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Studies on encapsulation of pelletized biomass Hashemi, Seyedeh Zahra 2013

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STUDIES ON ENCAPSULATION OF PELLETIZED BIOMASS  By  Seyedeh Zahra Hashemi B.A.Sc., Sharif University of Technology, 2011  A THESIS SUBMITTED IN PARTIAL FULLFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF  Master of Applied Science  in  The Faculty of Graduate Studies (Chemical and Biological Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)  July 2013 © Seyedeh Zahra Hashemi, 2013  Abstract Hygroscopicity and dust generation are among major challenges to the safe and cost effective use of wood pellets. Wood pellets can rot and disintegrate during storage due to the moisture adsorption from humid environment. In British Columbia, pellets are transported by rail from inland manufacturing plants to a shipping port and stored in silos. At the ports, pellets are loaded from the silo on to the ocean vessel for transport to overseas. Loading is stopped during rain because wood pellets disintegrate when they come into contact with water. The lost revenue from loading shutdown during rain can be large. Furthermore, breakage of wood pellets during handling and storage causes dustiness. Dust and fines may cause adverse health effect, fire, and explosion in storage and silos. Encapsulation of wood pellets with a hydrophobic membrane or surface modification can be a good way to increase water repellent capacity of wood pellets, and avoid dust generation. In this research, commercial wood pellets were coated with a wax solution, linseed oil, cellulose acetate, canola oil, etc. The treated pellets were either dipped in water or exposed to humid environment. The results showed that the investigated liquid coatings increased the durability of wood pellets in water. However, the tested liquid coatings did not decrease water vapor adsorption of pellets significantly. Surface treatments with O2 etching and CF4 plasma were applied to render wood pellets hydrophobic. It was demonstrated that CF4 plasma treatment increased water repellency of wood pellets while O2 etching without CF4 deposition step made pellets more hydrophilic. Surface modification with O2 etching combined with CF4 deposition created the most hydrophobic surface when pellets were dipped in water. However this combined plasma treatment did not decrease water vapor adsorption from humid environment.  ii  Preface This thesis was developed by the author under supervision of Professors Shahab Sokhansanj and Jim Lim. The author designed the experiments, developed experimental methods and performed the tests. The author analyzed the data and received advice on presentation of the results from her Graduate Committee and supervisors. Chapter 4 of this thesis was presented in 62nd Chemical Engineering Conference in Vancouver, October 14-17, 2012. The title of the oral presentation was “Water proofing of pelletized biomass”.  iii  Table of Contents Abstract ............................................................................................................................ ii Preface............................................................................................................................. iii Table of Contents ............................................................................................................ iv List of Tables ................................................................................................................. vii List of Figures ................................................................................................................. ix Nomenclature ................................................................................................................ xiii Acknowledgments......................................................................................................... xiv Chapter 1:  Introduction ................................................................................................ 1  1.1 Motivation of Study ................................................................................... 1 1.2 Objectives .................................................................................................. 2 Chapter 2:  Background ................................................................................................ 4  2.1 Coating for Food Products ......................................................................... 4 2.2 Coating for Textile Products ...................................................................... 4 2.3 Coating for Paper Products ........................................................................ 5 2.4 Coating for Pharmaceutical Products ......................................................... 6 2.5 General Coating Techniques ...................................................................... 6 2.5.1 Spray Drying Coating ......................................................................... 6 2.5.2 Fluidized Bed Coating ........................................................................ 7 2.5.3 Dry Powder Technique ....................................................................... 8 2.6 Wood Pellets Production............................................................................ 8 2.6.1 Characterization of Shape and Geometry of Wood Pellets ................ 9 2.7 Molecular Structure of Wood .................................................................. 10 2.8 Definition of Hygroscopicity ................................................................... 11 2.9 Definition of Hydroscopicity ................................................................... 12 2.10 Wettability.............................................................................................. 12 2.11 Contact Angle Theory ............................................................................ 13 iv  2.12 Lotus Effect ............................................................................................ 14 2.13 Surface Hydrophobicity ......................................................................... 14 2.14 Plasma Processing .................................................................................. 15 2.15 Plasma Treatment of Wood Surfaces ..................................................... 16 2.16 Summary ................................................................................................ 16 Chapter 3:  Materials and Methods ............................................................................. 25  3.1 Material and Setup ................................................................................... 25 3.2 Method ..................................................................................................... 27 3.2.1 Dip Coating ....................................................................................... 27 3.2.2 Plasma Treatment.............................................................................. 28 3.2.3 Hygroscopicity Test .......................................................................... 29 3.2.4 Hydroscopicity Test .......................................................................... 29 3.2.5 Contact Angle and Water Uptake Time Measurement ..................... 30 3.2.6 Swelling Test .................................................................................... 30 3.2.7 Porosity Measurement ...................................................................... 31 3.2.8 Diffusion Coefficient ........................................................................ 32 3.2.9 Fourier Transform Infrared Spectroscopy (FTIR) ............................ 33 3.2.10 Scanning Electron Microscope (SEM) ........................................... 33 Chapter 4:  Results and Discussion-Coating .............................................................. 37  4.1 Interaction with Liquid Water ................................................................ 37 4.1.1 Hydroscopicity Test .......................................................................... 37 4.1.2 Coating Effect on Droplet Contact Angle ......................................... 38 4.1.3 Droplet Uptake Time ........................................................................ 38 4.1.4 Swelling ............................................................................................ 39 4.2 Effect of Coatings on Wood Pellet Hygroscopicity ................................. 39 v  4.2.1 Coated Wood Pellet Water Vapor Absorption.................................. 39 4.3 Coating level and Cost Analysis .............................................................. 40 4.4 Discussion ................................................................................................ 41 Chapter 5:  Results and Discussion-Plasma Treatment .............................................. 51  5.1 Interaction with Liquid Water .................................................................. 51 5.1.1 Hydroscopicity Test on Plasma Treated Wood Pellets ..................... 51 5.1.2 Plasma Treatment Effect on Static Water Contact Angle ................. 51 5.1.3 Water Droplet Uptake Time.............................................................. 52 5.1.4 Swelling ............................................................................................ 53 5.2 Effect of Plasma Treatment on Wood Pellet Hygroscopicity .................. 53 5.3 Coating Effect on Surface Morphology- FTIR ........................................ 54 5.4 Discussion ................................................................................................ 55 Chapter 6:  Conclusion and Future Work ................................................................... 64  References ...................................................................................................................... 66 Appendix A: Coating Solution Characteristics .............................................................. 73 Appendix B: Experimental Data .................................................................................... 76 Appendix C: Hygroscopicity Test Results for Coated Pellets ....................................... 80 Appendix D: Physical Characteristics of Coating Solution ........................................... 84 Appendix E: Coating Thickness .................................................................................... 85 Appendix F: ATR-FTIR Spectra ................................................................................... 86  vi  List of Tables Table 2.1 Composition of cell wall of wood .................................................................. 17 Table 3.1 CF4 and O2 plasma gas operating condition for treating the surface of wood pellets ............................................................................................................................. 34 Table 4.1 Category of coated and uncoated wood pellet appearance during 30 minutes immersion in water ........................................................................................................ 43 Table 4.2 Contact angle for coated wood pellet with canola or with Cellulose acetate 44 Table 4.3 Effect of treatment on diffusion coefficient and porosity of pellets dipped in water ............................................................................................................................... 44 Table 4.4 Wood pellet weight gain after dip coating with different coating solution ... 45 Table 4.5 Pellet dimensions and assumptions for cost analysis ..................................... 46 Table 4.6 Determination of thickness for canola oil coated wood pellet to get a coating which increases the cost of pellet up to 10% ................................................................. 46 Table 4.7 Canola oil coating thickness calculated from experimental data for dipping method............................................................................................................................ 46 Table 5.1 Appearance of wood pellets treated with plasma during 30 minutes immersion in water ........................................................................................................ 56 Table 5.2 Contact angles of droplets before and after plasma treatment. The single water droplet is placed on the surface of a single pellet. ............................................... 57 Table 5.3 Porosity and diffusion coefficient of water penetration into pellets for CF4 treated pellets. Pellets are placed in humid environment for diffusion coefficient measurement. ................................................................................................................. 57 Table A.1 Coating material and characteristics ............................................................. 73 Table B.1 Treated and untreated wood pellet contact angle relevant to Table 4.2 and Table 5.2 ........................................................................................................................ 76 Table B.2 Moisture adsorption (wt.%) of untreated pellets placed s  .  . ......................................... 77  Table B.3 Moisture adsorption (wt.%) of canola s Table B.4 Moisture adsorption (wt. %) s  Figure 4.5 .............................. 77 s Figure 4.6 ................... 78 vii  s  Table B.5 Moisture adsorption (wt.%) s  Figure 4.7 ................................................... 78  Table B.6 Moisture adsorption (wt.%) of CF4  s  Figure 5.9 ................................................................................ 79 Table B.7 Moisture adsorption (wt.%) of O2 etched and CF4 deposited wood pellet at flowrate of 40cm3/min and untreated pellets placed in the environment chamber set at 30oC, 90% RH relevant to Figure 5.10 .......................................................................... 79 Table D.1 Viscosity and density of coating solutions at two different temperatures .... 84 Table E.1 Coating thickness calculated from experimental data for dipping method ... 85  viii  List of Figures Figure 1.1 Conceptual representation of an encapsulated wood pellet with a membrane. The membrane covers the entire surface of the wood pellet............................................ 3 Figure 2.1 Possible types of products obtained by spray drying a solution-feed (a)-(d) and a suspension-feed (e)-(f). ........................................................................................ 17 Figure 2.2 Batch fluid bed coating with bottom spray (Wurster coating) .................... 18 Figure 2.3 Wood pellets are cylindrical in geometry, having a diameter of 6.2 mm and length varying from 6 to 24 mm. Note the ends of pellets are irregular. ....................... 19 Figure 2.4 Structural formula of cellulose. The adsorbed water is bound to the hydroxyls (OH). ............................................................................................................. 20 Figure 2.5 Structural formula of hemicellulose. The adsorbed water is bound to the hydroxyls (OH) and carboxyl group (COOH) ............................................................... 20 Figure 2.6 Structural formula of lignin. Lignin molecular structure is too complex. Lignin acts like a binder between fibers. ....................................................................... 21 Figure 2.7 lignocellulose and its components. The plant cell walls containing hemicellulose, cellulose, and lignin forming a complicated structure. .......................... 21 Figure 2.8 Definition of contact angle of a drop of liquid on a slide surface. The larger the angle the lower the degree of wettability ................................................................. 22 Figure 2.9 The relation between a drop of liquid and a solid surface. (a) Homogeneous wetting (Wenzel model) where the liquid fills up surface indentation. (b) Heterogeneous wetting (Cassie–Baxter Model) where air bubbles are trapped inside the grooves of the rough surface underneath the drop. In model b the water droplet is not able to wet the microstructure spaces between the spikes. ............................................ 22 Figure 2.10 (a) Computer graphic of a lotus leaf surface (b) Scanning electron microscopy (SEM) image of lotus leaf shows the hierarchical surface structure .......... 23 Figure 2.11 Trans-esterification reactions between cellulose and triglycerides leads to the substitution of long-chain acyl group (RCO) in cellulose structure. Long-chain acyl group (RCO) is hydrophobic. ........................................................................................ 24 Figure 2.12 (a) A liquid turns to the gas by heating above critical point (b) The gas turns to plasma if the temperature keeps increasing ..................................................... 24 ix  Figure 3.1 Commercial white wood pellets (6.3 mm diameter) produced in British Columbia. Pure saw dust mixed with shavings is used to produce these pellets. .......... 34 Figure 3.2 (a) Schematic of industrial plasma device at UBC, (b) Trion Plasma Enhanced Chemical Vapour Deposition (PECVD) device. ........................................... 35 Figure 3.3 Categorising pellets dipped in water. (a) Category 1: There is no change on the pellets. (b) Category 2: wood particles separate from the wood pellet surface. (c) Category 4 & 6: cracks on the surface of pellets appear and pellets disintegrate. (d) Category 3 & 5: cracks on the surface of pellets are visible and pellets swell. ............. 36 Figure 4.1 Disintegration time (minutes) for thermally treated canola oil coated wood pellets. Coated wood pellets were placed in the oven maintained at 60oC or 110oC up to 80 minutes. The pellets were then dipped in water and the time for their disintegration was recorded. ................................................................................................................. 47 Figure 4.2 Effect of coating with cellulose acetate or with canola oil on water uptake time when treated wood pellets is immersed in water ................................................... 48 Figure 4.3 Effect of coatings on wood pellet swelling when wood pellet is immersed in water ............................................................................................................................... 48 Figure 4.4 Moisture content of coated and uncoated wood pellet s  s..................... 49  s  Figure 4.5  s s  Figure 4.6  s. ...................... 49  s  s s  Figure 4.7  s  s s ................. 50 s  s  s. ...................... 50  Figure 5.1 Effects of treatment with Plasma on wood pellet water uptake time. Wood pellets are immersed in water. ....................................................................................... 57 Figure 5.2 Water droplet penetration in (a) untreated wood pellet, (b) O2 etched plus CF4 treated wood pellet .................................................................................................. 58 Figure 5.3 SEM picture of untreated wood pellet. Cracks and fissures are visible spreading randomly on the surface of untreated wood pellet. ....................................... 58  x  Figure 5.4 SEM picture of O2 etched wood pellet. The O2 etching removed part of the surface. The remaining part is a rough surface that absorbed water in less than 1 min. 59 Figure 5.5 SEM picture of CF4 deposited wood pellet. CF4 was deposited at flow rate of 40 cm3/min. The CF4 treated surface exhibited less cracks compared to the untreated surface. ........................................................................................................................... 59 Figure 5.6 SEM picture of O2 etched and CF4 deposited wood pellet. First, mild O2 etching was performed on the surface. Then, CF4 was deposited. The condition for CF4 deposition was treatment 1 in Table 3.1. Most of the cracks disappeared. The O2 etched and CF4 deposited wood pellet surface was more hydrophobic than CF4 treated alone.60 Figure 5.7 Effect of CF4 deposition and O2 etching on wood pellet swelling when the pellet is immersed in water. ........................................................................................... 60 Figure 5.8 Moisture content of treated and untreated wood pellet s  s..................... 61 s  Figure 5.9 Moisture content of CF4 s  .  n reducing the  hygroscopicity of treated pellets was observed. ............................................................ 61 Figure 5.10 Moisture content of O2 etched and CF4 deposited wood pellet at flowrate of 40 cm3/min and untreated pellets placed in the environment chamber set at 30oC, 90% relative humidity for 72 hours. No effect on reducing the hygroscopicity of treated pellets was observed. ..................................................................................................... 62 Figure 5.11 FTIR of the untreated and treated pellet surface with CF4. The presence of a new band at 1739 cm-1 in CF4 deposited wood pellet spectrum confirms the presence of fluorocarbon bonds on the surface of treated pellet. ................................................. 63 .  s  s  s  s  relative humidity ...................... 80  Figure C.2 Moisture adsorption of bis(triethoxysilyl)ethane and untreated pellets placed s  C, 90% relative humidity .................................. 81  Figure C.3 Moisture adsorption of octadecyltriethoxysilane and untreated pellets placed in the environment chamber set at 30oC, 90% relative humidity .................................. 81 .  s  s s  s  s relative humidity ............................................ 82 xi  .  s  s s  .  s  s s  s  s relative humidity ............................................ 82 s relative humidity ............................................ 83  Figure F.1 FTIR of CF4 deposited wood pellet.............................................................. 86 Figure F.2 FTIR of untreated wood pellet ..................................................................... 87  xii  Nomenclature Symbol  Definition (Unit)  D  Wood pellet diameter (m)  D  Wood pellet moisture diffusivity (m2/h)  K  Computational parameter  L  Length of wood pellet (m)  P1  Pressure reading after pressurizing (Pa)  P2  Pressure reading after including VC (Pa)  PECVD  Plasma Enhanced Chemical Vapor Deposition  r  Roughness  S  Sample  W0  Weight of coated wood pellet at time zero (g)  Wt  Weight of wood pellet at time t (g )  WOD  Weight of oven dried pellet (g)  Greek Symbols ɣ  Surface tension (N/m)  Vp  True volume of wood pellet (cm3)  θY  Young contact angle (degree)  θW  Wenzel contact angle (degree)  θCB  Cassie-Baxter contact angle (degree)  εo  Porosity (fraction decimal)  ρp  Solid density (g/cm3)  ρ  Particle density (g/m3)  xiii  Acknowledgments Foremost, I would like to extend my deepest thanks to my supervisors Dr. Shahab Sokhansanj and Dr. Jim Lim for their inspiration. They have supported me throughout my thesis with their patience and knowledge. I will be forever grateful for the encouragement and guidance Dr. Sokhansanj provided me throughout my academic career. I would also like to acknowledge Mr. Staffan Melin, Research Director of the Wood Pellet Association of Canada (WPAC) for technical contributions to this work. I would like to thank BBRG members particularly Dr. Xiaoto Bi, Dr Anthony Lau, Ehsan Oveisi, Farhang Nesvaderani and Zahra Tooyserkani, PhD candidate at the Department of Chemical and Biological Engineering (CHBE), University of British Columbia. I want to acknowledge Dr. Chan Soo Kim, Senior Research Scientist of the Korean Institute of Science and Technology (KIST) who provided me with his knowledge in all phases of my research. Special thanks are also expressed to Mehrnegar Mirvakili, PhD candidate at Department of Chemical and Biological Engineering (CHBE), University of British Columbia, for providing her valuable advice and assistance in conducting plasma treatment experiments. The most loving thanks to my sister, brother and my parents for their endless love and support. I have missed them deeply during these years. I offer my final and deepest thanks to Mohammadreza Dabbaghian, who has been at my side through this project. I am so lucky to have him in my life.  xiv  Chapter 1: Introduction This chapter provides an introduction to the subject of the thesis, motivation for the study followed by a section outlining the objectives. A conceptual representation of the protective cover on a single pellet is shown.  1.1 Motivation of Study Wood pellets can adsorb moisture easily. This is why wood pellets are used as a bedding material for large and small animals. Although, moisture adsorption is good for animal bedding, it is a challenging issue in solid biofuel application. A wood pellet draws in the moisture when it comes in contact with liquid water or humid environment. After a while, cracks appear on the surface of the pellet and these cracks widen and become deeper. Eventually, the pellet breaks apart. The broken small particles become dust. Although moisture adsorption is not the only reason for the wood pellet dust generation, moisture accelerates this disintegration. It is reported that torrefaction of sawdust before pelletization reduces hydrophilic nature of wood particles (Li et. al, 2012). Torrefaction is a slow pyrolysis process under an oxygen free environment of 250-300oC up to 1 hour. Torrefaction destroys hydroxyl groups in hemicellulose. Increasing the severity of torrefaction renders wood pellet more hydrophobic (Li. et. al, 2012). The evidence shows that torrefied wood pellets though hydrophobic are prone to breakage that produces explosive dust. Encapsulation could also be an effective way of increasing the durability of torrefied wood pellets. In this thesis, two methods were investigated for encapsulating wood pellets. Method 1 is to coat wood pellets with a liquid solution to form a durable crust. In method 2, the surface of wood pellet was treated with Fluorocarbon (CF4) plasma enhanced chemical vapor deposition with or without oxygen (O2) etching to make the surface hydrophobic. Either of these two methods will add an extra operation at the end of wood pellet production plant in order to enhance wood pellet water repellency.  1  1.2 Objectives The overall goal of this research is to encapsulate a wood pellet to resist moisture ingress and disintegration. The specific objectives that were set for this thesis were (1) explore the effectiveness of different coating solutions as a barrier, (2) investigate the effectiveness of plasma enhanced chemical vapour deposition (PECVD) and O2 etching on wood pellet hygroscopicity and hydroscopicity. Figure 1.1 shows a conceptual representation of encapsulating a pellet with an impermeable membrane. This membrane covers the entire surface of a pellet. An effective membrane protects a pellet against rain and excessive humidity. The membrane also preserves the integrity of the pellets during its frequent handling and storage from the time the pellet is produced until the time it is used.  2  Figure 1.1 Conceptual representation of an encapsulated wood pellet with a membrane. The membrane covers the entire surface of the wood pellet.  3  Chapter 2: Background Biomass materials that are frequently exposed to rain and other elements of weather during storage, handling, and transport tend to spoil. A good coating can protect materials from a mold attack (Laurila, 2007). Plastic is used extensively as a coating material due to its excellent barrier and mechanical properties. As environmental issues attract more attention, plastic coatings will be substituted with more environmentally friendly materials including starch, protein, and polylactic acid (Laurila, 2007). This chapter reviews a few coating materials and application techniques.  2.1 Coating for Food Products Coating can play many different roles in the food industry. It can be used to change surface appearance, color or texture. Coatings can have particle separation, antioxidant, or barrier property. Protective coating in food industry avoids spoilage and leads to a longer shelf life. Ready-to-eat foods such as fruits are prone to spoilage and pathogenic microorganisms that cause shorter shelf life of the product (Laurila et al., 2007). Protective edible coatings for products have been used since the 12th century (Laurila et al., 2007). In China, waxes were applied to oranges and lemons to prevent water loss as a method of preservation (Laurila et al., 2007). In Canada, mineral oil, petrolatum and paraffin are used as protective coating on foods. The quantity of coating for food products is regulated by Food & Drug Act and Regulations (Canadian Produce Marketing Association).  2.2 Coating for Textile Products Textiles with a superhydrophobic coating can be used for any kind of application such as textile surfaces which are exposed to the humid environment (Zimmermann et al. 2012). Several methods have been developed to produce superhydrophobic textile including nanoparticle deposition, polymer grafting, and electrospinning (Zimmermann et al. 2012).  4  Silicone nanofilament coating is a method which is used to produce superhydrophobic surfaces by creating patterns. Zimmermann et al. (2012) created superhydrophobic textiles throu s s sq  A layer of fi  s  fi fi  process in gas phase. s was deposited onto the individual  s. This method fabricated nanostructure that is required for the  superhydrophobicity. Zhu et al. (2012) coated the fabric with Ag nanoparticles, followed by surface fl  ation to fabricate a rough and superhydrophobic texture with mechanical  stability.  2.3 Coating for Paper Products Paper is made up of a porous cellulose structure. Cellulose consists of microfibrils. Cellulose microfibrils are long-chain molecules in a crystalline state with amorphous regions regularly disrupting the crystalline structure (Khwaldia et al., 2010). The hydrophilic nature of cellulose makes the paper hydrophilic. The hydrophilicity of paper can be explained by the presence of the OH sites in cellulose and fiber network porosity. Packaging paper adsorbs water from the environment or food. Adsorption of water reduces physical and mechanical strength of paper. Moisture adsorption can occur in paper by diffusion of water vapor through both the void spaces and in condensed form through the fiber cell walls (Khwaldia et al., 2010). The use of renewable biopolymers in paper based packaging materials offers environmental advantages of recyclability and reutilization compared to conventional petroleum-based synthetic polymers. Protein, lipid and polysaccharide are biopolymers which are used as a coating on papers to reduce the ingression of moisture, oxygen, and carbon dioxide into paper packaging and food materials. Khwaldia (2009), Parris et al. (1998), Rhim et al. (2006), Sothornvit (2009), Parris et al. (1998) applied NaCAS/paraffin wax bilayer, corn zein/paraffin wax bilayer, soy protein isolate (SPI) with CaCl2 post treatment, hydroxypropyl methylcellulose (HPMC)/beeswax, and paraffin wax, respectively as a water barrier in paper coating. Rhim et al. (2006) investigated the effect of biopolymer coating, such as alginate and soy protein, on the physical strength and water resistance properties of 5  paper board. The effects of property modification of the biopolymers such as ionic cross linking of alginate film by CaCl2 treatment, cross linking of soy protein film by formaldehyde treatment, and compositing alginate or soy protein with a layered silicate were also investigated. They used wire bar for the coating process. Wire bar (Mayer rod) is a round steel bar that is wrapped very tightly with wire. A specific quantity of coating solution was poured on the paper and spread on the paper surface with wire bar. They found that biopolymer coating especially soy protein or alginate coating with CaCl2 increased water barrier properties of paper boards. 2.4 Coating for Pharmaceutical Products Tablet coatings are required for many reasons, including tablet appearance improvement, brand recognition, dose identification, improved stability, taste and odor masking, dust reduction, and as a binder (Barkly et al., 2006).  2.5 General Coating Techniques Different coating methods are used in industry. In this section, spray drying, fluidized bed and dry powder technique are explained. 2.5.1 Spray Drying Coating Spray drying is a process in which the liquid feed transforms into a dried particle form by spraying the feed into a hot drying gaseous medium (Masters, 1985). Recently, there has been a renewed interest in the use of spray drying to coat drugs with polymers to produce dust free and controlled release products. The advantages of spray drying include that it is one step technique and it is suitable for heat sensitive materials. There are two kinds of spray drying technique including spray drying a solution or spray drying a suspension. Lucy et al. (1992) did spray drying to coat theophylline (drug used by asthma patients) particles with an aqueous polymeric solution. Various polymers including hydroxypropylmethylcellulose acetate succinate (HPMCAS), hydroxypropylmethylcellulose (HPMC), methylcellulose (MC) and sodium carboxymethylcellulose (NaCMC) were studied to evaluate their spray-coating 6  properties. It was reported that drug release from the coated products was dependent on the hydrophilicity of the polymer (Lucy et al. 1992). They also indicated that a feed solution could form various products based on the different spray or formulation conditions (Figure 2.1 (a)-(d)): - Spray dried polymer without coating - Spray dried drug without coating - Theophylline coated with a thin polymeric layer - Polymer with drug protrusions on the surface The product formed from a suspension (the drug is of low solubility in the feed medium) could be (Figure 2.1(e)-(f)): - Free drug crystal - Polymer coated drug 2.5.2 Fluidized Bed Coating Fluid bed coating is a process in which particles are fluidized and a nozzle sprays the coating fluid on. The coating is then left out to dry. To provide a uniform coating on particles, small droplets and a low viscosity spray medium is required. Fluid bed coating technique is used for coating of microparticles, pellets, granules, or tablets. The advantages of fluidized bed coating technique are: - Uniform product coating is formed. - Either aqueous or organic coatings can be applied. - There is no need for an extra drying unit. - The filling and emptying of the machine can be done in an insulated place and without product spreading into the environment so it decreases the risk of contamination. - When using organic solvents, the process machines can also be made inert and used with a solvent recovery system (Cjtech Company). In organic-based system (polymer solution coating), polymer molecularly dissolved. Film formation happens by vaporization of organic solvent. After loss of solvent, polymer molecules connect with each other. In liquid-based system (polymer dispersion coating), polymer particles coalesce into a homogeneous format. A 7  plasticizer is used to decrease minimum film formation temperature. At last, a curing process is unavoidable to complete film formation. Lecomte et al. (2004) coated Propranolol HCL-loaded pellets with mixtures of a water insoluble and an enteric polymer (ethyl cellulose and Eudragit L). They found that in organic solutions compared to aqueous solution macro molecules has higher mobility which leads to a higher degree of polymer-polymer interpenetration. As a result, organic solutions cause tougher and less permeable film coating. Wurster process is a common coating method in the pharmaceutical industry. The apparatus that is used in Wurster process is a fludized bed with a spray nozzle at the bottom of the apparatus. Figure 2.2 shows a Wruster fluidized bed. Fluidizing air stream moves the particles upward past the spray nozzle. The nozzle sprays release droplets of coating solution or suspension concurrently with particle pathway flow. As particles moving upward into an expansion chamber, coating solution droplets deposit on particle surfaces. 2.5.3 Dry Powder Technique Dry powder coating is another technique which is used for tablet coating. Dry powder coating has advantages over other techniques. It does not need organic solvents, and it consumes less energy compared to other coating techniques (Pearnchob et al., 2003). Coating with polymer powders is an alternative to the coating with organic polymer solutions or aqueous polymer dispersions. Pearnchob et al. (2003) used dry powder coating process which was a modified fluidized bed Wurster-process. The polymer powder (Eudragit RS a copolymer of ethyl acrylate, ethylcellulose, and shellac) was fed via a powder feeder into the coating chamber, while the plasticizer/HPMC solution was sprayed from the liquid container at the same time. Particle collision between the liquid droplets, pellets and polymer particles results in good product motion/mixing.  2.6 Wood Pellets Production Wood pellets are made from compacted sawdust, shavings and ground wood chips, which are waste materials from trees used to make furniture, lumber, and other 8  products. Wood pellets are easy to handle, transport and store due to their uniform size, high density and low moisture content. In the pelletising process, if the raw material is large and dens, they go through a chipper to reduce the size of the particles. The particles are then dried down to a moisture content of 10 wt.% (w.b.)(Obernberger et. al, 2010). The dried material is run through hammer mill to reduce the particle size to around 1-2 mm. The ground particles are squeezed through the holes of a die under high pressure. The pressure causes lignin reformation which acts like a glue and binds wood particles. This friction between the holes in the press mill and wood particles is the reason for the wood pellets shiny surface. At the end of the process, the warm and soft pellets are cooled and dried by blowing air through a bed of moving pellets in a cooler. Wood pellet adsorb moisture because the pellet is made of hydrophilic wood particles with main constituents of cellulose, hemicelluloses, lignin and extractives (waxes, resins, etc.). Wood pellets made from clean saw dust without bark included may have an ash content of less than 0.5 wt.%. Wood pellets from bark which are contaminated with dirt could have an ash content of 2-10 wt.%. A thorough knowledge of molecular structure of wood can be useful to understand wood pellets hydrophilic nature. 2.6.1 Characterization of Shape and Geometry of Wood Pellets Current wood pellets are produced in cylindrical shape, compressed from a bulk of wood particles. Wood pellets may have cracks on their surfaces. The two ends of the cylinder are jagged. Figure 2.3 shows how wood pellets differ in terms of length, diameter, end parts and surface appearance. Diameter and length of fifty pellets were measured. The wood pellets diameter ranged from a minimum of 6.20 mm to 6.37 mm. The length varied from 20.0 mm to 25.5 mm. The diameter of the die holes determines the pellet diameter. The raw material passes through the die and leaves the die as an endlessly long cylindrical string. These strings are broken into smaller pieces by a cutter bar but mostly haphazardly which depends on their stiffness (Obernberger et al. 2010). Hence, commercial wood pellets have different lengths; even though, they were made from the same raw material and by the means of the same die. Pellets also break 9  during handling and transportation. Surface coating with another material requires knowledge about the physical and chemical properties of wood particles especially those particles that are on the surface of the pellets. These particles have been exposed to heat and friction. The chemical properties of this material may have been affected with respect to interface with coating materials.  2.7 Molecular Structure of Wood The wood cell wall consists of 3 major polymer components: cellulose which is the skeleton, hemicellulose which is the matrix and the lignin which is the encrusting substance binding the cells together. Lignin gives the rigidity to wood. Wood also contains extractives. It has been reported that the presence of the extractives in wood cell wall decrease wood wettability (Jordan et al., 1977). Table 2.1 summarizes the composition of the wood cell wall. The numbers are just a rough estimation of cellulose, hemicellulose, lignin, and extractives percentage in the wood cell wall. Wood can be categorized into two groups including softwood (ex. pine, cedar, spruce) and hardwood (ex. oak, aspen). The composition is different in softwood and hardwood. As a case in point, softwood constitute of 28-30% of lignin, while hardwoods contain 1824% lignin.  Cellulose Cellulose is the major part of the cell walls of green plants. Cellulose is made of hundred to several thousand of D-glucose units attached together in the form of long chains which are called microfibrils (Zillig, 2009) (Figure 2.4). When the cellulose chains are arranged evenly, it is called crystalline cellulose. When the cellulose chains are not ordered evenly, it is called amorphous cellulose. The amorphous cellulose is hygroscopic, whereas the crystalline cellulose is not. As a result, the different parts of cellulose have different properties.  Hemicelluloses Hemicellulose consists of a number of polysaccharides of different sugar units (Figure 2.5). The hygroscopicity of hemicellulose is the same as amorphous cellulose. 10  Lignin Lignin is a polymer of phenyl propene groups and it is made of large amorphous groups. Lignin has less hygroscopicity than amorphous cellulose and hemicellulose. Lignin in the cell wall found in middle lamella and gives stiffness to the cell wall (Figure 2.6).  Extractives Extractives are low molecular weight organic compounds. Mimms et al. (1993) reported that the wood extractives are fatty acids, resin acids, waxes and terpenes. Figure 2.7 shows the interaction of cellulose hemicellulose and lignin. Liyama et al. (1994) reported that lignin encrust cellulosic, non-cellulosic polysaccharides and protein in the cell wall. The lignin infiltrate in cellulosic microfibrils so an impermeable cell wall is created. There is covalent cross-linking between polysaccharides and lignin interface. Liyama et al. (1994) demonstrated that three different kind of linkage exists between polysaccharides and lignin. Two of linkages are direct covalent bond between lignin and polysaccharides including direct ester linkage and direct ether linkage.  2.8 Definition of Hygroscopicity The affinity of a substance to attract and hold water vapour from the surrounding environment is called hygroscopicity. Once the water is absorbed or adsorbed, it changes the adsorbing substance physically like an increase in volume, stickiness or other physical properties. As a case in point, moisture absorption from humid environment causes swelling, shrinkage, mold growth and rotting in hygroscopic wood (Time, 1998). Cellulose fibers such as cotton, paper, and a wide variety of other substances are hygroscopic. The hygroscopic materials have affinity for moisture in humid environment. The amount of moisture held in a hygroscopic substance is the function of the environment relative humidity and environment temperature. Wood hygroscopicity can be referred to its molecular structure. In crystalline cellulose, all hydroxyl sites are already bonded together so water molecules cannot penetrate (Walker, 2006). Water adsorption takes place in the amorphous regions of 11  cellulose because the hydroxyl groups in amorphous cellulose are free and capable of forming hydrogen bonds through diffusion of water (Walker 2006).  2.9 Definition of Hydroscopicity In this research, hydroscopicity is defined as the affinity of a substance to attract liquid water when the material comes in contact with rain or the material is immersed in water. Water in wood can be adsorbed into the wood as bound water or free water. Bound water is held within cell walls by adsorption force which causes volume changes. Free water adsorption occurs in free cell cavities called lumen and there is no bonding between free water and cell wall.  2.10 Wettability The surface is wetted with water completely when the water molecules affinity to themselves is lower than the affinity of water molecules to the substrate. Wettability of a solid surface can be quantified by measuring contact angle of water droplet on the surface. Two important factors which affect surface wettability are roughness and surface energy. For higher hydrophobicity, providing a proper surface roughness on the surface of substrate is required (Michael et al., 2007). Surface energy quantifies the disruption of intermolecular bonds that occur when a surface is created. Cutting a solid body into pieces disrupts its bonds, and therefore consumes energy. Low-energy surfaces have less affinity for water such as fluorocarbons and hydrocarbons. Contact angle (Figure 2.8) is defined as the tangent (angle) of a liquid drop with a solid surface at the base (Kwok et al., 1999). As contact angle becomes larger, the surface is more hydrophobic. The surfaces with contact angle larger than 90° are called hydrophobic surfaces and surfaces with contact angle smaller than 90° are called hydrophilic. Superhydrophobic surfaces have contact angle larger than 150°. Lotus leaves with contact angle of  is a good representative of  superhydrophobic surface (Yang-Tse et al., 2005). There are two kinds of wetting regimes on the rough surfaces including homogeneous and heterogeneous state (Marmur, 2003). In homogeneous state, the 12  water fills all the pores on the surface, and the surface is wetted completely. However, the air can fill the grooves which is called heterogeneous wetting (Marmur, 2003). Figure 2.9 elucidates the homogeneous and heterogeneous wetting states differences.  2.11 Contact Angle Theory Surface tension, represented by the symbol γ is defined as the force along a line of unit length, where the force is parallel to the surface but perpendicular to the line. If   SV ,  SL and  VL are defined as solid-vapour, solid-liquid, and vapour-liquid interfacial tension respectively, the contact angle (θY)  Y  ’s  Y  -  Laplace equation (Groenendijk, 2008).  cos Y    SV   SL  VL  (2-1)  Young equation is valid just for an ideal solid surface, which is smooth, rigid, chemically homogeneous, insoluble, and nonreactive (Marmur, 2006). From energy considerations, Wenzel (1936) established equation 2-2 to estimate contact angle for homogeneous, rough surfaces.  cos W  r cos Y  (2-2)  In Wenzel equation, W is apparent contact angle, θY is Y  ’s  r  is roughness ratio (equal to the actual surface area divided by the apparent solid surface area) and θY is the equilibrium contact angle of the liquid drop on the flat surface. Surface tension is a contractive tendency of the surface of a liquid that allows it to resist an external force. On heterogeneous surfaces, the surface tension varies from one point to another point so the Young contact angle keeps changing (Marmur, 2006). This heterogeneous surface is explained using the Cassie–Baxter equation,  cos CB  f SL r cos Y  f SL  1  (2-3)  fSL is defined as the fraction of water droplet in contact with solid surface. fSL is equal to 1 for homogeneous wetting which leads to Wenzel equation.  13  2.12 Lotus Effect Lotus leaves are famous due to very high water repellent surface. Neinhuis et al. (1997), the German botanists discovered the "lotus effect". Neinhuis et al. (1997) examined a lotus leaf surface under a high-powered microscope, and discovered that the surface was covered with microscopic bumps. These bumps caused surface water repellency. The water droplets beads up on the surface of lotus leaves and they do not spread. The superhydrophobicity and self-cleaning of the Lotus leaves was found to be a result of complex micro- and nanoscopic architecture of the surface including double roughness structures, slender pillars (Patankar, 2004), and hierarchical rough structure, as well as the epicuticular wax layer present on the leaf surface (Liu et al. 2006)( Figure 2.10). Epicuticular wax (bloom) consists of straight chain aliphatic hydrocarbons which render the surface more hydrophobic. It is found that the diameter of microscopic structure on the lotus leaf is around 5-9 micrometer (Feng et al. 2002). By mimicking from properties of lotus leaves, scientists have fabricated artificial superhydrophobic surfaces by applying different techniques such as anodic oxidation, electrodeposition, chemical etching, plasma etching, laser treatment, electrospinning, chemical vapour deposition, and sol–gel applications (Liu et al. 2006).  2.13 Surface Hydrophobicity A surface with contact angle larger than 150°C is superhydrophobic surface and superhydrophobicity needs a unique combination of surface roughness and low surface energy. The appropriate combination of roughness and surface energy can be obtained via various methods. (1) Create roughness on an inherently low-surface-energy material; (2) Add roughness to a hydrophilic surface and then modify it with a hydrophobic surface treatment method; (3) Modify a surface with low surface energy materials which add inherent roughness. The subject of cellulose hydrophobization has been an interesting research topic due to its broad application in different field such as wood, paper and textile industry. A cellulosic surface can be rendered hydrophobic by chemical or physical treatments.  14  Chemical treatment cause changes in the chemical structure of cellulose. In physical modification, there is no covalent attachment between cellulose and coating. Sizing is generally conducted during paper manufacture (Roberts, 1996) to make paper less hydrophilic. The sizing goal is to avoid inks and paints penetration in depth of the paper. In paper industry, different sizing agent such as alkenyl succinic acid anhydride (ASA), alk  k  (AKD)  s  fi  suspension (Gess and Rende, 2005; Lindstrom and Larsson, 2008; Roberts, 1996). Dankovich and Hsieh (2007) made hydrophobic cotton by transesterification reaction between soybean oil and cotton (Bayer et al., 2003). Transesterification reaction between triglyceride and cellulose hydroxyl leads to the covalent bonding of acyl chains to the wood cellulose (Figure 2.11).  2.14 Plasma Processing Plasma is an ionized gas that can be carrier of an intense energy. Phase transition happens when the intense energy is applied to a substance. Solid transforms to liquid, and liquid transforms to gas. If more energy is applied, the molecules intrinsic energy increases. The molecules collide, and atoms and molecules will break apart (Figure 2.12). Radicals and excited state species, sub-particles, electrons and ions are s  s  ( ’A s  . 2005).  Plasma can interact with solid surface in three ways. First, it can remove the outermost layer of the surface. This reaction is called etching or ablation. Plasma can also cause deposition, and coating of the surface. This plasma aided deposition is called plasma polymerization or plasma enhanced chemical vapor decomposition. Species in plasma can also modify a surface chemically or physically (Plasma treatment or activation) (Pykonen et al. 2008). In the plasma polymerization process, reactions between plasma species, between plasma and surface species, and between surface species occur (Biederman 2004). Plasma method has advantages over other surface modification methods. First, Plasma species do not penetrate below about 10 nm of the surface, which means that more than 99% of the bulk of a 10 µm thick film, for instance, remains totally unmodified during the plasma treatment (Navarro et al. 2003). Sahin et al. (2002) also 15  indicated that plasma treatment modifies just the top layer of the exposed substrate (100-200A). Plasma is a dry method so there is no need for energy consuming drying process which is necessary for wet processes.  2.15 Plasma Treatment of Wood Surfaces Plasma treatment has been found to be effective in increasing both hydrophobicity and hydrophilicity of wood surfaces depending on the gas and operating condition used in plasma process. Podgorski et al. (2000) treated pine samples with a mixture of CF4 and C3F6 for 15 min with a power of 900 W. They reported a decrease in wood piece wettability. On the other hand, plasma treatment increased surface hydrophilicity to improve the adhesion of wood with coatings. It was postulated that helium, argon, nitrogen and air plasma generate hydrophilic wood surface while adding methane or acetylene to argon plasma render wood surface hydrophobic (Rehn et al., 2003).  2.16 Summary Coating and encapsulation have been used for more than 100 (or even) years. The purpose of coating and surface treatment can be different in various industries. Hydrophobic coating is an important topic in paper, textile and wood industry. Surfaces could be covered with hydrophobic material but also the surface of the substrate can be modified chemically, thermally, and or mechanically. Most hydrophibicity methods are like mimicking from lotus leaf surface which has a superhydrophobic micro-nanostructured surface. Plasma treatment can deposit, etch and functionalize the surface. The process that happens during plasma treatment is the function of operating condition and cursor gas. Reviewed literature indicates that hydrophobicity methods discussed in this chapter decrease moisture adsorption from liquid water. No evidence on the influence of water vapor on the surface is provided.  16  Table 2.1 Composition of cell wall of wood (Source: http://classes.mst.edu/ide120/lessons/wood/cell_structure/index.html. accessed at201305-24).  Fibers  Matrix  Material  Structure  Cellulose Lignin Hemicellulose Water Extractives  Crystalline Amorphous Semi-crystalline Dissolved in the matrix Dissolved in the matrix  Approx. wt (%) 45-55 20-30 25-30 10 1-3  Figure 2.1 Possible types of products obtained by spray drying a solution-feed (a)-(d) and a suspension-feed (e)-(f). (Adapted from Lucy et al. 1992)  17  Figure 2.2 Batch fluid bed coating with bottom spray (Wurster coating)  18  Figure 2.3 Wood pellets are cylindrical in geometry, having a diameter of 6.2 mm and length varying from 6 to 24 mm. Note the ends of pellets are irregular. 19  Figure 2.4 Structural formula of cellulose. The adsorbed water is bound to the hydroxyls (OH).  Figure 2.5 Structural formula of hemicellulose. The adsorbed water is bound to the hydroxyls (OH) and carboxyl group (COOH) (Time, 1998)  20  Figure 2.6 Structural formula of lignin. Lignin molecular structure is too complex. Lignin acts like a binder between fibers. (Glazer et al., 1995)  Figure 2.7 lignocellulose and its components. The plant cell walls containing hemicellulose, cellulose, and lignin forming a complicated structure. (Adapted from USDA Agricultural Research Service) (Source: http://www.sfi.mtu.edu/FutureFuelfromForest/LignocellulosicBiomass.htm, accessed at 2013-05-6)  21  Figure 2.8 Definition of contact angle of a drop of liquid on a slide surface. The larger the angle the lower the degree of wettability  (a)  (b)  Figure 2.9 The relation between a drop of liquid and a solid surface. (a) Homogeneous wetting (Wenzel model) where the liquid fills up surface indentation. (b) Heterogeneous wetting (Cassie–Baxter Model) where air bubbles are trapped inside the grooves of the rough surface underneath the drop. In model b the water droplet is not able to wet the microstructure spaces between the spikes. (Adapted from Marmur, 2003)  22  (a)  (b) Figure 2.10 (a) Computer graphic of a lotus leaf surface (Thielicke W.) (b) Scanning electron microscopy (SEM) image of lotus leaf shows the hierarchical surface structure (Adapted from Ensikat et al., 2011)  23  Figure 2.11 Trans-esterification reactions between cellulose and triglycerides leads to the substitution of long-chain acyl group (RCO) in cellulose structure. Long-chain acyl group (RCO) is hydrophobic. (Adapted from Dankovich and Hsieh 2007).  (a)  (b)  Figure 2.12 (a) A liquid turns to the gas by heating above critical point (b) The gas turns to plasma if the temperature keeps increasing (Adapted from Max Planck Institute for Plama Physics) .  24  Chapter 3: Materials and Methods This chapter describes the wood pellet material and wood pellet surface treatments. The treatments consisted of two distinctive methods. For method 1, the surface of pellets was coated with a substance. For method 2, the surface of wood pellets was treated with plasma gases. The efficacy of treatments was measured by either immersing the treated pellet in liquid water or by placing the treated wood pellet in a humid chamber.  3.1 Material and Setup Commercial wood pellets used in all experiments were received from Premium Pellet Ltd. Figure 3.1 depicts a bulk of commercial wood pellet. Wood Pellets were made from 95% Mountain Pine Beetle wood harvested within three years of mortality in the Vanderhoof – Prince George area of BC. The pellets were stored in plastic containers and gradually used over a six months period. Various coating solutions were used to coat wood pellets. Ethyl 2-cyanocrylate (ECA) monomer, linseed oil, cellulose acetate, paraffin wax and acetone were purchased from Sigma-Aldrich Canada Ltd. (2149 Winston Park Dr. Oakville, Ontario L6H 6J8). Canola oil was bought from Canada Harvest (Richardson Oilsees Limited, Lethbridge, Alberta, T1J 3Y4). Mineral oil (Crystal Plus Oil 70T) received from STE oil company (2001 Clovis Barker Rd., San Marcos, TX 78666). Octadecyltriethoxysilane and bis(triethoxysilyl)ethane were used as received from Gelest Company (11 East Steel Road Morrisville, PA 19067). Below are the general descriptions of the coating solutions used in this research. Canola oil: canola oil is the oil obtained from rapeseed. Canada and the United States produce about 7 and 10 million tonnes of canola seed annually. Szczerbanik et al. (2005) coated Australian Nashi pears with canola oil to extend the storage life. Canola oil delayed the loss of green color during storage because it reduced the loss of carbon dioxide from the fruit and the oxygen adsorption (Szczerbanik et al., 2005).  25  Linseed oil: linseed oil is a liquid. Linseed oil is derived from the seeds of the flax plant. The oil is obtained by pressing, sometimes followed by solvent extraction. It is used to coat cricket bats to avoid wood moisture loss (Laver) Mineral oil: Mineral oil is a liquid which is the by-product of the petroleum distillation. Mineral oil is used to coat eggs to protect them against moisture and carbon dioxide transfer with environment. Paraffin wax: paraffin wax is derived from petroleum and consists of a mixture of hydrocarbon molecules containing between twenty and forty carbon atoms. Paraffin is used as a paper or cloth coating, shiny coating used in candy-making, and coating for hard cheese. Silicone fluid: silicones are polymers that have silicone with carbon, hydrogen, oxygen and other elements in their structure. Some common forms include silicone oil. Ethyl 2-cyanoacrylate: ethyl 2-cyanoacrylate (ECA) is an ethyl ester of 2cyano-2-propenoic acid. It is a colorless liquid with low viscosity. Cyanoacrylate is an acrylic resin that rapidly polymerises in the presence of water. The polymerization leads to the long, strong chains formation which causes joining the bonded surfaces together. Octadecyltriethoxysilane:  octadecyltriethoxysilane  is  an  organosilane  compound. Using a long chain hydrocarbon gives good hydrophobic properties, and there is no concern regarding fluorinated by-products being burned off (Gelest Company). Bis(triethoxysilyl)ethane: bis(triethoxysilyl)ethane is an organosilane. Gelest company has used dipodal silanes to encapsulate nanoparticles. Basically, with six alkoxy reactive groups the dipodal will crosslink all over the surface with the hope of reducing dust. It may also bridge between the cellulose particles, ultimately reducing dust (Gelest company). Cellulose acetate: cellulose acetates (CA) are esters of cellulose, which are obtained by reaction of cellulose with acetic anhydride and acetic acid in the presence of sulfuric acid.  26  More information about coating solution including state of material as received and application are provided in appendix A. Humidity chamber (ESPEC CORP, LHU-113, Japan) was provided an environment with fixed temperature (30° C) and fixed humidity (90%). Plasma Enhanced Chemical Vapor Deposition (PECVD) apparatus for surface treatment of wood pellets, Scanning Electron Microscopy (SEM) for surface morphology, and a FTIR-ATR (Attenuated Total Reflectance) for chemical bonds analysis were additionally employed. The porosity of wood pellets was measured by gas comparison pycnometer.  3.2 Method The experimental procedure to study the effect of different coating solution and surface treatment on wood pellet hydrophobicity as well as the materials and apparatus are explained. The coating and surface treatment methods are also presented in this section. 3.2.1 Dip Coating Once pellets received, their moisture contents were measured using the ASABE S358.2 (2010).  s  (  s s)  for 24 hours before coating process. Rhén et al. (2005) reported that the dominating variable for the moisture uptake was the initial moisture content in the pellet. The purpose of this initial drying was to keep the initial moisture content constant for all wood pellets. The dimensions of 200 g of pellets were measured using caliper. The mass of the pellets was measured on an electronic balance. Pellets were placed in separate small plastic bags and stored in lab at room temperature until use. Weight, length and diameter of oven-dried pellets were measured using a caliper and an electronic balance to a precision of 0.001 g. Pellets were chosen with no evidence of lateral cracks. Dip coating was used to create a thin film on wood pellets. Several 40 ml beakers were filled with different coating solution including canola oil, linseed oil, mineral oil, silicone oil, ethyl 2cyanocrylate (ECA), n-octadecyltriethoxysilane, bis(triethoxysilyl)ethane, molten 27  paraffin wax, and 5% solution of cellulose acetate in acetone. Paraffin wax was melted at 60°C before coating. One oven-dried pellet was placed in a perforated dish and dipped in each coating solution for 3 seconds at room temperature using a pair of tweezers. The pellet was removed out of the solution immediately. The experiment repeated for 5 pellets. For ethyl 2-cyanocrylate (ECA), five pellets were dipped in 5% ECA and left under ambient temperature overnight to dry and polymerize. The drying duration and condition were recommended by Bayer et al. (2011). Hypothesis was that acetone controls polymerization process and helps to have a uniform coating layer as well as decreasing the amount of ECA consumption. Acetone evaporates when left at room temperature. Solvent-based coating has been used in pharmaceutical application but concern is the environmental implication of the solvent (Barkley e al. 2006). 3.2.2 Plasma Treatment Oven-dried wood pellets surfaces were modified by plasma method. In laboratories, plasma is created by applying high voltage to a gas. Figure 3.2 (b) shows the Trion Plasma Enhanced Chemical Vapour Deposition (PECVD) device at the University of British Columbia. The plasma device is Trion/RIE (reactive ion etch) plasma enhanced chemical vapour deposition (PECVD) (model: ACD) with a vacuum loadlock, 250V AC, and a frequency of 60Hz. The device is located in the AMPEL clean room. The plasma is generally created by radio frequency or direct current discharge between two electrodes. The space between two electrodes is filled with the reacting gases (Figure 3.2 (a)). The gas ionized and created active species. CF4 was deposited on a group of wood pellets, while another group of pellets were etched with O2 and then CF4 deposition was applied. Processing parameters, such as treatment power, treatment time, gas types and operating pressure, can be varied by the application. The operating conditions for CF4 plasma treatment at 3 different flowrates and O2 etching are reported in Table 3.1. The operating conditions are modified conditions used by Balu (2009) and Mirvakili (2011) for their paper samples. All plasma treatments were preceded by a cleaning procedure of the reactor involving 3  28  steps of nitrogen venting the load-lock. The experiment for each set of operating condition was repeated for five pellets. 3.2.3 Hygroscopicity Test The 5 coated wood pellets coated with the same coating solution and 5 uncoated, oven-dried samples were placed in separate containers and in the humid chamber s  for 72 hours. At intervals, oven door was opened and the  sample was removed for weighing. Weights were initially taken at short intervals followed by 4 times daily and at last two times daily. Moisture content was calculated on an oven dried basis using following equation: Moisture Content (%)   Wt  W0 100 WOD  (3.1)  Where Wt, W0, and WOD are weight of coated pellet at time t, weight of coated pellet at time zero, and weight of oven dried pellet without coating, respectively. 3.2.4 Hydroscopicity Test Distilled deionized water was poured in 2 beakers. One untreated and one treated pellet was immersed in a separate beaker of water at room temperature (22°C) till they disintegrate. The appearance of pellets was visually determined during first 30 minutes. The appearance of pellets was classified into five groups (Figure 3.3): Category 1: There is no change on the pellets. Category 2: Wood particles separate from the wood pellet surface. Category 3: Mild cracks on the surface of pellets appear. Category 4: Lots of cracks on the surface of pellets are visible. Category 5: Pellets swell. Category 6: Pellets disintegrate. This experiment was repeated for 3 pellets from the same kind and for every treated pellet in order to compare each treated and untreated pellet.  29  3.2.5 Contact Angle and Water Uptake Time Measurement The water repellency of treated and untreated wood pellets was determined by measuring water contact angle on the surface. One wood pellet at a time was placed on a grey flat surface which was lightened by a lamp. A μL  s  z  droplet at 25 °C was dispensed on top of the cylindrical wood pellets with a pipette while the Nikon D90 digital camera keep taking movie from the side of both wood pellet surface and water droplet. The background was the white laboratory wall. A picture was captured from the movie at time zero. The image of water droplet on wood pellet at time zero was analysed with FTA 32 Version 2.0. Contact angles were measured by fitting a mathematical expression to the shape of the liquid drop and then calculating the slope of the tangent to the liquid drop at the liquid-solid-vapor (LSV) interface line. Liquid drop shape analysis with computer software gives the contact angle without operator intervention or judgment. The water droplet contact angle measurement technique is a modified process used by Mills et al. (2003) and Mirvakili (2011). Measuring contact angle hysteresis was not possible because the samples were cylindrical in shape and very porous. The water uptake time, which is defined as the time interval from the impact of the droplet to the complete penetration of the droplet in the wo  (  fl  can be seen) (Kress et al. 1999; Bente et al. 2004) was measured for coated and uncoated wood pellets. 3.2.6 Swelling Test The swelling is defined as the relative increase of the pellet area viewed from above at one minute after submersion into water. To measure wood pellet swelling, 4 petri dishes located on light table were filled with deionized water. A digital camera was located above and perpendicular to the rectangular light table in order to record the picture at time zero and after 1 minute submersion. Then, the area for each pellet at time zero and after 1 min was determined using ImageJ analysis software. The swelling of each pellet can be calculated using the following equation:  Swelling (%)   Af  Ai Ai  100  (3-2) 30  Where Ai is the initial area of a pellet at time 0 and Af is the final area of a pellet after submersion for 1 minute. Both minimum and maximum individual swelling values were eliminated. Then, the arithmetic average of the individual swelling values was calculated. 3.2.7 Porosity Measurement Solid density and particle density was measured for each pellet. Each pellet was weighed using a digital scale to 0.001 g. precision. Wood pellet solid density was calculated by measuring the volume of three wood pellets with a Quantachrome Multipycnometer (Quantachrome, Boyton Beach, FL, USA). The nitrogen was injected into void spaces of the pelletized biomass (about 15 psi). The pressure difference when a known quantity of pressurized nitrogen flows from a reference volume into a sample cell with samples was used to determine the wood pellet’s solid volume. Solid volume is the volume of solid particles minus any voids within pellets that is accessible to nitrogen gas. The solid volume was calculated using Equation 3-3 (Multipycnometer manual). Wood pellet volume measurements were repeated three times for each sample for determination of an average. P  VP  VC VR  1  1  P2   (3-3)  Where Vp is solid volume of wood pellet (cm3), VC is sample cell volume (cm3), VR is reference volume (cm3), P1 is pressure reading after pressurizing the reference volume (Pa) and P2 is pressure reading after including VC (Pa). The solid density is the ratio of three wood pellets weight and the true volume of them (Equation 3-4).  p   m Vp  (3-4)  The particle wood pellet density was calculated by the ratio of wood pellet weight and wood pellet particle volume. The wood pellet ends were ground with sand paper to form perfect cylindrical shape. The length (L) and diameter (D) of a wood pellet was measured with a calliper. The particle volume was calculated by the following equation: 31  V   4  D2 L  (3-5)  Porosity (εo) was determined by the use of Equation 3-6.   0  (1    ) 100 p  (3-6)  The porosity gives the percent voids within a pellet. 3.2.8 Diffusion Coefficient Crank (1956) provided the solution of diffusion equation for different geometrical shapes under certain boundary conditions. The Crank equation of diffusion for finite cylinder was fitted to experimental data. The assumptions, initial and boundary condition in this study were, 1- Wood pellets are homogeneous. 2- At time zero, the surface reaches equilibrium with chamber environment instantaneously. 3- Drying or wetting environment has constant temperature and humidity during the experiment. 4- The object has constant mass diffusivity. The solution of diffusion equation for finite cylinder is: M  Me Ka 2 n 2t    8  4 1 a    2  2 2 exp exp   K (2n  1) 2 t ( ) 2     2 2 M o M e   n 1 a  n  l     n 1 (2n  1)  (3-7)  where M is average moisture content of body (dry basis), Me is equilibrium moisture content of body (dry basis), Mo is initial moisture content of body (dry basis),  M  Me is moisture ratio, a is radius of cylinder, l is one-half the length of the cylinder, M o M e  32  αn is the nth positive root of J0 (aαn) =0, t is exposure time, and K is computational parameter which is equal to  D 2 . a2  The two ends of wood pellets were from broken pieces, they did not have a smooth surface. The ends were ground with sand paper to form perfect cylindrical shape. The length and diameter of wood pellets measured using electronic s.  s  C and 90 RH for 72 hours. The weights were taken periodically. Five replicates were measured for each set of pellets. The moisture ratio was calculated for each time reading. Matlab curve fitting toolbox was used to fit Equation 3-7 to the experimental data to estimate K. From K, diffusion coefficient was estimated. 3.2.9 Fourier Transform Infrared Spectroscopy (FTIR) Frontier FTIR with an ATR (Attenuated Total Reflectance) by Perkin Elmer was used to evaluate the surface chemistry before and after CF4 deposition. Surface chemistry can be described as the study of chemical reactions at interfaces. It is approximately related to surface engineering, which works toward modifying the chemical composition of a surface by applying different methods. Surface modification can be done by the use of selected elements or functional groups to make changes in the properties of the surface or interface. 3.2.10 Scanning Electron Microscope (SEM) For excess topography studies, scanning electron microscope was done on surface of treated and untreated wood pellets. First, pellets were coated with Platinum and Palladium under vacuum. All photographs were taken at 2.3 kV accelerating voltage by using Hitachi S-4700 Field Emission Scanning Electron Microscope (FESEM).  33  Table 3.1 CF4 and O2 plasma gas operating condition for treating the surface of wood pellets Treatment Gas Pressure Temperature Time Flowrate Power 3 (mTorr) ( ) (sec) (cm /min) (W) 1 CF4 1000 20 1200 40 200 2 CF4 1000 20 1200 30 200 3 CF4 1000 20 1200 20 200 4 O2 100 20 200 10 300 1 Torr is 1/760 of a standard atmosphere = 133.3 Pa. mTorr is miliTorr = 0.001 Torr  Figure 3.1 Commercial white wood pellets (6.3 mm diameter) produced in British Columbia. Pure saw dust mixed with shavings is used to produce these pellets.  34  (a)  (b) Figure 3.2 (a) Schematic of industrial plasma device at UBC, (b) Trion Plasma Enhanced Chemical Vapour Deposition (PECVD) device.  35  (a)  (b)  (c)  (d)  Figure 3.3 Categorising pellets dipped in water. (a) Category 1: There is no change on the pellets. (b) Category 2: wood particles separate from the wood pellet surface. (c) Category 4 & 6: cracks on the surface of pellets appear and pellets disintegrate. (d) Category 3 & 5: cracks on the surface of pellets are visible and pellets swell.  36  Chapter 4: Results and Discussion-Coating This chapter presents results of applying different coating material on the pellets. The resistance of pellets to water ingress is measured. First, the interaction of coated and uncoated wood pellets with water is compared. Then, the effect of coating on the water vapor diffusion through wood pellets is investigated.  4.1 Interaction with Liquid Water In the following section, the effect of different coatings on wood pellet interaction with liquid water are presented and discussed. 4.1.1 Hydroscopicity Test Coated and uncoated wood pellets showed different reaction when immersed in water. Table 4.1 represents coated and untreated wood pellets surface appearance during the first 30 minutes of immersion in water. Generally, coated wood pellets could hold their shape in water for longer time than untreated wood pellets. The uncoated wood pellets disintegrated after 3-4 minutes. Pellets coated with ethyl 2-cyanocrylate (ECA) kept their shape in water for 24 h without disintegration. In the presence of humidity and cellulose hydroxyl group, the ECA monomers polymerize and create a cladding around each individual fiber, and render surface water repellent (Bayer et al., 2011). ECA is the main component of commercial and household glues. The stickiness of ECA helps the coat adheres to the particles on the surface of wood pellet. Cellulose acetate solution in acetone is used for asymmetric membrane capsule because cellulose acetate is a water-insoluble polymer so it does not release the drug fast (Thombre et al., 1999). Cellulose acetate solution in acetone created a capsule around the wood pellets. The results in Table 4.1 shows that cellulose acetate coated wood pellet can hold the shape in water for approximately 25 minutes. The vegetable oil reduced water ingress initially but after a while (depending on curing condition) small particles from the surface separated. To have a permanent hydrophobic surface, transesterification reaction between cellulose and triglycerides is required. The reaction forms hydrophobic long acyl chains attached to the cellulose with 37  s  covalent bonds (Dankovich et al., 2007).  s. Figure 4.1 shows the results of the hydroscopicity s  test on the cured pellets.  s  s  s  the best condition to make the most durable pellet in liquid water. This is in accordance s  with earlier finding which shows that heati  was optimal in producing the most hydrophobic cotton cellulose treated with soybean oil (Dankovich et al., 2007). For further analysis, canola coated wood pellets were cured at for 20 minutes. Further investigation and surface chemistry analysis is required to understand whether or not any reaction happened on the surface of wood pellets treated with different types of oil or the oil just adhered to the surface of wood pellet without any covalent bond. 4.1.2 Coating Effect on Droplet Contact Angle Table 4.2 lists the contact angles for cellulose acetate coated, canola oil coated and untreated wood pellets. The contact angle on the surface of canola coated wood pellet is 85.17±3.81° and for untreated wood pellet is 71.90±3.31°. They showed that surface chemical modification by canola oil does not have significant effect on surface wettability. Water droplet contact angle on the surface of cellulose acetate coated pellet was 70.09±2.94° showing that cellulose acetate decreased the water droplet contact angle relatively. The results show that canola oil and cellulose acetate did not render the pellet surface hydrophobic. The reason that canola and cellulose acetate coated pellets could hold their cylindrical shape in water for longer period of time is that they mostly act as a binder between particles, and keep them together. 4.1.3 Droplet Uptake Time Figure 4.2 shows the period of time from the impact of the droplet to the complete penetration of the droplet in cellulose acetate and canola coated pellet. The results shows that it took about 5.5 min for a droplet to diffuse into a canola coated wood pellet, while a droplet disappeared on the surface of an untreated pellet after approximately 1 minute. The water uptake time for cellulose acetate coated wood pellet was approximately 7.5 min. Although a water droplet had a higher contact angle on the surface of canola oil 38  coated wood pellets than on the surface of cellulose acetate coated wood pellets, it was adsorbed faster into the canola oil treated pellet. It can be explained by the fact that cellulose acetate created a membrane around the wood pellet and blocked the pores whereas canola oil diffuse to the wood pellets pores and there is no protective layer on the wood pellet surface. 4.1.4 Swelling Figure 4.3 shows the relative swelling of treated and untreated wood pellets. The results for swelling test show that all proposed coating solutions decreased the wood pellet swelling significantly. Coated wood pellets swelling are less than 5% while the uncoated wood pellet relative surface increase was around 18%. The difference between coated wood pellets swelling is not considerable. This fact can be explained by the fact that all coated pellets are still stable in water after 1 minute; thus, longer immersion time is required to investigate the differences. However, the swelling results are no longer reliable if wood pellets immerse for longer time due to particle separation from wood pellets.  4.2 Effect of Coatings on Wood Pellet Hygroscopicity In the following section, the results which show the effect of different coatings on wood pellet water vapor adsorption from humid environment are discussed. 4.2.1 Coated Wood Pellet Water Vapor Absorption s  Figure 4.4 is a bar chart showing the final moisture content s  s  s  (  ). The untreated  samples showed the most hygroscopic behavior with a final moisture content of approximately 16  s  s  (  C and 90%  RH) followed by wood pellet coated with cellulose acetate. The moisture content of canola oil coated and cellulose acetate coated wood pellets was 9% and 15% respectively. Figure 4.5 and Figure 4.6 plot canola coated and cellulose acetate coated wood pellet moisture content as a function of time. As expected, the coating type had no effect on the shape of the moisture content profile. The results show that coating was unable to prevent 39  water vapor absorption because these techniques cannot block the pores with an impermeable membrane. Paraffin wax was the only coating that decreased the moisture absorption to 2%. The disadvantage to the use of paraffin wax was that the coating was not uniform on the surface and it was brittle. Large error bars in Figure 4.7 bear testimony to this fact. Canola and cellulose acetate coated wood pellets were chosen for further analysis. The plots of wood moisture content as a function of water vapor sorption time for all treated and untreated samples during moisture absorption in humid chamber is presented in Appendix C. Apparent diffusion coefficient can be useful to quantify reduction of moisture absorption rate by coating. Apparent diffusion coefficients for treated and untreated wood pellets are provided in Table 4.3. The results show that cellulose acetate and canola oil decreased the wood pellet diffusion coefficient by 23 and 10 percent respectively. The hypothesis was that surface hydrophobicity is not enough to decrease water vapor adsorption from humid surrounding environment. The presence of an impermeable layer on the surface of wood pellet is required to block the water vapor diffusion to the wood pellets.  4.3 Coating level and Cost Analysis Table 4.4 lists the weight gain of individual wood pellets after dip coating process. The weight gain is measured for five pellets from the same kind. Wood pellets adsorb 0.01 g – 0.10 g of coating solution. The amount of coating solution that is absorbed depends on wood pellet size, coating technique and density of coating solution. The density and viscosity of coating solutions are listed in Appendix D. Cost analysis can be helpful to evaluate a reasonable coating process and coating solution. A coating process technique can determine the coating level and as a result the coating thickness on the outer layer of wood pellet. Price of wood pellet is an important consideration in a competitive fuel market. Durable pellets do not generate dust and fine during handling and therefore the more durable pellets can be sold at higher price. We may assume that the coating of pellets results in savings by having less dust. Coated pellets may also have a higher heat value than uncoated pellets because of a less increase 40  in moisture content in pellets that are delivered to a final user. Coating wood pellets with a material that increase the wood pellet price at least by 10 percent is not unreasonable. Table 4.5 lists assumptions for thickness determination. The goal is to have a very thin layer of coating that increases the price of wood pellet up to 10%. Commercial wood pellet diameter is 6.35 mm and wood pellet length ranges from 10-25 mm. The canola oil price is assumed to be 2-10 $/kg. The density of canola as a coating agent is assumed to be 920 kg/m3 (NOAA Technical Memorandum). Table 4.6 lists the results for canola oil thickness determination. The results shows that a reliable technique is required to decrease the coating thickness to 1.41- 8.27 µm. It is also an important issue to consider the effect of coating on wood pellet hydrophobicity. As a result, an acceptable coating thickness would be a function of the required degree of hydrophobicity and coated wood pellet price. The canola oil coating thickness was also calculated for 5 wood pellets which were coated with dipping method. The results are listed in Table 4.7 showed that the thickness of coating on the wood pellet is approximately 54.5 µm with dip coating method; hence, dip coating cannot be applicable in industry. A suitable coating process is required to decrease coating thickness one order of magnitude. The coating thickness on various coated wood pellet are listed in Appendix E.  4.4 Discussion ECA has the most effect on wood pellet hydroscopicity, and paraffin wax has the most impact on reduction of water vapor adsorption from humid environment. However, none of these materials is suggested to be used as a potential wood pellet coating material before environmental impact assessment on these coatings. Although, the surface of canola coated wood pellets is more hydrophobic and can keep their shape in liquid water for longer time compared to cellulose acetate coated wood pellet, canola coated wood pellet take the water droplet into their pores faster. This can be explained by the fact that a cellulose acetate cladding around wood pellet avoid liquid water penetration into the pellet but as it is not hydrophobic it will be destroyed in water after a while and cause wood pellet disintegration. The results show that both surface 41  hydrophobicity and an impermeable capsule on the surface of wood pellet are required to avoid water vapor adsorption and liquid water penetration. Due to the manual coating process, the dip coating could not be done uniformly for all wood pellets so the coating level can cause the variation in the results. The commercial wood pellets are different in size, shape, and color. Differences in color can be the result of ununiformed mixture of raw material in wood pellet production stage. These differences lead to variations among moisture adsorption of five subsamples taken from each coated sample lot.  42  Time (min) 0-3 3-5 5-10 10-15 15-20 20-25 25-30  Table 4.1 Category of coated and uncoated wood pellet appearance during 30 minutes immersion in water Untreated Canola oil Linseed oil Mineral oil Silicone oil ECA OTES BTE CA 5 6 6 6 6 6 6  1 1 1 1 1 1 1  1 2 2 2 2 2 4&2&5  1 1 1 1 1 1 1  1 2 2 2 2 2 2  1 1 1 1 1 1 1  1 1 1 1 1 1 1  1 1 1 1 1 2 2  Paraffin wax 1 1 1 1 1 3 3&5  1 1 1 1 5 6 6 6  ECA = ethyl 2-cyanoacrylate OTES = octadecyltriethoxysilane BTE = bis(triethoxysilyl)ethane CA = cellulose acetate Category 1: There is no change on the pellet. Category 2: Wood particles separate from the wood pellet surface. Category 3: Mild cracks on the surface of pellets appear. Category 4: Lots of cracks on the surface of pellets are visible. Category 5: Pellets swell. Category 6: Pellets disintegrate.  43  Table 4.2 Contact angle for coated wood pellet with canola or with Cellulose acetate Coating Contact angle Untreated 71.90 ±3.31 Canola oil 85.17 ±3.81 Cellulose acetate 70.09 ±2.94 Table 4.3 Effect of treatment on diffusion coefficient and porosity of pellets dipped in water Coating Diffusion coefficient Porosity (m2/h) (%) Untreated 7.58E-08±1.33E-08 24.54±1.93 Canola oil 5.83E-08±5.90E-09 9.70±1.71 Cellulose acetate 6.78E-08±1.55E-08 22.50±1.32  44  Table 4.4 Wood pellet weight gain after dip coating with different coating solution Canola oil (dipping) S1 S2 S3 S4 S5 Oven dried pellet weight(g) 0.821 0.860 0.850 0.810 0.852 Coated pellet weight (g) 0.843 0.879 0.876 0.826 0.896 Weight gain (g) 0.022 0.019 0.026 0.016 0.044 linseed oil(dipping) S1 S2 S3 S4 S5 Oven dried pellet weight (g) 0.644 0.564 0.857 0.635 0.578 Coated Pellet weight (g) 0.692 0.615 0.621 0.68 0.613 Weight gain (g) 0.048 0.051 0.064 0.045 0.035 Octadecyltriethoxysilane (dipping) S1 S2 S3 S4 S5 Oven dried pellet weight (g) 0.650 0.504 0.421 0.549 0.612 Coated pellet weight (g) 0.708 0.564 0.501 0.615 0.688 Weight gain (g) 0.058 0.060 0.080 0.066 0.076 Cellulose acetate (dipping) S1 S2 S3 S4 S5 Oven dried pellet weight (g) 0.836 0.768 0.752 0.810 0.749 Coated pellet weight (g) 0.861 0.782 0.788 0.863 0.800 Weight gain (g) 0.025 0.014 0.036 0.053 0.051 ECA (dipping) S1 S2 S3 S4 S5 Oven dried pellet weight (g) 0.768 0.648 0.558 0.622 1.436 Coated Pellet weight (g) 0.822 0.701 0.602 0.869 1.509 Weight gain (g) 0.054 0.053 0.044 0.247 0.073 Silicone oil (dipping) S1 S2 S3 S4 S5 Oven dried pellet weight (g) 0.796 0.674 0.617 0.539 0.625 Coated pellet weight (g) 0.881 0.741 0.673 0.586 0.709 Weight gain (g) 0.085 0.067 0.056 0.047 0.084 Bis(triethoxysilyl)ethane (dipping) S1 S2 S3 S4 S5 Oven dried pellet weight (g) 0.722 0.643 0.617 0.594 0.558 Coated pellet weight (g) 0.775 0.734 0.703 0.668 0.619 Weight gain (g) 0.053 0.091 0.086 0.074 0.061  45  Oven dried pellet weight (g) Coated pellet weight (g) Weight gain (g)  S1 0.417 0.486 0.069  Mineral oil S2 S3 0.620 0.570 0.713 0.658 0.093 0.088  S4 0.507 0.566 0.059  S5 0.537 0.616 0.079  Table 4.5 Pellet dimensions and assumptions for cost analysis Wood pellet diameter (mm) 6.35 Wood pellet length (mm) 10 – 25 Coating price per pellet price 0.10 Pellet cost ($/ton) 90 Coating cost ($/ton of pellets) 9 3 Density of coating (kg/m ) 920 Coating liquid price ($/kg) 2 – 10 Table 4.6 Determination of thickness for canola oil coated wood pellet to get a coating which increases the cost of pellet up to 10% Coating weight per tonne of pellet kg/ton 0.90 – 4.50 Coating volume per tonne of pellet m3/ton 9.78E-04 – 4.89E-03 Volume of single pellet mm3 316.53 – 791.03 Pellet particle density kg/m3 1200 Individual pellet weight g 0.38 – 0.95 Number of pellets per tonne of pellet 1/ton 1.05E+06 – 2.63E+06 Coating volume on individual pellet mm3 1.86 – 4.64 2 Surface area of single wood pellet mm 262.70 – 562.01 Coating thickness on a single pellet mm 0.00141 – 0.00827 Table 4.7 Canola oil coating thickness calculated from experimental data for dipping method Sample Name S1 S2 S3 S4 S5 Initial length (mm) 22.91 23.16 22.81 22.43 22.62 Initial diameter (mm) 6.20 6.24 6.27 6.21 6.25 Coated pellet weight (g) 0.84 0.88 0.88 0.83 0.90 Oven dried pellet weight (g) 0.82 0.86 0.85 0.81 0.85 Coating weight (g) 0.02 0.02 0.03 0.02 0.04 3 Volume of coating (mm ) 23.90 20.70 28.30 17.40 47.80 2 Wood pellet surface (mm ) 506.00 514.00 511.00 497.00 505.00 Thickness (mm) 0.05 0.04 0.06 0.04 0.09  46  110 0C 60 0 C  Disintegration Time(min)  3.0  2.5  2.0  1.5  1.0  0.5 0  10  20  30  40  50  60  70  80  90  Heating Time(hr)  Figure 4.1 Disintegration time (minutes) for thermally treated canola oil coated wood pellets. Coated wood pellets were placed in the oven maintained at 60oC or 110oC up to 80 minutes. The pellets were then dipped in water and the time for their disintegration was recorded.  47  10  Water Uptake Time(min)  8  6  4  2  0  Untreated  Cellulose acetate  Canola oil  Figure 4.2 Effect of coating with cellulose acetate or with canola oil on water uptake time when treated wood pellets is immersed in water  20  Swelling(%)  15  10  5  0  ted  a tre Un  A EC  il il il E il e x BT ola o ed o ral o TES ne o tat wa e O o ce n e n s c a a i i n f l n i f C e Li Si m rra os Pa llul e C  Figure 4.3 Effect of coatings on wood pellet swelling when wood pellet is immersed in water 48  20  Moisture Content(%)  15  10  5  BT E on e oi l EC A C A M in er al oi l lic  Si  o ee il Pa d ra oil ffi n w O ax TE S  a  Li  ns  ol an C  U  nt  re  at  ed  0  Figure 4.4 Moisture content of coated and uncoated wood pellet s  s  20  Treated Untreated  18  Moisture content(%)  16 14 12 10 8 6 4 2 0 0  10  20  30  40  50  60  70  Time(hour)  s for 72 hours.  Figure 4.5 Moisture content of canola s  49  20  Treated Untreated  18  Moisture content (%)  16 14 12 10 8 6 4 2 0 0  10  20  30  40  50  60  70  Time(hour)  Figure 4.6 Moisture content of cellulose acetate coated and unt s  s for 72 hours  20  Treated Untreated  18  Moisture content (%)  16 14 12 10 8 6 4 2 0 0  10  20  30  40  50  60  70  Time(hour)  Figure 4.7 Moisture content of paraffin wax coated and untreated pellets placed in the environment chamber s for 72 hours.  50  Chapter 5: Results and Discussion-Plasma Treatment This chapter is dedicated to the results of testing the performance of Plasma Enhanced Chemical Vapor Deposition (PECVD) and oxygen etching on resistance of pellets to water ingress and water vapor adsorption.  5.1 Interaction with Liquid Water In the following section, the effect of plasma treatment on wood pellet interaction with liquid water is presented and discussed. 5.1.1 Hydroscopicity Test on Plasma Treated Wood Pellets Table 5.1 lists all combination of plasma treatment hydroscopicity test results. All treatments except O2 etching without CF4 deposition step increased stability of wood pellets in water. O2 etched and untreated wood pellets disintegrated after 2-3 minutes of immersion in water. CF4 deposition on the surface with the prior O2 etching step created the most durable pellet in water which kept its shape for 40-45 minutes. The results for treatment 1, 2, and 3 represent the effect of flow rate on wood pellet hydroscopicity. All the three treatments (1, 2 and 3) were conducted at pressure of 1000 mtorr and power of 200 W for 1200 seconds so the only difference between 3 wood pellet categories was their flow rates. CF4 deposition was performed at three levels of flowrate including 40cm3/min (Treatment1), 30cm3/min (Treatment 2) and 20cm3/min (Treatment 3). Wood pellets treated by PECVD using CF4 at flowrate of 40cm3/min showed the most stability in liquid water and they could keep their shape in water for at least 20-25 minutes. Treatment 2 and treatment 3 were conducted at flowrate of 30cm3/min and 20cm3/min, respectively. The wood pellets treated at flowrate of 30cm3/min could hold their shape in water for more than 10-15 minutes while wood pellets treated at flowrate of 20cm3/min did not show any evidence of hydrophobicity. By increasing feed flowrate, the wood pellet hydrophobicity was increased. 5.1.2 Plasma Treatment Effect on Static Water Contact Angle Table 5.2 lists contact angles for plasma treated wood pellets. The CF4 deposition increased wood pellet surface hydrophobicity. In addition, an increase in CF4 flowrate 51  increased wood pellet water droplet contact angle and water repellency. This is in agreement with earlier finding that as the CF4 flowrate increased, the hydrophobicity of treated paper was enhanced (Mirvakili, 2011). Although there was a minor difference between the contact angles of droplets on CF4 deposited wood pellets and contact angles of the pellets etched first and treated with CF4 plasma, the second group had larger contact angle. This result is in accordance with the result obtained from hydroscopicity test that CF4 deposition plus O2 etching creates the most hydrophobic wood pellet. The O2 etching without CF4 deposition step on surface of wood pellets rendered the treated wood pellets hydrophilic. Laurence et al. (2000) observed the same behaviour for their pine wood samples, and a lower contact angle values after oxygen plasma treatment. These results are in agreement with previous publication by Carlsson et al. (1991a, 1995). They treated the surface of kraft and bisulfite pulp sheets with oxygen plasma method. They reported that oxygen plasma rendered the surface hydrophilic due to the oxidation of extractives and lignin present on the substrate surfaces and consequent enrichment of the carboxylic acid groups. As discussed before, lignin and extractives are hydrophobic compared to the amorphous cellulose and hemicellulose. 5.1.3 Water Droplet Uptake Time Figure 5.1 shows the time interval from the impact of the droplet to the complete penetration of the droplet in wood pellet. The uptake time of a water droplet was increased after CF4 deposition while O2 etching without CF4 deposition step shortened the water droplet sorption time. On average, it took  s  μL  s  z  water to penetrate into a CF4 and O2 etched pellet in comparison with untreated pellet that absorbed water droplet in 1-2 minutes. Figure 5.2 depicts liquid water penetration in untreated and CF4 deposited plus O2 etched wood pellet surface, respectively. Figure 5.3 to Figure 5.6 represent SEM results for samples before and after plasma treatment. The surface of untreated pellets had mild cracks which appeared randomly. The O2 etching created a porous surface for fast water droplet penetration. Balu et al. (2008) reported that through O2 etching process, oxygen species including O· (oxygen atom radical) and O*(oxygen ion) react with cellulose to produce CO2, CO, and water vapor. This process leads to material removal from the amorphous domain and leave the 52  crystalline part intact (Balu et al., 2008). No apparent difference between the SEM images of CF4 deposited wood pellet and uncoated wood pellet was detectable. CF4 deposition on the O2 etched surface of wood pellet made the roughed, etched surface smoother with uniform features (Figure 5.6). It also partially connected bumps created by oxygen etching. This surface structure can be the reason of surface hydrophobicity. 5.1.4 Swelling If a pellet resists well to water, it stays intact and does not swell when submerged. Figure 5.7 shows the test results of swelling for CF4 deposited and CF4 plus O2 etched wood pellet compared to untreated pellets. The results showed that untreated pellet swelling was 16-17% while CF4 deposited wood pellet swelling value was approximately 11%-12% during 1 minute immersion in water. CF4 deposition plus O2 etching created the pellet which had the least swelling value during immersion which is less than 2 %.  5.2 Effect of Plasma Treatment on Wood Pellet Hygroscopicity It was observed that although the CF4 deposited and CF4 deposited plus O2 etched wood pellets are hydrophobic and exhibit very good liquid water repellency, the treated surfaces do not form a good water vapour barrier. Figure 5.8 is a bar chart that shows the moisture content of CF4 deposited, CF4 deposited plus O2 etched and untreated pellet located in humid chamber for 72 hours. The results show that the final moisture content of treated and untreated wood pellets were the same. Figure 5.9 and Figure 5.10 show moisture adsorption of CF4 deposited and CF4 deposited plus O2 etched wood pellets versus time from humid air for 72 hours. It is clear in the figures that the plots for treated and untreated wood pellets are the same. These results are in agreement with earlier data obtained by Magalhaes et.al (2001). They found that film deposition by plasmapolymerization on solid soft wood increases wood hydrophobicity, but it does not prevent water vapor adsorption. The results in Table 5.3 are in agreement with hygroscopicity test results. Table 5.3 lists the water vapor diffusion coefficient and the porosity for wood pellets before and after CF4 deposition. The results indicate that the rate of moisture adsorption is the same for CF4 deposited and untreated wood pellet. Furthermore, porosity 53  of treated and CF4 deposited wood pellet clarify that CF4 deposition did not impact wood pellet porosity significantly, and it did not block the pores on the surface of wood pellet to avoid nitrogen penetration through the void spaces.  5.3 Coating Effect on Surface Morphology- FTIR Figure 5.11 represents the spectrum for untreated and CF4 deposited wood pellet at flowrate of 40 cm3/min. It is difficult to find a clear difference between untreated samples and CF4 deposited wood pellet IR spectrum. Sahin et al. (2007) reported that CFx molecules covalently bond to paper surface, and the presence of the absorption band in the 1100-1500 cm-1 region confirms the presence of fluorocarbon film on the surface. Balu (2009) reported that bands at 1200 cm-1 (CFx stretch) and 1700 cm-1 (unsaturated fluorocarbon bonds) represent the presence of a fluorocarbon film. The C-O deformation (1100-1260 cm-1) overlap with CFx spectrum band (11001400 cm-1). As a result, comparing C-O and CFx FTIR absorption of fluorinated surface of paper, which includes in their structures C-O bonds, is difficult (Cruz-Barba et.al, 2002). Another reason that a clear difference is not considerable can be explained by the fact that CF4 is just deposited on the very thin surface layer (100 A) and spectral feature of underlying bulk volume can affect the result (Toriz et al 2005). Hence, underlying surface of the sample dominated the IR signatures (Cruz-Barba et.al, 2002). In Figure 5.11, a new absorption bands at 1739 cm-1 confirms the presence of fluorocarbon bonds on the surface of CF4 deposited wood pellet. The absorption band at 3341 cm-1 (OH stretch), 2924 cm-1 (C-H stretch), 1488 cm-1 (C-H deformation), 1027 cm-1 (C-O stretch) are detected. Furthermore, the absorption band at 3341 cm-1 (OH stretch) is supressed in treated pellet compared to the untreated pellet which can be explained by the fact that hydroxyl groups present on the surface of wood pellet has been reduced. The vibration band at 3100-3500 cm-1 is caused by vibration of alcoholic and phenolic OH groups in lignin involved in hydrogen bond and OH stretch. The 1500-1515 cm-1 band was solely attributed to the presence of aromatic ring vibration of lignin (Pandey, 1998; Bycove, 2008). The FTIR spectra for CF4 treated and untreated pellets are provided in Appendix F. 54  5.4 Discussion It was observed that CF4 deposition via Plasma Enhanced Chemical Vapor Deposition (PECVD) increased wood pellet surface hydrophobicity which was proved through water contact angle measurement, swelling test, liquid water uptake time and hydroscopicity test. O2 etching increased wood pellet surface hydrophilic property. Hence, roughness is not sufficient to render wood pellet surface hydrophobic, and the inherently hydrophilic cellulose fibers must also be treated with CF4. Moreover, the results demonstrated that CF4 deposition at flowrate of 40 cm3/min after O2 etching created the surface with the largest water contact angle, droplet uptake time, and disintegration time in comparison with wood pellets that were untreated or only treated with CF4. Although plasma treatment increased water repellency, it did not have any effect on water vapor adsorption from air. The cylindrical shape of wood pellets was a barrier for measuring contact angle. The surface should be flat for precise contact angle measurement. The results can give an estimation of hydrophobicity of surfaces and help us to compare untreated and treated wood pellets. However, wood pellets water contact angles cannot be compared with other flat surfaces contact angles such as paper to draw any conclusion. Besides, the water droplet should be placed on top of the cylindrical circumference which could not be done precisely.  55  Table 5.1 Appearance of wood pellets treated with plasma during 30 minutes immersion in water Time CF4 CF4 CF4 O2 etched O2 etched (min) deposited deposited deposited (treatment 4) and CF4 (treatment 1) (treatment 2) (treatment 3) deposited 0-3 1 1 1 1 1 3-6 1 1 2 6 1 6-10 1 2 2&5 6 1 10-15 1 2&5 6 6 1 15-20 1 6 6 6 1 20-25 2&5 6 6 6 1 25-30 6 6 6 6 2&5&4 Category 1: There is no change on the pellet. Category 2: Wood particles separate from the wood pellet surface. Category 3: Mild cracks on the surface of pellets appear. Category 4: Lots of cracks on the surface of pellets are visible. Category 5: Pellets swell. Category 6: Pellets disintegrate.  56  Table 5.2 Contact angles of droplets before and after plasma treatment. The single water droplet is placed on the surface of a single pellet. Condition Method Static contact angle 1 CF4 PECVD 114.55 ±11.70 2 CF4 PECVD 106.93 ±15.59 3 CF4 PECVD Hydrophilic 4 O2 etching Hydrophilic 5 CF4 deposited &O2 etched 115.76 ±19.17 Table 5.3 Porosity and diffusion coefficient of water penetration into pellets for CF4 treated pellets. Pellets are placed in humid environment for diffusion coefficient measurement. Coating Diffusion coefficient Porosity 2 (m /hr.) (%) Untreated 7.58E-08±1.33E-08 24.54±1.93 CF4 deposited 7.70E-08±1.19E-08 24.32±1.33  Water Uptake Time(min)  15  10  5  a Untre 0  ted  ed  sit ed ed Depo posit F e 4 C D s CF 4 Plu ched O 2Et  tch O2E  Figure 5.1 Effects of treatment with Plasma on wood pellet water uptake time. Wood pellets are immersed in water.  57  (a)  (b) Figure 5.2 Water droplet penetration in (a) untreated wood pellet, (b) O2 etched plus CF4 treated wood pellet  Figure 5.3 SEM picture of untreated wood pellet. Cracks and fissures are visible spreading randomly on the surface of untreated wood pellet.  58  Figure 5.4 SEM picture of O2 etched wood pellet. The O2 etching removed part of the surface. The remaining part is a rough surface that absorbed water in less than 1 min.  Figure 5.5 SEM picture of CF4 deposited wood pellet. CF4 was deposited at flow rate of 40 cm3/min. The CF4 treated surface exhibited less cracks compared to the untreated surface.  59  Figure 5.6 SEM picture of O2 etched and CF4 deposited wood pellet. First, mild O2 etching was performed on the surface. Then, CF4 was deposited. The condition for CF4 deposition was treatment 1 in Table 3.1. Most of the cracks disappeared. The O2 etched and CF4 deposited wood pellet surface was more hydrophobic than CF4 treated alone.  20  Swelling(%)  15  10  5  d  ite os  0  ate tre  Un  F4  d  p De  C lus P ed ch  d site po  De CF 4  O2  E  Figure 5.7 Effect of CF4 deposition and O2 etching on wood pellet swelling when the pellet is immersed in water.  60  Moisture Content(%)  15  10  5  0  d  d  ate  tre Un  CF 4  D  o ep  e sit  s Plu O2  CF 4  Figure 5.8 Moisture content of treated and untreated wood pellet placed in the environment chamber set at 30 C, 90% relative humidity after 72 hours 20  Treated Untreated  18  Moisture content (%)  16 14 12 10 8 6 4 2 0 0  10  20  30  40  50  60  70  Time(hour)  Figure 5.9 Moisture content of CF4 treated and untreated pellets placed in the environment chamber set at 30 C, 90% relative humidity. No effect on reducing the hygroscopicity of treated pellets was observed.  61  20  Treated Untreated  18  Moisture content (%)  16 14 12 10 8 6 4 2 0 0  10  20  30  40  50  60  70  Time(hour)  Figure 5.10 Moisture content of O2 etched and CF4 deposited wood pellet at flowrate of 40 cm3/min and untreated pellets placed in the environment chamber set at 30oC, 90% relative humidity for 72 hours. No effect on reducing the hygroscopicity of treated pellets was observed.  62  0.07 0.06  CF4 deposited wood pellet Untreated wood pellet  Absorbance  0.05 0.04 0.03 0.02 0.01 0.00 4000  3500  3000  2500  2000  1500  1000  Wave number(cm-1)  Figure 5.11 FTIR of the untreated and treated pellet surface with CF4. The presence of a new band at 1739 cm-1 in CF4 deposited wood pellet spectrum confirms the presence of fluorocarbon bonds on the surface of treated pellet.  63  Chapter 6: Conclusion and Future Work Even though the importance of wood pellet dust generation and water adsorption has been noted many times, less attention has been paid to the use of coatings as a water vapor and liquid water barrier. The scope of this thesis was to investigate the effect of different coating solution and plasma treatment including CF4 deposition and O2 etching on wood pellet moisture adsorption from both liquid water and a humid environment. Commercial wood pellets were coated with different coating solutions including canola oil, mineral oil, linseed oil, cellulose acetate, molten paraffin wax, ethyl 2-cyanocrylate, bis (triethoxysilyl)ethane and octadecyltriethoxysilane. The effect of each solution on hydrocscopicity and hygroscopicity of wood pellets were evaluated. Ethyl 2-cyanocrylate coated wood pellets were the most durable pellet in water and paraffin wax created the most impermeable coating around individual pellets which protected wood pellets from moisture adsorption in a humid environment. Based on the experimental results, CF4 deposition on the surface of wood pellet which had been exposed to O2 created the most hydrophobic wood pellet compared to other plasma treatment conditions. Increasing the amount of CF4 flowrate led to the decrease in wood pellet hydroscopicity. Moreover, it was observed that CF4 deposition on the surface of wood pellets did not impact the porosity of wood pellet to avoid nitrogen penetration into the void spaces of wood pellets. It is concluded that a hydrophobic surface can still absorb moisture from humid air. Wood pellet surface should be rendered hydrophobic by decreasing surface energy and creating roughness to avoid wood pellet disintegration during the rain, while this is not adequate to avoid water vapor adsorption from humid environment. The wood pellet pores should be blocked with an impermeable membrane to stop water vapor adsorption. The hygroscopicity and hydroscopicity test on torrefied pellets has shown the same results. Torrefied wood pellets keep their shape in water for a long period of time while they still adsorb moisture from humid environment. The water vapor adsorption of torrefied wood pellet can be the reason of porosity because torrefied wood pellets are more porous compared to regular wood pellets.  64  Recommendations for future work This research is the first attempt to render wood pellets water repellent with a post treatment process. Hence, further investigation needs to be conducted to find a coating solution which is protective and cost effective.  1- To produce wood pellets, the ground particles are squeezed through the holes of a die under high pressure. The pressure causes lignin reformation which binds wood particles. It is important to know whether the shiny surface of wood pellet composition is the same as the wood particles composition or it has more lignin. The chemical composition of wood pellet surface needs to be analyzed. 2- It was shown that plasma treatment with specific condition rendered wood pellets hydrophobic. The durability of the CF4 coatings through long-term aging experiments, and after natural weathering needs to be investigated. 3- The depth of permeation of CF4 plasma treatment in paper is estimated to be 100nm but there is no previous study on CF4 penetration into the wood pellet. 4- The effect of coating on wood pellets dust generation is not well understood so designing a small tumbler to measure wood pellet durability before and after treatment needs to be investigated. 5- For future work, additional experiments can be carried out to clarify the effect of wood pellet size and coating level on moisture adsorption. 6- There is no evidence to show whether any covalent bond is created between each coating solution and wood pellet surface. Chemical reactions happened on the surface of wood pellets after coating with various solutions can be studied. 7- Dip coating was used in this thesis because the goal was to find potential coating material. 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Journal of Colloid and Interface Science, 18 (22): 3662–3669.  72  Appendix A: Coating Solution Characteristics Table A.1 Coating material and characteristics Coating Material  State  Canola oil (Rapeseed oil)  Liquid  Application Oleic Acid (61%), Linoleic acid (21%)  1-Food 2-Biodisel 3-Fruit coating  Oleic Acid Linoleic Acid Linseed oil (Flaxseed oil)  Liquid  1-Wood finish 2-Wood preservation  Triglyceride in linseed oil Paraffin wax  Solid mp:57°C  Mixture of Alkanes in the C20-C40  73  1-Candle making 2-Cloth coating  Coating Material  State  Application  Silicone fluid  Liquid  1-used as Lubricants 2-used as hydraulic Fluids  Ethyl 2-cyanoacrylate  Liquid  1-Main component of glue 2- Used in liquid bandage  n-octadecyl triethoxysilane  Liquid  Octadecyl silanes are commonly used to modify a surface to make it hydrophobic (Gelest Company).  74  Coating Material  State  Application  1,2bis (triethoxysilyl)ethane  Liquid  Six alkoxy are reactive groups. The dipodal will crosslink all over the surface to reduce dust (Gelest Company).  Cellulose acetate  Solid powder  1-Tablet coating  75  Appendix B: Experimental Data Condition  1 2 3 5  Table B.1 Treated and untreated wood pellet contact angle relevant to Table 4.2 and Table 5.2 Treated and Untreated S1 S2 S3 S4 Average STDV Pellets  Untreated Canola oil Cellulose acetate CF4 deposited CF4 deposited CF4 deposited CF4deposited &O2 etched S : Sample  74.22 82.56 71.89 110.22 96.18 102.43 133.43  69.59 87.78 68.07 111.37 97.82 111.26 112.89  70.82 83.82 71.40 125.55 98.31 118.17 110.03  76  72.96 86.50 69.00 111.04 90.35 95.86 106.7  71.90 85.17 70.09 114.55 95.67 106.93 115.76  2.08 2.40 1.85 7.35 3.66 9.80 12.05  STDV with %95 confidence 3.31 3.81 2.94 11.70 5.82 15.59 19.17  Table B.2 Moisture adsorption (wt.%) of s Time(hour) S1 S2 S3 S4  0.0 1.0 1.5 4.0 6.0 8.0 22.5 24.5 29.0 31.5 46.0 53.0 70.0 72.0  0.00 76.60 77.58 81.48 82.87 83.98 88.02 88.02 88.30 88.58 88.86 89.00 89.00 89.14  0.00 3.17 4.08 7.25 8.91 10.27 14.20 14.35 14.80 15.11 15.56 15.71 16.01 16.01  0.00 3.25 4.29 7.89 9.63 10.79 14.85 14.97 15.31 15.66 15.89 16.24 16.24 16.36  0.00 3.11 4.14 7.54 9.17 10.36 14.35 14.50 14.79 15.24 15.53 15.98 15.98 5.83  Table B.3 Moisture adsorption (wt.%) s Time(hour) S1 S2 S3 S4  0.5 1 1.5 21 23 25 27 45 50 69.5 72  0.30 0.45 0.90 4.22 4.37 4.67 4.82 6.48 6.78 8.13 8.28  0.38 0.63 1.00 5.13 5.51 5.63 5.88 7.76 8.01 9.51 9.76  0.27 0.27 0.68 4.09 4.22 4.50 4.63 6.27 6.54 8.17 8.04  0.37 0.49 0.62 5.80 6.29 6.66 7.03 10.60 11.34 14.55 14.43  s S5  0.00 2.95 3.76 6.61 8.03 9.55 13.92 14.02 14.63 14.74 15.35 15.55 15.65 15.65  S5  0.15 0.31 0.46 4.29 4.60 4.75 4.91 6.75 7.06 8.59 8.59  77  Average  0.00 3.12 4.07 7.32 8.94 10.24 14.33 14.46 14.89 15.18 15.58 15.87 15.97 15.96  Average  0.29 0.43 0.73 4.71 5.00 5.24 5.45 7.57 7.95 9.79 9.82  .5 to 4.7 STDV  0.00 0.13 0.22 0.54 0.67 0.51 0.39 0.39 0.30 0.38 0.23 0.30 0.24 0.30  STDV with %95 confidence 0.00 0.16 0.28 0.68 0.84 0.64 0.48 0.49 0.37 0.47 0.28 0.38 0.30 0.37  Figure 4.5 STDV STDV with %95 confidence 0.08 0.10 0.13 0.16 0.20 0.24 0.66 0.82 0.78 0.97 0.81 1.01 0.90 1.12 1.60 1.99 1.77 2.20 2.43 3.02 2.38 2.95  s  Table B.4 Moisture adsorption (wt. %) s Time S1 S2 S3 S4 S5 (hour) 0 1 1.5 4 6 8 22.5 24.5 29 31.5 46 53 70 72  0.00 1.27 1.90 4.69 6.08 7.73 13.18 13.56 14.20 14.70 15.46 15.72 15.97 15.97  0.00 1.64 2.02 4.68 6.19 7.84 13.15 13.53 14.16 14.54 15.30 15.80 16.06 16.06  0.00 1.63 2.33 5.13 6.88 8.62 13.75 13.99 14.57 15.03 15.50 15.73 15.97 15.73  0.00 0.96 1.38 3.40 4.56 6.05 10.83 11.15 11.89 12.10 13.06 13.27 13.69 13.69  Table B.5 Moisture adsorption (wt.%) s Time(hour) S1 S2 S3 S4  0.5 1 1.5 21 23 25 27 45 50 69.5 72  0.00 0.00 0.00 0.23 0.23 0.23 0.23 0.68 0.23 0.68 0.90  0.00 0.00 0.00 0.00 0.00 0.21 0.21 0.21 0.21 0.41 0.62  0.00 0.00 0.00 0.21 0.21 0.21 0.42 0.63 0.63 1.05 1.05  0.27 0.14 0.27 2.20 2.34 2.47 2.61 4.12 4.40 5.91 6.18  Average  0.00 1.06 1.59 3.72 4.99 6.48 12.00 12.31 12.95 13.16 14.33 14.86 15.07 15.07  S5  0.14 0.00 0.14 0.57 0.57 0.71 0.71 1.28 1.42 2.13 2.27  78  0.00 1.31 1.85 4.32 5.74 7.34 12.58 12.91 13.55 13.91 14.73 15.08 15.35 15.31  Figure 4.6 STDV STDV with %95 confidence 0.00 0.00 0.28 0.35 0.33 0.41 0.65 0.81 0.84 1.05 0.94 1.17 1.05 1.30 1.04 1.29 0.99 1.23 1.11 1.37 0.94 1.17 0.97 1.20 0.90 1.12 0.88 1.09  s Figure 4.7 Average STDV  0.08 0.03 0.08 0.64 0.67 0.77 0.83 1.38 1.38 2.04 2.21  0.11 0.05 0.11 0.80 0.85 0.87 0.91 1.41 1.57 2.02 2.07  STDV with %95 confidence 0.14 0.07 0.14 0.99 1.06 1.09 1.12 1.75 1.95 2.51 2.56  s  Table B.6 Moisture adsorption (wt.%) of CF4 Time(hour)  0 1 1.5 4 6 8 22.5 24.5 29 31.5 46 53 70 72  S1  S2  0.00 2.87 3.87 7.00 8.50 9.87 14.00 14.25 14.62 14.88 15.50 15.50 15.62 15.75  0.00 3.29 4.43 8.23 9.75 11.01 15.06 15.32 15.70 15.70 16.08 16.20 16.33 16.33  S3  0.00 3.39 4.28 7.96 9.59 11.06 14.90 15.34 15.63 15.63 16.08 16.08 16.52 16.52  Figure 5.9 Average  S4  S5  0.00 2.71 3.62 6.85 8.40 9.95 14.21 14.47 14.99 14.99 15.63 15.76 16.02 16.02  0.00 2.18 2.99 6.09 7.47 8.85 13.56 13.79 14.25 14.37 15.29 15.40 15.75 15.86  0.00 2.89 3.84 7.23 8.74 10.15 14.35 14.63 15.04 15.11 15.71 15.79 16.05 16.10  STDV  0.00 0.43 0.51 0.78 0.84 0.82 0.56 0.61 0.56 0.50 0.32 0.31 0.34 0.29  STDV with %95 confidence 0.00 0.54 0.64 0.97 1.04 1.02 0.70 0.75 0.70 0.62 0.39 0.39 0.42 0.36  Table B.7 Moisture adsorption (wt.%) of O2 etched and CF4 deposited wood pellet at flowrate of 40cm3/min and untreated pellets placed in the environment chamber set at 30oC, 90% RH relevant to Figure 5.10 Time(hour) S1 S2 S3 S4 S5 Average STDV STDV with %95 confidence 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1 2.88 3.59 3.19 2.74 2.68 3.02 0.34 0.40 1.5 3.89 4.52 4.21 3.50 3.81 3.99 0.35 0.42 4 7.35 8.42 7.40 6.69 7.20 7.41 0.57 0.68 6 8.65 9.98 9.14 8.36 8.90 9.01 0.55 0.66 8 10.09 11.23 10.16 9.57 10.31 10.27 0.54 0.65 22.5 14.27 15.13 13.93 13.98 14.27 14.32 0.43 0.52 24.5 14.55 15.60 14.08 14.44 14.55 14.64 0.51 0.61 29 14.84 15.76 14.22 14.74 14.83 14.88 0.49 0.59 31.5 14.84 15.91 14.51 15.20 15.25 15.14 0.47 0.56 46 15.56 16.38 14.95 15.50 15.82 15.64 0.47 0.56 53 15.85 16.38 14.95 15.81 16.10 15.82 0.48 0.57 70 15.85 16.69 15.09 16.11 16.24 16.00 0.53 0.63 72 15.99 16.85 15.38 16.11 16.24 16.12 0.47 0.56  79  Appendix C: Hygroscopicity Test Results for Coated Pellets 20  Treated Untreated  18  Moisture content (%)  16 14 12 10 8 6 4 2 0 0  10  20  30  40  50  60  70  Time(hour)  Figure C.1 Moisture adsorption of ethyl 2-cyanocrylate coated and untreated pellets placed in the environment chamber set at 30 C, 90% relative humidity  80  20  Treated Untreated  18  Moisture content (%)  16 14 12 10 8 6 4 2 0 0  10  20  30  40  50  60  70  Time(hour)  Figure C.2 Moisture adsorption of bis(triethoxysilyl)ethane s relative humidity  s  20  Treated Untreated  18  Moisture content (%)  16 14 12 10 8 6 4 2 0 0  10  20  30  40  50  60  70  Time(hour)  Figure C.3 Moisture adsorption of octadecyltriethoxysilane and untreated pellets placed in the environment chamber set at 30oC, 90% relative humidity  81  20  Treated Untreated  18  Moisture content (%)  16 14 12 10 8 6 4 2 0 0  10  20  30  40  50  60  70  Time(hour)  Figure C.4  s  s  s s  s relative humidity  20  Treated Untreated  18  Moisture content (%)  16 14 12 10 8 6 4 2 0 0  10  20  30  40  50  60  70  Time(hour)  Figure C.5  s  s  s  s s  relative humidity  82  20  Treated Untreated  18  Moisture content (%)  16 14 12 10 8 6 4 2 0 0  10  20  30  40  50  60  70  Time(hour)  Figure C.6 Moisture adsorption of mineral oil coated and untreated pellets placed in the s relative humidity  83  Appendix D: Physical Characteristics of Coating Solution  Canola Oil Mineral oil ECA BTE Silicon oil Molten wax Linseed oil OTES CA solution  Table D.1 Viscosity and density of coating solutions at two different temperatures Viscosity at T1 Viscosity at T2 Density at T1 Density at T2 3 (cP) (cP) (gr/cm ) (gr/cm3) 57.00 (25 C) 33.00 (40 C) 0.91 N/A 15.30 (25 C) N/A 0.76 N/A N/A N/A 1.04 N/A N/A N/A 0.96 (25 C) N/A 48.00 (25 C) 38.20 (40 C) 0.97 (25 C) 0.95 (40 C) 21.00-22.00 (65 C) 4.20-7.40 (98 C) 0.87-0.91 (25 C) 0.77-0.78 (75 C) 33.10cp (27 C) N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A  84  Measured density (gr/cm3) 0.81 0.82 1.00 0.88 0.89 0.76 0.90 0.88 0.76  Appendix E: Coating Thickness Table E.1 Coating thickness calculated from experimental data for dipping method S1 S2 S3 S4 S5 Linseed oil thickness (mm) 0.20 0.18 0.30 0.26 0.18 Silicone oil thickness (mm) 0.20 0.20 0.21 0.13 0.16 Octadecyltriethoxysilane thickness (mm) 0.15 0.19 0.22 0.23 0.26 Bis(triethoxysilyl)ethane thickness (mm) 0.22 0.18 0.18 0.19 0.47 Mineral oil thickness (mm) 0.23 0.16 0.18 0.20 0.19 Cellulose acetate thickness (mm) 0.07 0.07 0.08 0.11 0.10 Paraffin wax thickness (mm) 0.21 0.17 0.28 0.18 0.20 Ethyl 2-cyanoacrylate thickness (mm) 0.17 0.14 0.14 0.14 0.15  85  Appendix F: ATR-FTIR Spectra  Figure F.1 FTIR of CF4 deposited wood pellet  86  Figure F.2 FTIR of untreated wood pellet  87  

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