic anhydride had an acid number of 34.4 mg KOH / g.  A blend of three parts beeswax and one part ethylene maleic anhydride had an acid number of 22.4 mg KOH / g, while a 3:1 blend of Sasolwax M3M and ethylene maleic anhydride had an acid number of 8.6 mg KOH / g.  Since Fischer-Tropsch and mineral waxes all had acid numbers of zero, blends that contained any of these waxes and an equal amount of beeswax, had acid numbers of 9.2 mg KOH / g.        67  Table 3.5. Empirical acid number of waxes according to ASTM D1386-10 Wax Origin Acid value  (mg KOH  / g) Stearic acid Vegetable  215.3 Soy wax Vegetable  31.5 Beeswax + EMA* (3:1) Blend 22.4 Beeswax Animal 18.5 Beeswax + Sasolwax C (1:1) Blend 9.2 Beeswax + Vaseline (1:1) Blend 9.2 Beeswax + Synthetic Beeswax (1:1) Blend 9.2 Sasolwax M3M + EMA* (3:1) Blend 8.6 Carnauba wax Vegetable  6.8 Lanolin Animal 5 Sasolwax C Fischer-Tropsch 0 Tekniwax 801 Fischer-Tropsch 0 Tekniwax 600 Petroleum 0 Sasolwax M3M Fischer-Tropsch 0 Merkur 300 Petroleum jelly  0 Vaseline Petroleum jelly 0 Microcrystalline wax Petroleum 0 Synthetic Beeswax Petroleum 0 *EMA = Ethylene maleic anhydride 3.3.7 Relationships between contact angles on pure wax and on wax-treated OSB surfaces As mentioned above, the water droplets placed on glass slides coated with stearic acid had the highest initial contact angles, but this may have been due to the rough surfaces that stearic acid formed upon crystallisation (Figures 3.9 – 3.10).  Unlike the other waxes, stearic acid formed large crystals that could be seen with the naked eye, as mentioned above.  These large crystals caused surfaces coated with stearic acid to be much rougher than those of the other wax types.  For this reason, and the pronounced effect of surface roughness on contact angles (Wenzel 1949), stearic acid samples were excluded from analysis of the effects of wax type on the contact angles of water droplets on pure wax surfaces.   There was no correlation between the initial contact angles of water droplets on pure wax surfaces and those on wax-treated OSB surfaces. However, the initial contact angles of water droplets on pure wax surfaces were positively correlated with the t<90° times of water droplets   68  on both pure wax surfaces (p < 0.001) and wax-treated OSB surfaces (p = 0.02) (Figures 3.19 – 3.20).  There was no statistically significant (p > 0.05) relationship between the initial contact angles of water droplets on wax-treated OSB surfaces and the t<90° times on either of the two surface types.  Figure 3.19.  Relationship between (1) the initial contact angle of 5µL water droplets placed on glass slides coated with different wax types and (2) the time it took those droplets to spread and form contact angles of less than 90° on a pure wax surface (α = 0.05) 1001021041061081101120 5 10 15 20 25 30 35 40 45Initial contact angle on pure wax (°) t<90° on pure wax (min) y = 102.3 + 0.2x R2 = 0.54 p < 0.001   69     Figure 3.20. Relationship between (1) the initial contact angle of 5µL water droplets placed on glass slides coated with different wax types and (2) the time it took water droplets placed on wax-treated OSB surfaces to spread and form contact angles of less than 90° (α = 0.05) 3.3.8 Relationships between contact angles and melting point temperatures There was a weak positive correlation (p = 0.04; R2 = 0.25) between the initial contact angles of water droplets placed on pure wax surfaces and the melting point temperatures of the different wax types (Figure 3.21).  1001021041061081101120 5 10 15 20 25 30 35Initial contact angle on pure wax (°) t<90° on OSB (min) y = 101.4 + 0.2x R2 = 0.30 p = 0.02   70   Figure 3.21. Relationship between (1) the melting point temperatures of the different wax types and (2) the initial contact angles of 5µL water droplets placed on pure wax surfaces (α = 0.05) Furthermore, the melting point temperatures of the different waxes had a moderate positive correlation (p < 0.001; R2 = 0.57) with the t<90° times of water droplets on wax-treated OSB surfaces (Figure 3.22).  There was, however, no relationship between melting point temperatures and the initial contact angles formed on wax-treated OSB surfaces, or between the melting point temperatures and the t<90° times of water droplets on pure wax surfaces.   10010210410610811011230 40 50 60 70 80 90Initial contact angle on pure wax (°) Melting point temperature (°C) y = 99.6 + 0.09x R2 = 0.25 p = 0.04   71   Figure 3.22.  Relationship between (1) the melting point temperatures of the different wax types and (2) the times it took 5µL water droplets to spread and form contact angles of less than 90° on OSB surfaces treated with different wax types (α = 0.05) 3.4 Discussion In the introduction to this chapter I hypothesized that the initial contact angles of water droplets placed on molten wax-treated OSB surfaces would be higher than those on untreated OSB surfaces, and that the t<90° times on wax-treated surfaces would be longer than those on untreated surfaces.  I was also interested in examining the relationship between the acid number (polarity) of wax and the contact angles that water droplets form on wax-treated OSB surfaces.  In the following paragraphs I discuss: (1) the extent to which my results support or refute the aforementioned hypothesis; and (2) the relationship between the wax polarity and water-repellency of wax-treated surfaces. The initial contact angles of water droplets on wax-treated OSB surfaces were not significantly different from those on untreated surfaces.  This suggests that wax treatment did not affect the water repellency of OSB, however, the t<90° times on most wax-treated OSB surfaces were much longer than those of untreated OSB surfaces.  The initial contact angles of water droplets on pure wax surfaces were all greater than 100°, indicating that all the waxes were hydrophobic as expected.  The t<90° times on wax-treated OSB surfaces are likely to have been affected by 01020304050607080901000 5 10 15 20 25 30 35Melting point temperature (°C) t<90 ° on OSB (min) y = 33.6 + 1.44x R2 = 0.57 p < 0.001   72  penetration of the waxes into wood strands.  This supposition is supported by the observation that there was no relationship between t<90° times on pure wax surfaces and t<90° times on wax-treated OSB surfaces.  This suggests that most, but not all, waxes penetrated the OSB surfaces and did not form coatings.  Wax-treated OSB surfaces with no coatings probably retained their surface morphology, which could have affected the initial contact angle measurements.   There were no clear relationships between the polarity of the waxes and the contact angles on either pure wax surfaces or wax-treated OSB surfaces.  Adam and Jessop (1925) suggested that when molten wax with polar functional groups solidifies, the polar functional groups orient themselves in layers between the aliphatic chains, thus leaving the terminal methyl groups exposed at the surface.  Such orientation would result in similar contact angles for polar and nonpolar waxes.  My findings accord with this suggestion. There was a positive correlation between the melting point temperatures of the waxes and the t<90° times on wax-treated OSB surfaces.  This observation suggests that there were underlying interactions between the OSB surfaces and the wax; interactions which are related to the melting point temperatures.   According to Wolfmeier et al. (2000) the melting point temperature of wax increases as the length of the carbon chain and the number of polar functional groups increases, and it decreases as the degree of branching increases.  Furthermore, it has been observed that wax emulsions which consist of long chain n-alkanes, are more effective at reducing WA and TS of MDF and particleboard than those made with short chain n-alkanes (Roffael and May 1983; Schriever and Roffael 1984; Hague 1995; Roffael et al. 2005).  Hsu et al. (1988) also suggested that a high number of branched carbon chains could reduce the water repellency of paraffin wax.  My findings also suggest that the chemical structure of waxes (possibly the length and degree of branching of the carbon chains) may have affected the water repellency of wax-treated OSB.  Alternatively, the physical properties of the wax and whether it formed a coating on OSB may also be affected by its melting point temperature.   73  The average initial contact angles of water droplets on untreated OSB surfaces were higher than anticipated.  Based on previous findings I expected the initial contact angle on untreated OSB to be between 75° (Unsal et al. 2010) and 108° (Semple et al. 2009), but instead the average initial contact angle of water droplets on untreated OSB was 118.62°.   There are a number of factors that could account for this discrepancy between my results and those of previous studies: (1) thermal modification of OSB surfaces during sample preparation; (2) presence of resin and wax sizing on strands at the surface of the OSB samples; (3) presence of silicone release agent from press platens; and (4) the rough surface of untreated OSB.   My results suggest that the initial contact angle of water droplets on the surface of untreated OSB may not be a good indicator of the moisture resistance of OSB.  Instead, it appears that t<90° times might be better at predicting the WA and TS of OSB panels.  Most of the initial contact angles on pure wax surfaces were within the expected ranges of 94° to  109° for vegetable waxes (Holloway 1969),  and 105° to 114°  for paraffin waxes (Adam 1963).  Meiron et al. (2004) reported a slightly larger contact angle for beeswax, but this was expected since they measured the advancing contact angle, which is always larger than the static contact angle which I measured (Adam 1963).  Similarly, Bartell et al. (1936) measured a slightly larger contact angle for carnauba wax.  The initial contact angles of water droplets on stearic acid (128°) were markedly larger than those reported in the literature.  Adam and Jessop (1925) reported the contact angles of water droplets on stearic acid to be anywhere between 50° and 105°, depending on the orientation of its polar groups.  This discrepancy can be explained by the rough surface that molten stearic acid formed when it solidified on the glass slides.  The surfaces that Adam and Jessop measured were presumably smooth, since they were cut from a solid lump (Adam and Jessop 1925). The melting point temperatures of waxes from animals (beeswax and lanolin) and plants (carnauba wax and soy wax) agreed well with those found in the literature (Wolfmeier et al. 2000).  Similarly, the melting point temperatures measured for the Fischer-Tropsch and paraffin waxes provided by Sasolwax (South Africa) matched those reported in the material safety data sheets (MSDS) that accompanied them.  The melting point temperatures of microcrystalline   74  wax and synthetic beeswax were similar to those of other paraffin waxes (Wolfmeier et al. 2000). The melting point temperature of Vaseline was not verified.  The melting point temperatures of wax blends could be verified using a simple calculation based on the proportions of blended waxes and the melting point temperatures of the individual waxes (Bennett 1963).  Thus, by combining ethylene maleic anhydride with beeswax or Sasolwax M3M, wax blends with higher melting point temperatures were created.  According to the definition of wax proposed by the German Association for Fat Science, waxes must have melting points above 40°C (Wolfmeier et al. 2000).  Based on this definition two of the waxes in this thesis cannot technically be defined as waxes.  Nevertheless, for convenience, they will still be referred to as waxes in the rest of this text. Sasolwax C had a melting point of 29°C and lanolin had a melting point of 35°C. The viscosities of all the waxes were within the expected range, as defined by the German Association for Fat Science (Wolfmeier et al. 2000).  The acid value numbers also agree with values reported in the literature (Wolfmeier et al. 2000).  By combining ethylene maleic anhydride with beeswax or Sasolwax M3M, wax blends with increased polarity were produced. The SEM photomicrographs of beeswax and carnauba wax on OSB resembled those published by Greener-Donhowe and Fennema (1993).  The authors prepared very thin films using the same type of waxes and examined the microstructure of the prepared surfaces. They reported that tiny pores were visible in the surface of the wax.  It is possible that these small pores may develop into larger cracks when thicker wax films solidify; such as the films prepared in this study.  For carnauba wax, such cracks can be explained by its large density increase upon crystallisation, while its smooth surface can be explained by its fine crystalline structure.  Conversely, beeswax formed coatings which did not develop visible fractures, possibly because the wax is softer and more flexible than carnauba wax.  Greener-Donhowe and Fennema (1993) did not observe any defects on the surface of thin beeswax films either.  According to Tulloch (1970) the flexibility of beeswax results from the presence of a small amount of unsaturated hydrocarbons in the wax.  No literature that contained SEM photomicrographs of the surfaces Vaseline or Fischer-Tropsch waxes could be found.   75  Water droplets placed on pure microcrystalline wax surfaces took a long time (42.7 min) to form contact angles smaller than 90°.  Water droplets placed on these surfaces flattened slightly as water evaporated over time, however, before the contact angle became smaller than 90°, the droplets suddenly contracted and beaded up again, increasing the contact angle.  Droplets placed on other wax types behaved in a similar “slip-and-stick” manner, but their contact angles decreased well below 90° before the droplets contracted and beaded up again.  The high resolution profilometry image of the surface of a glass slide coated with microcrystalline wax showed that this wax solidified to form microscopic peaks and valleys, similar to the strongly hydrophobic surfaces found on some plant leaves (Barthlott and Neinhuis 1997).  Despite this observation, the average surface roughness (Ra) of pure microcrystalline wax surfaces appeared to be similar to those of many of the other wax types.  Ra  is the  arithmetic mean deviation of a surface profile’s peaks and valleys from its center line.  Thus, the microscopic peaks and valleys on microcrystalline wax may not have been accounted for by the Ra value that was measured.  One unexpected finding was that water droplets placed on glass slides coated with Merkur 300 spread faster than those of water droplets on most of the other wax types.  However, once these droplets spread out they remained on the surface for much longer than those on any of the other wax-coated surfaces.  It is possible that Merkur 300 may have contained an oil that created a film over the water droplet, thus preventing water from evaporating. Further research is necessary to fully test this hypothesis. 3.5 Conclusion I conclude that contact angles on pure wax surfaces are not good indicators of the water repellency of wax-treated OSB surfaces, since most molten waxes tended to penetrate OSB when applied to the surface of OSB.  The contact angle measurements of the waxes tested in this chapter were not useful as a measure of the effect that polarity had on the water repellency of wax-treated OSB.  The most reliable indicator of the water repellency of wax-treated OSB surfaces is the t<90° times of water droplets on wax-treated OSB surfaces.    76  The water repellency of wax-treated OSB increases as wax melting point temperature increases.  This suggests that waxes with higher melting point temperatures might be able to form more effective water-repellent barriers than waxes with low melting point temperature, when they are sprayed onto the surface of hot OSB.   On the other hand lower melting point waxes may be able to penetrate OSB to a greater extent than higher melting point waxes and form a more effective water repellent barrier.  I examine the effect of wax melting point temperature on the effectiveness of molten-wax treatment for OSB in the next chapter.    77  Chapter 4. Effects of wax treatments on thickness swelling  4.1 Introduction It is well known that the effectiveness of water repellents applied to solid wood decrease over time when treated samples are immersed in water or exposed to weather (Adam 1963; Borgin 1965 ; Miniutti et al. 1961; Verrall 1971; Voulgaridis and Banks 1979).  The effectiveness of such water repellents can be improved by increasing the penetration of the water repellent into wood (Borgin 1965).  Water repellents, such as wax, can be displaced by water, since waxes are only weakly bonded to wood cell walls (Rowell and Banks 1985).  Borgin (1965) called such displacement of wax in water-repellent treated wood “preferential wetting”.  Preferential wetting can be slowed by limiting the penetration of water into areas where the water repellent is deposited.  Thus, a wax that is able to penetrate deeper into OSB may be less susceptible to preferential wetting than one that does not penetrate OSB to the same extent.   Hence, deeper penetration of wax into OSB may create a more effective water-repellent barrier than wax that does not penetrate as deeply. When molten wax is sprayed onto the surface of OSB, its melting point and rheology is likely to affect its ability to penetrate into the surface (Hsu et al. 1988).  Waxes have low viscosities at temperatures above their congealing points, and when they are in this state, they have less resistance to flow.  Dullien et al. (1989) showed how capillary forces caused molten paraffin wax to rise upwards through a pack of small glass beads.  Numerous other studies, especially in the fields of petroleum geology and soil sciences, have also investigated the flow of oils and liquid hydrocarbons through porous media (Debye and Cleland 1959; Morrow 1970; Liu et al. 2011).   The volumetric flow of fluids through porous media can be estimated using Darcy’s law which states that volumetric flow is inversely proportional to the viscosity of the fluid (Equation 4.2).     78  Darcy’s law     (     )(     )         (Equation 4.1) Where:                                                                                                                                                                         Accordingly, Scheikl and Dunky (1998) noted that the penetration of liquids into wood surfaces is retarded by increasing the viscosity of the liquids.  When molten wax is sprayed onto the surface of hot OSB the wax directly in contact with the board will remain molten and at a relatively low viscosity until the temperature of the board cools below the congealing point of the wax.  As wax congeals and solidifies its viscosity will increase and its ability to penetrate porous substrates will decrease accordingly (and eventually stop).  Grigsby and Thumm (2012a) characterized the distribution and mobility of wax on wood fibres during the manufacture of medium density fibreboard and found that the mobility of waxes were greatest during hot pressing, when they were molten.  Hsu and Bender (1988) suggested that a liquid wax with a high viscosity would be less able to spread over and wet wood fibres.   According to Bennett (1963) the penetration of wax into paper may be increased by: (1) increasing wax temperature; (2) lowering wax viscosity; or (3) adding solvents or oils.  Conversely, Bennet (1963) explained that wax penetration into paper can be minimized by: (1) reducing wax temperature; (2) increasing wax viscosity; (3) applying wax to a surface with a low temperature; and (4) increasing the melting point of the wax.  If molten wax is sprayed onto hot OSB, with all other factors remaining the same, waxes with low melting points will remain liquid, and at lower viscosities, for longer than waxes with high melting points. Based on Darcy’s law (Equation 4.1.), this may enable more wax to flow and penetrate deeper into the board, thus blocking a larger number of inter-strand voids and creating a more effective water-repellent barrier. If this is correct waxes with low melting points may be more effective water-repellent treatments for   79  OSB than waxes with high melting points. In Chapter 3, however, I showed that higher melting point waxes were more effective at restricting the spread of water on wax-treated OSB.  Based on these arguments, I hypothesize that the melting point temperatures of waxes will affect their ability to restrict the moisture uptake and TS of OSB.  This chapter seeks to determine the relationship between wax melting point and the effectiveness of molten wax treatments applied to OSB. 4.2 Materials and methods 4.2.1 Experimental design A randomized block design was used to determine the effect of a single fixed factor (wax type) on TS and rate of TS of OSB.  Waxes that covered a wide spectrum of melting points were chosen.  A wax treatment was considered effective if the wax was able to penetrate OSB without forming a visible coating on top of the sample and if the treated OSB samples swelled less, or at a slower rate, than untreated controls.  The swelling of untreated OSB samples (control) and samples treated with seven different waxes were examined.   The experiment was replicated seven times, using panels supplied by Tolko Industries, Canada.  A single panel was used for each experimental replication (block) and panels were sampled from the production line at different times to account for random variations in board properties caused by variation in raw materials and the manufacturing process.  The total sample population of the experiment was 56 samples (8 treatments x 7 panels).   Eight samples, measuring 120 x 100 mm2, were cut from each panel, and a wax type was randomly assigned to each of the seven samples. The samples were treated accordingly, and one sample was left untreated as a control.  All samples were immersed in water, at 20 ± 2°C, for 21 days and TS measurements were recorded every 1 min, using linear variable displacement transducers.  Analysis of variance, for a randomized block design, was used to examine the effect of wax type on the following response variables: (1) total thickness swelling after 21 days; (2) rate of TS   80  expressed as the time it took samples to reach 25% and 50% of their total thickness swell (25% TTS and 50% TTS); and (3) amount of TS after 2 h, 24 h, 72 h, 240 h, and 480 h.  The hierarchical design of the experiment accounted for random variation between panels, as well as the fixed effects of wax type.  The amount of wax applied to each sample was included as a covariant in the statistical analysis to account for variation in response variables due to differences in the amount of wax sprayed onto samples.  The statistical program Genstat 12.1 (VSN International 2009) was used to analyze the data with a 95% confidence interval (α = 0.05) and to check the assumptions of ANOVA, as described in Chapter 3.  A sub-routine (convsstrt), within Genstat, was used to compare the performance of all the wax types, as well as individual wax types, to that of the untreated control.   Results are presented in graphs and error bars on each graph (± standard error of difference, p < 0.05) can be used to estimate whether differences between individual means are statistically significant.  4.2.2 Waxes Seven waxes were chosen based their melting point temperatures, as mentioned in the introduction (Table 4.1).  The congealing point of each wax was determined according to ASTM D938-12 and the drop melting point temperature was determined according to ASTM D127-08.  Dynamic viscosities, at temperatures between 95°C and congealing point, were measured using a stress-controlled rheometer (Anton Paar MCR 501).     Table 4.1. The origin, melting point tempeatures, and viscosities of seven waxes Wax Origin Melting point (°C)  Viscosity (mPa·s) at Congealing point Drop point  95°C Congealing point + 10°C Sasolwax C Fischer-Tropsch  29 31  2.20 4.34 Lanolin Animal 35 -  34.5 223 Vaseline Petroleum Jelly 53 59  6.14 7.98 Tekniwax 600 Petroleum 62 63  7.05 9.59 Sasolwax M3M Fischer-Tropsch  63 68  5.11 6.17 Beeswax Animal 64 65  11.2 15.6 Carnauba wax Vegetable  81 81  24.9 25.7    81   Figure 4.1.  The seven waxes used in this chapter (and one wax that was not included) after dynamic viscosities were measured using a stress-controlled rheometer (Anton Paar MCR 501).  (A) Sasolwax M3M;  (B) Vaseline; (C) carnauba wax; (D) lanolin; (E) Sasolwax C; (F) Tekniwax 600; (G) beeswax  4.2.3 Oriented strandboard Seven independent OSB panels, measuring 2440 x 1220 x 18 mm, were supplied by Tolko Industries, Canada.  The panels consisted of 95% aspen wood, 4% resin and 1% emulsified wax; by weight (Blau, K., personal communication, February 4, 2013).  The core to surface ratio of the panels was 1:1, with 4% liquid phenol formaldehyde used in the surface and 4% pMDI adhesive used in the core.  The emulsified wax (Cascowax EW-58S) was manufactured by Hexion Specialty Chemicals, Springfield, OR. The panels were pressed at approximately 200°C and had a moisture content of 1 - 2% when leaving the press.  Panels were sampled from the production line at different times to account for random variation in board properties caused by variation in raw materials and the manufacturing process.   4.2.4 Sample preparation Samples for each experimental replication (block) were cut from a single OSB panel.  A table saw (Altendorf F45 ELMO) was used to trim off 200 mm from one end of each board.  Two more strips, 1220 x 120 mm2, were then sawn from each freshly cut side.  A cross-cut saw (Omga T55-300) was used to trim off 50 mm from the ends of each strip and the remaining C A B D E F G Not included in study   82  lengths were cross-cut into 100 mm wide samples.  Eight samples, 120 x 100 mm2, were chosen at random and a wax treatment (wax type or control) was randomly assigned to each of them. The samples were labeled on their top surface using a permanent marker and their edges were sealed using a two-part epoxy resin (G-2, System Three).  The lower surface of each sample was coated with a layer of spar varnish (Cabot Spar Varnish #8042 Satin).  Before the spar varnish and the epoxy resin cured, aluminium foil was tightly wrapped around each sample, so that only the top surface of the sample was uncovered (Figure 4.2).  The wrapped samples were left to cure overnight and the excess foil was neatly trimmed off using a utility knife.  Sealed samples were oven dried at 105 ± 1°C for a minimum of 24 h, weighed and placed in a vacuum oven at 90 ± 1°C. Samples were then individually placed in a second oven (170°C), between two heated metal plates (1 kg each), for 10 min.  This was done to mimic the temperatures reached when OSB is pressed, and to ensure that the surface was hot enough to prevent molten wax, which was subsequently sprayed onto the samples, from solidifying too quickly upon contact with the surface of the board.   83   Figure 4.2. An OSB sample prior to application of molten wax  4.2.5 Wax application Wax was sprayed onto the exposed upper surface of each sample using a pneumatic hot wax spray gun (Champ 10s, Glue Machinery Corporation) (Figure 4.3. ).  The gun consisted of a temperature controlled heating chamber that was set at 100°C.  The air pressure inside the chamber was set at 300 kPa and the air pressure at the nozzle tip was set at 200 kPa.  The spray nozzle had a single orifice (0.6 mm), which was opened and closed pneumatically with a ball and spring mechanism (Figure 4.4).  When the gun was activated, the pressure from inside the chamber forced the ball to compress the spring.  This allowed molten wax from inside the chamber to flow around the ball and out of the orifice.  Behind the nozzle a second pneumatic line helped atomize the molten wax that escaped.  When pressure was released the spring pushed the ball back and closed the nozzle, preventing liquid wax form dripping out.  Videos of the application process can be found on the appended CD.   Edges were sealed with epoxy Bottom surfaces were coated with spar varnish Sample were wrapped in aluminium foil so that only their upper surface was exposed to water   84   Figure 4.3. The Champ 10s pneumatic spray gun used to spray molten wax onto the OSB samples. Solid wax is inserted into the temperature controlled heating chamber at the back of the spray gun (left). The contol panel (right) is used to set the pressure inside the heating chamber and spray pressure at the nozzle tip  Figure 4.4.  A schematic drawing of the Champ 10s spray gun’s nozzle assembly.  The spring, the ball and the stopper is housed inside the spray nozzle. The ball and spring is held in place by the stopper, which is screwed into the back of the nozzle. The spray nozzle, with the three parts inside it, is screwed onto the head of the spray gun body. The spray cap is also screwed onto the spray gun body, and it covers the spray-nozzle assembly. Molten wax is forced out of the spray gun when the chamber pressure is high enough to force the ball to compress the spring. A second pneumatic line, at the top of the spray gun body, helps to atomize the molten wax that escapes   85  Samples were treated with 200 g / m2 of wax (approximately 2% based on oven dry board weight).  There was variation in the amount of wax applied to individual samples, as mentioned above (Table 4.2).  Application rates had a standard deviation of 62 g / m2.  This variation was accounted for in the analysis of data by including the weight of wax applied to each sample as a covariant.  After application of waxes all treated samples and untreated controls were placed in a conditioning room at 20 ± 1 °C and 65 ± 5% relative humidity for a minimum of one week. Table 4.2. Amounts of wax applied to individual samples Replication Wax applied (g/m2) Beeswax Carnauba Lanolin Sasolwax M3M Sasolwax C Tekniwax 600 Vaseline 1 260.0 323.3 299.2 277.5 275.0 251.7 270.0 2 318.3 302.5 279.2 244.2 279.2 230.0 265.8 3 139.2 241.7 186.7 140.8 169.2 211.7 179.2 4 215.8 240.0 197.5 225.0 219.2 205.0 206.7 5 230.8 168.3 144.2 225.8 108.3 145.0 126.7 6 121.7 172.5 135.0 132.5 125.8 112.5 130.8 7 159.2 136.7 162.5 130.0 166.7 113.3 170.8 Mean 206.4 226.4 200.6 196.5 191.9 181.3 192.9 σ 70.7 70.6 64.6 60.7 68.0 57.0 58.3 4.2.6 Thickness swelling measurement The TS of all samples in a single experimental replication (block) were made simultaneously, using a swellometer (Oh et al. 2000, Evans and Cullis 2008).  OSB samples were mounted horizontally in a metal frame, at the bottom of a stainless steel tank (70 x 40 x 15 cm).  Each sample was gently held down by a thin metal bar that ran across its treated surface.  Compressed springs, above the bars, supplied a small amount of downward force, which kept the buoyant OSB samples stationary when immersed in water, without restricting TS (Figure 4.5, left).        Directly above each sample, midway along one edge, and 25 mm in from the edge a dedicated linear variable differential transducer (LVDT) measured TS (Figure 4.5, right).  Once each LVDT was zeroed onto the surface of the OSB samples any further changes in thickness were picked up by the LVDT converted into proportional electrical signals, which were interpreted by a   86  computer and recorded in millimetres.  Each transducer was lowered onto an OSB sample and secured as soon as its foot pad made contact with the sample.  The transducers were then zeroed and the tank was filled with approximately 25 litres of tap water.  Samples were immersed in water at 20 ± 2°C for a total of 21 days and thickness measurements were recorded every 1 min.   Figure 4.5. Eight OSB samples mounted in the swellometer tank and immersed in water (left).  Each sample had one linear variable differential transducer (LVDT) mounted above it, which measured thickness swelling over time. A close up (right) of a LVDT with its footpad zeroed onto the surface of an OSB sample treated with molten Vaseline  4.3 Results The overall effect of wax treatments on the TS of OSB is summarized in Table 4.3.  Wax-treatments did not have a significant effect on the TTS (total thickness swelling) of samples 21 days of immersion in water.  Wax treatment, however, had a significant effect on the rate and extent of TS that occurred over periods of ten days or less.  Wax-treated samples swelled less and at a slower rate than untreated samples during the first ten days immersion in water.      87  Table 4.3. The effect of wax treatments on the thickness swelling of OSB samples immersed in water (α = 0.05)   Total thickness swelling (mm) * Rate of thickness swelling (h) †  Thickness swelling (mm) 25% of TTS 50% of TTS  2 h 24 h 72 h 240 h 480 h Untreated samples (n=7) 2.74 44 103.1  0.06 0.41 1.04 2.29 2.706 Wax-treated samples (n=49) 2.65 93.5 181.7  0.01 0.22 0.65 1.76 2.572 p-value 0.59 0.01 0.002  < 0.001 0.003 < 0.001 0.02 0.52 LSD‡ 0.34 35.77 47.51  0.02 0.13 0.22 0.42 0.42 * Total thickness swelling after 21 days of immersion in water † Rate of thickness swelling as time to reach 25% or 50% of total thickness swelling ‡ Least significant difference (α = 0.05) Table 4.4 summarises the effect that each wax had on the TS of OSB samples.  The rate of TS was significantly different for samples treated with different waxes.  There were significant differences in the swelling of untreated samples and samples treated with wax after 24 h (p = 0.04), 72 h (p < 0.001), and 240 h (p = 0.01) of immersion in water, but there were no significant differences in the swelling of untreated and different types of wax-treated samples after 2 h or 480 h (p > 0.05).  There were also significant (p = 0.003) differences in the TTS of samples treated with different waxes.  The best performing wax treatment was beeswax, which consistently was the most effective wax at reducing the rate of swelling of samples.         88  Table 4.4. The effect of wax on the thickness swelling of OSB samples immersed in water (α = 0.05)   Total thickness swelling  (mm) * Rate of thickness swelling (h) †  Thickness swelling (mm)   25% of TTS 50% of TTS  2 h 24 h 72 h 240 h 480 h Untreated  2.74 44.0 103.1  0.06 0.41 1.04 2.29 2.71 Beeswax 2.03 139.7 246.2  0.01 0.09 0.32 1.18 2.12 Vaseline 2.68 135.0 220.9  0.01 0.12 0.38 1.43 2.56 T600 2.73 100.3 193.6  0.01 0.22 0.64 1.69 2.44 Sasolwax C 2.59 85.5 182.6  0.01 0.22 0.65 1.78 2.5 M3M 3.04 77.6 163.6  0.01 0.24 0.80 2.13 2.98 Carnauba 2.84 64.2 133.4  0.01 0.25 0.82 2.20 2.79 Lanolin 2.66 52.1 131.4  0.03 0.37 0.91 1.94 2.61 p-value 0.003 0.002 0.004  0.70 0.04 < 0.001 0.01 0.09 LSD‡ 0.45 47.32 62.85  0.02 0.17 0.29 0.56 0.55 * Total thickness swelling after 21 days of immersion in water † Rate of thickness swelling as time to reach 25% or 50% of total thickness swelling ‡ Least significant difference (α = 0.05) 4.3.1 Wax application and physical appearance of wax-treated samples There were noticeable differences in the way different wax types atomized and sprayed onto OSB surfaces.  When carnauba wax was sprayed, for example, some of the molten wax droplets solidified in the air, before they struck the surface of the OSB.  The solid wax droplets briefly remained on the hot surface of the OSB as a powder before they melted and later re-solidified.  Carnauba wax did not appear to penetrate the surface of OSB; instead it formed a thick coating that later fractured and developed large cracks.  The fractured areas did not adhere well to the surface and tended to flake off when the wax-coated OSB was handled or immersed in water.  Lanolin did not appear to penetrate the surface either, even when small quantities were applied.  Most of the other waxes also formed visible coatings on OSB surfaces, but only when more than approximately 170 g / m2 of wax was applied to samples.  Sasolwax C did not form a visible coating on any of the sample surfaces, and Vaseline only formed a coating when more than approximately 260 g / m2 of it was applied onto OSB samples.  Differences in the hardness of the waxes were apparent.  Beeswax felt softer than carnauba wax.  Coatings formed by beeswax were also smoother and contained less cracks than those formed by carnauba wax.    89  Coatings formed by Sasolwax M3M also appeared to be harder than beeswax coatings, whereas those formed by Tekniwax 600 appeared to be softer.  Unlike carnauba wax, none of the other wax coatings flaked off as easily when handled, or when coated OSB samples were immersed in water.  Waxes other than carnauba wax and lanolin, appeared to penetrate the surface of OSB when less than approximately 170 g / m2 of wax was sprayed onto the samples.  Once coated, wax-treated OSB samples were conditioned at 20 ± 1°C and 65 ± 5 % r.h. for a minimum of one week.  Those samples with no visible coatings were slightly darker, but otherwise indistinguishable from the untreated controls.  Figure 4.6.  Close up of the surface of OSB sprayed with approximately 270 g /m2  of molten carnauba (left) wax and  Vaseline (right).  Note that the high application rate caused surface coatings to form, even though the OSB samples were hot (170°C) when the waxes were sprayed onto them.  Carnauba wax coatings cracked and flaked off when touched, while Vaseline formed a defect-free coating that filled the surface voids 4.3.2 Effect of wax type on total thickness swelling The average TTS of all OSB samples immersed in water for 21 days was 2.66 mm.  There was no significant difference between the mean TTS of the wax-treated samples (2.65 mm) and the untreated control samples (2.74 mm).  There were, however, significant differences (p = 0.003) between the TTS of samples treated with different wax types (Figure 4.7).   Samples treated with beeswax had an average TTS of 2.03 mm; significantly less than untreated samples, as well   90  as samples treated with other wax types (Figure 4.7).  Samples treated with Sasolwax M3M swelled the most (3.04 mm); significantly more than beeswax and Sasolwax C (2.59 mm) treated samples.  Figure 4.7.  Effect of wax type on the total thickness swelling of wax-treated OSB samples after 21 days of immersion in water  Non-overlap of error bars indicates that means are significantly different at the 5% level.  The least signficant difference (LSD)  is 0.45 mm 4.3.3 Effect of wax treatment and wax type on the rate of thickness swelling Over the first 24 hours all samples treated with wax, except for those treated with lanolin, increased in thickness at a slower rate than untreated samples (Figure 4.8).  Beeswax and Vaseline treated samples swelled markedly less than samples treated with other wax types.  Beeswax was the only wax type which significantly reduced total thickness swelling after 21 days, as mentioned above.    91   Figure 4.8.  The average thickness swelling of untreated and wax-treated OSB samples that were immersed in water for 24 h (n = 7).  Refer to attached CD for numerical values The long term TS curves for beeswax and Vaseline treated samples were noticeably different from those of other treated samples.  This was because these two wax types were more effective than other waxes at reducing TS of samples during short-term water exposure (Figure 4.9).   92   Figure 4.9.  The average thickness swelling of untreated and wax-treated OSB samples that were immersed in water for 21 days (n = 7).  Refer to attached CD for numerical values Overall, wax treatments had a highly significant effect on the time it took samples to reach 25% (p = 0.008) and 50% (p = 0.002) of their total thickness swelling (TTS) (Figure 4.10).  Untreated OSB samples took on average of 44 h to swell to 25% of TTS and 103 h 6 min to swell to 50% of TTS.  In contrast, wax treated samples remained below 25% of TTS for 96 h 30 min and below 50% TTS for 181 h 42 min.  It therefore took 2.2 times longer for wax treated samples to swell to 25% of TTS and 1.76 times longer to swell to 50% of TTS.   93   Figure 4.10.  Effect of wax treatments on the time it took OSB to reach 25% and 50% total thickness swelling (TTS). Non-overlap of error bars indicates that means are significantly different at the 5% level.  The least signficant difference (LSD) for 25% TTS is 35.7 h and the LSD for 50% TTS is 47.5 h  The type of wax sprayed onto OSB samples also had a highly significant effect on the time to reach 25% (p = 0.002) and 50% (p = 0.004) of TTS (Figure 4.11).  Samples treated with beeswax, Vaseline, or Tekniwax-600 remained below both 25% and 50% of TTS for significantly (p < 0.005) longer than untreated samples.  Beeswax treated samples remained below 25% of TTS for 3.18 times longer; Vaseline treated samples for 3.07 times longer; and Tekniwax 600 treated samples for 2.28 times longer.  Similarly, beeswax samples remained below 50% of TTS for 2.39 times longer than untreated samples; Vaseline for 2.14 times longer; and Tekniwax 600 for 1.88 times longer.   Sasolwax C treated samples, which also took longer to swell to 50% of TTS than untreated samples, took 1.77 times longer to reach 50% of TTS than untreated samples.  Samples treated with beeswax or Vaseline remained below 25% of TTS for longer than those of samples treated with the other wax types, except for those treated with Tekniwax 600.  Samples treated with Tekniwax 600 remained below 25% of TTS for longer than untreated samples and those treated with lanolin, but not significantly longer than those of samples treated with other wax types.  Beeswax samples remained below 50% of TTS for longer than   94  any of the other types of wax-treated samples.  Furthermore, the rate of swelling of samples treated with beeswax was lower than those of all of the other types of wax-treated samples; except for those treated with Vaseline or Tekniwax-600.  Vaseline treated samples took longer to reach 50% of TTS than untreated samples or those treated with carnauba wax and lanolin, but not significantly longer than those of samples treated with other wax types.   Figure 4.11.  Effect of wax type on the time it took wax-treated OSB samples to reach 25% and 50% of total thickness swelling (TTS). Non-overlap of error bars indicates that means are significantly different at the 5% level.  The least significant difference (LSD) for 25% TTS is 47.3 h and the LSD for 50% TTS is 62.8 h     95  4.3.4 Effect of wax treatment and wax type on thickness swelling  Wax treatments, on average, had a significant effect on the TS of OSB samples after they were immersed in water for 2 h (p<0.001), 24 h (p = 0.003), 72 h (p<0.001) and 240 h (p = 0.017); but not after 480 h of immersion (Figure 4.12).   After 2 h the thickness of untreated samples had increased by 0.056 mm (0.4%), while the thickness of wax-treated samples increased by 0.012 mm (0.08%).  Wax treatments had therefore reduced TS by 78.7% after 2 h of immersion in water.   After 24 h, the thickness of untreated samples had increased by 0.41 mm (2.58%) and wax-treated samples had increased by 0.22 mm (1.36%); a 47.8% reduction in TS. After 72 h, the thickness of untreated samples had increased by 1.04 mm (6.5%) and treated samples had increased by 0.65 mm (4.1%); a 37.9 % reduction in TS.  After 240 h, the thickness of untreated samples had increased by 2.3 mm (14.3 %) and treated samples had increased by 1.8 mm (11.1 %); a 22.9% reduction in TS as a result of wax treatment.   96   Figure 4.12.  Effect of wax treatments on the thickness swelling of OSB after 2 h, 24 h, 72 h, and 240 h.  Non-overlap of error bars indicates that means are significantly different at the 5% level.  The least signficant differences (LSD) for 2 h, 24 h, 72 h and 240 h are 0.02 mm, 0.13 mm, 0.22 mm, and 0.42 mm, respectively.  Note the different y-axis scales for each plot, always starting at zero There were no significant differences in the swelling of different types of wax-treated samples after 2 h and 480 h.  There were, however, significant differences between wax-treated samples after 24 h (p = 0.036), 72 h (p < 0.001), and 240h (p = 0.007) (Figure 4.13).    97  Untreated samples swelled significantly more than any of the wax-treated samples during the first 24 h, except for samples treated with carnauba wax or lanolin.   Beeswax was the most effective treatment followed by Vaseline. Treatment with beeswax reduced the TS of OSB after 24 h by 79.2 % and treatment with Vaseline reduced swelling by 70.2 %.  Both beeswax and Vaseline treated samples also swelled significantly less than lanolin treated samples.  Figure 4.13.  Effect of individual wax types on the thickness swelling of OSB samples after 24 h, 72 h, and 240 h of immersion in water.  Also included (bottom right) are the melting point temperatures of the different waxes.  Non-overlap of error bars indicates that means are significantly different at a 5% level.  The least significant differences (LSD) for 24 h, 48 h, and 240 h are 0.17 mm, 0.29 mm, and 0.56 mm, respectively          98  After 72 h, the TS of samples treated with beeswax, Vaseline, Tekniwax 600 or Sasolwax C were significantly less than that of the untreated controls.  Samples treated with beeswax swelled significantly less than those of samples treated with all other wax types, except for samples treated with Vaseline.  Treatment of samples with beeswax reduced TS of OSB after 72 h by 69.3% and treatment with Vaseline reduced swelling by 63.5%.  Samples treated with Vaseline also swelled significantly less than samples treated with carnauba wax, lanolin, or Sasolwax M3M.  Treatment with Tekniwax 600 reduced TS by 38.7 % and Sasolwax C treatment reduced TS by 37.5% after 72 h.   After 240 h, the TS of untreated samples was significantly greater than those of samples treated with beeswax, Vaseline, or Tekniwax 600.  Treatment with beeswax reduced TS by 48.4% and beeswax treated samples swelled significantly less than samples treated with other wax types; except for those treated with Tekniwax 600 or Vaseline.  Samples treated with Vaseline swelled 37.52% less than untreated samples and also significantly less than samples treated with carnauba wax or Sasolwax M3M.  Treatment of samples with Tekniwax 600 reduced TS by 26.32% after 240 h of immersion in water. 4.3.5 Relationship between wax melting point and thickness swelling There was no correlation between the melting point temperatures of different wax types and TS of OSB samples treated with those waxes.  Furthermore, there was no relationship between the TS of wax-treated samples and the viscosities of the waxes at 95°C.  4.4 Discussion In the introduction to this chapter suggested that low melting (LM) point waxes might be more effective than high melting (HM) point waxes at creating a water-repellent barrier when they are sprayed molten onto hot OSB surfaces. There was little correlation between the melting point temperatures of the waxes and the TS of wax-treated OSB samples.  HM waxes were more likely to form coatings on top of the surface,   99  rather than penetrate into OSB as envisioned.  LM waxes rarely formed surface coatings.  Instead they likely pretreated the top layer of the OSB panels, and the wax was invisible to the naked eye.   HM waxes, such as beeswax, may have formed coatings that were more effective water repellent barriers than the sub-surface barriers created by most of the LM waxes.  This supposition could partly explain why there was no clear relationship between melting point temperature of waxes and TS of wax-treated samples.  The results from the previous chapter suggested that the water repellency of wax-treated OSB increased as wax melting point temperatures increased.  This supposition could also partly explain why some of the HM waxes performed better than the LM waxes.  It appears that the ability of a molten wax to form an effective water-repellent barrier in OSB is affected by a complex combination of its physical and chemical properties. The most obvious reason why some HM waxes did not penetrate into the board, but rather solidified on top of the surface, was because the spray temperature was kept constant, at 100°C, regardless of the melting point of the wax which was sprayed.  Some HM waxes were only sprayed a few degrees higher than their congealing point temperatures, while LM waxes were discharged from the spray gun at temperatures far higher than their congealing points.  Carnauba wax, for example, was sprayed at only 19°C (100°C - 81°C) above its congealing point, while Sasolwax C was sprayed at 69°C (100°C - 31°C) above its congealing point.  Given this temperature difference, it is very likely that LM waxes took longer to cool down and solidify than HM waxes.  When molten wax cools down and its temperature approaches congealing point its viscosity and resistance to flow increases dramatically (Hsu and Bender 1988). Thus, HM waxes were more likely to solidify on top of the surface than penetrate into the sample.  In support of this suggestion Grigsby and Thumm (2012a) showed that when wax is used during the manufacture of medium density fibreboard (MDF), it spreads more readily over the MDF fibres when the temperature of the wax is far above its congealing point.  According to Maloney (1993) molten wax that is sprayed onto OSB strands during blending, seldom travels more than 300 – 450 mm through the air before solidifying.   Lanolin was not able to effectively penetrate the surface of OSB, even when small quantities were applied.  This is probably   100  because of its high viscosity when its temperature is close to its congealing point and also possibly due to the presence of wool fibres in the wax.  Wax treatments in general decreased the rate of TS, but there was no significant difference in the extent of TS of wax-treated samples and untreated samples after 21 days of immersion in water.  Therefore, according to the categories that Rowell and Banks (1985) defined for water-repellents for solid wood (Section 2.4), the wax treatments used in this study can be defined as a Type-I water repellent treatment.  In other words: spraying the surface of OSB with molten wax reduces the board’s the rate of liquid water uptake, but not its extent of TS.  Beeswax was the only wax that reduced the extent of swelling after 21 days, however, it is possible that if beeswax treated samples were immersed in water for longer they would have swelled to the same extent as untreated samples. The definition by Rowell and Banks (1985) does define the time period for testing and characterization of water repellents, since it is not necessary for solid wood.  However, for OSB, and other particleboards, a (defined) testing time should be specified, since it is likely that most OSB treated with water repellents will “swell to the same extent” as untreated controls if left immersed in water for long enough.   During building construction, when OSB panels are exposed to rain and high humidity, Type-I water repellent treatments might be able to slow the rate of liquid WA, until construction is complete and the building envelope is sealed. Thus, the mechanical strength of the boards should be preserved and any other unwanted effects caused by water will also be reduced.  In practice OSB panels are rarely totally immersed in water, as was the case in this study. It is far more likely that the panels will only be exposed to alternating periods of rain and sunshine.  Thus, the test methods used here are relatively severe (Taylor et al. 2008) and any treatment that can significantly reduce OSB’s rate of TS during a 24 h water immersion test may be useful in practice. It should be noted that the rate of TS for samples treated with beeswax or Vaseline was different to that of samples treated with other wax types (Figure 4.9).  The slower rate of swelling was possibly the result of a combination of effects: (1) the water repellent properties   101  of the waxes; (2) the softness of the waxes; and (3) the unexpected defect-free coatings that Vaseline and particularly beeswax formed when high spread rates were used.  Soft waxes, similar to beeswax and Vaseline, have provided flexibility to water-repellent coatings for more than half a century (Hilditch 1965).  Harder coatings, such as those formed by carnauba wax and Sasolwax M3M, cracked and flaked off as the samples swelled.  Evidence for such cracking of carnauba wax coatings was seen in the SEM photomicrographs in Chapter 3.  Such cracks, if present in carnauba wax treated samples, may have opened pathways for moisture ingress into OSB samples.  In contrast, there was also evidence from Chapter 3 that beeswax coatings had greater integrity and this may, in part, explain why the molten beeswax treatment was more effective at restricting swelling than the other treatments, particularly when OSB samples were first immersed in water.   Another possible explanation for the slower rate of swelling of samples treated with beeswax could be related to the polarity of the wax, which may have caused it to adhere more strongly to the OSB surfaces than other wax types.  According to Adam (1963), water repellents with polar functional groups are more attracted to wood than those without such groups.  Finally, it may also be that the presence of propolis in beeswax, allowed the wax to adhere more strongly to the OSB surface.  Propolis is a type of resin that is produced by bees to protect and seal the honeycomb.  A study, which looked at the possibilities of using propolis for wood finishing concluded that, although there were only limited opportunities for its direct use as a wood finish, propolis was, nevertheless, hydrophobic and could be an effective component of coatings when combined with other natural water repellents, such as wax (Budija et al. 2008). Although wax treatments significantly reduced the TS of OSB, the extent of TS of all samples, including the untreated controls, was probably restricted by the epoxy resin that was used to edge-seal samples prior to the immersion test.  For this reason it is not possible to directly compare the swelling results to industry standards.  The literature, however, contains two comparable studies that also measured the dimensional stability of OSB samples that were edge sealed with epoxy resin (Semple et al. 2009, Evans and Cullis 2008).  Semple et al. (2009) sprayed linseed oil-wax solutions onto the surface of hot OSB and found that treatments were   102  most effective at reducing the short-term TS of OSB when the linseed oil hardened to form a coating that covered the surface voids of the boards.  They also found that linseed oil coatings that contained beeswax were less effective than those that contained carnauba wax.  These results are contrary to my results, however, they support the suggestion that beeswax and Vaseline treated samples here may have performed well because of the presence of coatings which sometimes formed on the surface, rather than as a result of other factors, such as the hydrophobicity of the wax.   Evans and Cullis (2008) used a roller coater to coat the surfaces of OSB samples with UV-cured finishes, as mentioned above.  They reported that, after 72 h of immersion in water, the thickness swelling of uncoated control samples was approximately 1.2 mm, while the thickness of surface-coated OSB samples had increased by approximately 0.3 mm.  These findings agree well with my results and also support the suggestion that beeswax and Vaseline treated samples performed well because they tended to form surface coatings.   Other properties, which were not examined in this study, but which may also affect the water repellency of wax-treated OSB, include the oil content of wax and its hardness.  The oil content of wax can be measured according to ASTM D721 – 06, while wax hardness can be measured according to the needle penetration test  ASTM D1321 -10.  Rodríguez-Valverde et al. (2006) investigated the effect of oil content on the water repellency of paraffin wax emulsions and found that oil contents below 14% increase the water-proofing capacity of wax emulsions, but that higher percentages decrease water repellency.   In contrast, Hsu and Bender (1988) concluded that oil content does not directly affect the water repellency of wax. Hsu et al. (1990) also reached the same conclusion.  The measured the TS of waferboard that contained slack wax sizing with different oil contents ranging from 0 - 30%.  Further research is therefore necessary to determine whether the oil content and hardness of wax has an effect on the ability of molten wax treatments to dimensionally stabilize OSB.  Slack wax, for example, may be a relatively inexpensive option to use as hot wax spray treatment, since it is readily available and is already used by the wood composite industry.  Its oil content, however, is known to be 5 – 12% (Wolfmeier et al. 2000), and therefore it may not be the most effective wax at stabilizing OSB.   103  Lastly, I suggest that to compare different wax treatments more accurately the difference between the spray temperature and the wax melting point temperature must remain constant for all waxes.  I suggest that the maximum amount of wax that can be applied to an OSB surface, without forming an unwanted surface coating, will depend on: (1) the melting temperature of the wax; (2) the temperature at which the wax is sprayed; (3) the rate at which the discharged wax cools before it comes in contact with the OSB surface; and (4) the surface temperature of the OSB.  I propose a maximum spread rate of less than 170 g / m2 for most waxes; however, this will depend on the wax being sprayed and the spraying conditions, as described above.  4.5 Conclusion Molten wax spray treatments can reduce the TS rate of OSB in the absence of a surface coating, as hypothesized in the introduction.  The formation of surface coatings, however, made it difficult to draw conclusions about whether there is a relationship between the melting point temperatures of waxes and their ability to dimensionally stabilize OSB.  I conclude that the ability of a molten wax to penetrate the surface of OSB and form an effective water-repellent barrier is affected by a complex combination of its physical and chemical properties.  Molten wax treatment effectively reduced the rate of WA of treated OSB, but not the extent of TS.  Therefore, I conclude that wax treatments can provide OSB with enhanced protection during short periods of exposure to liquid water, but they will not be suitable for OSB exposed outdoors. Finally, I conclude that to compare the ability of molten waxes to dimensionally stabilize OSB, the spray temperatures should be tailored and adjusted according to the type of wax being sprayed.   A sliding scale system is proposed, whereby the difference between the spray temperature and wax melting point temperature remains constant for all wax types.  I propose to employ this method in the next chapter.    104  Chapter 5. Effects of wax polarity and melting point temperature on water absorption and thickness swelling 5.1 Introduction In Chapter 4, I observed that samples treated with beeswax swelled significantly less than untreated and some wax-treated samples, especially when samples were first immersed in water.  I suggested that this was mainly because beeswax formed defect-free surface coatings at the surface of treated OSB.  I examined whether the polarity of waxes had an effect on their performance.  My results were inconclusive.  Beeswax performed well, but the other two polar waxes performed poorly.  One of the latter waxes, carnauba wax, tended to form surface coatings that cracked, and the other polar wax, raw lanolin, was contaminated by wood fibres and was one of the least hydrophobic waxes. In this chapter I seek to better test the hypothesis that polar waxes will be more effective wax treatments for OSB than nonpolar waxes.  To do this 16 different waxes, including nine polar waxes, were sprayed in a molten state onto the surfaces of OSB samples and samples were floated face down on water for 72h.  It has been suggested that waxes with polar groups have a higher affinity for wood than those without such groups (Adam 1963; Borgin 1965; Rowell and Banks 1985). Stamm and Hansen (1935) impregnated solid wood with various types of wax and found that those that contained polar groups were more effective water repellents than nonpolar waxes.   The hydrophobicity of wax, however, decreases as the number and the size of polar functional groups increases (Holloway 1969).  This, in turn, may reduce the effectiveness of wax as a water-repellent treatment for OSB.  Borgin (1965) suggested that effective water repellents for solid wood should consist of a combination of hydrophobic components that repel water, and hydrophilic components that increase the attraction of the water repellent to wood.  Accordingly, I hypothesize that polar waxes that are strongly hydrophobic will be more effective at dimensionally stabilizing OSB than nonpolar waxes or polar waxes with lower hydrophobicity.   105  In Chapter 4, I also concluded that waxes should be compared by spraying them at temperatures high above their individual melting points so that each one could penetrate into the surface of OSB rather than forming a surface coating.  For this purpose I also suggested that less than 170 g / m2 of wax should be applied onto the surface of OSB samples.  The waxes that are tested in this chapter have a large range of melting point temperatures and the spray temperatures for each wax type was adjusted so that the difference between the spray temperatures and the wax melting points remain constant for all waxes.  Spray temperatures were kept high enough to avoid the formation of thick surface coatings on OSB.  In Chapter 4 the formation of surface coatings with some of the higher melting point waxes made it difficult to establish whether there was a clear relationship between the melting point temperatures of waxes and their ability to dimensionally stabilize OSB.  In this chapter, using the refined methodology described above, I again tested the hypothesis that low melting point waxes will be more effective at dimensionally stabilizing OSB than high melting point waxes.   To better test these hypotheses (effects of polarity and melting point temperature) five wax blends were prepared by combining polar waxes with waxes that had large range of melting point temperatures. Two of these wax blends, one based on beeswax and another based on a Fischer-Tropsch wax (Sasolwax M3M), each contained a 25% ethylene maleic anhydride (EMA), by weight. EMA was added to increase the melting point temperature and polarity of the waxes.  The other three wax blends were prepared at a 1:1 weight ratio.  One of them consisted of the two best performing waxes from Chapter 4, beeswax (polar) and Vaseline (nonpolar).  The other two were similar blends of beeswax and paraffin wax (nonpolar and high melting point), as well as beeswax and a Fischer-Tropsch wax (Sasolwax C, nonpolar and low melting point).    106  5.2 Materials and methods 5.2.1 Experimental design A randomized block design was used to determine the effect of a single fixed factor (wax type) on water absorption (WA) and thickness swelling (TS) of OSB.  Sixteen waxes were chosen based on their melting points and polarity (Table 5.1).  Each wax was individually sprayed onto OSB samples. Untreated samples and a commercially available “moisture resistant” OSB acted as controls.  Each experimental block consisted of 18 samples (16 wax-treated + 1 untreated control + 1 “moisture resistant” sample).   The experiment was replicated seven times, each time using samples cut from independent panels (as in Chapter 4).  The total sample population for the experiment was therefore 126 (18 treatments x 7 panels).     Analysis of variance for a randomized block design was used to examine the effect of wax type on the following response variables: (1) water absorption (WA) after 2 h, 24 h, 48 h and 72 h; and (2) thickness swelling (TS) after 2 h, 24 h, 48 h and 72 h.  The hierarchical design of the experiment accounted for random variation between panels, as well as the fixed effect of wax type.  The amount of wax applied to each sample was included as a covariant.  The statistical program Genstat 12.1 (VSN International 2009) was used to analyze the data with a 95% confidence interval (α = 0.05) and to check the assumptions of ANOVA (as described in Chapter 3).  A sub-routine (convsstrt), within Genstat, was used to compare the response variables of untreated OSB samples with those of all wax-treated samples, as well as samples treated with each individual wax type.   The same sub-routine was used for a second analysis, which compared the performance of all wax-treated samples and individual wax types with those of untreated “moisture resistant” OSB.  Results are presented in graphs and error bars on each graph (± standard error of difference, p < 0.05) can be used to estimate whether differences between individual means are statistically significant.  Stepwise linear regression was used to establish relationships between WA and TS measurements and the wax properties reported in Chapter 3.  The free statistical analysis software “RStudio” was used for this purpose (RStudio 2014).    107  5.2.2 Waxes Sixteen waxes were chosen based on their melting point temperatures and polarity (Table 5.1).  Supplier details and methods used to prepare wax blends are provided in Section 3.2.1.  The congealing point of each wax was determined according to ASTM D938-12 and the drop melting point temperature was determined according to ASTM D127-08, as described in Section 3.2.5.  The apparent viscosity of each wax was measured using the standard test method ASTM D2669 – 06, as described in Section 3.2.6.   Table 5.1. The names, abbreviations, origin, melting point, and viscosity of 16 waxes Wax  Abbrev Origin MP (°C)† Viscosity (cP) at MP + 25°C Acid value (mg KOH/g) Sasolwax C Sc F-T ‡ 31 5.30 0 Tekniwax 801 T801 F-T 44 7.50 0 Soy wax Soy Vegetable  54 15.8 31.5 Merkur 300 M300 Petroleum 55 6.00 0 Beeswax + Sasolwax C (1:1) Bee+Sc Blend 59 10.2 9.2 Vaseline Vas Petroleum 59 9.50 0 Beeswax + Vaseline (1:1) Bee+Vas Blend 62 11.4 9.2 Stearic acid Stearic acid Vegetable  63 7.70 215.3 Beeswax Bee Animal 65 14.5 18.5 Sasolwax M3M M3M F-T 68 8.10 0 Beeswax + Synthetic Beeswax (1:1) Bee+Synth Blend 73 16.2 9.2 Microcrystalline wax Micro Petroleum 73 17.5 0 Synthetic Beeswax Synth Petroleum 77 8.40 0 Carnauba wax Car Vegetable  81 22.2 6.8 Sasolwax M3M +  EMA*(3:1) M3M+EMA Blend 85 29.5 8.6 Beeswax + EMA* (3:1) Bee+EMA Blend 87 51.3 22.4 † MP =  Drop melting point temperature      ‡ F-T = Fischer-Tropsch      * Ethylene maleic anhydride      5.2.3 Oriented strandboard Seven independent OSB panels, measuring 2440 x 1220 x 18 mm3, were supplied by Tolko Industries, Canada.  These samples are sometimes referred to as “regular OSB” samples, or simply as “untreated OSB”.  A single panel was used for each experimental replication (block).    108  The panels were sampled from the production line at different times, as mentioned above.  More information on the composition of the OSB panels can be found in Section 4.2.3.   Each experimental replication also included a single commercially available, “moisture resistant” OSB sample (150 x 150 mm2), manufactured by a U.S. company.  These samples are referred to as “MR” hereafter.  Seven independent MR panels were provided by the Centre for Advanced Wood Processing, at UBC.  A single 150  x 150 mm2 sample was cut from a random location on each panel, using a table saw (Altendorf F45 ELMO).   5.2.4 Sample preparation The preparation of samples for each seven experimental replications (blocks) occurred at different times.  All samples (except for the MR samples) in each block were cut from a single board.  A table saw (Altendorf F45 ELMO) was used to trim off 100 mm from one end of each board.  Seven strips, 1220 x 150 mm2 each, were then sawn from the freshly-cut side.  A cross-cut saw (Omga T55-300) was used to trim off 50 mm from the ends of each strip and the remaining lengths were cross-cut into fifty-six 150 x 150 mm2 samples.   All OSB samples were placed in an oven, at 105 ± 2°C for a minimum of 24 h or until they reached equilibrium moisture content.  The oven dry weight of each sample was measured and 17 samples with the most similar weights were selected to reduce the strong effect that density has on WA and TS.    A wax treatment (wax type or control) was randomly assigned to each of the selected samples.  The average oven dry thickness of the Tolko samples in the sample population was 18.7 mm, with a standard deviation of 0.4 mm, and the average dry density was 597 kg / m3, with a standard deviation 19 kg / m3.  The average oven dry thickness of the MR samples was 17.6 mm and the average density was 649 kg / m3.        The 18 oven dried samples in each block (16 wax-treated + 1 untreated control + 1 MR sample) were placed in a vacuum oven at 90 ± 1°C and were individually removed and placed in a second oven (170°C), between two heated metal plates (1 kg each), for 10 min before wax application (as in Chapter 4).     109  5.2.5 Wax application Wax was sprayed onto the surface of each sample using a pneumatic hot wax spray gun, as described in Section 4.2.5.  Each wax was applied at 25°C above its melting point, and the gun had a constant chamber pressure of 300 kPa and spray pressure of 200 kPa.   To determine how much wax was applied to each sample, the mass of each sample was recorded immediately after wax application (Table 5.2).  Samples were sprayed with an average of 76 g / m2 wax (or 0.7% by weight), with a standard deviation of 21 g / m2.  The minimum amount applied onto a single sample was 45 g / m2 and the maximum was 138 g / m2 (or 0.4% and 1.2% by weight, respectively).   Table 5.2. Summary of the amount of each wax type applied to seven samples Wax Type Wax applied per sample (g / m2) Mean σ Min Max Beeswax + Synthetic Beeswax (1:1) 80.44 25.92 55.56 131.11 Beeswax + Vaseline (1:1) 78.60 28.07 51.11 138.22 Beeswax 79.68 21.54 55.56 118.67 Beeswax + EMA* (3:1) 81.52 20.68 46.67 105.33 Microcrystalline wax 72.44 15.97 46.67 93.33 Synthetic Beeswax 75.11 24.91 50.67 128.89 Sasolwax M3M + EMA* (3:1) 75.62 14.75 59.11 96.44 Tekniwax 801 72.13 14.07 56.44 100.89 Stearic acid 84.44 25.84 47.11 129.33 Vaseline 81.71 25.94 54.22 129.78 Carnauba wax 68.63 20.10 45.33 104.44 Sasolwax M3M 72.38 27.90 50.22 133.33 Beeswax + Sasolwax C (1:1) 75.94 17.88 45.78 96.00 Merkur 300 70.41 17.01 49.78 99.56 Soy wax 75.68 16.73 54.67 95.56 Sasolwax C 76.13 23.74 54.22 124.44 *EMA = Ethylene maleic anhydride     Treated samples were placed in a climate controlled room at 20 ± 1 °C and 65 ± 5% r.h. for a minimum of five days.  All conditioned samples were reweighed before and after their edges were sealed with a white silicone sealant (GE Silicone II 100% Silicone # P-WGH291).  The mass of the silicone applied to samples was calculated.  The sealed samples were conditioned for two additional days to allow the silicone to cure.  All samples were therefore conditioned for a   110  minimum of seven days. The initial mass of each sample before liquid water exposure was calculated by subtracting the mass of the wax and the silicone from the total mass of the sample.  The initial mass was then used to calculate the initial moisture content of samples based on the oven dry weight that was measured upon sample selection (Section 5.2.4).   The oven dry mass and the oven dry thickness of the untreated and wax-treated samples were not significantly different (p > 0.05).  In contrast, after conditioning, there were significant (p = 0.006) differences in the initial moisture content of samples that were treated with different types of wax.  The average initial moisture content of the sample population was 6.2%, with a standard deviation of 1.4%.  Untreated control samples had the highest average initial moisture content (6.5%), while samples treated with microcrystalline wax, had the lowest (5.8%).  5.2.6 Water absorption and thickness swelling measurement For this experiment a water float test was used, instead of the conventional soak test (NIST 2004, ASTM 2012b).  Water float tests are commonly used to determine the liquid water permeability of surface coatings for solid wood (EN 2005), but a float test was also recently employed by Evans et al (2013) to test the differential edge swelling of OSB.  Approximately 150 L of fresh tap water was poured into a 257 L water tank, which measured 1840 x 930 x 150 mm3.  Once the water temperature stabilized at room temperature (20 ± 3°C), the samples were carefully placed on the surface of the water, where they floated for three days.  The water in the tank was refreshed once a day to reduce the negative effects that changes in water pH levels have on WA and TS (Blau, K., personal communication, February 4, 2013).  Samples were removed from the tank after 2 h, 24 h, 48 h, and 72 h. Once the samples were removed, they were then placed on a flat surface, lightly blotted with tissue paper to remove excess water and left to dry for 10 min.  Samples were weighed and their thicknesses were measured using a digital laboratory micrometer (Evans et al. 2013).  Four thickness measurements were taken per sample, midway along and 15 mm from each edge.  The four measurements were averaged and the averages were recorded.  After the 72 h measurements, the samples were placed in a climate controlled room at 20 ± 1°C at 65 ± 5% r .h. for a minimum of two and a maximum of   111  four weeks.  All the conditioned samples were then reweighed and their thicknesses were measured using a digital micrometer, as above.  All samples from each individual experimental replication were measured at the same time, regardless of the conditioning period.  Figure 5.1. Samples were floated face down on water for 72 h.  The weight and the thickness of each sample was measured after 2 h, 24 h, 48 h, and 72 h  5.3 Results The overall effects of wax treatments on the WA and TS of OSB are summarized in Table 5.3.  This table also compares the WA and TS of wax-treated samples with those of commercial MR samples.  Wax treatments had a significant effect on WA, as well as the degree of TS of samples for all exposure periods when results are compared to those of untreated controls.  WA was significantly different at all time periods: 2 h (p < 0.001); 24 h (p < 0.001); 48 h (p = 0.006); and 72 h (p = 0.037).  Similarly, TS was significantly different at 2 h (p < 0.001), 24 h (p = 0.008), 48 h (p = 0.042), and 72 h (p = 0.043).  Samples treated with wax consistently absorbed less water and swelled less than the untreated controls.  When compared to the MR samples there were significant differences in WA at 2 h (p < 0.001), 48 h (p = 0.002), and 72 h (p < 0.001), but not at 24 h. There were also significant differences in TS at 2 h (p = 0.005), 24 h (p < 0.001), 48 h (p < 0.001), and 72 h (p < 0.001).    112  Table 5.3. The effects of wax treatments on the water absorption and thickness swelling of OSB samples, and a comparison between wax-treated samples and “moisture resistant” samples.  All samples were floated face down on water for 72 h and measured at 2 h, 24 h, 48 h and 72 h (α = 0.05)   Water absorption (mL) Thickness swelling (mm)   2 h 24 h 48 h 72 h 2 h 24 h 48 h 72 h Wax-treated samples  (n = 112) 3.68 16.78 30.39 46.33 0.16 0.63 1.02 1.41 Untreated controls (n = 7) 6.4 21.87 36.49 53.51 0.25 0.77 1.17 1.6 p-value †  < 0.001 < 0.001 0.006 0.037 < 0.001 0.008 0.042 0.043 Least significant difference ‡ 0.66 2.57 4.63 7.32 0.04 0.11 0.16 0.19 Untreated MR (n = 7) 4.79 14.32 22.53 30.29 0.09 0.31 0.54 0.6 p-value †  < 0.001 0.095 0.002 < 0.001 0.005 < 0.001 < 0.001 < 0.001 Least significant difference ‡ 0.69 2.46 4.61 7.4 0.04 0.12 0.17 0.2 † Wax-treated samples are significantly different to control samples if p < 0.05 ‡ Any difference larger than the least significant difference is significantly different (p < 0.05) The WA and TS of untreated and the different types of wax-treated samples was significantly different for all recorded time periods (Table 5.4.).  Similarly, when wax-treated samples are compared with MR samples there were also significant differences in TS at all recorded time periods.  However, for WA there were only significant differences at 2 h, 24 h, and 48 h (p < 0.001).     113  Table 5.4. The effect of individual wax on the water absorption and thickness swelling of OSB samples that were floated face down on water for 2 h, 24 h, 48 h and 72 h, as well as a comparison between wax-treated samples and “moisture resistant” samples   Water absorption (mL) Thickness swelling (mm)   2 h 24 h 48 h 72 h 2 h 24 h 48 h 72 h Beeswax + Synth Beeswax 2.26 11.73 23.3 37.11 0.12 0.46 0.78 1.12 Beeswax + Vaseline 1.98 11.57 24.72 42.08 0.09 0.45 0.79 1.19 Beeswax 2.45 14.13 26.46 43.15 0.10 0.52 0.83 1.27 Beeswax + EMA* 2.57 14.78 29.00 46.3 0.11 0.49 0.87 1.27 Microcrystalline wax 2.68 14.54 27.08 41.73 0.13 0.52 0.93 1.32 Synthetic Beeswax 2.50 14.65 28.44 46.44 0.10 0.55 0.91 1.22 Sasolwax M3M + EMA*  3.29 18.07 32.89 49.97 0.12 0.6 1.00 1.43 Tekniwax 801 4.03 16.92 29.84 43.97 0.21 0.62 1.00 1.36 Stearic acid 3.85 15.03 25.73 37.99 0.18 0.62 0.93 1.28 Vaseline 3.53 16.33 31.05 48.36 0.16 0.62 1.06 1.50 Carnauba wax 2.76 15.24 28.30 43.53 0.16 0.65 1.07 1.44 Sasolwax M3M 3.93 18.18 32.16 48.14 0.17 0.68 1.08 1.52 Beeswax + Sasolwax C 4.01 17.95 32.18 48.26 0.16 0.73 1.17 1.62 Merkur 300 5.10 19.95 33.52 48.37 0.21 0.76 1.13 1.50 Soy wax 5.96 21.63 36.49 53.29 0.24 0.80 1.20 1.64 Sasolwax C 6.49 22.78 37.97 53.34 0.28 0.81 1.29 1.65 Untreated controls 6.40 21.87 36.49 53.51 0.25 0.77 1.17 1.60 p-value† < 0.001 < .001 < 0.001 0.047 < 0.001 < 0.001 < 0.001 < 0.001 Least significant difference ‡ 0.91 3.53 6.35 10.04 0.06 0.15 0.22 0.27 Untreated “moisture resistant” 4.79 14.32 22.53 30.29 0.09 0.31 0.54 0.60 p-value † < 0.001 < 0.001 < 0.001 0.054 < 0.001 < 0.001 < 0.001 0.002 Least significant difference ‡ 0.94 3.37 6.32 10.15 0.06 0.16 0.23 0.28 † Wax-treated samples were significantly different to control samples if p < 0.05 ‡ Any difference larger than the least significant difference was significantly different (p < 0.05) * EMA = Ethylene maleic anhydride      114  5.3.1 Relationship between water absorption and thickness swelling There was a very strong linear relationship between the WA and TS of OSB samples over a 72 h period (Figure 5.2).  Figure 5.2. The relationship between water absorption and thickness swelling of untreated and wax-treated OSB samples that were floated face down on water for 72 h.  Moisture resistant samples not included The relationship between WA and TS was strongly affected by the length of time that samples were floated on water (Figure 5.3), with the positive correlation becoming stronger after longer exposure periods.  After 2 h, the coefficient of determination (R2) was 0.51, but this increased to R2 = 0.6 after 24 h, and R2 = 0.62 after 48 h.  After 72 h hours the R2 was 0.71 or, in other words, 71% of the variation in TS could be explained by the amount of water that samples absorbed.  It can also be seen that the slope of the trend lines decreased with increasing exposure to water.  This finding indicates that similar amounts of water caused more TS during initial exposure periods than they did after longer exposure periods.  It also suggests that the relationship between WA and TS of OSB may be curvilinear and not linear.   0.00.51.01.52.02.53.00 10 20 30 40 50 60 70 80Thickness swelling (mm) Water absorption (mL) y = 0.12 + 0.028x R2 = 0.92 p < 0.0001   115   Figure 5.3. Relationships between water absorption and thickness swelling of untreated and wax-treated OSB samples that were floated face down on water for 72 h.  Measurements were made after 2 h (top left), 24 h (top right), 48 h (bottom left) and 72 h (bottom right) 5.3.2 Wax application and physical appearance of wax-treated samples After samples were treated with wax they appeared slightly darker, but otherwise they were indistinguishable from untreated samples.   Unlike the treatments in Chapter 4, lower application rates and adjusted spray temperatures prevented the formation of any thick surface coatings.  I noted, however, that some of the most polar waxes, particularly stearic acid, tended to agglomerate on top of large strands, before seeping into the surface.  Such behaviour was also noticed during contact angle measurements in Chapter 3.  01230 20 40 60 8072h Thickness swelling (mm) 72h Water absorption (mL) y = 0.34 + 0.023x R2 = 0.71 p < 0.0001  01230 20 40 60 8048h Thickness swelling (mm)  48h Water absorption (mL)  y = 0.21 + 0.026x R2 = 0.62 p < 0.0001  01230 20 40 60 8024h Thickness swelling (mm)  24h Water absorption (mL)  y = 0.09 + 0.032x R2 = 0.6 p < 0.0001  01230 20 40 60 802h Thickness swelling (mm)  2h Water absorption (mL)  y = 0.017 + 0.04x R2 = 0.51 p < 0.0001   116  5.3.3 Effect of wax treatments and wax type on water absorption On average, OSB samples absorbed more water during the first 24 h period than during any of the subsequent time-periods (Table 5.5).   Table 5.5. Average water absorption of all OSB samples*   Water absorption (mL)  2 h 24 h 48 h 72 h Mean 3.8 16.8 30.5 46.5 σ 1.7 4.6 7.8 12.8 * Sample population includes “moisture resistant” samples, untreated controls, and all wax-treated samples     On average, wax-treated samples absorbed less water than untreated water during water exposure time periods (Figure 5.3).  One of the best performing wax types was a blend of beeswax and synthetic beeswax.  OSB samples treated with this wax type absorbed less water than those of MR samples after 2h and 24 h of exposure to water, but not after 48 h and 72 h.  Figure 5.4. Average water absorption of: (1) untreated OSB (n = 7); (2) all wax-treated samples (n = 112); (3) OSB samples treated with a blend of beeswax and synthetic beeswax (n = 7); and (4) “moisture resistant” OSB (n = 7).  All samples were floated on water for 72 h and measurements were taken after 2 h, 24 h, 48 h, and 72 h Wax treatments had a significant (p > 0.05) effect on WA of OSB samples for all time periods (Figures 5.4 – 5.5).  When wax-treated samples are compared with MR samples, significant 01020304050600 6 12 18 24 30 36 42 48 54 60 66 72Water absorption (mL) Water exposure time (h) Untreated Average wax treated Best wax treatment MR   117  differences are apparent for WA at 2 h (p < 0.001), 48 h (p = 0.002) and 72 h (p < 0.001), but not after 24 h.  After 2 h, wax-treated samples had, on average, absorbed 44% less water than untreated samples; untreated samples absorbed 6.4 mL of water, while wax-treated samples absorbed 3.6 mL (Figure 5.4, left).  MR samples absorbed 4.8 mL of water after 2 h of floating on water; 25% more water than the average wax-treated samples. After 24 h, wax-treated samples absorbed 24.7% less water than untreated samples; untreated samples absorbed 22 mL of water, in total, while wax-treated samples absorbed 16.5 mL of water in total (Figure 5.4, right).  There was no significant (p > 0.05) difference in the amount of water absorbed by wax-treated samples and MR samples after 24 h of floating on water.  Figure 5.5. Average effect of wax treatments on the water absorption of OSB samples that were floated face down on water for 2 h (left) and 24 h (right), as well as comparison between the water absorption of these samples and those of “moisture resistant” (MR) OSB samples.  Two independent statistical analyses were conducted for each water exposure period (2 h and 24 h), each time comparing the wax treatments to a different control.  The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level.  The least significant difference (LSD) between untreated samples and wax-treated samples after 2 h and 24 h was 0.66 mL and 2.57 mL, respectively (error bars drawn).  The LSD between untreated samples and MR samples after 2 h and 24 h was 0.69 mL and 2.46 mL, respectively (not drawn)    118  After 48 h, wax-treated samples absorbed only 18% less water than untreated samples; untreated samples absorbed 36.5 mL of water, in total, while wax-treated samples absorbed 30 mL of water (Figure 5.6, left).  Furthermore, after 48h, wax-treated samples absorbed 25% more water than MR samples, which had absorbed 22.5 mL of water in total.  Finally, after 72 h, wax-treated samples absorbed 14.5% less water than untreated samples; untreated samples absorbed 53.5 mL of water, in total, while wax-treated samples absorbed 45.8 mL of water (Figure 5.6, right). MR samples absorbed 30.3 mL of water after 72 h; 34% less water than wax-treated samples.     Figure 5.6. Average effect of wax treatments on the water absorption of OSB samples that were floated face down on water for 48 h (left) and 72 h (right), as well as comparison between the water absorption of these samples and those of “moisture resistant” (MR) OSB samples.  Two independent statistical analyses were conducted for each water exposure period (48 h and 72 h), each time comparing the wax treatments to a different control.  The two controls (Untreated and MR) have clear data points.   Non-overlap of error bars indicates that means are significantly different at a 5% level.  The least significant difference (LSD) between untreated samples and wax-treated samples after 48 h and 72 h was 4.63 mL and 7.32 mL, respectively (error bars drawn).  The LSD between untreated samples and MR samples  after 48 h and 72 h was 4.61 mL and 7.4 mL, respectively (not drawn)      119  There were significant differences in the WA of untreated samples and different types of wax-treated samples for all time periods, as well as significant differences in the WA of MR samples and different types of wax-treated samples at 2 h, 24 h, and 48 h (p < 0.001).  There were also significant differences in WA of different types of wax-treated samples at each of the time periods (Figures 5.6 – 5.9).  After 2 h, untreated samples had absorbed 6.4 mL of water, significantly more than most of the other wax-treated samples; except for those treated with Sasolwax C (6.5 mL) or soy wax (6 mL) (Figure 5.7).  Samples treated with a blend of beeswax and Vaseline absorbed the lowest amount of water after 2 h (2 mL); 69% less than untreated samples.  Samples treated with a blend of beeswax and Vaseline, however, did not absorb significantly (p > 0.05) less water than six of the other waxes types.  MR samples absorbed 4.8 mL of water after 2 h; significantly (p < 0.001) more than nine of the different types of wax-treated samples, but significantly less than samples treated with Sasolwax C or soy wax.     120   Figure 5.7. Effect of wax type on the water absorption of wax-treated OSB samples that were floated face down on water for 2 h, as well as a comparison between the water absorption of these samples and “moisture resistant” (MR) OSB samples.  Two independent statstical analyses were conducted, each time comparing the wax treaments to a different control.  The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) between untreated samples and wax-treated samples is 0.91 mL (error bars drawn), while the LSD between MR samples and wax-treated samples is 0.94 mL (not drawn)   After 24 h, untreated samples absorbed 22 mL of water in total; significantly (p < 0.001) more than most of the wax-treated samples (Figure 5.7 ).  However, there was no significant (p > 0.05) difference between the amounts of water absorbed by untreated samples after 24 h and samples treated with Sasolwax C (22.8 mL), soy wax (21.6 mL), or Merkur 300 (20 mL).  Once again, samples treated with a blend of beeswax and Vaseline absorbed the least amount of water.  After 24 h these samples absorbed 11.57 mL of water in total; 47% less than untreated samples, and significantly (p < 0.001) less than most of the other types of wax-treated samples. Samples treated with a blend of beeswax and Vaseline, however, did not absorb significantly (p > 0.05) less water after 24 h than six of the different types of wax-treated samples.  These included all samples treated with any beeswax combination, except for those treated with a blend of beeswax and Sasolwax C.  MR samples absorbed 14.3 mL of water after 24 h and there   121  were no wax-treated samples that absorbed significantly (p < 0.001) less water than these MR samples at this time.  However, there were six of the different types of wax-treated samples that absorbed significantly (p < 0.001) more water.  Figure 5.8. Effect of wax type on the water absorption of wax-treated OSB samples that were floated face down on water for 24 h, as well as a comparison between the water absorption of these samples and “moisture resistant” (MR) OSB samples.  Two independent statistical analyses were conducted, each time comparing the wax treatments to a different control.  The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) between untreated samples and wax-treated samples is 3.53 mL (error bars drawn), while the LSD between MR samples and wax-treated samples is 3.37 mL (not drawn)     After 48 h, untreated samples absorbed 36.5 mL of water in total; significantly (p < 0.001) more than many of the wax-treated samples (Figure 5.9).  However there was no significant difference in the WA of untreated controls and those of seven of the different wax-treated samples.  Samples that absorbed the lowest amount of water after 48 h, were those treated with a blend of beeswax and synthetic beeswax.  These samples absorbed 23.3 mL of water in total; 36.1% less than that of untreated samples, and significantly less than most of the other wax-treated samples.  The WA of samples treated with a blend of beeswax and synthetic   122  beeswax, however, was not significantly (p > 0.05) different from those of samples treated with seven of the other wax types.  Once again, these wax types included all those containing beeswax, except a blend of beeswax and Sasolwax C.  MR samples absorbed a total of 22.5mL of water after 48 h; significantly (p < 0.001) less than nine of the different types of wax-treated samples.  There were no wax-treated samples that absorbed significantly (p < 0.001) less water than MR samples.  Figure 5.9. Effect of wax type on the water absorption of wax-treated OSB samples that were floated face down on water for 48 h, as well as a comparison between the water absorption of these samples and “moisture resistant” (MR) OSB samples. Two independent statstical analyses were conducted, each time comparing the wax treaments to a different control.  The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) between untreated samples and wax-treated samples is 6.35 mL (error bars drawn), while the LSD between MR samples and wax-treated samples is 6.32 mL (not drawn)   After 72 h, untreated samples absorbed 53.5 mL of water in total, significantly (p = 0.047) more than samples treated with any of the following five wax types: beeswax (43.2 mL); a blend of beeswax and Vaseline (42 mL); microcrystalline wax (41 mL); stearic acid (38 mL); or a blend of beeswax and synthetic beeswax (37.11 mL) (Figure 5.10).  Samples treated with a blend of beeswax and synthetic beeswax once again absorbed the least amount of water after 72 h.    123  They absorbed significantly less water than untreated samples (31% less), as well as less than those of samples treated with seven of the different types of wax.    Figure 5.10. Effect of wax type on the water absorption of wax-treated OSB samples that were floated face down on water for 72 h.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) between untreated samples and wax-treated samples is 10 mL   5.3.4 Effect of wax treatments and wax type on thickness swelling On average, OSB samples swelled more during the first 24 h of the float test than during any of the subsequent 24 h periods (Table 5.6).   Table 5.6. Average thickness swelling of all OSB samples*   Thickness swelling (mm)  2 h 24 h 48 h 72 h Mean 0.17 0.63 1.02 1.42 σ 0.10 0.19 0.26 0.36 * Sample population includes “moisture resistant” samples, untreated controls, and all wax-treated samples    124  On average wax-treated OSB samples swelled less than untreated OSB samples for all time periods (Figure 5.10).  One of the best performing wax types was a blend of beeswax and synthetic beeswax.  OSB samples treated with this wax type swelled much less than untreated OSB samples at all time periods, but never less than those of MR samples.   Figure 5.11. Average thickness swelling of: (1) untreated OSB (n = 7); (2) all wax-treated samples (n = 112); (3) OSB samples treated with a blend of beeswax and synthetic beeswax (n = 7): and (4) “moisture resistant” OSB (n = 7).  All samples were floated on water for 72 h and measurements were taken after 2 h, 24 h, 48h, and 72 h  Wax treatments had a significant (p < 0.05) effect on the TS of OSB for all time periods (Figures 5.11 - 5.12).  When wax-treated samples are compared with MR samples there were also significant differences for all the time periods. After 2 h of floating on water, the average TS of wax-treated samples was 37% less than that of untreated samples (Figure 5.12, left).  The thickness of untreated samples had increased by 0.25 mm, while the thickness of wax-treated samples had increased by only 0.16 mm.  The thickness of MR samples had increased by 0.09 mm, 41% less than the average wax-treated samples. 0.00.20.40.60.81.01.21.41.61.80 6 12 18 24 30 36 42 48 54 60 66 72Thickness swelling (mm) Water exposure time (h) Untreated Average wax treated Best wax treatment MR   125  After 24 h, the TS of wax-treated samples, on average, was 20% less than that of untreated samples (Figure 5.12, right).  The thickness of untreated samples had increased by 0.77 mm in total, while the thickness of wax-treated samples had increased by 0.62 mm.  The thickness of MR samples had increased by 0.31 mm in total;, 52% less than that of untreated samples.  Figure 5.12. Average effect of wax treatments on the thickness swelling of OSB samples that were floated face down on water for 2 h (left) and 24 h (right), as well as a comparison between the water absorption of these samples and those of “moisture resistant” (MR) OSB samples.  Two independent statistical analyses were conducted for each water exposure period (2 h and 24 h), each time comparing the wax treatments to a different control. The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) between untreated samples and wax-treated samples after 2 h and 24 h was 0.04 mm and 0.11 mm, respectively (error bars drawn).  The LSD between untreated samples and MR samples after 2 h and 24 h was 0.04 mm and 0.12 mm, respectively (not drawn)  After 48 h, the TS of wax-treated samples, on average, was 15% less than that of untreated samples (Figure 5.13, left).  The thickness of untreated samples had increased by 1.17 mm in total, while the thickness of wax-treated samples had increased by 1 mm.  The thickness of MR samples had increased by 0.54 mm in total, 46% less than that of untreated samples.   After 72 h, the average TS of wax-treated samples was 13% less than that of untreated samples (Figure 5.13, right).  The thickness of untreated samples had increased by 1.6 mm in total, while   126  the thickness of wax-treated samples had increased by 1.4 mm.  The thickness of MR samples had increased by 0.6 mm in total, 57% less than that of untreated samples.             Figure 5.13. Average effect of wax treatments on the thickness swelling of OSB samples that were floated face down on water for 48 h (left) and 72 h (right), as well as a comparison between the water absorption of these samples and those of “moisture resistant” (MR) OSB samples. Two independent statistical analyses were conducted for each water exposure period (2 h and 24h), each time comparing the wax treatments to a different control. The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level.  The least significant difference (LSD) between untreated samples and wax-treated samples after 48 h and 72 h was 0.16 mm and 0.19 mm, respectively (error bars drawn).  The LSD between untreated samples and MR samples after 2 h and 24 h was 0.17 mm and 0.2 mm, respectively (not drawn) There were significant differences in the TS of untreated OSB samples and the different types of wax-treated samples for all time periods, as well as significant differences in the TS of the different wax-treated samples and MR samples for all time periods.  There were also significant differences in TS of samples treated with different wax types for all time periods (Figures 5.13 – 5.16).  After 2 h, the thickness of untreated samples had increased by 0.25 mm; significantly more than that of most of the wax-treated samples (Figure 5.14).  There was, however, no significant (p < 0.001) difference between the TS of untreated samples, after 2 h, and that of samples treated with any of the following four wax types: (1) Sasolwax C (0.28); (2) soy wax   127  (0.24 mm); (3) Tekniwax 801 (0.21 mm); or  (4) Merkur 300 (0.21 mm).  Samples treated with a blend of beeswax and Vaseline swelled the least (0.09 mm); about 65% less than untreated samples and significantly (p < 0.001) less than those of most of the other wax-treated samples. Samples treated with a blend of beeswax and Vaseline, however, did not swell significantly (p > 0.05) more than those of six of the other wax treated samples. This group of six included all waxes that contained beeswax, except for samples treated with a blend of beeswax and Sasolwax C.  The group of six also included both wax types that contained ethylene maleic anhydride.  The TS of MR samples was significantly (p < 0.001) less than those of most of the different wax-treated samples.  MR samples, however, did not swell significantly less than samples treated with a blend of beeswax and Vaseline or any of the samples treated with the waxes in the group of six mentioned above.    128   Figure 5.14.  Effect of wax type on the thickness swelling of wax-treated OSB samples that were floated face down on water for 2 h, as well as a comparison between the thickness swelling of these samples and “moisture resistant” (MR) OSB samples. Two independent statstical analyses were conducted, each time comparing the wax treaments to a different control. The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) for both statistical analyses is 0.06 mm (error bars drawn) After 24 h, the thickness of untreated samples had increased by 0.77 mm in total (Figure 5.15).  The TS of samples treated with the following seven wax types was significantly (p < 0.001) less than that of untreated samples: (1) a blend of Sasolwax M3M and ethylene maleic anhydride (0.60 mm); (2) synthetic beeswax (0.55 mm); (3) beeswax (0.52 mm); (4) microcrystalline wax (0.52 mm); (5) a blend of beeswax and ethylene maleic anhydride (0.49 mm); (6) a blend of beeswax and synthetic beeswax (0.46 mm); and (7) a blend of beeswax and Vaseline (0.45 mm).  Samples treated with a blend of beeswax and Vaseline had the smallest thickness increase after 24 h; about 41% less than that of untreated samples and significantly less than those of nine of the other types of wax-treated samples.  MR samples had significantly (p < 0.001) less TS than most of the different wax-treated samples after 24 h, except for samples treated with: (1) a blend of beeswax and synthetic beeswax; or (2) a blend of beeswax and Vaseline.   129   Figure 5.15. Effect of wax type on the thickness swelling of wax-treated OSB samples that were floated face down on water for 24 h, as well as a comparison between the thickness swelling of these samples and “moisture resistant” (MR) OSB samples. Two independent statistical analyses were conducted, each time comparing the wax treatments to a different control.  The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) between untreated samples and wax-treated samples is 0.15 mm (error bars drawn), while the LSD between MR samples and wax-treated samples is 0.16 mm (not drawn)    After 48 h, the thickness of untreated samples had increased by 1.17 mm in total; significantly (p < 0.001) more than those of seven of the different types of wax-treated samples (Figure 5.16).  These seven wax types, once again, included all beeswax containing waxes, except for a blend of beeswax and Sasolwax C.  Samples treated with a blend of beeswax and synthetic beeswax had the smallest thickness increase after 48 h; about 34% less than that of untreated samples and significantly (p < 0.001) less than those of nine of the other types of wax-treated samples.   After 48 h, the TS of MR samples was significantly (p < 0.001) less than those of any of the samples treated with wax.   130   Figure 5.16. Effect of wax type on the thickness swelling of wax-treated OSB samples that were floated face down on water for 48 h, as well as a comparison between the thickness swelling of these samples and “moisture resistant” (MR) OSB samples. Two independent statstical analyses were conducted, each time comparing the wax treaments to a different control.  The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) between untreated samples and wax-treated samples is 0.22 mm (error bars drawn), while the LSD between MR samples and wax-treated samples is 0.23 mm (not drawn) After 72 h, the thickness of untreated samples had increased by 1.6 mm; significantly (p < 0.001) more than those of seven of the other types of wax-treated samples, including most of the wax types containing beeswax (Figure 5.17).   Samples treated with a blend of beeswax and synthetic beeswax had the smallest thickness increase; about 30% less than that of untreated samples and significantly less than those of eight of the other types of wax-treated samples.  After 72 h, the TS of MR samples was significantly (p = 0.002) less than those of any of the samples treated with wax.   131   Figure 5.17. Effect of wax type on the thickness swelling of wax-treated OSB samples that were floated face down on water for 72 h, as well as a comparison between the thickness swelling of these samples and “moisture resistant” (MR) OSB samples. Two independent statistical analyses were conducted, each time comparing the wax treatments to a different control.  The two controls (Untreated and MR) have clear data points.  Non-overlap of error bars indicates that means are significantly different at a 5% level. The least significant difference (LSD) between untreated samples and wax-treated samples is 0.27 mm (error bars drawn), while the LSD between MR samples and wax-treated samples is 0.28 mm (not drawn)       132  After floating on water for 72 h and conditioning at 20 ± 1°C and 65 ± 5% r .h. for a minimum of two weeks and a maximum of four, the average moisture content of all OSB samples (excluding MR samples) was 11.9%.  The standard deviation in moisture content was 0.3%.  There were significant (p = 0.003) differences between the moisture contents of samples treated with different wax types, as well as between wax-treated and untreated samples.  Untreated samples had a conditioned moisture content of 11.9%.  Samples treated with Sasolwax C had the highest conditioned moisture content (12.58%), while samples treated with a blend of beeswax and synthetic beeswax had the lowest (11.45%).   Both the wax-treated and untreated OSB samples that were floated on water for 72 h continued to swell when they were removed and placed in a conditioning room for 2 – 4 weeks (Figure 5.18).  This continued swelling will henceforth be termed as “time-delayed thickness swelling”.  There were significant (p = 0.01) differences in the time-delayed TS of untreated samples and wax-treated samples.  On average, untreated OSB samples swelled by 0.125 mm, while wax-treated samples swelled by 0.25 mm.   Thus, the time-delayed TS of wax-treated samples was approximately 103% more than that of untreated samples.   There were also significant (p = 0.023) differences between the time-delayed TS of samples treated with different types of waxes.  Samples treated with carnauba wax had the lowest amount of time-delayed TS (0.146 mm), approximately 16.8% more than untreated samples.  Samples treated with microcrystalline wax had the highest amount of time-delayed TS (0.4 mm), approximately 218.4% more than that of untreated samples.  The time-delayed TS of samples treated with petroleum jellies, Vaseline and Merkur 300, was 164% and 140% more than that of untreated samples, respectively. Samples treated with a blend of beeswax and Vaseline swelled 145.6% more than untreated samples, while samples treated with a blend of beeswax and synthetic beeswax swelled 132.8% more.  The average time-delayed TS of MR samples (0.27 mm) was comparable to that of the different wax-treated samples.   133   Figure 5.18. The time-delayed thickness swelling of OSB samples treated with different wax types.  Measurements were taken after the samples were floated face down on water for 72 h and then conditioned at 20 ± 1°C and 65 ± 5% r.h. for a minimum of two weeks  and a maximum of four weeks.  Non-overlap of error bars indicates that means are significantly different at a 5% level.  All samples from each individual experimental replication were measured at the same time, irrelevant of their conditioning period There was no significant difference (p = 0.58) between the total thickness swelling of untreated and wax-treated OSB samples after they were floated face down on water for 72 h and then conditioned at 20 ± 1°C and 65 ± 5% r.h. for a minimum of two and a maximum of four weeks.  There were, however, significant (p = 0.005) differences between the TS of samples treated with different wax types, as well as between those samples and untreated samples (Figure 5.19).  Untreated samples had a total thickness swelling of 1.72 mm.  Samples treated with two of the different types of wax-treatments swelled significantly less than this (p = 0.005); the samples treated with a blend of beeswax and synthetic beeswax had a total thickness swelling of only 1.41 mm, while samples treated with stearic acid had a total thickness swelling of 1.45 mm.  The average total thickness swelling of MR samples (0.87 mm) was significantly less than those of untreated and wax-treated OSB samples.   134   Figure 5.19.  Total thickness swelling of untreated and wax-treated OSB samples after they were floated face down on water for 72 h and then conditioned at 20 ± 1°C and 65 ± 5% r.h. for a minimum of two and a maximum of four weeks.  Non-overlap of error bars indicates that means are significantly different at a 5% level.  All samples from each individual experimental replication were measured at the same time, irrelevant of their conditioning period  5.3.5 Effects of initial moisture content on water repellency, water absorption and thickness swelling There was a weak negative correlation (p = 0.019; R2 = 0.34) between the initial moisture content of samples (untreated and wax treated) and the time it took for 5 µL water droplets to spread over wax-treated OSB surfaces and form contact angles of less than 90° (t<90°) (Figure 5.20).  Samples treated with wax types with long t<90° times, therefore, generally adsorbed less water vapour while stored in the conditioning room than samples treated with wax types with short t<90° times.   135   Figure 5.20.  Relationship between (1) the initial moisture content of wax-treated samples that were  oven dried, wax treated and then conditioned at 20 ± 1°C and 65 ± 5% r.h. for a minimum of seven days, and (2) the time it took for 5 µL water droplets to spread over wax-treated OSB surfaces and form contact angles of less than 90° There were weak positive correlations between the initial moisture content of OSB samples (untreated and wax treated) and the WA of the same samples, after they were floated face down on water for 2 h (p = 0.01; R2 = 0.34) and 24 h (p = 0.03; R2 = 0.27) (Figure 5.21).  There were no significant (p > 0.05) relationships between the initial moisture content of wax-treated samples and WA at 48 h and 72 h.  In general, samples that had low initial moisture contents, when exposed to water for the first time, absorbed less water during the first 24 h than samples that had high initial moisture contents. 5.85.96.06.16.26.36.46.50 5 10 15 20 25 30 35Initial moisture content (%) t<90° on OSB (min) y = 6.5 - 0.015x R2 = 0.34 p = 0.019     136   Figure 5.21.  Relationships between (1) the initial moisture content of wax-treated samples that were oven dried, wax treated and conditioned at 20 ± 1°C and 65 ± 5% r.h. for a minimum of seven days, and (2) the water absorption of the samples after they were floated  face down on water for 2 h (left) and 24 h (right) There were moderate to weak correlations between the initial moisture content of the OSB samples and the TS of the same samples, after they were floated face down on water for 2 h (p = 0.002; R2 = 0.47), 24 h (p = 0.009; R2 = 0.38), 48 h (p = 0.027; R2 = 0.29), and 72 h (p = 0.031; R2 = 0.27)  (Figure 5.22).  The positive correlation was affected by the length of exposure time, becoming weaker after longer floatation periods.  Similar relationships to those between water absorption and initial moisture content were present between thickness swelling and initial moisture content.  In general, samples that had low initial moisture content, when exposed to water for the first time, swelled less over 72 h than samples that had high initial moisture contents. 05101520255.8 6 6.2 6.4 6.62h Water absorption (mL) Initial moisture content (%) y = 4.6x - 24.7 R2 = 0.34 p = 0.01   05101520255.8 6 6.2 6.4 6.624h Water absorption (mL) Initial moisture content (%) y = 9.4x -41.7 R2 = 0.27 p = 0.03     137   Figure 5.22. Relationships between (1) the initial moisture content of wax-treated samples that were oven dried, wax-treated and conditioned at 20 ± 1°C and 65 ± 5% r.h. for a minimum of seven days, and (2) the thickness swelling of the samples after they were floated  face down on water for 2 h (top left), 24 h (top right), 48 h (bottom left), and 72 h (bottom right) 5.3.6 Effects of water repellency of wax-treated surfaces on water absorption and thickness swelling There were moderate to weak negative correlations between the times it took for 5µL water droplets to spread and form contact angles of less than 90° on wax-treated OSB surfaces (t<90°), and the amount of water absorbed by wax-treated OSB samples that were floated face down on water for 2 h (p < 0.001; R2 = 0.55), 24 h (p = 0.005; R2 = 0.43), 48 h (p = 0.008; R2 = 0.38), and 72 h (p = 0.024; R2 = 0.3) (Figure 5.23). 0.00.20.40.60.81.01.21.41.61.85.8 6 6.2 6.4 6.62h Thickness swelling (mm) Initial moisture content (%) y = 0.22x - 1.2  R2 = 0.47 p = 0.002  0.00.20.40.60.81.01.21.41.61.85.8 6 6.2 6.4 6.624h Thickness swelling (mm) Initial moisture content (%) y = 0.39x - 1.82 R2 = 0.38 p = 0.009 0.00.20.40.60.81.01.21.41.61.85.8 6 6.2 6.4 6.648h Thickness swelling (mm) Initial moisture content (%) y = 0.44x - 1.72 R2 = 0.29 p = 0.027 0.00.20.40.60.81.01.21.41.61.85.8 6 6.2 6.4 6.672h Thickness swelling (mm) Initial moisture content (%) y = 0.48x - 1.55 R2 = 0.27 p = 0.031   138   Figure 5.23. Relationships between (1) the times it took for 5 µL water droplets to spread over wax-treated surfaces and form a contact angles of less than 90° (t<90°), and (2) the water absorption of wax-treated OSB samples that were floated face down on water for 2 h (top left), 24 h (top right), 48 h (bottom left), and 72 h (bottom right) There were also moderate to weak negative correlations between the times it took for 5µL water droplets to spread and form contact angles of less than 90° on wax-treated OSB surfaces (t<90°), and the TS of wax-treated OSB samples that were floated face down on water for 2 h (p < 0.001; R2 = 0.58), 24 h (p = 0.012; R2 = 0.35), 48 h (p = 0.016; R2 = 0.33), and 72 h (p =0.043; R2 = 0.25) (Figure 5.24).  01020304050600 10 20 30 402h Water absorption (mL) t<90° on OSB (min) y = 6.7 - 0.15x R2 = 0.55 p = < 0.001 01020304050600 10 20 30 4024h Water absorption (mL) t<90° on OSB (min) y = 22.9 - 0.29x R2 = 0.43 p = 0.005 01020304050600 10 20 30 4048h Water absorption (mL) t<90° on OSB (min) y = 37.8 - 0.36x R2 = 0.38 p = 0.008 01020304050600 10 20 30 4072h Water absorption (mL) t<90° on OSB (min) y = 53.8 - 0.36x R2 = 0.3 p = 0.024   139   Figure 5.24. Relationships between (1) the times it took for 5µL water droplets to spread over wax-treated surfaces and form a contact angles of less than 90° (t<90°) and (2) the thickness swelling of wax-treated OSB samples that were floated face down on water for 2 h (top left), 24 h (top right), 48 h (bottom left), and 72 h (bottom right) 5.3.7 Effects of melting point temperatures on water absorption and thickness swelling There were moderate and weak negative correlation between the melting point temperatures of waxes applied to samples and WA after 2 h (p = 0.001; R2 = 0.55) and 24 h (p = 0.02; R2 = 0.32), respectively (Figure 5.25).  However, there were no statistically significant relationships between the melting point temperatures of the different waxes and WA of wax-treated samples after 48h (p = 0.055) and 72 h (p = 0.2).   0.00.51.01.52.00 10 20 302h Thickness swelling (mm) t<90° on OSB (min) y = 0.29 - 0.006x R2 = 0.58 p < 0.001 0.00.51.01.52.00 10 20 3024h Thickness swelling (mm) t<90° on OSB (min) y = 0.82 - 0.009x R2 = 0.35 p = 0.012 0.00.51.01.52.00 10 20 3048h Thickness swelling (mm) t<90° on OSB (min) y = 1.26 - 0.012x R2 = 0.33 p = 0.016 0.00.51.01.52.00 10 20 3072h Thickness swelling (mm)  t<90° on OSB (min) y = 1.64 - 0.011x R2 = 0.25 p = 0.043   140   Figure 5.25. Relationships between the melting point temperatures of the waxes sprayed onto OSB surfaces and the water absorption of wax-treated samples that were floated face down on water for 2 h (left) and 24 h (right) There were also negative correlations between the melting point temperatures and TS of wax-treated samples that were floated face down on water for 2 h (p < 0.001; R2 = 0.67), 24 h (p = 0.014; R2 = 0.36), 48 h (p = 0.026; R2 = 0.31), and 72 h (p = 0.049; R2 = 0.25) (Figure 5.26).  The length of exposure to water had a strong effect on the correlations; with correlations being strong at 2 h and weaker at 24 h, 48 h and 72 h.   051015202520 40 60 80 1002h Water absorption (mL) Drop melting point (°C) y = 7.84 - 0.066x R2 = 0.55 p = 0.001 051015202520 40 60 80 10024 h Water absorption (mL) Drop melting point (°C) y = 24.28 - 0.12x R2 = 0.32 p = 0.02   141   Figure 5.26. Relationships between the melting point temperatures of the waxes sprayed onto the surface of OSB and the thickness swelling of wax-treated samples that were floated face down on water for 2 h (top left), 24 h (top right), 48 h (bottom left), and 72 h (bottom right) Finally, there was also a weak correlation (p = 0.04; R2 = 0.26) between the melting point temperatures of different wax types and the time-delayed TS of wax-treated samples that were floated face down on water for 72 h and then conditioned at 20 ± 1°C and 65 ± 5% r.h. for a minimum of two and a maximum of four weeks (Figure 5.27).    00.511.5220 40 60 80 1002h Thickness swelling (mm) Drop melting point (°C) y = 0.36 - 0.003x R2 = 0.67 p < 0.001  00.511.5220 40 60 80 10024h Thickness swelling (mm) Drop melting point (°C) y = 0.92  - 0.005x R2 = 0.36 p = 0.014 00.511.5220 40 60 80 10048h Thickness swelling (mm)  Drop melting point (°C) y = 1.37  - 0.006x R2 = 0.31 p = 0.026 00.511.5220 40 60 80 10072h Thickness swelling (mm) Drop melting point (°C) y = 1.76  - 0.006x R2 = 0.25 p = 0.049   142   Figure 5.27. Relationship between the melting point temperatures of different wax types and the total thickness swelling of wax-treated OSB samples that were floated face down on water for 72 h and then conditioned at 20 ± 1°C and 65 ± 5% r.h. for a minimum of two and a maximum of four weeks 5.4 Discussion In the introduction to this chapter I hypothesized that polar waxes with strong hydrophobic properties would be more effective at dimensionally stabilizing OSB than nonpolar waxes or polar waxes with low hydrophobicity.  I also restated the hypothesis developed in Chapter 4, which argued that low melting (LM) point waxes would be more effective at stabilizing  the dimensions of OSB than high melting (HM) waxes. Results in this chapter confirm those described in Chapter 4 and allow me to reject the hypothesis, that LM point waxes are more effective than HM point waxes at dimensionally stabilizing OSB.  Contrary to expectations, there was a negative correlation between melting point temperature of waxes and the TS of wax-treated samples for all water exposure periods, as well as for the time-delayed TS after samples were removed from the water tank and conditioned in a climate controlled room.  This negative correlation was strongest for short periods of exposure to liquid water and became weaker as the length of exposure increased.  There were also moderate to weak negative correlations between the melting point 00.20.40.60.811.21.41.61.8220 30 40 50 60 70 80 90 100Total thickness swelling (mm) Drop melting point temperature (°C) y = 2 - 0.005x R2 = 0.26 p = 0.04    143  temperatures of waxes and the WA of wax-treated samples during the first 24 h of liquid water exposure.  There were no statistically significant relationships between the acid value numbers of the wax types and the WA or TS of wax-treated samples.  Since the polarity of wax increases as its acid value number increases, polarity did not appear to influence the ability of wax to dimensionally stabilize OSB.  Upon closer examination, however, it was noted that the best performing waxes, during both short and long term exposure of OSB to water, were those that contained both beeswax (polar) and a nonpolar wax.  Of these beeswax blends, the best ones were blends of beeswax and paraffin waxes (Vaseline or synthetic beeswax), although beeswax also performed well on its own. Samples treated with only beeswax, or only Vaseline, consistently swelled more than samples treated with a blend of the two waxes.  Similarly, samples treated with only beeswax, or only synthetic beeswax, consistently swelled more than samples treated with a blend of the two waxes. Waxes with high polarity and strong affinity to wood, but low hydrophobicity, such as soy wax and stearic acid were less effective particularly in the short term. Two strongly hydrophobic, nonpolar paraffin waxes, microcrystalline wax and synthetic beeswax, provided excellent protection against TS.  Fischer-Tropsch waxes, on the other hand, were some of the least effective waxes.  For example, a Fischer-Tropsch and beeswax blend (beeswax + Sasolwax C) did not perform well even though, as noted above, the other beeswax blends were some of the most effective water repellents for OSB.  Beeswax has polar functional groups that may have allowed it to bond well to wood strands, whereas paraffin wax, with its saturated hydrocarbon structure, may have provided additional hydrophobicity. This agrees with the suggestions of Borgin (1965) and the findings of Borgin and Corbertt (1970; 1974), that water repellents for solid wood need to contain both hydrophobic and hydrophilic components.  Hilditch (1965) and Borgin (1965) also reported that paraffin wax imparted excellent dimensional stability to solid wood.  These observations partially support the hypothesis that polar waxes with strong hydrophobic properties will be more effective at dimensionally stabilizing OSB than nonpolar waxes, or polar waxes with low hydrophobicity.     144  In this chapter I used a water float test, instead of the conventional soak test, to test the effectiveness of the molten wax treatments at dimensionally stabilizing OSB.  Water float tests are commonly used to determine the liquid water permeability of coatings on solid wood (EN 2005).  In Chapter 4, I used a water immersion test and based on a previous study by Evans et al. (2013).  I expected the TS of samples floated on water in this chapter to be lower than those that were immersed in the previous chapter.  The opposite was the case.  My results showed that TS measured in the water float test was greater than that measured in Chapter 4.  This may be because more wax was applied to the samples in Chapter 4, which created more effective barriers against moisture ingress.  The edges of samples in Chapter 4 were also sealed using epoxy resin, which probably restricted TS even further.  In this chapter, samples were edge sealed with less restrictive, more elastic, silicone sealer.  The silicone may have restricted swelling less than the epoxy sealant used in Chapter 4.  The majority of the WA and TS measured in this chapter most likely occurred in the exposed face layers of the OSB samples, since the samples were floated on water and because the rate and extent of TS of OSB is known to be highest in the surface layers (Winistorfer and Xu 1996; Wang and Winistorfer 2003; Gu et al. 2005; Tackie et al. 2008). Wang and Winistorfer (2003) reported that the two surface layers of OSB may account for 74.36% of the overall swelling after 2 h and for 57.3% after 24 h.  Any wax treatment that can effectively reduce TS  of samples floated on water should, therefore, also be effective at reducing the swelling of the entire board.  In a report by Taylor and Wang (2007), it was shown that the edge swelling of the same brand of MR OSB that was used as a control in this chapter was approximately half that of regular OSB panels after 24 h and 72 h of immersion in water.   In a later paper it was reported that the TS of the same brand of MR boards was 2.35% after 24 h, while the swelling of regular OSB panels was 8.3% (Taylor et al. 2008).  After 72 h, the TS of MR boards was 12.14%, while the TS of regular OSB was 24.5%.  In accord with the results of Taylor et al. (2008), my results also indicate that MR samples swelled roughly half as much as regular OSB after 24 h.  In contrast,   145  however, my results showed more TS for the MR samples after 72 h than the results of Taylor et al. (2008). The time-delayed thickness swelling and final moisture content results suggested that wax-treated samples dried at a slower rate than untreated samples.  In accord with this suggestion, Feist (1982) coated waferboard surfaces with various film-forming finishes and exposed them to natural weathering for 21 – 43 months.  He observed that fungal growth occurred in many of the samples because the coatings were unable to prevent water ingress.  Furthermore, the coatings appeared to trap the absorbed water within the panels.  My results also suggest that wax treatments may have trapped water inside the board and slowed the rate of drying, as mentioned above.  The majority of studies that have examined the water repellent effects of wax on solid wood or OSB almost exclusively looked at paraffin wax.  Furthermore, no previous studies  have examined the use molten wax treatments for dimensionally stabilizing OSB.  Therefore, it is difficult to compare my results with those of other researchers. However, my results are partially supported by Borgin and Corbertt’s (1970) work.  They used various waxes as water repellents for radiata pine wood.  Their water repellents contained 2.5%, 10%, 25% or 50% of wax dissolved in mineral turpentine.  The waxes included some of the waxes I tested, such as paraffin waxes, petroleum jelly, beeswax, and carnauba wax.  They did, however not blend any of their waxes as I did.  They found that all of the waxes were effective at preventing water uptake and swelling, but the best performing waxes were paraffin waxes.  A number of waxes which included the prefix “Sasolwaks” in their name were less effective than the other wax types.  It is assumed that these waxes were Fischer-Tropsch waxes, similar to the Fischer-Tropsch waxes I sourced from Sasolwax, South Africa.  Borgin and Corbertt also showed that beeswax’s ability to prevent swelling improved over time and it was consistently better than that of carnauba wax and petroleum jelly at dimensionally stabilizing wood.  From their results they concluded paraffin waxes could perform even better if they contained hydrophilic groups.  Many of their results agree with my findings.   146  The study that is the most relevant to mine is one by Semple et al. (2009).  They sprayed unheated water-based wax emulsions or linseed oil-wax solutions onto the surface of hot OSB.  The waxes in their study included soy wax, beeswax, carnauba wax, and paraffin wax.  They found that linseed oil-wax solutions containing beeswax rarely performed better than those containing paraffin or soy wax, and almost never performed better than those containing carnauba wax.  This discrepancy between their results and mine may be explained by the fact that their waxes were sprayed as oil based solutions and not as neat molten wax, as was the case here. The very strong positive relationship between the WA and TS of wax-treated OSB was strongly affected by the length of time samples were exposed to water.  As mentioned, the positive correlation was stronger after longer exposure periods.   This supports the concept that liquid water first enters the inter-strand voids within OSB, where it does not directly lead to TS (Wu and Piao 1999; Semple et al. 2009).  This suggestion also accords with the research of van Houts et al. (2004) who used nuclear magnetic resonance imaging to show that WA by OSB occurs via inter-strand voids.  The correlation between TS and WA strengthens over time, because as the inter-strand voids become saturated with water, water will only be able to diffuse into wood cell walls where it causes swelling.  Wax treatments that are effective at blocking inter-strand voids within OSB will therefore be able to limit initial water uptake and slow the rate of TS, but not the ultimate amount of TS.    Although the linear relationship between WA and TS occurred for all exposure periods, the varied slopes and intercepts of the regression lines at different time periods suggest that absorption of similar amounts of water caused more TS during initial exposure periods than it did during later periods.  Thus the relationship between WA and TS might be curvilinear and not linear.  Greater swelling during initial periods is probably caused by wood swelling and recovering strains developed when flakes were compressed and densified during hot-pressing (Neusser et al. 1965; Halligan 1970; Hsu et al. 1988; Kelly 1977; Wu and Suchsland 1997).   147  The hydrophobicity of wax-treated surfaces and the differences in the initial moisture content were correlated with the WA and TS of the wax-treated samples that were floated on water.  However, contrary to expectations, samples with low initial moisture contents absorbed less water and swelled less during the first 24 h than samples with high initial moisture content.  A similar relationship was observed between initial moisture content and TS after 72 h.  The correlation between the water repellency of wax-treated OSB surfaces and the WA and TS of wax-treated OSB samples also displayed a similar relationship. Thus, the same wax types which slowed the rate of water vapour adsorption during the conditioning period also slowed the rate of liquid WA during the water float test.  This observation suggests, that strongly hydrophobic waxes are more effective water-repellent treatments for OSB. An unexpected finding was that the TS of samples treated with stearic acid was quite high relative to WA.  This may have been because stearic acid tended to agglomerate around one area when it was applied to OSB, thus reducing WA and TS in certain areas only.  These areas, where the wax agglomerated, swelled noticeably less than the surrounding “untreated” areas and caused variable TS across the sample.     Lastly, it seems that the hardness and flexibility of wax is not important for wax treatments that do not form surface coatings.  There was, for example, no evident trend between the WA and TS of OSB samples treated with soft waxes, such as Vaseline or Merkur 300, and those treated with hard waxes, such as carnauba wax, Sasolwax M3M or stearic acid. 5.5 Conclusion  Wax treatments were able to reduce the rate of WA and TS of OSB for short periods of exposure to water, but not the extent of TS after long periods of exposure.   I therefore conclude that the wax treatments are useful water-repellent treatments for OSB exposed to water for short periods of time, but not for boards immersed in water for a long time. HM waxes performed better than LM.  Strongly hydrophobic, nonpolar waxes, such as paraffin wax, were also effective treatments. However, my results suggest that the addition of polar   148  waxes may improve their performance.  I therefore conclude that molten wax treatments that contain both polar and nonpolar waxes will be more effective at dimensionally stabilizing OSB than waxes that contain only hydrophobic nonpolar waxes or polar waxes on their own.     149  Chapter 6. General discussion, suggestions for further research and conclusions 6.1 General discussion The wax treatments developed and tested in this thesis significantly reduced the WA and TS of OSB, as hypothesized in Chapter 1.  Results in Chapter 4 supported my overall hypothesis, but some of the high melting (HM) point waxes formed coatings on the surface of the OSB, rather than acting as a penetrating water repellent as desired.  Wax coatings can be easily removed from surfaces by abrasion and are therefore undesirable from a practical standpoint.  Subsequent research in Chapter 5 used an application method that minimized the occurrence of such surface coatings.  The results in Chapter 5 showed that such wax treatments significantly reduced the WA and TS of OSB.  The treatments were very effective when treated OSB samples were first exposed to liquid water, but their effectiveness decreased with further exposure to water.  Thus the molten wax treatments can be classified as Type-I treatments, according to the definitions of dimensional stabilizing treatments for solid wood proposed by Rowell and Banks (1985).   Results from Chapter 5 also showed that HM waxes were more effective water repellents for OSB than LM waxes, contrary to expectations.  According to contact angle measurements in Chapter 3, HM waxes were more hydrophobic than LM waxes, which may partly explain why they performed better than LM waxes.  It appears that in the absence of a surface coating, the hydrophobicity of wax is more important than its ability to flow into and penetrate OSB surfaces; contrary to what was speculated in Chapter 4.  This suggestion is also supported by studies which observed that wax emulsions with long n-alkanes chain are more effective at reducing the WA and TS of MDF and particleboard than those made with short n-alkanes chain (Roffael and May 1983; Schriever and Roffael 1984; Hague 1995; Roffael et al. 2005).   Results from Chapter 3 and 5 suggested that wax treatments that contained both polar and nonpolar waxes were more effective at dimensionally stabilizing OSB than treatments that contained only polar wax or only nonpolar wax.  Molten blends of beeswax and paraffin wax   150  performed very well and improved the stability of regular OSB samples to a level where their short term resistance to water matched that of highly moisture resistant OSB, which commands a premium in the market place. For example, after 24 h of exposure to water there was no significant difference between the TS of OSB treated with a blend of beeswax and synthetic beeswax (a paraffin wax) and that of the “moisture resistant” samples.  However, after 24 h the rate of swelling of “moisture resistant” samples slowed, whereas the regular OSB samples treated with wax continued to swell.  These results suggest that it may be possible for OSB manufacturers to improve the short-term thickness stability (but not the long-term stability) of their product by directly spraying wax blends onto the surface of their hot, freshly-pressed, OSB.  Molten wax treatments for OSB may be a cost effective way of improving the dimensional stability of OSB, considering that premium “moisture resistant” OSB  panels (1.2 m x 2.44 m) can cost up to three times more than regular OSB (Evans, P.D., personal communication, March 5, 2014). My results also suggest that the water repellency of wax-treated OSB surfaces is correlated with the WA and TS of wax-treated samples .  In Chapter 3, I found that the t<90° times of water droplets on wax-treated OSB surfaces can be used to indicate the water repellency of the surface.  Wax-treated OSB surfaces with long t<90° times appeared to be more hydrophobic than those with short t<90° times.  My results in Chapter 5 suggest that the rate of water vapour adsorption of wax-treated OSB samples decreased as the hydrophobicity of the wax-treated surface increased.  All OSB samples were oven dried directly before wax application, and were immediately placed in a climate controlled room for a minimum of seven days thereafter.  Some of the experimental blocks remained in the conditioning room for as long as 28 days before they were exposed to liquid water.  According to the average initial moisture contents that were measured at the end of these conditioning periods (before first exposure liquid water), wax-treated samples which were treated with wax types that had long t<90° times absorbed significantly less water vapour, while being stored in the climate controlled room, than those treated with waxes that had short t<90° times. This result was surprising, since the bottom surfaces of the OSB samples were unsealed and the edges were only sealed after five days of conditioning.  It is known that the rate of water vapour uptake by solid wood   151  is not affected by the hydrophobic properties of a water repellent, but rather by its ability to block voids which provide pathways for water vapour (Gibson 1965).  It appears, therefore, that the ability of wax to block ingress of water vapour in OSB increases as its hydrophobicity increases.  This suggests that strongly hydrophobic waxes are better at blocking sorption sites in OSB than less hydrophobic waxes.  Further research would be necessary to confirm this suggestion. The technology necessary to industrially to spray molten wax onto OSB already exists.  In fact, the very first commercial waferboard plant sprayed its wafers with molten wax before hot pressing (Clarck 1980).  Similar spray lines could be installed directly after an OSB press, so that the surfaces of the freshly pressed boards could be sprayed with wax while they are still hot.  This setup should work particularly well in factories that use a continuous press, but it may also be suitable for those that use a batch press.  Wax treatment can be applied as a separate process, to a fraction of the total production, without interfering with the production of commodity products.  Spraying molten wax onto OSB directly after pressing will also have benefits over other technologies currently available to dimensionally stabilize OSB, such as thermal and chemical modification.  For example, no pre-treatment of the wood strands is necessary, thus the boards are more likely to retain their mechanical properties after being sprayed with wax.  Wax treatments might be further improved by hot stacking the freshly-pressed boards after wax application.  Maloney (1993) reported that wax sizing migrates when particleboards are hot stacked, thus improving the water repellency of the boards.  Paraffin waxes, such as slack wax, are non-toxic and bio-degradable by-products of the petroleum industry (Wolfmeier et al. 2000).  Unfortunately the use of renewable waxes, such as beeswax (which performed very well here), is often not economically viable, since these waxes are more expensive than paraffin or synthetic waxes because there are limited supplies of them (Wolfmeier et al. 2000).    One possible disadvantage of molten wax treatments for OSB is the increased risk of fires in production plants.  According to Amthor (1972), wax sizing does not increase the inflammability   152  of particleboard, but further research is needed to confirm whether this is the case for OSB treated with molten wax.  Another possible limitation is that the treated surfaces may not be able to accept paints, varnishes, or other surface coatings.  Structural OSB, however, is not usually used in applications where such surface coatings are required.   Spraying wax onto the surface of OSB might be a cost-effective way to produce dimensionally stable OSB products, which could compete with the expensive premium-grade OSB products currently available in the marketplace.  Premium-grade OSB is bonded with pMDI resin, which costs approximately $ 567 (CAD) / ton, while wax is much cheaper, approximately $430 (CAD) / ton. 6.2 General conclusions The pronounced thickness swelling that OSB undergoes when it is exposed to moisture is a major shortcoming of this type of structural panel.  Many available technologies, such as thermal and chemical treatments, are able to reduce the thickness swelling of OSB, however, few of them have proven to be commercially viable, except for speciality products. Most of the available dimension-stabilizing technologies for OSB have negative effects on board properties, such as loss of internal bond strength and a decrease in modulus of rupture.  Spraying molten wax onto the surface of OSB offers a new approach to improve the dimensional stability of OSB, with many advantages and few disadvantages over those that have been used in the past.    Molten wax can, under the right conditions, be sprayed onto the surface of hot OSB without forming a thick surface coating.  When wax was applied in this manner, it increased the water repellency of OSB and effectively slowed the rate of water absorption and thickness swelling of samples exposed to water for short periods of time.  I conclude that molten wax treatments can be an effective way of protecting OSB from the adverse effects of short-term water exposure.   The hydrophobicity of wax increases as its melting point temperature increases.  There was a negative correlation between the melting point temperatures of waxes and the TS of wax-  153  treated samples that were exposed to water.  Waxes with long, unbranched carbon chains therefore provided good protection to OSB during short periods of exposure to water.  The addition of a more polar wax appeared to increase the effectiveness of such molten wax treatments.  I conclude that the best performing wax treatments were those that were strongly hydrophobic and contained both polar and nonpolar waxes components.  It may therefore be possible to improve the performance of waxes, which are currently used by industry to dimensionally stabilize OSB, by blending them with polar waxes or additives that increase their polarity. 6.3 Suggestions for further research Additional research is required to determine how the water-repellent barriers formed by wax treatments prevent moisture ingress and egress.  If they prevent moisture egress then the practical implications would be undesirable, as high moisture contents in OSB may favour fungal decay. Wax is known to restrict the rate of diffusion of water in wood strands (Neimsuwan et al. 2008).  According to Ye et al. (2006), however, moisture content is not a reliable indicator of mold susceptibility of OSB.  Additional research is therefore required to determine whether wax treatments of OSB might increase the risk of fungal decay. Additional research is also required to determine if the performance of the best wax blends can be improved by further optimizing spraying parameters and the quantities of wax applied to OSB. It is possible that wax blends may be more effective if they are sprayed at higher temperatures or if the OSB is hotter.  Optimization of atomization parameters (droplet size and velocity) during the spraying of wax onto OSB may also influence the performance of the treatments and is an area worthy of further investigation.  Further research is also necessary to determine the minimum application rate that is required for wax-treatment to be effective at reducing WA and TS.  Research is needed to better understand why beeswax blends performed better than other molten wax-treatments.  It was not possible to explain their superior performance in terms of   154  melting point temperature and polarity.  Nor was it possible to recommend an ideal wax in terms of these two properties.  Testing the effects of wax hardness and oil content on the performance of wax-treatments might provide some useful insights, but since all these basic properties are correlated and dependent on the chemical composition of the wax, further research using more refined materials (waxes and wood substrates) is needed.  Visualizing the location of the waxes within OSB may also provide insights as to how wax-treatments are able to affect water ingress into OSB.  I recommend the use of fluorescent microscopy for this purpose. Scholz et al. (2010a) used a coloured wax to measure the penetration of wax that was impregnated into Scots pine and European beech.    Waxes can also be labeled with a fluorescent dye before being sprayed onto the surface of wood (Ede et al. 1998; Grigsby and Thumm 2012b). Alternatively the wood strands may be labeled with a fluorescent stain before the board is pressed, thus visualising the wax location by using negative staining techniques (Kamke et al. 1996; Saunders and Kamke 1996).  Both of these recommended methods will require destruction of the test sample.  One possible non-destructive test method that may be used to locate wax in OSB is X-ray micro computed tomography.  Due to the small density difference between wax and OSB, however, it may be difficult to create the required contrast between wax and wood.  Nevertheless, one research group has used X-ray CT to visualize wax inside solid wood (Scholz et al. 2010b; Scholz et al. 2010c).  Another non-destructive technique that could be used to visualize wax in OSB is autoradiography.  For example, Levi et al. (1970) demonstrated how autoradiography could be used to visualize wax in solid wood and the same technique could be used to visualize wax in thin sections of OSB.  Molten wax spray treatments have obvious potential as an edge treatment for OSB.  Thickness swelling of OSB is pronounced at the edges of the OSB panels and several North American companies have developed ways of restricting the edge swelling of OSB exposed to water (Evans et al. 2013).  Commercially available edge seals are usually silicone or latex based and contain only small amounts of wax as a hydrophobic filler (Winterowd et al. 2003).  Further   155  research is required to determine whether molten wax treatments applied to the edges of panels can perform better than current commercial edge sealants.     According to standard methods that test the dimensional stability of OSB, samples should be immersed in water.  In Chapter 5 a water float test was used as a more realistic way of comparing surface treatments.  As a result I am unable to compare my results to those of previous studies.  In Chapter 4, I used an immersion test, however, the presence of epoxy edge seals may have restricted swelling, thus also making it difficult to compare my results to those of previous studies.  Therefore, additional research, using standard immersion tests are required to compare the effectiveness of molten wax treatments with other treatments that dimensionally stabilize OSB.  In addition to standard immersion tests, it is also necessary to expose full-sized, wax-treated panels to cyclic wetting and drying and then measure the TS of the OSB panels in both wet and dry conditions.  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Raw data for contact angle measurements of 5 µL water droplets placed on glass slides coated with different wax types  Block Wax Initial contact angle (°) Time < 90 (min) 1 Beeswax 106.00 12.50 1 Beeswax + Ethylene maleic anhydride (3:1) 108.85 16.75 1 Beeswax + Sasolwax C (1:1) 102.14 13.00 1 Beeswax + Synthetic beeswax (1:1) 104.61 13.00 1 Beeswax + Vaseline (1:1) 103.13 7.25 1 Carnauba 97.78 6.00 1 Lanolin 100.81 0.25 1 Merkur 300 106.53 1.50 1 Microcrystalline wax 110.64 38.50 1 Stearic acid 124.48 29.75 1 Sasolwax C 102.63 0.50 1 Sasolwax M3M 106.40 11.00 1 Sasolwax M3M + Ethylene maleic anhydride (3:1) 109.04 17.25 1 Soy wax 104.06 9.50 1 Synthetic beeswax 102.36 9.00 1 Tekniwax 600 107.09 39.50 1 Tekniwax 801 106.86 22.50 1 Vaseline 100.79 6.50 2 Beeswax 104.92 11.75 2 Beeswax + Ethylene maleic anhydride (3:1) 102.59 11.25 2 Beeswax + Sasolwax C (1:1) 104.85 14.25 2 Beeswax + Synthetic beeswax (1:1) 105.52 13.25 2 Beeswax + Vaseline (1:1) 104.42 12.00 2 Carnauba 99.02 7.00 2 Lanolin 95.07 0.07 2 Merkur 300 104.74 1.00 2 Microcrystalline wax 108.45 34.75 2 Stearic acid 137.23 37.00 2 Sasolwax C 91.36 0.50 2 Sasolwax M3M 102.36 13.00 2 Sasolwax M3M + Ethylene maleic anhydride (3:1) 107.70 15.50 2 Soy wax 111.92 13.00 2 Synthetic beeswax 102.93 23.50 2 Tekniwax 600 106.77 37.50 2 Tekniwax 801 106.90 37.00   171  Block Wax Initial contact angle (°) Time < 90 (min) 2 Vaseline 101.48 9.00 3 Beeswax 106.47 12.75 3 Beeswax + Ethylene maleic anhydride (3:1) 111.27 19.00 3 Beeswax + Sasolwax C (1:1) 103.13 14.00 3 Beeswax + Synthetic beeswax (1:1) 107.13 11.25 3 Beeswax + Vaseline (1:1) 105.23 10.00 3 Carnauba 101.60 11.00 3 Lanolin 106.45 0.88 3 Merkur 300 103.19 1.50 3 Microcrystalline wax 107.87 35.50 3 Stearic acid 127.17 34.25 3 Sasolwax C 101.87 2.50 3 Sasolwax M3M 103.11 14.00 3 Sasolwax M3M + Ethylene maleic anhydride (3:1) 104.76 17.25 3 Soy wax 107.68 18.75 3 Synthetic beeswax 101.30 13.00 3 Tekniwax 600 108.93 40.00 3 Tekniwax 801 108.09 12.00 3 Vaseline 104.26 10.50 4 Beeswax 103.67 10.50 4 Beeswax + Ethylene maleic anhydride (3:1) 103.52 12.25 4 Beeswax + Sasolwax C (1:1) 107.45 18.00 4 Beeswax + Synthetic beeswax (1:1) 109.17 12.00 4 Beeswax + Vaseline (1:1) 103.53 9.00 4 Carnauba 100.84 9.50 4 Lanolin 98.10 0.03 4 Merkur 300 98.90 1.00 4 Microcrystalline wax 108.01 39.50 4 Stearic acid 112.48 19.75 4 Sasolwax C 104.65 1.50 4 Sasolwax M3M 108.51 22.00 4 Sasolwax M3M + Ethylene maleic anhydride (3:1) 108.93 19.50 4 Soy wax 107.82 8.25 4 Synthetic beeswax 101.38 11.00 4 Tekniwax 600 108.87 32.50 4 Tekniwax 801 106.94 21.50 4 Vaseline 101.18 6.50 5 Beeswax 105.73 15.25 5 Beeswax + Ethylene maleic anhydride (3:1) 112.29 24.25 5 Beeswax + Sasolwax C (1:1) 108.34 22.75 5 Beeswax + Synthetic beeswax (1:1) 104.73 18.00 5 Beeswax + Vaseline (1:1) 108.92 7.50 5 Carnauba 106.48 11.00   172  Block Wax Initial contact angle (°) Time < 90 (min) 5 Lanolin 94.32 0.02 5 Merkur 300 102.49 1.00 5 Microcrystalline wax 110.13 59.50 5 Stearic acid 108.34 22.75 5 Sasolwax C 107.66 2.00 5 Sasolwax M3M 108.55 18.00 5 Sasolwax M3M + Ethylene maleic anhydride (3:1) 113.46 20.75 5 Soy wax 105.80 20.75 5 Synthetic beeswax 101.82 11.50 5 Tekniwax 600 107.90 23.50 5 Tekniwax 801 106.85 32.00 5 Vaseline 102.83 9.00 6 Beeswax 107.13 17.00 6 Beeswax + Ethylene maleic anhydride (3:1) 112.07 19.00 6 Beeswax + Sasolwax C (1:1) 107.94 23.25 6 Beeswax + Synthetic beeswax (1:1) 110.93 19.75 6 Beeswax + Vaseline (1:1) 107.93 11.75 6 Carnauba 92.76 5.50 6 Lanolin 98.78 1.02 6 Merkur 300 104.74 1.00 6 Microcrystalline wax 109.73 52.00 6 Stearic acid 118.60 26.25 6 Sasolwax C 105.29 6.50 6 Sasolwax M3M 106.53 15.00 6 Sasolwax M3M + Ethylene maleic anhydride (3:1) 114.40 22.25 6 Soy wax 99.53 8.75 6 Synthetic beeswax 102.36 12.50 6 Tekniwax 600 108.52 21.00 6 Tekniwax 801 105.86 16.50 6 Vaseline 100.70 7.50 7 Beeswax 105.90 16.50 7 Beeswax + Ethylene maleic anhydride (3:1) 113.79 21.25 7 Beeswax + Sasolwax C (1:1) 106.06 24.25 7 Beeswax + Synthetic beeswax (1:1) 109.56 17.75 7 Beeswax + Vaseline (1:1) 107.36 26.75 7 Carnauba 96.55 5.50 7 Lanolin 101.31 0.05 7 Merkur 300 99.55 1.50 7 Microcrystalline wax 106.88 50.25 7 Stearic acid 122.36 32.00 7 Sasolwax C 93.62 0.50 7 Sasolwax M3M 103.47 14.00 7 Sasolwax M3M + Ethylene maleic anhydride (3:1) 112.47 22.25   173  Block Wax Initial contact angle (°) Time < 90 (min) 7 Soy wax 108.98 29.25 7 Synthetic beeswax 106.35 16.50 7 Tekniwax 600 100.50 25.00 7 Tekniwax 801 107.87 32.00 7 Vaseline 98.89 6.50 8 Beeswax 107.37 16.75 8 Beeswax + Ethylene maleic anhydride (3:1) 109.24 18.00 8 Beeswax + Sasolwax C (1:1) 105.08 16.25 8 Beeswax + Synthetic beeswax (1:1) 107.86 17.50 8 Beeswax + Vaseline (1:1) 109.72 9.25 8 Carnauba 100.97 13.00 8 Lanolin 100.72 0.12 8 Merkur 300 103.02 1.50 8 Microcrystalline wax 109.00 46.25 8 Stearic acid 132.05 42.50 8 Sasolwax C 97.08 0.50 8 Sasolwax M3M 108.55 18.00 8 Sasolwax M3M + Ethylene maleic anhydride (3:1) 113.76 20.50 8 Soy wax 103.84 15.25 8 Synthetic beeswax 101.65 8.00 8 Tekniwax 600 112.45 46.25 8 Tekniwax 801 106.11 19.50 8 Vaseline 99.73 7.00 9 Beeswax 105.56 14.50 9 Beeswax + Ethylene maleic anhydride (3:1) 116.44 23.25 9 Beeswax + Sasolwax C (1:1) 102.99 23.00 9 Beeswax + Synthetic beeswax (1:1) 110.58 17.50 9 Beeswax + Vaseline (1:1) 104.21 14.50 9 Carnauba 102.54 11.50 9 Lanolin 103.66 0.33 9 Merkur 300 106.88 2.00 9 Microcrystalline wax 112.49 41.00 9 Stearic acid 133.25 38.25 9 Sasolwax C 106.19 3.50 9 Sasolwax M3M 105.09 11.00 9 Sasolwax M3M + Ethylene maleic anhydride (3:1) 107.60 15.75 9 Soy wax 110.81 19.50 9 Synthetic beeswax 102.37 9.00 9 Tekniwax 600 109.82 58.25 9 Tekniwax 801 106.49 10.50 9 Vaseline 96.77 7.50 10 Beeswax 105.02 13.00 10 Beeswax + Ethylene maleic anhydride (3:1) 107.39 15.75   174  Block Wax Initial contact angle (°) Time < 90 (min) 10 Beeswax + Sasolwax C (1:1) 100.82 12.75 10 Beeswax + Synthetic beeswax (1:1) 110.54 18.00 10 Beeswax + Vaseline (1:1) 104.55 10.00 10 Carnauba 107.38 12.00 10 Lanolin 106.47 1.03 10 Merkur 300 103.18 2.00 10 Microcrystalline wax 110.31 34.75 10 Stearic acid 139.76 31.75 10 Sasolwax C 102.47 2.00 10 Sasolwax M3M 107.03 31.50 10 Sasolwax M3M + Ethylene maleic anhydride (3:1) 108.09 17.00 10 Soy wax 106.74 14.00 10 Synthetic beeswax 105.27 15.00 10 Tekniwax 600 106.84 29.00 10 Tekniwax 801 106.31 10.50 10 Vaseline 103.04 13.00 11 Beeswax 103.37 13.50 11 Beeswax + Ethylene maleic anhydride (3:1) 106.84 16.00 11 Beeswax + Sasolwax C (1:1) 106.43 24.75 11 Beeswax + Synthetic beeswax (1:1) 106.99 16.00 11 Beeswax + Vaseline (1:1) 104.99 12.75 11 Carnauba 102.31 11.00 11 Lanolin 101.08 0.17 11 Merkur 300 108.00 0.90 11 Microcrystalline wax 111.41 37.75 11 Stearic acid 133.02 35.75 11 Sasolwax C 105.15 5.37 11 Sasolwax M3M 109.66 29.50 11 Sasolwax M3M + Ethylene maleic anhydride (3:1) 106.99 16.00 11 Soy wax 109.29 12.50 11 Synthetic beeswax 111.38 26.75 11 Tekniwax 600 109.82 57.50 11 Tekniwax 801 110.45 28.25 11 Vaseline 113.91 17.00      175  Appendix Table 1.2. ANOVA table for initial contact angles of 5 µL water droplets placed on glass slides coated with different wax types (α = 0.05) Source of variation d.f. Missing values SS MS F p-value Block 10  266.8 26.68 2.07 0.029 Wax 17  6929.51 407.62 31.63 < 0.001 Residual 169 -1 2177.71 12.89    Total 196 -1 8879.22       Missing value: Stearic acid (Block 5) Appendix Table 1.3. Table of means for initial contact angles of 5 µL water droplets placed on glass slides coated with different wax types (α = 0.05) Wax Mean initial contact angle (°) Lanolin 100.62 Carnauba wax 100.75 Sasolwax C 101.63 Vaseline 102.14 Synthetic beeswax 103.56 Merkur 300 103.75 Beeswax + Sasolwax C (1:1) 105.02 Beeswax 105.56 Beeswax + Vaseline (1:1) 105.82 Sasolwax M3M 106.30 Soy wax 106.95 Tekniwax 801 107.16 Tekniwax 600 107.95 Beeswax + Synthetic beeswax (1:1) 107.96 Beeswax + Ethylene maleic anhydride (3:1) 109.48 Microcrystalline wax 109.54 Sasolwax M3M + Ethylene maleic anhydride (3:1) 109.74 Stearic acid 128.13 Mean 106.78 Least significant difference   3.02 Missing value: Stearic acid (Block 5) Appendix Table 1.4. ANOVA table for the time it took 5 µL water droplets placed on glass slides coated with different wax types to form contact angles of less than 90° (α = 0.05) Source of variation d.f. SS MS F p-value Block 10 655.3 65.53 2.07 0.288 Wax 17 24504 1441.41 45.61 < 0.001 Residual 170 5372.1 31.6    Total 197 30531.4         176   Appendix Table 1.5. Table of means for the time it took 5 µL water droplets placed on glass slides coated with different wax types to form contact angles of less than 90° (α = 0.05) Wax Time < 90° (min) Lanolin 0.36 Merkur 300 1.35 Sasolwax C 2.31 Vaseline 9.09 Carnauba wax 9.37 Beeswax + Vaseline (1:1) 11.89 Beeswax 14.00 Synthetic beeswax 14.16 Soy wax 15.41 Beeswax + Synthetic beeswax (1:1) 15.82 Beeswax + Ethylene maleic anhydride (3:1) 17.89 Sasolwax M3M 17.91 Sasolwax M3M + Ethylene maleic anhydride (3:1) 18.55 Beeswax + Sasolwax C (1:1) 18.75 Tekniwax 801 22.02 Stearic acid 31.82 Tekniwax 600 37.28 Microcrystalline wax 42.70 Mean 16.70 Least significant difference 4.73  Appendix Table 1.6. Raw data for contact angle measurements of 5 µL water droplets placed on OSB surfaces treated with different wax types (α = 0.05) Block Wax Initial contact angle (°) Time < 90° (min) 1 Beeswax 129.00 29.78 1 Beeswax + Ethylene maleic anhydride (3:1) 118.05 22.35 1 Beeswax + Sasolwax C (1:1) 132.20 41.68 1 Beeswax + Synthetic beeswax (1:1) 115.22 22.02 1 Beeswax + Vaseline (1:1) 131.68 31.68 1 Carnauba wax 108.09 12.52 1 Lanolin 97.20 0.01 1 Merkur 300 135.37 28.85 1 Microcrystalline wax 111.24 19.53 1 Stearic acid 105.17 7.35 1 Sasolwax C 130.02 18.18 1 Sasolwax M3M 121.20 18.70 1 Sasolwax M3M + Ethylene maleic anhydride (3:1) 130.29 30.85   177  Block Wax Initial contact angle (°) Time < 90° (min) 1 Soy wax 94.90 4.78 1 Synthetic beeswax 106.48 15.02 1 Tekniwax 600 113.88 14.85 1 Tekniwax 801 115.65 1.85 1 Untreated OSB 132.98 22.20 1 Vaseline 111.63 12.53 2 Beeswax 121.72 28.00 2 Beeswax + Ethylene maleic anhydride (3:1) 125.30 38.68 2 Beeswax + Sasolwax C (1:1) 115.94 25.85 2 Beeswax + Synthetic beeswax (1:1) 123.38 33.35 2 Beeswax + Vaseline (1:1) 118.64 23.68 2 Carnauba wax 117.00 26.18 2 Lanolin 114.67 0.35 2 Merkur 300 130.48 43.02 2 Microcrystalline wax 108.77 22.85 2 Stearic acid 126.45 21.85 2 Sasolwax C 119.15 5.18 2 Sasolwax M3M 114.75 24.52 2 Sasolwax M3M + Ethylene maleic anhydride (3:1) 115.14 25.18 2 Soy wax 112.64 20.52 2 Synthetic beeswax 120.36 30.02 2 Tekniwax 600 119.92 27.85 2 Tekniwax 801 118.63 19.18 2 Untreated OSB 102.69 0.52 2 Vaseline 116.72 21.52 3 Beeswax 132.10 10.68 3 Beeswax + Ethylene maleic anhydride (3:1) 120.09 27.35 3 Beeswax + Sasolwax C (1:1) 114.52 28.35 3 Beeswax + Synthetic beeswax (1:1) 119.33 26.18 3 Beeswax + Vaseline (1:1) 117.17 19.68 3 Carnauba wax 115.70 25.85 3 Lanolin 107.62 0.52 3 Merkur 300 117.94 12.02 3 Microcrystalline wax 117.62 25.18 3 Stearic acid 131.15 34.68 3 Sasolwax C 111.58 1.02 3 Sasolwax M3M 121.97 15.18 3 Sasolwax M3M + Ethylene maleic anhydride (3:1) 115.41 20.68 3 Soy wax 111.60 14.68 3 Synthetic beeswax 108.75 7.18 3 Tekniwax 600 129.22 28.18 3 Tekniwax 801 124.55 20.85 3 Untreated OSB 115.88 1.52   178  Block Wax Initial contact angle (°) Time < 90° (min) 3 Vaseline 127.47 8.52 4 Beeswax 126.07 32.52 4 Beeswax + Ethylene maleic anhydride (3:1) 109.49 19.35 4 Beeswax + Sasolwax C (1:1) 118.53 17.52 4 Beeswax + Synthetic beeswax (1:1) 126.79 37.35 4 Beeswax + Vaseline (1:1) 123.04 22.18 4 Carnauba wax 127.87 37.35 4 Lanolin 126.96 0.68 4 Merkur 300 138.74 25.52 4 Microcrystalline wax 117.62 25.18 4 Stearic acid 117.28 18.35 4 Sasolwax C 120.67 2.52 4 Sasolwax M3M 119.79 30.85 4 Sasolwax M3M + Ethylene maleic anhydride (3:1) 126.92 34.68 4 Soy wax 101.12 9.85 4 Synthetic beeswax 109.01 13.18 4 Tekniwax 600 125.75 22.85 4 Tekniwax 801 125.60 16.18 4 Untreated OSB 122.59 1.35 4 Vaseline 125.79 4.68 5 Beeswax 120.67 30.35 5 Beeswax + Ethylene maleic anhydride (3:1) 110.66 22.85 5 Beeswax + Sasolwax C (1:1) 125.69 38.25 5 Beeswax + Synthetic beeswax (1:1) 123.73 39.02 5 Beeswax + Vaseline (1:1) 130.22 35.52 5 Carnauba wax 110.59 19.52 5 Lanolin 122.70 0.52 5 Merkur 300 113.60 11.52 5 Microcrystalline wax 126.51 31.18 5 Stearic acid 101.37 10.18 5 Sasolwax C 133.11 3.18 5 Sasolwax M3M 127.63 31.02 5 Sasolwax M3M + Ethylene maleic anhydride (3:1) 115.53 24.18 5 Soy wax 97.75 7.68 5 Synthetic beeswax 119.08 27.02 5 Tekniwax 600 109.35 4.68 5 Tekniwax 801 127.38 8.85 5 Untreated OSB 136.77 23.52 5 Vaseline 117.22 25.02 6 Beeswax 113.03 23.18 6 Beeswax + Ethylene maleic anhydride (3:1) 116.20 27.35 6 Beeswax + Sasolwax C (1:1) 128.34 37.52 6 Beeswax + Synthetic beeswax (1:1) 122.52 28.18   179  Block Wax Initial contact angle (°) Time < 90° (min) 6 Beeswax + Vaseline (1:1) 113.71 17.02 6 Carnauba wax 106.79 16.85 6 Lanolin 112.31 0.85 6 Merkur 300 112.77 17.35 6 Microcrystalline wax 103.62 14.52 6 Stearic acid 108.37 16.52 6 Sasolwax C 116.92 1.52 6 Sasolwax M3M 114.91 26.85 6 Sasolwax M3M + Ethylene maleic anhydride (3:1) 115.47 21.19 6 Soy wax 111.46 21.18 6 Synthetic beeswax 118.31 27.02 6 Tekniwax 600 128.70 30.68 6 Tekniwax 801 122.27 21.68 6 Untreated OSB 100.81 0.52 6 Vaseline 112.15 16.85  Appendix Table 1.7. ANOVA table for initial contact angles of 5 µL water droplets placed on OSB surfaces treated with different wax types (α = 0.05) Source of variation d.f. SS MS F p-value Block 5 488.24 97.65 1.44 0.216 Wax 18 2588.74 143.82 2.13 0.011 Residual 90 6086.52 67.63    Total 113 9163.5            180   Appendix Table 1.8. Table of means for initial contact angles of 5 µL water droplets placed on OSB surfaces treated with different wax types (α = 0.05) Wax Mean initial contact angle (°) Soy wax 104.91 Lanolin 113.58 Synthetic beeswax 113.66 Microcrystalline wax 114.23 Carnauba wax 114.34 Stearic acid 114.97 Beeswax + Ethylene maleic anhydride (3:1) 116.63 Vaseline 118.50 Untreated OSB 118.62 Sasolwax M3M + Ethylene maleic anhydride (3:1) 119.79 Sasolwax M3M 120.04 Tekniwax 600 121.14 Beeswax + Synthetic beeswax (1:1) 121.83 Sasolwax C 121.91 Tekniwax 801 122.35 Beeswax + Vaseline (1:1) 122.41 Beeswax + Sasolwax C (1:1) 122.54 Beeswax 123.77 Merkur 300 124.82 Mean 118.42 Least significant difference  9.43  Appendix Table 1.9.  ANOVA table for the time it took 5 µL water droplets placed on OSB surfaces treated with different wax types to form contact angles of less than 90° (α = 0.05) Source of variation d.f. SS MS F p-value Block 5 370 74 1.15 0.339 Wax 18 7675.36 426.41 6.6 < 0.001 Residual 90 5812.37 64.58    Total 113 13857.73            181  Appendix Table 1.10. Table of means for the time it took 5 µL water droplets placed on OSB surfaces treated with different wax types to form contact angles of less than 90° (α = 0.05) Wax Mean time < 90° (min) Lanolin 0.49 Sasolwax C 5.27 Untreated OSB 8.27 Soy wax 13.12 Tekniwax 801 14.77 Vaseline 14.85 Stearic acid 18.16 Synthetic beeswax 19.91 Tekniwax 600 21.52 Carnauba wax 23.04 Merkur 300 23.05 Microcrystalline wax 23.08 Sasolwax M3M 24.52 Beeswax + Vaseline (1:1) 24.96 Beeswax 25.75 Sasolwax M3M + Ethylene maleic anhydride (3:1) 26.13 Beeswax + Ethylene maleic anhydride (3:1) 26.32 Beeswax + Synthetic beeswax (1:1) 31.02 Beeswax + Sasolwax C (1:1) 31.53 Mean 19.78 Least significant difference  9.218  Appendix Table 1.11. Average surface roughness (Ra  = arithmetic mean deviation) of 10 x 10 mm2 areas on glass slides coated with different wax types. Block Wax Ra (µm) 1 Beeswax 5.16294 1 Beeswax + Ethylene maleic anhydride (3:1) 3.94652 1 Beeswax + Sasolwax C (1:1) 4.44696 1 Beeswax + Synthetic beeswax (1:1) 6.4234 1 Beeswax + Vaseline (1:1) 3.31673 1 Carnauba  2.82196 1 Lanolin 1.81064 1 Merkur 300 5.0747 1 Microcrystalline wax 2.71587 1 Sasolwax C 17.4593 1 Sasolwax M3M 5.98865 1 Sasolwax M3M + Ethylene maleic anhydride (3:1) 2.21281 1 Soy wax 5.50108 1 Stearic acid 47.6893   182  Block Wax Ra (µm) 1 Synthetic beeswax 3.80497 1 Tekniwax 600 7.02603 1 Tekniwax 801 3.2914 1 Vaseline 6.33682 2 Beeswax 5.68171 2 Beeswax + Ethylene maleic anhydride (3:1) 4.2811 2 Beeswax + Sasolwax C (1:1) 5.11672 2 Beeswax + Synthetic beeswax (1:1) 3.29567 2 Beeswax + Vaseline (1:1) 4.20563 2 Carnauba  3.16309 2 Lanolin 1.41078 2 Merkur 300 5.01177 2 Microcrystalline wax 2.77735 2 Sasolwax C 12.616 2 Sasolwax M3M 6.093 2 Sasolwax M3M + Ethylene maleic anhydride (3:1) 2.21808 2 Soy wax 6.07501 2 Stearic acid 55.1341 2 Synthetic beeswax 4.05762 2 Tekniwax 600 39.8572 2 Tekniwax 801 4.82457 2 Vaseline 5.67487 3 Beeswax 6.61471 3 Beeswax + Ethylene maleic anhydride (3:1) 8.20241 3 Beeswax + Sasolwax C (1:1) 20.4388 3 Beeswax + Synthetic beeswax (1:1) 5.02035 3 Beeswax + Vaseline (1:1) 4.78488 3 Carnauba  2.70228 3 Lanolin 1.66666 3 Merkur 300 4.81865 3 Microcrystalline wax 3.48744 3 Sasolwax C 12.9994 3 Sasolwax M3M 5.92905 3 Sasolwax M3M + Ethylene maleic anhydride (3:1) 2.07191 3 Soy wax 9.39039 3 Stearic acid 103.733 3 Synthetic beeswax 5.06654 3 Tekniwax 600 21.5233 3 Tekniwax 801 4.22715 3 Vaseline 5.30703    183  Appendix Table 1.12. ANOVA table for the natural logarithm of the average surface roughness (Ra  = arithmetic mean deviation) of 10 x 10 mm2 areas on glass slides coated with different wax types (α = 0.05) Source of variation d.f. SS MS F p-value Block 2 0.75 0.38 3.48 0.0385 Wax 17 35.99 2.12 19.66 <.001 Residual 34 3.66 0.11    Total 53 40.40       Appendix Table 1.13. Table of means for the natural logarithm of the average surface roughness (Ra  = arithmetic mean deviation) of 10 x 10 mm areas on glass slides coated with different wax types (α = 0.05) Wax ln(Ra) Beeswax 1.756 Beeswax + Ethylene maleic anhydride (3:1) 1.644 Beeswax + Sasolwax C (1:1) 2.047 Beeswax + Synthetic beeswax (1:1) 1.555 Beeswax + Vaseline (1:1) 1.400 Carnauba  1.061 Lanolin 0.483 Merkur 300 1.603 Microcrystalline wax 1.090 Sasolwax C 2.653 Sasolwax M3M 1.792 Sasolwax M3M + Ethylene maleic anhydride (3:1) 0.773 Soy wax 1.916 Stearic acid 4.172 Synthetic beeswax 1.453 Tekniwax 600 2.901 Tekniwax 801 1.402 Vaseline 1.750 Mean 1.747 Least significant difference 0.536     184  Appendix Figure 1.1. FTIR spectra for twelve wax types   EMA = Ethylene maleic anhydride    3500 3000 2500 2000 1500 1000Transmittance (%) Wavenumber (cm-1) BeeswaxCarnauba waxSoy waxStearic acidEMASasolwax M3MSasolwax CMerkur 300Synthetic beeswaxTekniwax 801Tekniwax 600Vaseline  185  Appendix 2 - Chapter 4  Appendix Table 2.1. Raw data for Total thickness swelling, Half swell, and Quarter swell Block Control vs Treated Wax Quart swell (h) Half swell (h) Total thickness swelling (mm) 1 treated Beeswax 144.9 247.9 2.4 1 treated Carnauba 57.6 126.5 3.4 1 control Control 44.0 91.3 2.9 1 treated Lanolin 79.7 152.5 3.4 1 treated Sasolwax M3M 69.1 129.2 3.7 1 treated Sasolwax C 94.9 182.0 2.7 1 treated Tekniwax 600 169.8 276.0 2.2 1 treated Vaseline 130.2 213.0 3.0 2 treated Beeswax 207.8 320.7 1.7 2 treated Carnauba 66.1 161.3 2.7 2 control Control 52.8 92.6 2.9 2 treated Lanolin 50.0 162.4 2.7 2 treated Sasolwax M3M 138.4 236.0 3.1 2 treated Sasolwax C 47.7 114.3 2.5 2 treated Tekniwax 600 48.0 142.3 2.4 2 treated Vaseline 71.5 219.1 2.6 3 treated Beeswax 247.0 353.8 2.0 3 treated Carnauba 88.7 150.3 3.1 3 control Control 68.8 128.1 3.4 3 treated Lanolin 25.6 111.0 3.1 3 treated Sasolwax M3M 65.3 148.4 2.8 3 treated Sasolwax C 179.7 376.4 2.0 3 treated Tekniwax 600 245.2 374.3 1.5 3 treated Vaseline 206.4 296.1 2.7 4 treated Beeswax 116.2 242.1 1.3 4 treated Carnauba 79.5 167.9 2.1 4 control Control 28.1 143.8 2.1 4 treated Lanolin 21.5 41.2 1.6 4 treated Sasolwax M3M 114.0 246.7 2.5 4 treated Sasolwax C 105.9 207.8 2.9 4 treated Tekniwax 600 58.1 131.2 3.1 4 treated Vaseline 262.6 340.2 3.0 5 treated Beeswax 101.8 206.0 1.8 5 treated Carnauba 61.8 132.5 2.9 5 control Control 51.3 112.9 3.0 5 treated Lanolin 62.3 146.7 2.7 5 treated Sasolwax M3M 66.3 151.7 3.0 5 treated Sasolwax C 59.6 135.2 2.5   186  Block Control vs Treated Wax Quart swell (h) Half swell (h) Total thickness swelling (mm) 5 treated Tekniwax 600 84.6 214.7 2.8 5 treated Vaseline 133.3 222.9 2.4 6 treated Beeswax 71.5 150.6 3.3 6 treated Carnauba 61.2 113.5 3.5 6 control Control 21.2 61.4 2.7 6 treated Lanolin 54.3 99.6 3.2 6 treated Sasolwax M3M 39.6 87.8 3.6 6 treated Sasolwax C 57.4 138.0 2.9 6 treated Tekniwax 600 54.6 117.2 3.1 6 treated Vaseline 48.0 92.1 2.8 7 treated Beeswax 88.7 202.2 3.2 7 treated Carnauba 34.5 82.0 2.2 7 control Control 41.7 91.4 2.2 7 treated Lanolin 71.5 206.7 1.8 7 treated Sasolwax M3M 50.5 145.4 2.5 7 treated Sasolwax C 53.3 124.3 2.7 7 treated Tekniwax 600 41.7 100.0 2.7 7 treated Vaseline 92.8 162.7 2.4  Appendix Table 2.2. ANOVA table for Total thickness swelling (α = 0.05) Source of variation d.f. Missing values SS MS F p-value Block 6  4.7818 0.797 4.66 0.0009 Control vs Treated 1  0.0509 0.0509 0.3 0.589 Wax type vs wax type 6  4.1442 0.6907 4.04 0.003 Residual 40 -2 6.843 0.1711    Total 53 -2 14.7057       Missing value: Beeswax (block 6); Tekniwax 600 (block 1)  Appendix Table 2.3. ANO A table for Time to half swell (α = 0.05) Source of variation d.f. SS MS F p-value Block 6 85197 14199 4.18 0.0019 Control vs Treated 1 37839 37839 11.15 0.002 Wax type vs wax type 6 77119 12853 3.79 0.004 Residual 42 142588 3395    Total 55 342743          187  Appendix Table 2.4. ANO A table for Time to quarter swell (α = 0.05) Source of variation d.f. SS MS F p-value Block 6 42536 7089 3.68 0.0044 Control vs Treated 1 15007 15007 7.8 0.008 Wax type vs wax type 6 47514 7919 4.12 0.002 Residual 42 80817 1924    Total 55 185874        Appendix Table 2.5. Table of means for Total thickness swelling, Half swell, and Quarter swell (α = 0.05)  Wax Half swell (h) Quarter swell (h) Total thickness swell (mm) Beeswax 246.2 139.7 2.03 Carnauba 133.4 64.2 2.84 Control 103.1 44 2.74 Lanolin 131.4 52.1 2.66 Sasolwax M3M 163.6 77.6 3.04 Sasolwax C 182.6 85.5 2.59 Tekniwax 600 193.6 100.3 2.73 Vaseline 220.9 135 2.68 Mean 171.85 87.3 2.743 Least significant difference 62.85 47.32 0.4468  Appendix Table 2.6. Raw data for thickness swelling Block Control vs Treated Wax 2 h 24 h 72 h 240 h 480 h 1 treated Beeswax 0.001 0.002 0.186 1.156 2.324 1 treated Carnauba 0.007 0.328 1.049 2.737 3.407 1 control Control 0.091 0.378 1.153 2.506 2.889 1 treated Lanolin 0.007 0.199 0.765 2.498 3.344 1 treated Sasolwax M3M 0.002 0.400 0.968 2.928 3.674 1 treated Sasolwax C 0.020 0.173 0.465 1.764 2.641 1 treated Tekniwax 600 -0.012 -0.020 0.040 0.905 2.113 1 treated Vaseline -0.002 0.033 0.284 1.712 2.893 2 treated Beeswax 0.004 -0.001 0.028 0.565 1.586 2 treated Carnauba 0.003 0.262 0.724 1.900 2.650 2 control Control 0.056 0.364 1.042 2.625 2.917 2 treated Lanolin 0.040 0.416 0.836 1.726 2.639 2 treated Sasolwax M3M 0.002 -0.083 0.339 1.589 3.026 2 treated Sasolwax C 0.028 0.381 0.841 2.133 2.527   188  Block Control vs Treated Wax 2 h 24 h 72 h 240 h 480 h 2 treated Tekniwax 600 0.014 0.381 0.762 1.844 2.349 2 treated Vaseline 0.072 0.401 0.655 1.390 2.522 3 treated Beeswax -0.003 -0.005 0.014 0.483 1.592 3 treated Carnauba 0.020 0.155 0.557 2.257 2.979 3 control Control 0.071 0.363 0.895 2.696 3.248 3 treated Lanolin 0.102 0.772 1.281 2.468 3.033 3 treated Sasolwax M3M -0.002 0.189 0.762 2.218 2.730 3 treated Sasolwax C 0.003 -0.012 0.154 0.662 1.568 3 treated Tekniwax 600 -0.003 -0.012 0.019 0.365 1.083 3 treated Vaseline -0.003 -0.006 -0.020 0.964 2.204 4 treated Beeswax 0.000 -0.027 0.174 0.627 1.145 4 treated Carnauba -0.001 0.128 0.480 1.413 2.022 4 control Control 0.024 0.503 0.781 1.565 2.127 4 treated Lanolin -0.006 0.450 1.103 1.254 1.572 4 treated Sasolwax M3M -0.001 0.048 0.411 1.224 2.381 4 treated Sasolwax C 0.007 0.290 0.580 1.891 2.850 4 treated Tekniwax 600 0.001 0.208 1.003 2.227 3.028 4 treated Vaseline 0.005 -0.017 -0.034 0.607 2.868 5 treated Beeswax -0.008 0.010 0.314 1.056 1.775 5 treated Carnauba 0.003 0.142 0.825 2.418 2.912 5 control Control 0.033 0.247 1.043 2.321 2.915 5 treated Lanolin -0.008 0.113 0.790 1.914 2.686 5 treated Sasolwax M3M 0.002 0.189 0.818 2.233 3.025 5 treated Sasolwax C 0.013 0.251 0.764 1.798 2.444 5 treated Tekniwax 600 -0.004 0.139 0.620 1.601 2.731 5 treated Vaseline 0.001 0.001 0.239 1.327 2.318 6 treated Beeswax 0.039 0.336 0.834 2.446 3.259 6 treated Carnauba 0.028 0.324 1.134 2.862 3.442 6 control Control 0.089 0.723 1.480 2.431 2.648 6 treated Lanolin -0.003 0.374 1.131 2.792 3.199 6 treated Sasolwax M3M 0.009 0.556 1.555 2.990 3.606 6 treated Sasolwax C 0.000 0.273 0.864 2.103 2.818 6 treated Tekniwax 600 0.034 0.396 0.973 2.644 3.096 6 treated Vaseline 0.010 0.354 1.089 2.248 2.742 7 treated Beeswax 0.031 0.290 0.685 1.928 3.154 7 treated Carnauba 0.018 0.405 0.967 1.840 2.143 7 control Control 0.031 0.318 0.875 1.862 2.200 7 treated Lanolin 0.054 0.267 0.458 0.946 1.779 7 treated Sasolwax M3M 0.049 0.390 0.777 1.697 2.441 7 treated Sasolwax C 0.008 0.215 0.877 2.079 2.656 7 treated Tekniwax 600 0.013 0.413 1.037 2.209 2.676 7 treated Vaseline -0.003 0.099 0.442 1.756 2.394   189  Appendix Table 2.7. ANOVA for 2 h thickness swelling (α = 0.05) Source of variation d.f. SS MS F p-value Block 6 0.005153 0.000859 1.74 0.1321 Control vs Treated 1 0.012 0.012 24.26 < 0.001 Wax type vs wax type 6 0.001903 0.000317 0.64 0.697 Residual 42 0.020777 0.000495    Total 55 0.039834        Appendix Table 2.8.  ANOVA for 24 h thickness swelling (α = 0.05) Source of variation d.f. SS MS F p-value Block 6 0.43565 0.07261 3.07 0.0127 Control vs Treated 1 0.2397 0.2397 10.14 0.003 Wax type vs wax type 6 0.35646 0.05941 2.51 0.036 Residual 42 0.99256 0.02363    Total 55 2.02438        Appendix Table 2.9. ANOVA for 72 h thickness swelling (α = 0.05) Source of variation d.f. SS MS F p-value Block 6 2.23085 0.37181 5.13 0.0004 Control vs Treated 1 0.94584 0.94584 13.06 <.001 Wax type vs wax type 6 2.11718 0.35286 4.87 <.001 Residual 42 3.04179 0.07242    Total 55 8.33567        Appendix Table 2.10. ANOVA for 240 h thickness swelling (α = 0.05) Source of variation d.f. SS MS F p-value Block 6 7.3652 1.2275 4.53 0.001 Control vs Treated 1 1.6795 1.6795 6.2 0.017 Wax type vs wax type 6 5.7088 0.9515 3.51 0.007 Residual 42 11.3851 0.2711    Total 55 26.1386           190  Appendix Table 2.11. ANOVA for 480 h thickness swelling (α = 0.05) Source of variation d.f. SS MS F p-value Block 6 4.7316 0.7886 2.98 0.0149 Control vs Treated 1 0.1098 0.1098 0.42 0.523 Wax type vs wax type 6 3.1287 0.5215 1.97 0.091 Residual 42 11.1003 0.2643    Total 55 19.0705        Appendix Table 2.12. Table of means for thickness swelling (α = 0.05) Wax 2 h 24 h 72 h 240 h 480 h Beeswax 0.01 0.09 0.32 1.18 2.12 Carnauba 0.01 0.25 0.82 2.20 2.79 Control 0.06 0.41 1.04 2.29 2.71 Lanolin 0.03 0.37 0.91 1.94 2.61 Sasolwax M3M 0.01 0.24 0.80 2.13 2.98 Sasolwax C 0.01 0.22 0.65 1.78 2.50 Tekniwax 600 0.01 0.22 0.64 1.69 2.44 Vaseline 0.01 0.12 0.38 1.43 2.56 Mean 0.02 0.24 0.69 1.83 2.59 Least significant difference 0.024 0.166 0.290 0.278 0.554       191  Appendix 3 - Chapter 5 Appendix Table 3.1. Raw data for oven dry mass, oven dry thickness, and initial moisture content of untreated and wax-treated OSB samples.  Block Wax Oven dry mass (g) Oven dry thickness (mm) Spread rate (g / m2) Initial moisture content (%) 1 Beeswax 240.00 18.48 118.7 8.80 1 Beeswax + Ethylene maleic anhydride (3:1) 242.38 18.54 96.4 8.10 1 Beeswax + Sasolwax C (1:1) 254.87 18.58 84.4 7.59 1 Beeswax + Synthetic beeswax (1:1) 255.07 18.59 131.1 7.36 1 Beeswax + Vaseline (1:1) 237.30 18.53 138.2 8.20 1 Carnauba 232.01 18.53 104.4 8.97 1 Control 245.56 18.72 0.0 7.73 1 Sasolwax M3M 239.39 18.62 133.3 8.36 1 Sasolwax M3M + Ethylene maleic anhydride (3:1) 247.20 18.76 96.4 8.45 1 Merkur 300 251.03 18.66 99.6 8.50 1 Microcrystalline 242.18 18.45 93.3 7.43 1 Stearic acid 235.03 18.65 129.3 8.86 1 Sasolwax C 233.43 18.57 124.4 9.24 1 Soy wax 236.59 18.76 90.2 8.76 1 Synthetic beeswax 240.73 18.59 128.9 8.59 1 Tekniwax 801 246.40 18.48 100.9 8.50 1 Vaseline 239.85 18.53 129.8 8.60 2 Beeswax 239.78 18.59 89.8 6.78 2 Beeswax + Ethylene maleic anhydride (3:1) 237.10 18.73 105.3 6.43 2 Beeswax + Sasolwax C (1:1) 236.77 18.72 96.0 6.81 2 Beeswax + Synthetic beeswax (1:1) 237.16 18.68 89.8 6.92 2 Beeswax + Vaseline (1:1) 237.46 18.48 66.2 7.05 2 Carnauba 237.46 18.62 67.6 7.09 2 Control 238.62 18.42 0.0 7.40 2 Sasolwax M3M 239.10 18.73 67.1 7.15 2 Sasolwax M3M + Ethylene maleic anhydride (3:1) 246.52 18.40 65.3 6.82 2 Merkur 300 241.43 18.40 69.8 6.58 2 Microcrystalline 242.40 18.86 80.9 6.82 2 Stearic acid 243.50 18.49 75.6 7.27 2 Sasolwax C 239.91 18.82 83.6 7.04 2 Soy wax 239.48 18.47 83.6 7.29 2 Synthetic beeswax 237.09 18.55 73.3 6.77 2 Tekniwax 801 240.94 18.86 72.4 6.99 2 Vaseline 242.42 18.52 74.7 6.81 3 Beeswax 254.14 19.23 85.8 6.55 3 Beeswax + Ethylene maleic anhydride (3:1) 251.87 19.27 81.3 7.41   192  Block Wax Oven dry mass (g) Oven dry thickness (mm) Spread rate (g / m2) Initial moisture content (%) 3 Beeswax + Sasolwax C (1:1) 253.77 19.19 68.9 7.00 3 Beeswax + Synthetic beeswax (1:1) 258.66 19.17 69.3 6.47 3 Beeswax + Vaseline (1:1) 258.48 19.34 72.0 6.79 3 Carnauba 257.28 19.25 79.6 6.84 3 Control 256.70 19.21 0.0 6.93 3 Sasolwax M3M 255.04 19.10 67.6 6.85 3 Sasolwax M3M + Ethylene maleic anhydride (3:1) 261.85 19.25 74.2 6.71 3 Merkur 300 253.96 19.30 71.6 6.97 3 Microcrystalline 260.93 19.20 70.2 6.45 3 Stearic acid 258.70 19.23 89.3 7.09 3 Sasolwax C 258.55 19.15 80.0 6.60 3 Soy wax 267.38 19.29 84.9 6.84 3 Synthetic beeswax 253.65 19.25 70.7 7.03 3 Tekniwax 801 261.30 19.43 66.7 6.56 3 Vaseline 256.48 19.45 79.1 7.85 4 Beeswax 251.47 19.46 70.7 7.08 4 Beeswax + Ethylene maleic anhydride (3:1) 259.10 19.54 95.1 6.61 4 Beeswax + Sasolwax C (1:1) 265.55 19.22 94.7 6.42 4 Beeswax + Synthetic beeswax (1:1) 259.29 19.59 89.3 6.67 4 Beeswax + Vaseline (1:1) 261.27 19.47 84.0 6.67 4 Carnauba 259.71 19.12 60.0 7.18 4 Control 253.40 19.40 0.0 7.35 4 Sasolwax M3M 249.02 19.43 70.2 7.30 4 Sasolwax M3M + Ethylene maleic anhydride (3:1) 259.47 19.21 95.6 6.59 4 Merkur 300 254.10 19.02 82.7 6.78 4 Microcrystalline 270.09 19.11 77.3 6.27 4 Stearic acid 259.89 19.12 79.6 7.17 4 Sasolwax C 253.08 19.09 64.0 7.02 4 Soy wax 256.66 19.11 95.6 6.74 4 Synthetic beeswax 254.48 18.99 68.0 5.80 4 Tekniwax 801 260.19 18.86 76.0 6.64 4 Vaseline 264.41 19.04 76.9 6.88 5 Beeswax 252.21 18.40 79.1 5.24 5 Beeswax + Ethylene maleic anhydride (3:1) 247.72 18.37 83.6 5.07 5 Beeswax + Sasolwax C (1:1) 254.05 18.25 77.3 4.86 5 Beeswax + Synthetic beeswax (1:1) 247.81 18.37 66.7 5.09 5 Beeswax + Vaseline (1:1) 252.90 18.24 72.4 5.00 5 Carnauba 246.44 18.00 74.2 5.19 5 Control 245.20 18.59 0.0 6.15 5 Sasolwax M3M 249.15 17.88 64.4 4.66 5 Sasolwax M3M + Ethylene maleic anhydride (3:1) 246.44 17.75 66.7 5.37   193  Block Wax Oven dry mass (g) Oven dry thickness (mm) Spread rate (g / m2) Initial moisture content (%) 5 Merkur 300 246.64 18.03 66.2 5.01 5 Microcrystalline 253.10 18.17 81.8 4.75 5 Stearic acid 245.28 17.87 100.4 5.29 5 Sasolwax C 251.61 18.34 66.7 5.66 5 Soy wax 248.89 18.37 63.6 5.36 5 Synthetic beeswax 250.55 18.51 71.1 5.34 5 Tekniwax 801 253.39 17.83 65.8 4.95 5 Vaseline 245.19 18.03 99.6 4.79 6 Beeswax 266.99 18.63 55.6 4.50 6 Beeswax + Ethylene maleic anhydride (3:1) 264.25 18.59 46.7 4.82 6 Beeswax + Sasolwax C (1:1) 257.43 18.76 64.4 5.13 6 Beeswax + Synthetic beeswax (1:1) 261.88 18.53 61.3 4.77 6 Beeswax + Vaseline (1:1) 265.10 18.97 66.2 4.80 6 Carnauba 260.25 18.71 45.3 5.22 6 Control 261.91 18.70 0.0 5.19 6 Sasolwax M3M 257.47 18.62 50.2 5.15 6 Sasolwax M3M + Ethylene maleic anhydride (3:1) 259.30 18.67 72.0 4.64 6 Merkur 300 262.34 18.79 53.3 5.02 6 Microcrystalline 259.91 18.49 46.7 4.83 6 Stearic acid 261.11 18.66 69.8 4.99 6 Sasolwax C 257.88 18.70 60.0 5.00 6 Soy wax 259.73 18.67 57.3 5.14 6 Synthetic beeswax 259.84 18.55 63.1 4.89 6 Tekniwax 801 259.44 18.48 56.4 4.81 6 Vaseline 264.74 18.61 57.8 4.95 7 Beeswax 253.27 18.71 58.2 4.48 7 Beeswax + Ethylene maleic anhydride (3:1) 257.45 18.85 62.2 4.01 7 Beeswax + Sasolwax C (1:1) 253.43 18.74 45.8 4.50 7 Beeswax + Synthetic beeswax (1:1) 250.29 18.69 55.6 4.43 7 Beeswax + Vaseline (1:1) 256.13 18.65 51.1 4.32 7 Carnauba 255.12 18.71 49.3 4.55 7 Control 252.52 18.64 0.0 4.41 7 Sasolwax M3M 254.66 18.71 53.8 4.42 7 Sasolwax M3M + Ethylene maleic anhydride (3:1) 252.10 18.65 59.1 4.19 7 Merkur 300 251.55 18.67 49.8 4.45 7 Microcrystalline 250.59 18.57 56.9 4.37 7 Stearic acid 257.23 18.80 47.1 4.49 7 Sasolwax C 257.19 18.74 54.2 4.28 7 Soy wax 251.67 18.85 54.7 4.42 7 Synthetic beeswax 253.27 18.70 50.7 4.12 7 Tekniwax 801 254.14 18.71 66.7 4.15   194  Block Wax Oven dry mass (g) Oven dry thickness (mm) Spread rate (g / m2) Initial moisture content (%) 7 Vaseline 252.28 18.57 54.2 4.54  Appendix Table 3.2. ANO A table for the oven dried mass of OSB samples (α = 0.05) Source of variation d.f. SS MS F p-value Block 6 6918 1153 64.83  < 0.0001 Wax 16 255.88 15.99 0.9 0.572 Residual 96 1707.25 17.78    Total 118 8881.13        Appendix Table 3.3. ANO A table for the oven dried thickness of OSB samples (α = 0.05) Source of variation d.f. SS MS F p-value Block 6 14.662 2.444 97.22  < 0.0001 Wax 16 0.379 0.024 0.94 0.524 Residual 96 2.413 0.025    Total 118 17.454        Appendix Table 3.4. ANOVA table for mass of wax applied on the 15 x 15 cm2 surface of OSB samples (α = 0.05) Source of variation d.f. SS MS F p-value Block 6 17.42979 2.90496 45.79  < 0.0001 Wax 15 1.06429 0.07095 1.12 0.352 Residual 90 5.70953 0.06344    Total 111 24.20361           195  Appendix Table 3.5. ANO A table for the initial moisture content of OSB samples (α = 0.05) Source of variation d.f. SS MS F p-value Block 6 204.9809 34.1635 335.96  < 0.0001 Wax 16 3.8227 0.2389 2.35 0.006 Residual 96 9.7623 0.1017    Total 118 218.5659        Appendix Table 3.6.  Table of means for the oven dry mass, oven dry thickness, spread rate, and initial moisture content of untreated and wax-treated OSB samples (α = 0.05) Wax Oven dry mass (g) Oven dry thickness  (mm) Spread rate (g / m2) Initial moisture condition (%) Beeswax 251.12 18.78 275.7 6.20 Beeswax + Ethylene maleic anhydride (3:1) 251.41 18.84 269.6 6.07 Beeswax + Sasolwax C (1:1) 253.70 18.78 268.6 6.04 Beeswax + Synthetic beeswax (1:1) 252.88 18.80 264.8 5.96 Beeswax + Vaseline (1:1) 252.66 18.81 272.0 6.12 Carnauba 249.75 18.71 286.0 6.43 Control 250.56 18.81 286.8 6.45 Sasolwax M3M 249.12 18.73 278.6 6.27 Sasolwax M3M + Ethylene maleic anhydride (3:1) 253.27 18.67 271.6 6.11 Merkur 300 251.58 18.70 275.0 6.19 Microcrystalline 254.17 18.69 259.8 5.85 Stearic acid 251.53 18.69 286.8 6.45 Sasolwax C 250.24 18.77 284.8 6.41 Soy wax 251.49 18.79 282.8 6.36 Synthetic beeswax 249.94 18.73 270.1 6.08 Tekniwax 801 253.69 18.66 270.5 6.09 Vaseline 252.20 18.68 282.0 6.35 Mean 251.72 18.74 275.6 6.20 Least significant difference 4.51 0.17 15.2 0.34      196  Appendix Table 3.7.  Raw data for water absorption of untreated and wax-treated OSB samples    Control vs. Treated   Wax Water absorption (mL) Block 2 h 24 h 48 h 72 h 1 treated Beeswax 0.680 13.440 32.420 54.610 1 treated Beeswax + Ethylene maleic anhydride (3:1) 4.150 24.430 46.470 73.660 1 treated Beeswax + Sasolwax C (1:1) 4.270 17.280 30.480 44.900 1 treated Beeswax + Synthetic beeswax (1:1) 0.720 7.010 15.390 25.820 1 treated Beeswax + Vaseline (1:1) 1.450 14.500 34.260 60.230 1 treated Carnauba 2.560 16.660 28.730 40.570 1 control Control 7.000 28.440 49.430 71.270 1 treated Sasolwax M3M 1.540 14.370 28.540 42.710 1 treated Sasolwax M3M + Ethylene maleic anhydride (3:1) 2.740 18.410 31.760 43.850 1 treated Merkur 300 2.310 14.520 26.170 38.160 1 treated Microcrystalline 3.360 23.820 43.720 66.580 1 treated Stearic acid 2.380 10.620 16.740 24.150 1 treated Sasolwax C 7.600 34.460 60.160 80.400 1 treated Soy wax 4.690 19.710 34.330 48.790 1 treated Synthetic beeswax 1.700 14.640 30.290 50.310 1 treated Tekniwax 801 2.620 14.370 25.570 40.910 1 treated Vaseline 2.070 19.990 44.180 70.380 1 control “moisture resistant” 5.040 12.750 18.650 25.230 2 treated Beeswax 1.940 10.740 21.190 31.880 2 treated Beeswax + Ethylene maleic anhydride (3:1) 1.800 15.880 31.730 47.860 2 treated Beeswax + Sasolwax C (1:1) 2.790 19.940 35.610 49.970 2 treated Beeswax + Synthetic beeswax (1:1) 1.920 11.210 22.890 34.730 2 treated Beeswax + Vaseline (1:1) 1.440 11.380 25.770 42.480 2 treated Carnauba 2.060 12.500 23.700 34.600 2 control Control 5.610 20.060 33.490 46.300 2 treated Sasolwax M3M 3.240 17.250 30.190 43.380 2 treated Sasolwax M3M + Ethylene maleic anhydride (3:1) 2.590 17.310 31.640 45.590 2 treated Merkur 300 3.970 19.570 34.560 47.660 2 treated Microcrystalline 1.670 12.610 25.300 41.330 2 treated Stearic acid 2.480 12.290 23.880 35.310 2 treated Sasolwax C 5.790 20.980 33.620 44.310 2 treated Soy wax 4.770 20.580 34.890 50.450 2 treated Synthetic beeswax 1.910 9.990 20.700 32.380 2 treated Tekniwax 801 3.820 19.390 32.600 44.400 2 treated Vaseline 2.540 13.870 26.420 39.300 2 control “moisture resistant” 4.530 14.730 23.040 30.630 3 treated Beeswax 2.950 11.700 21.350 33.010 3 treated Beeswax + Ethylene maleic anhydride (3:1) 2.760 13.950 27.230 39.960 3 treated Beeswax + Sasolwax C (1:1) 4.600 15.500 25.220 34.510 3 treated Beeswax + Synthetic beeswax (1:1) 1.550 7.980 16.150 24.420   197     Control vs. Treated   Wax Water absorption (mL) Block 2 h 24 h 48 h 72 h 3 treated Beeswax + Vaseline (1:1) 2.240 9.400 18.910 28.340 3 treated Carnauba 3.710 14.850 28.170 44.290 3 control Control 6.710 18.270 28.540 37.110 3 treated Sasolwax M3M 6.240 19.070 30.750 42.320 3 treated Sasolwax M3M + Ethylene maleic anhydride (3:1) 4.920 18.340 30.140 41.940 3 treated Merkur 300 7.190 20.690 32.460 45.570 3 treated Microcrystalline 3.030 12.630 24.480 36.600 3 treated Stearic acid 5.500 16.930 26.020 34.710 3 treated Sasolwax C 6.870 17.910 28.150 38.530 3 treated Soy wax 8.940 23.220 34.840 44.960 3 treated Synthetic beeswax 3.360 14.400 26.390 38.540 3 treated Tekniwax 801 4.960 16.430 28.290 39.610 3 treated Vaseline 4.770 15.830 26.310 35.890 3 control “moisture resistant” 3.860 10.900 16.230 20.680 4 treated Beeswax 2.860 13.820 31.130 53.200 4 treated Beeswax + Ethylene maleic anhydride (3:1) 2.050 10.740 22.700 37.560 4 treated Beeswax + Sasolwax C (1:1) 4.620 19.050 34.050 51.350 4 treated Beeswax + Synthetic beeswax (1:1) 3.070 12.700 25.520 42.260 4 treated Beeswax + Vaseline (1:1) 1.860 10.210 22.260 39.410 4 treated Carnauba 3.380 14.900 28.750 45.760 4 control Control 6.410 17.850 31.800 51.180 4 treated Sasolwax M3M 4.520 17.310 30.810 45.650 4 treated Sasolwax M3M + Ethylene maleic anhydride (3:1) 2.870 16.860 34.350 54.510 4 treated Merkur 300 5.380 18.540 30.330 45.670 4 treated Microcrystalline 2.700 11.910 21.460 33.340 4 treated Stearic acid 5.460 20.790 38.230 57.340 4 treated Sasolwax C 6.060 17.430 27.720 38.140 4 treated Soy wax 6.070 21.980 39.580 64.190 4 treated Synthetic beeswax 2.000 11.590 23.390 41.520 4 treated Tekniwax 801 4.510 16.340 31.160 47.600 4 treated Vaseline 3.600 12.850 22.920 34.860 4 control “moisture resistant” 7.040 17.600 26.510 33.910 5 treated Beeswax 1.970 11.050 22.380 40.660 5 treated Beeswax + Ethylene maleic anhydride (3:1) 1.460 12.400 28.350 53.740 5 treated Beeswax + Sasolwax C (1:1) 5.520 23.240 42.600 71.540 5 treated Beeswax + Synthetic beeswax (1:1) 2.850 17.070 36.120 62.480 5 treated Beeswax + Vaseline (1:1) 1.850 12.330 29.200 58.240 5 treated Carnauba 1.950 18.540 36.120 59.340 5 control Control 6.520 28.420 49.310 80.610 5 treated Sasolwax M3M 3.440 18.520 33.510 56.130 5 treated Sasolwax M3M + Ethylene maleic anhydride (3:1) 4.510 24.030 44.170 73.360   198     Control vs. Treated   Wax Water absorption (mL) Block 2 h 24 h 48 h 72 h 5 treated Merkur 300 5.700 23.690 41.450 64.060 5 treated Microcrystalline 2.190 11.660 22.470 36.820 5 treated Stearic acid 3.880 18.020 31.810 52.390 5 treated Sasolwax C 5.600 24.400 44.360 71.590 5 treated Soy wax 5.840 25.060 45.740 70.500 5 treated Synthetic beeswax 2.130 20.580 42.640 77.350 5 treated Tekniwax 801 4.330 18.480 31.590 46.760 5 treated Vaseline 3.200 16.420 37.230 72.580 5 control “moisture resistant” 4.900 16.580 24.470 32.470 6 treated Beeswax 3.710 16.820 30.220 45.510 6 treated Beeswax + Ethylene maleic anhydride (3:1) 3.290 14.490 24.310 35.200 6 treated Beeswax + Sasolwax C (1:1) 3.820 15.080 25.460 35.450 6 treated Beeswax + Synthetic beeswax (1:1) 3.340 13.870 24.000 36.540 6 treated Beeswax + Vaseline (1:1) 2.670 11.440 19.930 29.480 6 treated Carnauba 2.950 13.680 23.670 36.080 6 control Control 7.850 22.310 34.100 46.390 6 treated Sasolwax M3M 4.440 18.590 31.430 45.880 6 treated Sasolwax M3M + Ethylene maleic anhydride (3:1) 2.790 14.200 24.910 37.460 6 treated Merkur 300 5.100 17.010 25.700 33.610 6 treated Microcrystalline 3.090 14.130 24.530 34.970 6 treated Stearic acid 4.050 13.400 20.840 29.080 6 treated Sasolwax C 8.460 24.230 37.650 52.040 6 treated Soy wax 5.710 18.200 28.240 39.120 6 treated Synthetic beeswax 3.840 15.450 24.970 35.470 6 treated Tekniwax 801 4.530 16.930 27.630 38.920 6 treated Vaseline 5.110 18.070 28.950 40.230 6 control “moisture resistant” 4.680 15.880 29.460 43.500 7 treated Beeswax 3.070 21.350 49.630 79.320 7 treated Beeswax + Ethylene maleic anhydride (3:1) 2.500 11.550 22.220 36.120 7 treated Beeswax + Sasolwax C (1:1) 2.460 15.560 31.810 50.120 7 treated Beeswax + Synthetic beeswax (1:1) 2.400 12.260 23.020 33.520 7 treated Beeswax + Vaseline (1:1) 2.380 11.740 22.710 36.390 7 treated Carnauba 2.740 15.550 28.940 44.050 7 control Control 4.710 17.770 28.730 41.700 7 treated Sasolwax M3M 4.100 22.160 39.890 60.880 7 treated Sasolwax M3M + Ethylene maleic anhydride (3:1) 2.640 17.350 33.260 53.080 7 treated Merkur 300 6.017 25.637 43.987 63.837 7 treated Microcrystalline 2.750 15.050 27.600 42.450 7 treated Stearic acid 3.210 13.190 22.560 32.930 7 treated Sasolwax C 5.020 20.030 34.120 48.340 7 treated Soy wax 5.680 22.690 37.780 55.010   199     Control vs. Treated   Wax Water absorption (mL) Block 2 h 24 h 48 h 72 h 7 treated Synthetic beeswax 2.580 15.920 30.680 49.480 7 treated Tekniwax 801 3.440 16.480 32.020 49.610 7 treated Vaseline 3.440 17.250 31.370 45.300 7 control “moisture resistant” 3.460 11.810 19.360 25.600  Appendix Table 3.8. ANOVA table for water absorption of untreated and wax-treated samples after 2 h (α = 0.05) Source of variation d.f. SS MS F p-value Block 6 44.2324 7.3721 10.16 < 0.001 Control vs Treated 1 52.1282 52.1282 71.84 < 0.001 Wax type vs wax type 15 183.7183 12.2479 16.88 < 0.001 Residual 96 69.6575 0.7256    Total 118 8881.13        Appendix Table 3.9. ANOVA table for water absorption of “moisture resistant” and wax-treated samples after 2 h (α = 0.05) Source of variation d.f. Missing value SS MS F p-value Block 6  41.3926 6.8988 8.86 < 0.0001 Huber vs Treated 1  9.6175 9.6175 12.35 < 0.001 Wax type vs wax type 15  186.3194 12.4213 15.95 < 0.001 Residual 95 -1 73.9632 0.7786    Total 117 -1 308.5205       Missing value: Beeswax (Block 7)  Appendix Table 3.10. ANOVA table for water absorption of untreated and wax-treated samples after 24 h (α = 0.05) Source of variation d.f. SS MS F p-value Block 6 187.04 31.17 2.87 0.0123 Control vs Treated 1 192.56 192.56 17.71 < 0.001 Wax type vs wax type 15 1063.08 70.87 6.52 < 0.001 Residual 96 1044 10.88    Total 118 2486.68       *”moisture resistant” excluded   200  Appendix Table 3.11. ANOVA table for water absorption of “moisture resistant” and wax-treated samples after 24 h (α = 0.05) Source of variation d.f. Missing value SS MS F p-value Block 6  128.706 21.451 2.16 0.052 Huber vs Treated 1  28.278 28.278 2.84 0.095 Wax type vs wax type 15  1111.656 74.11 7.45 < 0.001 Residual 95 -1 945.01 9.947    Total 117 -1 2202.647       Missing value: Beeswax (Block 7)  Appendix Table 3.12. ANOVA table for water absorption of untreated and wax-treated samples after 48 h (α = 0.05) Source of variation d.f. Missing value SS MS F p-value Block 6  1362.67 227.11 6.44 < 0.001 Control vs Treated 1  281.86 281.86 7.99 0.006 Wax type vs wax type 15  1786.63 119.11 3.38 < 0.001 Residual 95 -1 3350.15 35.26    Total 117 -1 6767       Missing value: Beeswax (Block 7) *”moisture resistant” excluded Appendix Table 3.13. ANOVA table for water absorption of “moisture resistant” and wax-treated samples after 48 h (α = 0.05) Source of variation d.f. Missing value SS MS F p-value Block 6  1033.93 172.32 4.93 0.0002 Control vs Treated 1  362.38 362.38 10.37 0.002 Wax type vs wax type 15  1784.32 118.95 3.4 < 0.001 Residual 95 -1 3319.81 34.95    Total 117 -1 6493.54       Missing value: Beeswax (Block 7)       201  Appendix Table 3.14. ANOVA table for water absorption of untreated and wax-treated samples after 72 h (α = 0.05) Source of variation d.f. Missing value SS MS F p-value Block 6  7169.63 1194.94 13.55 < 0.0001 Control vs Treated 1  396.5 396.5 4.5 0.037 Wax type vs wax type 15  2366.34 157.76 1.79 0.047 Residual 95 -1 8378.74 88.2    Total 117 -1 18301.96       Missing value: Beeswax (Block 7) *”moisture resistant” excluded Appendix Table 3.15. ANOVA table for water absorption of “moisture resistant” and wax-treated samples after 72 h (α = 0.05) Source of variation d.f. Missing value SS MS F p-value Block 6  5753.28 958.88 10.64 < 0.0001 Control vs Treated 1  1576.07 1576.07 17.49 < 0.001 Wax type vs wax type 15  2363.68 157.58 1.75 0.054 Residual 95 -1 8561.41 90.12    Total 117 -1 18253.11       Missing value: Beeswax (Block 7)  Appendix Table 3.16.  Raw data for thickness swelling of untreated and wax-treated OSB samples   Block Control vs. Treated   Wax Thickness swelling (mm) 2 h 24 h 48 h 72 h 1 treated Beeswax 0.033 0.336 0.712 1.269 1 treated Beeswax + Ethylene maleic anhydride (3:1) 0.133 0.631 1.142 1.564 1 treated Beeswax + Sasolwax C (1:1) 0.155 0.721 1.111 1.512 1 treated Beeswax + Synthetic beeswax (1:1) 0.040 0.124 0.328 0.636 1 treated Beeswax + Vaseline (1:1) 0.032 0.539 0.967 1.514 1 treated Carnauba 0.167 0.633 0.944 1.182 1 control Control 0.195 0.743 1.216 1.703 1 treated Sasolwax M3M 0.092 0.726 1.119 1.483 1 treated Sasolwax M3M + Ethylene maleic anhydride (3:1) 0.100 0.519 0.672 0.992 1 treated Merkur 300 0.160 0.668 0.894 1.141 1 treated Microcrystalline 0.160 0.788 1.334 1.816 1 treated Stearic acid 0.100 0.493 0.719 0.916 1 treated Sasolwax C 0.320 1.265 1.715 2.067 1 treated Soy wax 0.227 0.794 1.104 1.434 1 treated Synthetic beeswax -0.048 0.333 0.731 1.144   202    Block Control vs. Treated   Wax Thickness swelling (mm) 2 h 24 h 48 h 72 h 1 treated Tekniwax 801 0.195 0.523 0.867 1.132 1 treated Vaseline 0.050 0.361 1.081 1.451 1 control “moisture resistant” 0.077 0.187 0.267 0.347 2 treated Beeswax -0.015 0.370 0.703 1.017 2 treated Beeswax + Ethylene maleic anhydride (3:1) 0.169 0.655 1.321 1.711 2 treated Beeswax + Sasolwax C (1:1) 0.048 0.688 1.236 1.683 2 treated Beeswax + Synthetic beeswax (1:1) 0.094 0.475 0.781 1.105 2 treated Beeswax + Vaseline (1:1) 0.428 0.581 0.999 1.457 2 treated Carnauba 0.159 0.595 1.123 1.260 2 control Control 0.214 0.851 1.268 1.651 2 treated Sasolwax M3M 0.130 0.650 1.064 1.614 2 treated Sasolwax M3M + Ethylene maleic anhydride (3:1) 0.077 0.675 1.143 1.543 2 treated Merkur 300 0.133 0.865 1.388 1.805 2 treated Microcrystalline -0.040 0.180 0.790 1.339 2 treated Stearic acid 0.110 0.547 1.034 1.545 2 treated Sasolwax C 0.158 0.647 0.982 1.281 2 treated Soy wax 0.181 0.846 1.326 1.762 2 treated Synthetic beeswax 0.086 0.458 0.740 1.077 2 treated Tekniwax 801 0.093 0.688 1.137 1.492 2 treated Vaseline 0.082 0.593 1.028 1.431 2 control “moisture resistant” 0.074 0.304 0.490 0.631 3 treated Beeswax 0.186 0.507 0.792 1.073 3 treated Beeswax + Ethylene maleic anhydride (3:1) 0.080 0.418 0.702 0.974 3 treated Beeswax + Sasolwax C (1:1) 0.273 0.753 1.056 1.384 3 treated Beeswax + Synthetic beeswax (1:1) 0.049 0.253 0.427 0.588 3 treated Beeswax + Vaseline (1:1) 0.134 0.398 0.658 0.897 3 treated Carnauba 0.232 0.689 1.094 1.448 3 control Control 0.205 0.558 0.852 1.095 3 treated Sasolwax M3M 0.249 0.700 1.074 1.336 3 treated Sasolwax M3M + Ethylene maleic anhydride (3:1) 0.061 0.394 0.702 0.970 3 treated Merkur 300 0.289 0.807 1.141 1.386 3 treated Microcrystalline -0.136 0.264 0.556 0.788 3 treated Stearic acid 0.252 0.624 0.929 1.189 3 treated Sasolwax C 0.267 0.683 1.012 1.303 3 treated Soy wax 0.432 0.879 1.185 1.630 3 treated Synthetic beeswax 0.163 0.529 0.757 0.943 3 treated Tekniwax 801 0.192 0.545 0.852 1.138 3 treated Vaseline 0.235 0.603 0.947 1.219 3 control “moisture resistant” 0.077 0.260 0.369 0.459 4 treated Beeswax 0.170 0.706 1.096 1.729 4 treated Beeswax + Ethylene maleic anhydride (3:1) 0.059 0.354 0.607 0.993   203    Block Control vs. Treated   Wax Thickness swelling (mm) 2 h 24 h 48 h 72 h 4 treated Beeswax + Sasolwax C (1:1) 0.219 1.003 1.564 1.959 4 treated Beeswax + Synthetic beeswax (1:1) 0.177 0.640 1.019 1.414 4 treated Beeswax + Vaseline (1:1) 0.083 0.341 0.594 1.053 4 treated Carnauba 0.145 0.564 0.976 1.392 4 control Control 0.284 0.781 1.203 1.694 4 treated Sasolwax M3M 0.207 0.704 1.214 1.639 4 treated Sasolwax M3M + Ethylene maleic anhydride (3:1) 0.182 0.880 1.473 1.904 4 treated Merkur 300 0.192 0.678 1.051 1.403 4 treated Microcrystalline 0.174 0.689 1.016 1.330 4 treated Stearic acid 0.279 0.892 1.274 1.721 4 treated Sasolwax C 0.262 0.724 1.036 1.317 4 treated Soy wax 0.235 0.791 1.287 1.888 4 treated Synthetic beeswax 0.127 0.491 0.745 1.091 4 treated Tekniwax 801 0.248 0.701 1.130 1.595 4 treated Vaseline 0.174 0.677 1.058 1.420 4 control “moisture resistant” 0.088 0.519 0.634 0.745 5 treated Beeswax 0.090 0.446 0.789 1.255 5 treated Beeswax + Ethylene maleic anhydride (3:1) 0.046 0.282 0.676 1.333 5 treated Beeswax + Sasolwax C (1:1) 0.211 0.764 1.324 2.036 5 treated Beeswax + Synthetic beeswax (1:1) 0.159 0.726 1.190 1.787 5 treated Beeswax + Vaseline (1:1) 0.097 0.431 0.937 1.505 5 treated Carnauba 0.149 0.946 1.514 2.097 5 control Control 0.336 0.995 1.527 2.244 5 treated Sasolwax M3M 0.197 0.673 1.074 1.642 5 treated Sasolwax M3M + Ethylene maleic anhydride (3:1) 0.160 0.736 1.407 2.144 5 treated Merkur 300 0.374 0.990 1.454 2.151 5 treated Microcrystalline 0.161 0.566 0.926 1.309 5 treated Stearic acid 0.183 0.736 1.075 1.570 5 treated Sasolwax C 0.229 1.003 1.539 2.126 5 treated Soy wax 0.267 0.985 1.508 2.079 5 treated Synthetic beeswax 0.108 0.879 1.490 2.421 5 treated Tekniwax 801 0.206 0.668 1.030 1.404 5 treated Vaseline 0.175 0.538 0.958 1.918 5 control “moisture resistant” 0.144 0.433 0.625 0.781 6 treated Beeswax 0.188 0.569 0.926 1.297 6 treated Beeswax + Ethylene maleic anhydride (3:1) 0.202 0.573 0.821 1.097 6 treated Beeswax + Sasolwax C (1:1) 0.148 0.603 0.936 1.208 6 treated Beeswax + Synthetic beeswax (1:1) 0.201 0.566 0.944 1.292 6 treated Beeswax + Vaseline (1:1) 0.151 0.421 0.699 0.971 6 treated Carnauba 0.172 0.573 0.852 1.178 6 control Control 0.346 0.847 1.230 1.564   204    Block Control vs. Treated   Wax Thickness swelling (mm) 2 h 24 h 48 h 72 h 6 treated Sasolwax M3M 0.197 0.520 0.825 1.145 6 treated Sasolwax M3M + Ethylene maleic anhydride (3:1) 0.155 0.445 0.685 1.056 6 treated Merkur 300 0.129 0.560 0.814 1.014 6 treated Microcrystalline 0.142 0.575 0.928 1.241 6 treated Stearic acid 0.183 0.540 0.882 1.019 6 treated Sasolwax C 0.541 1.061 1.448 1.803 6 treated Soy wax 0.193 0.599 0.917 1.197 6 treated Synthetic beeswax 0.177 0.636 0.956 1.227 6 treated Tekniwax 801 0.424 0.677 1.043 1.347 6 treated Vaseline 0.300 0.848 1.156 1.479 6 control “moisture resistant” 0.107 0.321 1.023 0.790 7 treated Beeswax 0.100 0.678 1.477 2.226 7 treated Beeswax + Ethylene maleic anhydride (3:1) 0.120 0.517 0.820 1.182 7 treated Beeswax + Sasolwax C (1:1) 0.112 0.543 0.992 1.580 7 treated Beeswax + Synthetic beeswax (1:1) 0.099 0.441 0.741 1.044 7 treated Beeswax + Vaseline (1:1) 0.104 0.441 0.695 0.943 7 treated Carnauba 0.126 0.556 0.986 1.554 7 control Control 0.191 0.605 0.886 1.218 7 treated Sasolwax M3M 0.156 0.787 1.219 1.746 7 treated Sasolwax M3M + Ethylene maleic anhydride (3:1) 0.092 0.528 0.947 1.421 7 treated Merkur 300 0.183 0.770 1.195 1.631 7 treated Microcrystalline 0.136 0.590 0.960 1.403 7 treated Stearic acid 0.159 0.507 0.580 1.000 7 treated Sasolwax C 0.219 0.822 1.260 1.644 7 treated Soy wax 0.190 0.711 1.097 1.501 7 treated Synthetic beeswax 0.122 0.551 0.982 1.491 7 treated Tekniwax 801 0.128 0.504 0.951 1.389 7 treated Vaseline 0.145 0.744 1.182 1.570 7 control “moisture resistant” 0.084 0.115 0.368 0.470  Appendix Table 3.17. ANOVA table for the natural logarithm of thickness swelling of untreated and wax-treated samples after 2 h (α = 0.05) Source of variation d.f. Missing value SS MS F p-value Block 6  0.156024 0.026004 9.64 < 0.0001 Control vs Treated 1  0.039406 0.039406 14.61 < 0.001 Wax type vs wax type 15  0.228871 0.015258 5.66 < 0.001 Residual 94 -2 0.253596 0.002698    Total 116 -2 0.662365          205  Appendix Table 3.18.  ANOVA table for the natural logarithm of thickness swelling of “moisture resistant” and wax-treated samples after 2 h (α = 0.05) Source of variation d.f. Missing value SS MS F p-value Block stratum 6  0.145201 0.0242 8.98 < 0.0001 Control vs Treated 1  0.022363 0.022363 8.29 0.005 Wax type vs wax type 15  0.230313 0.015354 5.69 < 0.001 Residual 93 -3 0.250737 0.002696    Total 115 -3 0.630775        Appendix Table 3.19. ANOVA table for the thickness swelling of untreated and wax-treated samples after 24 h (α = 0.05) Source of variation d.f. Missing value SS MS F p-value Block 6  0.3586 0.05977 2.91 0.0113 Control vs Treated 1  0.15011 0.15011 7.32 0.008 Wax type vs wax type 15  1.41791 0.09453 4.61 <.001 Residual 95 -1 1.9491 0.02052    Total 117 -1 3.85845        Appendix Table 3.20. ANOVA table for the thickness swelling of “moisture resistant” and wax-treated samples after 24 h (α = 0.05) Source of variation d.f. Missing value SS MS F p-value Block 6   0.32709 0.05451 2.47 0.028 Control vs Treated 1  0.65193 0.65193 29.57 < 0.001 Wax type vs wax type 15  1.70896 0.11393 5.17 < 0.001 Residual 95 -1 2.09423 0.02204    Total 117 -1 4.7572        Appendix Table 3.21. ANOVA table for the thickness swelling of untreated and wax-treated samples after 48 h (α = 0.05) Source of variation d.f. Missing value SS MS F p-value Block 6   1.23288 0.20548 4.82 0.0002 Control vs Treated 1  0.18089 0.18089 4.24 0.042 Wax type vs wax type 15  2.40553 0.16037 3.76 < 0.001 Residual 95 -1 4.05254 0.04266    Total 117 -1 7.81258          206  Appendix Table 3.22. ANOVA table for the thickness swelling of “moisture resistant” and wax-treated samples after 48 h (α = 0.05) Source of variation d.f. Missing value SS MS F p-value Block 6  1.0553 0.17588 3.9 0.0014  Control vs Treated 1  1.41787 1.41787 31.41 < 0.001 Wax type vs wax type 15  2.40267 0.16018 3.55 < 0.001 Residual 95 -1 4.28875 0.04514    Total 117 -1 9.12533       Appendix Table 3.32. ANOVA table for the thickness swelling of untreated and wax-treated samples after 72 h (α = 0.05) Source of variation d.f. Missing value SS MS F p-value Block 6   4.25298 0.70883 11.37 < 0.0001 Control vs Treated 1  0.26283 0.26283 4.22 0.043 Wax type vs wax type 15  2.91041 0.19403 3.11 < 0.001 Residual 94 -2 5.86016 0.06234    Total 116 -2 13.227        Appendix Table 3.33. ANOVA table for the thickness swelling of “moisture resistant” and wax-treated samples after 72 h (α = 0.05) Source of variation d.f. Missing value SS MS F p-value Block 6   4.31308 0.71885 10.75 < 0.0001  Control vs Treated 1  4.21984 4.21984 63.12 <.001 Wax type vs wax type 15  2.71429 0.18095 2.71 0.002 Residual 95 -1 6.3514 0.06686    Total 117 -1 17.5887            207  Appendix Table 3.34. Raw data for Final moisture content, Total thickness swelling, and Time-delayed thickness swelling Block Wax Final moisture content (%) Time-delayed thickness swelling (mm) Total thickness swelling (mm) 1 Beeswax + Synthetic beeswax (1:1) 9.93 0.14 0.77 1 Beeswax + Vaseline (1:1) 12.01 0.12 1.63 1 Beeswax 11.92 0.00 1.27 1 Beeswax + Ethylene maleic anhydride (3:1) 11.25 -0.16 1.41 1 Beeswax + Sasolwax C (1:1) 10.77 0.05 1.57 1 Carnauba 11.14 -0.20 0.98 1 Control 10.74 -0.22 1.49 1 “moisture resistant” 7.08 2.39 2.73 1 Sasolwax M3M 11.37 -0.16 1.32 1 Sasolwax M3M + Ethylene maleic anhydride (3:1) 10.96 -0.13 0.86 1 Merkur 300 11.13 -0.08 1.06 1 Microcrystalline 10.85 -0.02 1.79 1 Stearic acid 10.58 -0.20 0.71 1 Sasolwax C 12.64 -0.33 1.74 1 Soy wax 11.35 -0.22 1.21 1 Synthetic beeswax 11.67 0.03 1.18 1 Tekniwax 801 11.24 0.05 1.18 1 Vaseline 12.08 0.19 1.64 2 Beeswax + Synthetic beeswax (1:1) 11.32 0.02 1.12 2 Beeswax + Vaseline (1:1) 11.99 -0.04 1.41 2 Beeswax 11.33 0.02 1.04 2 Beeswax + Ethylene maleic anhydride (3:1) 11.96 -0.05 1.66 2 Beeswax + Sasolwax C (1:1) 12.29 -0.18 1.50 2 Carnauba 11.37 -0.07 1.19 2 Control 11.66 -0.19 1.46 2 “moisture resistant” 9.73 0.04 0.67 2 Sasolwax M3M 11.90 -0.14 1.47 2 Sasolwax M3M + Ethylene maleic anhydride (3:1) 11.66 0.00 1.54 2 Merkur 301 12.34 0.02 1.82 2 Microcrystalline 11.85 0.09 1.43 2 Stearic acid 11.35 -0.11 1.43 2 Sasolwax C 12.19 0.10 1.38 2 Soy wax 12.05 -0.14 1.62 2 Synthetic beeswax 11.21 0.02 1.10 2 Tekniwax 801 11.75 0.04 1.54 2 Vaseline 11.39 0.07 1.50 3 Beeswax + Synthetic beeswax (1:1) 10.70 0.17 0.75 3 Beeswax + Vaseline (1:1) 10.81 0.13 1.03   208  Block Wax Final moisture content (%) Time-delayed thickness swelling (mm) Total thickness swelling (mm) 3 Beeswax 11.03 0.05 1.12 3 Beeswax + Ethylene maleic anhydride (3:1) 11.52 0.07 1.04 3 Beeswax + Sasolwax C (1:1) 11.41 -0.06 1.33 3 Carnauba 11.53 -0.03 1.42 3 Control 10.79 -0.08 1.02 3 “moisture resistant” 9.84 0.37 0.83 3 Sasolwax M3M 11.50 0.04 1.38 3 Sasolwax M3M + Ethylene maleic anhydride (3:1) 11.40 0.12 1.09 3 Merkur 302 12.09 0.11 1.49 3 Microcrystalline 11.39 0.27 1.06 3 Stearic acid 11.12 -0.04 1.15 3 Sasolwax C 11.79 0.11 1.41 3 Soy wax 11.54 -0.18 1.45 3 Synthetic beeswax 11.49 0.07 1.02 3 Tekniwax 801 11.38 0.13 1.27 3 Vaseline 12.44 0.03 1.25 4 Beeswax + Synthetic beeswax (1:1) 11.27 -0.06 1.36 4 Beeswax + Vaseline (1:1) 11.62 0.18 1.23 4 Beeswax 12.04 0.01 1.74 4 Beeswax + Ethylene maleic anhydride (3:1) 11.70 0.16 1.15 4 Beeswax + Sasolwax C (1:1) 12.05 0.10 2.06 4 Carnauba 11.76 0.06 1.45 4 Control 12.17 -0.05 1.64 4 “moisture resistant” 26.36 -1.32 -0.57 4 Sasolwax M3M 11.90 -0.09 1.55 4 Sasolwax M3M + Ethylene maleic anhydride (3:1) 12.10 -0.01 1.89 4 Merkur 303 12.32 0.27 1.67 4 Microcrystalline 10.89 0.07 1.40 4 Stearic acid 12.25 -0.04 1.68 4 Sasolwax C 11.68 0.05 1.37 4 Soy wax 12.24 0.05 1.94 4 Synthetic beeswax 10.40 0.03 1.12 4 Tekniwax 801 11.77 0.07 1.67 4 Vaseline 11.16 0.03 1.45 5 Beeswax + Synthetic beeswax (1:1) 12.98 0.37 2.15 5 Beeswax + Vaseline (1:1) 12.83 0.59 2.09 5 Beeswax 11.38 0.23 1.49 5 Beeswax + Ethylene maleic anhydride (3:1) 12.91 0.47 1.80 5 Beeswax + Sasolwax C (1:1) 13.88 0.54 2.58 5 Carnauba 12.28 0.18 2.28 5 Control 13.74 0.31 2.55   209  Block Wax Final moisture content (%) Time-delayed thickness swelling (mm) Total thickness swelling (mm) 5 “moisture resistant” 10.04 0.02 0.80 5 Sasolwax M3M 13.32 0.71 2.35 5 Sasolwax M3M + Ethylene maleic anhydride (3:1) 12.96 0.27 2.41 5 Merkur 304 13.67 0.82 2.97 5 Microcrystalline 12.71 0.89 2.20 5 Stearic acid 12.68 0.40 1.97 5 Sasolwax C 14.16 0.55 2.68 5 Soy wax 12.92 0.14 2.22 5 Synthetic beeswax 13.61 0.32 2.75 5 Tekniwax 801 12.58 0.55 1.95 5 Vaseline 13.32 0.54 2.45 6 Beeswax + Synthetic beeswax (1:1) 10.90 0.29 1.59 6 Beeswax + Vaseline (1:1) 10.53 0.24 1.21 6 Beeswax 11.13 0.31 1.61 6 Beeswax + Ethylene maleic anhydride (3:1) 10.83 0.35 1.45 6 Beeswax + Sasolwax C (1:1) 11.15 0.31 1.52 6 Carnauba 11.04 0.21 1.39 6 Control 11.11 0.10 1.67 6 “moisture resistant” 11.19 0.13 0.92 6 Sasolwax M3M 11.56 0.31 1.46 6 Sasolwax M3M + Ethylene maleic anhydride (3:1) 11.18 0.42 1.48 6 Merkur 305 10.80 0.24 1.26 6 Microcrystalline 10.81 0.20 1.44 6 Stearic acid 10.29 0.20 1.22 6 Sasolwax C 12.25 0.34 2.14 6 Soy wax 10.81 0.20 1.39 6 Synthetic beeswax 10.62 0.23 1.46 6 Tekniwax 801 10.87 0.20 1.54 6 Vaseline 11.11 0.30 1.77 7 Beeswax + Synthetic beeswax (1:1) 13.34 1.12 2.16 7 Beeswax + Vaseline (1:1) 12.20 0.93 1.88 7 Beeswax 14.09 0.70 2.92 7 Beeswax + Ethylene maleic anhydride (3:1) 11.98 0.91 2.09 7 Beeswax + Sasolwax C (1:1) 13.67 1.00 2.58 7 Carnauba 12.39 0.87 2.42 7 Control 13.09 1.00 2.22 7 “moisture resistant” 9.95 0.25 0.72 7 Sasolwax M3M 13.65 0.97 2.71 7 Sasolwax M3M + Ethylene maleic anhydride (3:1) 13.27 1.14 2.56 7 Merkur 306 13.67 0.73 2.36 7 Microcrystalline 13.92 1.28 2.69   210  Block Wax Final moisture content (%) Time-delayed thickness swelling (mm) Total thickness swelling (mm) 7 Stearic acid 12.38 0.97 1.97 7 Sasolwax C 13.35 0.81 2.45 7 Soy wax 14.12 1.27 2.77 7 Synthetic beeswax 13.15 1.09 2.58 7 Tekniwax 801 13.19 1.01 2.40 7 Vaseline 14.07 1.16 2.73  Appendix Table 3.35. ANOVA table for Final moisture content (α = 0.05) Source of variation d.f. SS MS F p-value Block 6 79.8992 13.3165 52.67 0 Control vs Treated 1 0.0044 0.0044 0.02 0.895 Wax type vs wax type 15 9.8363 0.6558 2.59 0.003 Residual 96 24.2736 0.2529    Total 118 114.0135        Appendix Table 3.36. ANOVA table for Total thickness swelling (α = 0.05) Source of variation d.f. SS MS F p-value Block 6 24.69145 4.11524 62.72 0 Control vs Treated 1 0.02001 0.02001 0.3 0.582 Wax type vs wax type 15 2.38831 0.15922 2.43 0.005 Residual 96 6.29901 0.06561    Total 118 33.39877        Appendix Table 3.37. ANOVA table for Time-delayed thickness swelling (α = 0.05) Source of variation d.f. SS MS F p-value Block 6 14.64518 2.44086 153.55 0 Control vs Treated 1 0.10878 0.10878 6.84 0.01 Wax type vs wax type 15 0.47672 0.03178 2 0.023 Residual 96 1.52608 0.0159    Total 118 16.75676         211   Appendix Table 3.38. Table of means for Final moisture content, Total thickness swelling, and Time-delayed thickness swelling  Wax Final moisture (%) Total thickness swelling (mm) Time-delayed thickness swelling (mm) Beeswax 11.847 1.597 0.188 Beeswax + Ethylene maleic anhydride (3:1) 11.735 1.515 0.25 Beeswax + Sasolwax C (1:1) 12.173 1.876 0.253 Beeswax + Synthetic beeswax (1:1) 11.493 1.415 0.291 Beeswax + Vaseline (1:1) 11.713 1.498 0.307 Carnauba 11.646 1.59 0.146 Control 11.9 1.721 0.125 Sasolwax M3M 12.172 1.749 0.234 Sasolwax M3M + Ethylene maleic anhydride (3:1) 11.935 1.691 0.258 Merkur 300 12.287 1.804 0.30 Microcrystalline 11.773 1.716 0.398 Stearic acid 11.523 1.447 0.167 Sasolwax C 12.58 1.881 0.233 Soy wax 12.149 1.799 0.158 Synthetic beeswax 11.737 1.599 0.257 Tekniwax 801 11.826 1.65 0.293 Vaseline 12.224 1.828 0.33 Mean 11.924 1.669 0.246 Least significant difference 0.5376 0.2738 0.1348  

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