"Forestry, Faculty of"@en . "DSpace"@en . "UBCV"@en . "Filler, Merl Campbell"@en . "2012-01-06T06:08:57Z"@en . "1961"@en . "Master of Forestry - MF"@en . "University of British Columbia"@en . "Three particle boards, one flake board, one multi-layer board, and a plywood panel, all of 3/8-inch thickness, were overlaid with 1/20-inch Philippine mahogany veneer, using a urea-formaldehyde adhesive. Both non-overlaid and overlaid boards were subjected to physical and mechanical tests involving the glue line and the boards themselves.\r\nResults of the glue-line shear test indicated that glue-line failure between the veneer and the boards only occurred in the boards of higher density. Overlaying the boards decreased dimensional change in a plane parallel to the length of the board but slightly increased it parallel to the width of the board. Boards composed of flakes had better strength properties than those composed of particles. No delamination of the board occurred during accelerated aging; however, deterioration in the board core was extensive.\r\nIn general, overlaying the boards tended to minimize differences in strength properties between boards, and improved the strength properties so as to be almost comparable to those of plywood. Overlaying decreased warping in the boards. Some physical properties of the boards, such as resistance to warping and face-checking, were more satisfactory than those of plywood."@en . "https://circle.library.ubc.ca/rest/handle/2429/39899?expand=metadata"@en . "COMPARATIVE EVALUATION OP SOME PHYSICAL AND MECHANICAL PROPERTIES OP VENEER-OVERLAID AND NON-OVERLAID PARTICLE BOARD b y MERL C. FILLER, JR. B.S. 6f Wood U t i l i z a t i o n , 1956 Pennsylvania State U n i v e r s i t y A Thesis submitted i n p a r t i a l f u l f i l m e n t of the requirements f o r the Degree of Master of Forestry i n the Faculty of F o r e s t r y We accept t h i s t h e s i s as conforming to the standard required from candidates f o r the Degree of Master of Forestry Members of the Faculty of Forestry The U n i v e r s i t y of B r i t i s h Columbia A p r i l 1961 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r a n a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l m a k e i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s m a y b e g r a n t e d b y t h e H e a d o f my D e p a r t m e n t o r b y h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t b e a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , V a n c o u v e r #, C a n a d a . i i ABSTRACT Three p a r t i c l e boards, one flake board, one m u l t i - l a y e r board, and a plywood panel, a l l of 3 / 8 - i n c h thickness, were o v e r l a i d with 1 / 2 0 - i n c h P h i l i p p i n e mahogany veneer, using a urea-formaldehyde adhesive. Both non-overlaid and o v e r l a i d boards were subjected to p h y s i c a l and mechanical t e s t s i n v o l v i n g the glue l i n e and the boards themselves. Results of the g l u e - l i n e shear t e s t i n d i c a t e d that glue-, l i n e f a i l u r e between the veneer and the boards only occurred i n the boards of higher density. Overlaying the boards decreased.dimensional change i n a plane p a r a l l e l to the length of the board but s l i g h t l y increased i t p a r a l l e l to t. the width of the board. Boards composed of fl a k e s had b e t t e r strength p r o p e r t i e s than those composed of p a r t i c l e s . No delamination of the board occurred during accelerated aging; however, d e t e r i o r a t i o n i n the board core was extensive. In general, overlaying the boards tended to minimize di f f e r e n c e s i n strength properties between boards, and improved the strength properties so as to be almost com-parable to those of plywood. Overlaying decreased warping i n the boards. Some p h y s i c a l properties of the boards, such as resistance to warping and face-checking, were more s a t i s f a c t o r y than those of plywood. i i i ACKNOWLEDGEMENT Acknowledgement i s made to William R. Prancis of the Simpson Logging Company who i n s p i r e d the i n i t i a l work on t h i s t h e s i s , and to Dr. R.W. Wellwood of the U n i v e r s i t y of B r i t i s h Columbia under whose.guidance the project was conducted and c a r r i e d to completion. Thanks are due to L e s l i e Paszner f o r assistance i n t e s t i n g and i n gathering data, to Dr. J.H.G. Smith f o r a i d i n analyzing the s t a t i s t i c s , and to Mr. R.W. Kennedy f o r reviewing the manuscript. The author i s g r a t e f u l to Messrs. H.G.M. Colbeck, W.V. Hancock, W.M. McGowan, P.L. Northcott, and W.J. Smith of the Porest Products Laboratories of Canada, Vancouver, f o r assistance i n the overlaying and t e s t i n g phase of the p r o j e c t . Acknowledgement and thanks are made to the suppliers of p a r t i c l e hoards and plywood, and to Monsanto Canada Limited, Vancouver, f o r f u r n i s h i n g the adhesive, and f o r making a v a i l a b l e t h e i r t e s t i n g equipment. i v ) TABLE OF CONTENTS Page INTRODUCTION . . . . . 1 MANUFACTURING PROCESS 5 PRODUCT VARIABLES 11 Species s e l e c t i o n and preparation 11 Adhesive materials 14-Curing conditions 16 Product properties 17 Density 17 Dimensional s t a b i l i t y 18 P a r t i c l e and fl a k e o r i e n t a t i o n 20 Nail- h o l d i n g a b i l i t y 21 Strength properties . 22 PROCEDURE 24-Procurement of material 24-Preliminary overlaying 26 F i n a l lay-up 30 TEST METHODS AND PROCEDURES 33 Glue-line shear 34-Mechanical t e s t s other than g l u e - l i n e shear . . . . 34-Physical t e s t s 4-3 Accelerated aging 4-7 Page DISCUSSION OP RESULTS 48 Glue-line shear 48 Tension p a r a l l e l to length and width of surface . . 51 S t a t i c bending 54 Modulus of rupture 54 Modulus of e l a s t i c i t y 55 L a t e r a l n a i l resistance 57 Nail-withdrawal resistance . . . 58 Dimensional change 59 Warping 62 Accelerated aging 65 CONCLUSIONS AND RECOMMENDATIONS 68 BIBLIOGRAPHY 71 APPENDICES 74 A. Tension P a r a l l e l to Surface of Non-overlaid and Overlaid Boards and Plywood B. Analysis of Variance of Tension P a r a l l e l to Surface as Af f e c t e d by Overlay and Grain D i r e c t i o n C. Modulus of Rupture of Non-overlaid and Overlaid Boards and Plywood D. Analysis of Variance of Modulus of Rupture as Aff e c t e d by Overlay and Grain D i r e c t i o n E. Modulus of E l a s t i c i t y of Non-overlaid and Overlaid Boards and Plywood v i Page P. Analysis of Variance of Modulus of E l a s t i c i t y as A f f e c t e d by Overlay and Grain D i r e c t i o n G. L a t e r a l N a i l Resistance of Non-overlaid and Overlaid Boards and Plywood H. Analysis of Variance of L a t e r a l N a i l Resistance as A f f e c t e d by Veneer-overlay I. Nail-withdrawal Resistance of Non-overlaid Boards and Plywood J. Analysis of Variance of Nail-withdrawal Resistance as A f f e c t e d by Veneer-overlay v i i LIST OF TABLES Table Page I. Moisture Content and Specific Gravity of Boards 27 II. Amount of Delamination Occurring i n 4 - by 4 -inch Samples of Overlaid Board after 3 Cycles of a 4-hour Soak and a 20-hour Dry at 95\u00C2\u00B0F . . . 29 III. Thicknesses of Boards and Veneer Before and After Pressing 29 IV. Glue-line Shear Test 49 V. Analysis of Variance for Glue-line Shear Test 49 VI. A. Summary of Mechanical Properties of Non-overlaid Board 52 B. Summary of Mechanical Properties of Overlaid Board 52 VII. Dimensional Change i n Thickness and Length of Panels Between 75 and 25 Percent Relative Humidity 60 VIII. Warping in Panels at 75 and 25 Percent Relative Humidity 63 v i i i LIST OF FIGURES Figure Page 1. Schematic Drawing of Miller-Hofft Multi-Platen Particle or Flake Board Manufacturing Process 6 2. Interwood Glue Spreader Used for Applying Adhesive to Boards 31 3. Berthelson Oil-heated Hot-press for Bonding Veneer to Particle Boards 31 4. Cutting Plan of 2- by 4-foot Non-overlaid and Veneer-overlaid Boards and Plywood 35 5. Tinius Olsen Universal Testing Machine 37 6. Typical Load-deflection Curves 40 7. Lateral Nail Resistance Test Assembly 42 8. Nail-withdrawal Test Assembly 42 9. Method Used for Measuring Twist i n Panels . . . . 45 10. Thickness Measuring Micrometer Dial 46 11. Types of Failure Occurring in Tension P a r a l l e l . . 46 12. Accelerated Aging Samples 67 1 INTRODUCTION During the summer of 1959\u00C2\u00BB at which time the author worked f o r the Simpson Logging Company of Shelton, Washington, a project was undertaken i n v o l v i n g the overlaying of p a r t i c l e board with veneer. A l i t e r a t u r e survey at that time, and a current one i n conjunction with t h i s study, revealed l i t t l e information a v a i l a b l e on the ph y s i c a l and mechanical properties of o v e r l a i d p a r t i c l e hoard. The basis of t h i s p roject was to investigate f u r t h e r some of the properties of o v e r l a i d p a r t i c l e board. The development of new uses f o r p a r t i c l e board promises to have a far-reaching e f f e c t on the wood-using industry. Presently the uses of p a r t i c l e hoard are many, ranging from core stock i n f u r n i t u r e to highly decorative wall paneling. I f o v e r l a i d p a r t i c l e hoard could be developed with strength properties comparable to plywood, such a panel might serve a s t r u c t u r a l as we l l as a decorative purpose. I t might he used as wa l l paneling, movable p a r t i t i o n s , shelves, and s l i d i n g doors. Por these uses, both the ph y s i c a l and mechanical properties are important. Wood p a r t i c l e hoard may be defined as a f l a t panel composed of di s c r e t e p a r t i c l e s of wood bonded together with a suitable binder. Veneer-faced or veneer-overlaid 2 p a r t i c l e board refers to a panel having a face and back p l y of a wood veneer. Generally, when p a r t i c l e board i s o v e r l a i d , cross-banding i s provided i n order to decrease 'telegraphing' of the surface p a r t i c l e s through the surface of the face p l i e s . This i s also known as 'show-through'. The cross-banding also increases dimensional s t a b i l i t y . One object of t h i s study was to determine the properties of o v e r l a i d p a r t i c l e board i f cross-banding i s not c a r r i e d out. Marra (16) div i d e s the types of wood elements used i n the manufacture of p a r t i c l e board i n t o ' p a r t i c l e s ' and 'flakes'. The term ' p a r t i c l e ' r e f e r s to wood elements of small s i z e formed by hammermill action on chips or planer shavings. The term 'flake' r e f e r s to elements produced by s p e c i a l c u t t e r heads on s o l i d wood. Marra states that f l a k e s are characterized by t h e i r appreciable length compared to t h e i r thickness. The wood gr a i n runs i n the f l a t , l o n g i -t u d i n a l d i r e c t i o n of the f l a k e . This nomenclature w i l l be followed i n the text of the t h e s i s . Unfortunately the word ' p a r t i c l e board', as used i n the wood industry, has come to mean any type of wood composition board, regardless of the p h y s i c a l elements going in t o i t s make-up. Since boards are produced by p a r t i c l e s , f l a k e s , or by combinations of both, the word 'board' w i l l be used here i n r e f e r r i n g to wood composition board of a general nature. Three boards of the p a r t i c l e type, one board of the flake type, and one board c o n s i s t i n g of a p a r t i c l e center 3 and flake surfaces, were used i n the evaluation. For com-parative purposes, an exterior-grade Douglas f i r plywood panel was also included. Boards of 3/8-inch thickness were selected. This thickness of hoard was selected because i t might he applicable f o r both s t r u c t u r a l and decorative purposes. Furthermore, some of the p h y s i c a l defects, such as warping, might more r e a d i l y manifest themselves with a thinner hoard. A b i g problem governing the use of p a r t i c l e hoard i s dimensional s t a b i l i t y . Another i s warping, e s p e c i a l l y i n the f l a t - p r e s s e d type of board used here. Overlaying a hoard with wood veneer might increase i t s strength properties enough to enable i t to be used as a s t r u c t u r a l m a t e r i a l . F u j i i (6) studied the e f f e c t of overlay material on p a r t i c l e board. He stated that the f l e x u r a l strength and s t i f f n e s s of the board could be appreciably increased by overlaying with a material that could absorb a concentration of stresses i n tension and compression. Furthermore, the veneer overlay might tend to decrease dimensional change i n the panel. The small component of l o n g i t u d i n a l shrinkage and swelling of the wood veneer would r e s t r a i n dimensional change i n the board, at l e a s t i n the d i r e c t i o n of the board p a r a l l e l to the grain of the veneer. I t was the intent of t h i s study.,; therefore, to make a comparative evaluation of the properties of o v e r l a i d and non-overlaid hoard, and o v e r l a i d and non-overlaid plywood. 4 More s p e c i f i c a l l y , the purposes were t o : 1. D i s t i n g u i s h d i f f e r e n c e s e x i s t i n g i n the p h y s i c a l p r o p e r t i e s , such as warping and dimensional change, between o v e r l a i d and non-overlaid board and plywood. 2. A s c e r t a i n i f d i f f e r e n c e s existed i n the strength p r o p e r t i e s , such as t e n s i l e strength, ultimate strength i n bending, and s t i f f n e s s , between o v e r l a i d and non-overlaid boards and plywood. 3. Determine i f d i f f e r e n c e s e x i s t e d i n the p h y s i c a l and mechanical properties p a r a l l e l and perpendicular to the g r a i n of the face veneer of the panel. 4. Determine i f d i f f e r e n c e s e x i s t e d i n the p h y s i c a l and mechanical properties p a r a l l e l and perpendicular to the machine d i r e c t i o n of the board (the longest d i r e c t i o n of a 4- by 8-foot board and the l o n g i -t u d i n a l d i r e c t i o n of the face p l i e s of plywood). The boards used i n t h i s study were of the m u l t i -p l a t e n f l a t - p r e s s e d type. The type of process used to manufacture t h i s type of board i s described. A review i s also made of the manufacturing v a r i a b l e s and of how these v a r i a b l e s a f f e c t the properties of the f i n i s h e d board. 5 MANUFAC TURING PROCESS The processes f o r manufacturing p a r t i c l e hoard are c l a s s i f i e d as the multi-platen hot-press, the extrusion, and the continuous-pressing method. Many ram i f i c a t i o n s are found i n the process i t s e l f , and the processes used i n the manufacture of these hoards are not i d e n t i c a l . Nonetheless, the general flow scheme, shown i n Figure 1, applies w e l l enough to form an understanding of the general multi-platen hot-press manufacturing method. The following process, as ou t l i n e d , has been extracted from the Wood P a r t i c l e Board Handbook 1(11). Raw, green, wood material, i n a coarse form such as cordwood, enters the system at a primary reduction u n i t , which i s normally a knife hog. Other types of wood residue enter the system at the appropriate place, depending on whether they are dry or have already been reduced i n s i z e . This l a t t e r material i s u s u a l l y veneer c l i p p i n g s or planer shavings. The primary hog reduces the material i n t o a si z e small enough f o r further handling by a secondary, or hammer-m i l l hog. P a r t i c l e s leaving t h i s f i r s t hog are pneumatically conveyed to a rotary dryer where they are d r i e d to about 10 Hereafter r e f e r r e d to as the Handbook fines to boiler dry wood wo.ste wet wood was resin pump weightometer \u00E2\u0080\u00A2 unloa der hot-press loader p re :^rnnr ves s 10 n rolls e ^ r p r j feed c a u l s gravity conveyor spacing conveyor. Figure I. Schemat ic D iagram of M i I Ier -Hof f t Mult i-platen P a r t i c l e or F lake B o a r d Manufacturing P r o c e s s . Source.- Industrial Experimental Program. 1956. Wood part ic le boa rd handbook . North Caro l ina State Co l lege. Ra le igh, p. 2 4 . 7 percent moisture content, depending on the requirements of the p a r t i c u l a r process. A f t e r drying, the p a r t i c l e s are conveyed to the secondary reduction u n i t f o r f u r t h e r grinding. K i l n - d r i e d residue u s u a l l y enters the system at t h i s point. The f i n a l reduction unit produces the desired p a r t i c l e or f l a k e s i z e to he used i n the board. These p a r t i c l e s are conveyed to a c o l l e c t o r . From the c o l l e c t o r the p a r t i c l e s are screened and the oversize p a r t i c l e s and f i n e s are removed. P a r t i c l e s \" o f acceptable s i z e are blown to a second c o l l e c t o r . Large, oversize p a r t i c l e s are r e -hogged, while the f i n e s are sent to the b o i l e r to be used as f u e l . Acceptable p a r t i c l e s are passed from the c o l l e c t o r to a storage b i n where a screw-type conveyor removes material from the bottom at a constant rat e . The p a r t i c l e s are fed onto a 'weightometer' which automatically controls the amount of p a r t i c l e s as they are conveyed into the mixer. In the mixer the p a r t i c l e s come into contact with the r e s i n adhesive which i s sprayed in t o the same end of the mixer that receives the p a r t i c l e mass. P a r t i c l e s and r e s i n are thoroughly mixed before being discharged i n t o a surge b i n , u s u a l l y located on a lower f l o o r . From the surge b i n the mixture i s fed at a c o n t r o l l e d rate across the width of a f l a t , endless b e l t or chip-spreading unit that t r a v e l s continuously beneath the b i n . Here, on the chip-spreading u n i t , the mat i s leveled to the 8 required thickness. Material which i s removed i s returned to the surge b i n . Beneath the chip spreader i s a power-driven conveyor which t r a v e l s at the same rate of speed as the b e l t . Metal cauls are g r a v i t y fed onto the conveyor and pass d i r e c t l y under the mass of moving p a r t i c l e s as they f a l l o f f the end of the b e l t of the spreader u n i t . The f a l l i n g of the mass acts to ag i t a t e and d i s t r i b u t e the f i n e s throughout the mat. The caul with i t s mat t r a v e l s through an unheated pre-compression u n i t . This mechanism consists of an upper and lower track which compacts the mat and also shapes the sides. In some processes the mat i s edge-trimmed following compression. Prom the cold-pressing uni t the caul progresses to a speed-up conveyor which causes a spacing between i t and the preceding c a u l . Spacing allows the loader time to receive each mat and to charge the press with a f u l l load at the end of each press c y c l e . The loader holds the same number of cauls as does the hot press. The number of cauls may range from 4 to 20. When the loader has received a f u l l charge the press opens, and a f t e r discharge of the cured boards, the new load i s i n j e c t e d i n t o i t . The process of loading, charging the hot press with the new load, and unloading i s completely automatic. The press unloader removes the pressed boards and cauls from the press at the completion of the curing c y c l e . 9 At t h i s point the cured hoards are automatically separated from the cauls. Cauls are returned to the process f o r reloading while the boards are stacked to allow a period conditioning. A f t e r the required conditioning period the hoards are edge-trimmed. In some processes, the boards may he edge-trimmed before conditioning. E s s e n t i a l l y , t h i s multi-platen hot press operation may he broken down into four broad phases; these are, p a r t i c l e (or f l a k e ) preparation, p a r t i c l e treatment, mat formation, and hot pressing. In the process where a three-layer hoard i s pro-duced, that i s , a hoard with a high-quality surface f l a k e , and p a r t i c l e s i n the center, the process i s modified somewhat. A f t e r the wood enters the system, e i t h e r at the debarker or a f t e r the dryer, the surface f l a k e s and inner p a r t i c l e s are channeled separately. Each channel contains i t s own primary reduction u n i t , storage hopper, secondary reduction u n i t , dryer screens, conveying u n i t s , weightometer, wood-glue mixers, and p a r t i c l e spreaders f o r mat forming. One type of board used i n t h i s p r o j e c t consisted of three-layer construction, the surface being of Douglas f i r (Pseudotsuga menziesii (mirb.) Franco) f l a k e s , and the inner core of pine (genus Pinus) p a r t i c l e s . Chips from the separate-flow channels merge at the mat-forming u n i t . I n d i v i d u a l cauls, moving on a 10 conveyor b e l t , pass beneath the chip-spreading u n i t s . These u n i t s are so arranged that a t h i n mat or bottom l a y e r i s f i r s t deposited on the c a u l . The caul i s moved to the next u n i t and the middle l a y e r i s deposited. The caul i s again moved to receive the top l a y e r and the mat i s then pre-pressed. Thus the process i s the same as the one just described. I t should be noted that the process described here i s an example, and the processes by which the boards used i n t h i s study were made po s s i b l y a l l had v a r i a t i o n s . I t i s not within the scope of t h i s report to elaborate on the i n d i v i d u a l manufacturing methods. 11 PRODUCT VARIABLES Species s e l e c t i o n and preparation One type of board w i l l d i f f e r g r e a t l y i n ph y s i c a l and mechanical properties from another. In addition to the v a r i a t i o n s e x i s t i n g i n the manufacturing process, the v a r i a t i o n i n the properties of the species used i n the boards i s great, and the re s u l t a n t properties of the board are a f f e c t e d . A l l boards used i n t h i s p r o j e c t were formed from coniferous species. I t i s stated i n the Handbook (11) that species i s not the c o n t r o l l i n g f a c t o r i n p a r t i c l e board production. Although hardwoods are generally denser than softwoods, the f a c t o r s of hardness and c o m p r e s s i b i l i t y are the most important. Softwoods w i l l form more dense and compact boards than hard-woods under a given pressure. Since the p a r t i c l e s of the softwoods can be r e a d i l y compacted, stronger boards are obtained because of b e t t e r bonding. Strength properties of the board increase with a decrease i n the s p e c i f i c g r a v i t y of the wood used i n the board. The breakdown of ' p a r t i c l e s ' used i n wood composition-board production as described by the Handbook i s i n t o s p l i n t e r - t y p e p a r t i c l e s , f l a k e s , and shavings. 12 Splinter-type p a r t i c l e s are oblong and may range from short, chunky shapes to needle-like shapes. Flakes, as already described, are t h i n , rectangular p a r t i c l e s with c l o s e l y c o n t r o l l e d dimensions, and are produced by a c u t t i n g action so that f i b r e damage i s held to a minimum. Planer shavings are also produced hy a c u t t i n g action hut have no c o n t r o l l e d dimension or f i b r e o r i e n t a t i o n . Boards obtain t h e i r strength i n two ways, from the i n d i v i d u a l wood f i b r e s and from the r e s i n bond. A given amount of r e s i n can e f f e c t i v e l y cover a c e r t a i n area; i f the area covered i s too large, the r e s i n f i l m w i l l be t h i n and a weak bond w i l l r e s u l t . Turner (24) found that length, width, and thickness a l l c o n t r o l the surface area of the p a r t i c l e , and of these, thickness had the greatest e f f e c t . Generally, bonding strength increased as the width and length of the p a r t i c l e increased. Since sawdust has a large surface-i weight r a t i o i t required more surface area bonding and ex-h i b i t e d the lowest strength properties. Turner stated that large, t h i n f l a k e s were the most desired since they were more compressible and a b e t t e r bond r e s u l t e d . Turner and Kern (25) found a c e r t a i n flake thickness and r e s i n concentration beyond which strength properties of the hoard decreased. I f boards with t h i n f l a k e s had too low a concentration of r e s i n on the surface, poor bonding would r e s u l t . There was a converse l i m i t , i n that no advantage was gained hy increased r e s i n amount. Thus 13 there i s an optimum point where both f l a k e s i z e and r e s i n amount should be maintained. As the length of the p a r t i c l e increases, the strength increases, up to a c e r t a i n point. Too large p a r t i c l e s tend to have a s h i e l d i n g action on the r e s i n sprayed i n t o the p a r t i c l e mass, thus causing lack of bonding. P a r t i c l e width has l i t t l e e f f e c t on board strength, assuming that the t o t a l t e n s i l e strength of p a r t i c l e s , p a r a l l e l to the grain, v a r i e s with width i n d i r e c t proportion to the f l a t area which t r a n s f e r s the strength ( 1 1 ) . Again, too wide a p a r t i c l e might tend to have a s h i e l d i n g e f f e c t on the r e s i n . There i s an optimum siz e f o r thickness, length and width. P a r t i c l e shape has the primary e f f e c t on strength, while r e s i n content i s secondary i n importance. Dimensional s t a b i l i t y i s also a f f e c t e d by p a r t i c l e thickness. Wood which i s compressed tends to swell to i t s o r i g i n a l s i z e upon moisture pick-up, i f i t s moisture content i s the same as the moisture content of the o r i g i n a l wood. Because thinner chips need not be compressed as much as t h i c k e r ones f o r a board of given strength, panels composed of thinner chips have l e s s tendency to swell. Heebink and Harm (8) found that boards produced with 1-inch-long f l a k e s had l e s s dimensional change than board composed of shavings, s l i v e r s , and sawdust. They a t t r i b u t e d t h i s to the increased binding e f f i c i e n c y of the r e s i n . 14 I t i s stated i n the Handbook (page 190) that Klauditz found that l a t e r a l n a i l - h o l d i n g a b i l i t y of the hoard was dependent on the s p e c i f i c g r a v i t y , and to some extent on the p a r t i c l e s i z e , whereas perpendicular n a i l - h o l d i n g a b i l i t y was based e n t i r e l y on s p e c i f i c g r a v i t y . In a project such as t h i s , consideration must he given to properties other than strength. Boards composed of s p l i n t e r s tend to have gaps i n the surface i f p a r t i c l e s of the same size are used throughout the board. When smaller p a r t i c l e s and f i n e s are introduced in t o the board the dimensional s t a b i l i t y w i l l be reduced. Unequal d i s t r i b u t i o n of f i n e s r e s u l t s i n unequal expansion and contraction of the board during moisture content changes, since the smaller p a r t i c l e s w i l l pick up a greater percent of moisture through t h e i r l a r g e r surface area per u n i t volume. Adhesive materials Many materials have been used to bond wood p a r t i c l e s together, but f o r f l e x i b i l i t y , strength, and permanence the synthetic r e s i n s are preferred. Of these the urea-formaldehyde r e s i n s predominate. Phenolic re s i n s are also used hut are somewhat more c o s t l y . Maxwell, Kitazawa, Duncan, and Hine (18) suggest that extensive research he made on the economical a p p l i c a t i o n of phenolic res i n s i n hoards, i n order to create more uses f o r the hoard. They state that phenolic-bonded boards, once accepted 15 by f i r e underwriters and b u i l d i n g code o f f i c i a l s , migbt replace plywood f o r sheathing and e x t e r i o r uses. Currently, phenolic-urea-formaldehyde r e s i n s are being used i n most composition boards. Melamine-urea-formaldehyde combinations are used only to a l i m i t e d extent because of t h e i r greater cost. C a t a l y s t s are used i n the curing of the board, i n order to hasten a polymerization or polycondensation of the r e s i n . The c a t a l y s t w i l l a f f e c t the surface q u a l i t y of the board. Too rap i d a cure r e s u l t s i n an incompressible p a r t i c l e or f l a k e , which w i l l manifest i t s e l f outwardly as a roughened surface condition ( 1 1 ) . Extenders, which are usually f l o u r s , are added to the r e s i n mix to reduce r e s i n costs and to a i d i n the 'holding' of the adhesive to the p a r t i c l e surface. Extenders also a i d i n the d i s t r i b u t i o n of the r e s i n f i l m . M i l l e r (17) found that strength proper t i e s , with the exception of hardness, increased with increased amounts of extenders. He found that adding an extender such as wheat f l o u r to the mix had the same e f f e c t as increasing the r e s i n by the same amount. The same r e s u l t might have been achieved by increasing p a r t i c l e moisture content or increasing r e s i n v i s c o s i t y . A d d i t i v e s , although not pertinent to t h i s study, might be pentachlorophenol f o r preservative measures, and wax f o r water repellency. 16 Studies on r e s i n content of p a r t i c l e board showed that as r e s i n content was increased strength properties of the hoards increased (11). Also, as r e s i n content increased percent water absorption decreased and thickness swelling decreased. Increases i n r e s i n content therefore tended to strengthen the bond and reduce swelling. Marian (15) pointed out that r e s i n amount was not as important as the manner by which i t was d i s t r i b u t e d . Curing conditions A f t e r the r e s i n i s added, the p a r t i c l e hoard i s placed under conditions of heat and pressure to e f f e c t the bonding into the f i n i s h e d product. Temperature, pressure, time, and moisture content are a l l r e l a t e d to the production of the f i n i s h e d board. A moisture content between 10 and 14 percent i s the normal requirement of the pre-compressed mat before hot-pressing. Excessive moisture w i l l lead to ' b l i s t e r s ' forming i n the p a r t i c l e board during pressing. Too l i t t l e moisture reduces the p l a s t i c i t y of the wood p a r t i c l e s . Excessive moisture also tends to r a i s e the r e s i n concentration i n the center of the hoard and to lower i t near the surfaces. This i s due to r e s i n and moisture migration because of the dif f e r e n c e s i n vapour pressures within the board during hot pressing. To reduce swelling and shrinking the f i n a l moisture content of the hoard should he as close as i s 17 f e a s i b l e to the equilibrium moisture content that the board w i l l experience i n service. The pressure exerted on the p a r t i c l e mass forms the hoard and holds the p a r t i c l e s i n place while the hinder hardens. Gottstein (7) found that i n c r e a s i n g the forming pressure s i g n i f i c a n t l y increased strength properties as well as s p e c i f i c g r a v i t y . The denser boards also r e s i s t e d moisture pick-up, and dimensional change was reduced. Heat i s necessary i n board production to cure or set the binder. The curing time must he long enough f o r a complete bonding of the r e s i n . Excessive temperatures may produce premature drying of the surfaces, excessive r e s i n cure ( r e s u l t i n g i n b r i t t l e and f l a k y r e s i n ) , and scorching of the surfaces. Product properties For an understanding of the fundamental p h y s i c a l and mechanical properties investigated i n t h i s t h e s i s i t i s e s s e n t i a l that some conditions a f f e c t i n g these properties be examined. Density. Density, or s p e c i f i c g r a v i t y , i s a measure of the compactness of the i n d i v i d u a l p a r t i c l e s or flak e s and the additives within the hoard. Strength properties increase with an increase i n density. One of the problems i n hoard manufacture i s to obtain a uniform 18 density throughout the hoard. When the p a r t i c l e s are unevenly d i s t r i b u t e d over the caul p r i o r to hot pressing, the f i n i s h e d boards w i l l have areas of unequal density. Later, i f moisture content changes occur, the d i f f e r e n t d e n s i t i e s w i l l cause uneveness of dimensional change and warping may take place (11). Dimensional s t a b i l i t y . Many present a p p l i c a t i o n s of p a r t i c l e or f l a k e board require reasonable c o n t r o l over dimensional change, hence t h i s i s a c r i t i c a l area of study i n board production. Since the material i n p a r t i c l e board i s arranged homogeneously, dimensional changes are more uniform when compared with whole wood. Turner and Kern (25) l i s t the va r i a b l e s a f f e c t i n g the moisture absorbing a b i l i t y of p a r t i c l e board: 1. The volume of the voids i n and between the p a r t i c l e s , 2. c a p i l l a r y passages to the voids, 3. surface area of the p a r t i c l e s , 4. d e n s i f i c a t i o n of each p a r t i c l e by the bonding pressure, 5. the amount of p a r t i c l e surface area not covered with r e s i n , 6. permeability of the r e s i n binder, 7. depth of impregnation of each wood p a r t i c l e by r e s i n , 8. the o r i g i n a l moisture content of the wood p a r t i c l e s , and 9. the nature of tfye moisture ( v i s c o s i t y , surface tension, e t c . ) . Any production v a r i a b l e that a f f e c t s these f a c t o r s also a f f e c t s dimensional s t a b i l i t y . Increase of r e s i n , increase of bonding pressure, and ad d i t i o n of a wax s i z i n g 19 a l l reduce moisture absorption. One method to combat the i n s t a b i l i t y of the hoard would he to overlay i t with some material, i n t h i s case wood veneer. The wood veneer, having a l o n g i t u d i n a l shrinkage (or swelling) value of l e s s than 1 percent would r e s t r a i n the forces causing dimensional change i n the length of the board, providing the grai n of the wood was p a r a l l e l to the length of the hoard. Presumably, an overlay material would not reduce dimensional change i n thickness. For a short duration the wood overlay might r e t a r d the moisture from entering the board. Over a long period the hoard would expand to i t s normal thickness. I t i s possible that l a t e r a l forces would develop from the o v e r l a i d board being r e s t r a i n e d i n i t s l o n g i t u d i n a l movement and these forces manifest themselves i n the thickness d i r e c t i o n . I f t h i s were the case an overlay material might increase dimensional change i n thickness. Dimensional change i n the p a r t i c l e board, besides being due to the normal swelling and shrinking of wood, i s also due to 'springback'. Springback r e f e r s to the release of the compressive forces incurred i n the board during manufacture. Boards composed of l i g h t e r woods have a greater tendency to springback. Following an increase i n moisture content, hoards composed of thinner f l a k e s w i l l swell l e s s , probably because such hoards do not require as much chip deformation f o r a given density, and there i s more surface area f o r the r e s i n to e f f e c t i v e l y cover the material(24). 20 P a r t i c l e and f l a k e o r i e n t a t i o n . In the f l a t - p r e s s e d hoards the p a r t i c l e s are oriented l o n g i t u d i n a l l y i n the same d i r e c t i o n as the grain i n wood. Accordingly,^ most of the dimensional change i s i n the thickness d i r e c t i o n of the board. Since the p a r t i c l e s w i l l not l i e with the i n d i v i d u a l grain i n each p a r t i c l e p a r a l l e l to the length of the board, the p a r t i c l e s should exert a r e s t r a i n i n g a c t i o n on each other to reduce dimensional change i n length and width. Rahtu, Holm, and Aalto (20) found that differences between the transverse and l o n g i t u d i n a l dimensional change were not s i g n i f i c a n t . The d i f f e r e n c e s e x i s t i n g , i f any, between the transverse and l o n g i t u d i n a l d i r e c t i o n of the board are again investigated i n t h i s t h e s i s . As previously mentioned, telegraphing or show-through i s the e f f e c t of the impression of i n d i v i d u a l p a r t i c l e s or flakes appearing through the o v e r l a i d veneer. This i s caused by the swelling of some of the surface f l a k e s , r e s u l t i n g i n a roughened appearance. Denser boards tend to telegraph more than l i g h t e r ones (17). Por ease of veneering, the surface of the board must be without ridges and depressions, f o r the veneer to wholly contact the surface and form a good bond. High density boards are sa i d to be more d i f f i c u l t to veneer since they do not 'give' or f l a t t e n . When veneering, care must be taken that the veneering pressure i s not great enough to crush the board (21). 21 N a i l - h o l d i n g a b i l i t y . Studies have been made on the n a i l - h o l d i n g e f f e c t of p a r t i c l e boards. Some of the fa c t o r s l i s t e d hy Kennedy and N i l e s (12) which a f f e c t l a t e r a l n a i l resistance are: II 1. Size and shape of n a i l , 2. composition of material, 3. pressure between contacting surfaces of wood, 4. f i n i s h of contacting wood surfaces, 5v depth of penetration, 6. d i r e c t i o n of n a i l i n g , whether r a d i a l or t a n g e n t i a l , 7. duration of load, 8. rate of loading, H 9. length of time between d r i v i n g and t e s t i n g . For nail-withdrawal resistance, Mack (14) found that the method of d r i v i n g the n a i l , rate of loading, and length of time between d r i v i n g and t e s t i n g had n e g l i g i b l e e f f e c t on resis t a n c e . S p e c i f i c g r a v i t y appeared to be the c o n t r o l l i n g f a c t o r . Mack stated that p r e - d r i l l i n g n a i l holes improved resistance by reducing the rupture of the f i b r e s around the n a i l . Boards have l e s s resistance to n a i l withdrawal and l a t e r a l n a i l movement than normal wood. Wakefield (26) found that boards f a i l e d i n l a t e r a l n a i l movement because of a tearing around the n a i l r e s u l t i n g from forces on the wood. The face of the hoard might he strengthened with an overlay. By applying veneer, t h i s material might absorb some of the forces and the n a i l would not break away. The n a i l -withdrawal t e s t was undertaken to f i n d what degree of improvement, i f any, might be obtained from overlaying. 22 Strength properties* Values a v a i l a b l e on the strength properties of wood composition hoard cover a wide range. In \"Fibreboard and P a r t i c l e board\" (5) the values f o r modulus of rupture range from 1500 to 7000 p s i , f o r modulus of e l a s t i c i t y 150,000 to 700,000 p s i , and f o r t e n s i l e strength p a r a l l e l to the surface, from 700 to 3500 p s i . These values include boards made from p a r t i c l e s , s l i v e r s , and f l a k e s . The value a g i s t e d i n the Handbook (11) are s i m i l a r . Flake boards have a higher modulus of rupture (2000 to 6500 p s i ) than boards made from s p l i n t e r s or planer shavings (1500 to 4000 p s i ) . Flake boards also have a higher modulus of e l a s t i c i t y (300,000 to 650,000 p s i ) than these other boards (150,000 to 4-50,000 p s i ) . As already mentioned, p a r t i c l e s i z e and shape has a great e f f e c t on strength properties. P a r t i c l e and f l a k e types, i n order of decreasing strength properties are: f l a t f l a k e s , h e l i c a l f l a k e s , strands, e x c e l s i o r , f i b r e s , planer shavings, and sawdust (24). Besides p a r t i c l e s i z e and shape, an increase in' r e s i n content increases strength of the board, The r e s i n binder penetrates into the f i n e m i c e l l a r structure of the wood and prevents the adsorption of moisture by the c e l l u l o s e which o r d i n a r i l y leads to the swelling of wood. S t r i c k l e r (22) stated that although species of wood, type of r e s i n adhesive, r e s i n quantity and d i s t r i b u t i o n , wax content, i f any, and size and o r i e n t a t i o n of p a r t i c l e s a l l 23 affect strength properties, the one factor most direc t l y related to strength was hoard density. In testing urea- and phenolic-bonded hoards under long-term loading, Bryan (2) found that strength reduction was approximately the same as for whole wood. F u j i i (6) overlaid 1/8-inch Douglas f i r veneer on a 3/8-131011 board made from planer shavings and increased the stiffness value from 277,000 psi to 1,900,000 ps i . The modulus of rupture value was increased from 1910 psi to 11,100 p s i . On a 3/8-inch multi-layer hoard with a flake surface, the values were increased from 618,000 psi to 2,120,000 p s i for stiffness, and from 3,130 psi to 13,500 psi for modulus of rupture. In a l l cases i n bending, the grain of the veneer was pa r a l l e l to the span of the specimen. F u j i i found that cross-banding did not contribute appreciably to flexural strength and stiffness of the panels. There was reason to believe that the so-called Philippine mahogany veneer overlay used i n this study might greatly increase the strength properties of the board. Furthermore, the overlay should decrease dimensional change i n the hoard i n the manner already described. 24 PROCEDURE Procurement of material Pive commercial boards, a l l of the multi-platen f l a t - p r e s s e d type, and a plywood panel were procured from companies i n the United States and Canada. Since two boards were obtained from each company, i t was assumed by the w r i t e r that these boards represented the t o t a l population of each make of board. S e l e c t i o n of only two boards of each type was based on the premise that v a r i a t i o n between the types of boards was greater than v a r i a t i o n between i n d i v i d u a l boards of each type. Further-more, the object was also to determine the e f f e c t of the overlay veneer on the boards i n general. Procurement of ad d i t i o n a l samples of each board was precluded by the ad d i t i o n a l amount of labour and materials involved. The boards were designated by l e t t e r s and w i l l be so r e f e r r e d to throughout the text of t h i s t h e s i s . The composition of each type of board and the l e t t e r s assigned to each are shown below. A l l boards were 2 feet by 4 fe e t i n dimension and 3/8-inch i n thickness. > 25 Board Designation Type A p a r t i c l e B E P p a r t i c l e p a r t i c l e f l a k e m u l t i - l a y e r plywood Composition eastern white pine (Pihus strobus L.) southern pine (genus Pinus) Douglas f i r (Pseudotsuga menziesii (Mirb.) Franco) Douglas f i r planer shavings and f l a k e s cut from veneer cores surface f l a k e s of Douglas f i r , and center p a r t i c l e s of white f i r (genus Abies), sugar pine (Pinus lambertiana Dougl.), and ponderosa pine (Pinus ponderosa Laws.) 3-ply, s o l i d two sides, BB, Douglas f i r , bonded with phenolic r e s i n Of the two boards from each type tested, one was used 1 f o r the overlay and one was tested without an overlay. Extra boards furnished by the companies allowed preliminary t e s t i n g to be conducted to determine correct press conditions. The overlay veneer was 1/ 2 0-inch P h i l i p p i n e mahogany (genus Shorea). The veneer was r a d i a l - s l i c e d , ribbon grain. Grain pattern was consistent throughout, a requirement necessary f o r warping t e s t s . For bonding the veneer to the board, a urea-formaldehyde hot- or c o l d - s e t t i n g adhesive was used. Upon a r r i v a l i n the laboratory, the hoards were unpacked and placed on s t i c k e r s i n a humidity room where they reached a moisture content i n equilibrium with the surrounding atmosphere. The veneer was placed i n the same atmosphere. The hoards remained there f o r two weeks before preliminary t e s t i n g was done on them. Test samples d i s -closed an average moisture content of 7\u00C2\u00AB8 percent f o r the boards and 7\u00C2\u00BB2 percent f o r the veneer a f t e r conditioning. Moisture content was based on amount of moisture i n samples to oven-dry weight. Indivi d u a l values are shown i n Table I. Values f o r s p e c i f i c g r a v i t y before and a f t e r pressing are also shown i n Table I. Preliminary overlaying A preliminary study was made on small samples before pressing of the boards to determine the effectiveness of the adhesive, and to a r r i v e at s a t i s f a c t o r y pressing conditions. Boards A and B were o v e r l a i d at three d i f f e r e n t press conditions and with three d i f f e r e n t glue spreads. Curing was done on a Carver laboratory press. This press i s h y d r a u l i c a l l y operated, with 6- by 6-inch platens, e l e c t r i c a l l y heated, with temperature c o n t r o l within 2}&\u00C2\u00B0P of that desired. The adhesive used was from the same batch as that used i n the f i n a l lay-up of the 2- by 4-foot panels. The d i f f e r e n t press conditions were: 1. 110\u00C2\u00B0P f o r 20 minutes at 1 2 5 p s i , 2. 160\u00C2\u00B0P f o r 1 5 minutes at 1 2 5 p s i , and 3 . 245\u00C2\u00B0F f o r 7 minutes at 1 2 5 p s i . Table I. Moisture Content and S p e c i f i c Gravity of Boards Type Moisture Content Before Lay-up (%) S p e c i f i c Gravity* Before Lay-up S p e c i f i c Gravity A f t e r Pressing A B C D E P Veneer 7 . 4 7 .6 8.5 7.7 7 . 9 7 . 6 7.2 0 . 6 3 0 .71 0 . 6 9 0 .65 0.64 0 . 5 0 0.67 0.66 0.68 0.69 0.61 0.50 -* S p e c i f i c g r a v i t y based on oven-dry weight and volume. 28 On both types of panels, glue spreads of 40 and 60 pounds per thousand square feet single glue line were used under the f i r s t press conditions. Under the second press conditions board A had glue spreads of 40 and 60 pounds, while board B had glue spreads of 30 and 40 pounds. With the third set of press conditions glue spreads of 30 and 40 pounds were used on both panels. After lay-up and pressing, the overlaid samples were trimmed to 4- by 4-inches and subjected to 3 cycles of the cold-soak delamination test. One cycle of this test consisted of soaking the samples for 4 hours at room temperature, and drying for 20 hours at 95\u00C2\u00B0*' ( 3 9 ) . Results of this test are shown i n Table II. Delamination occurred only on the samples pressed at 110\u00C2\u00B0P for 20 minutes. Amount of glue spread was not a c r i t i c a l factor. Because of the f e a r of b l i s t e r s or 'blows' occurring during the f i n a l pressing of the boards, the third set of press conditions was eliminated. Steam forming i n the board might seriously affect the board-to-veneer glue-bond. Press conditions of 160\u00C2\u00B0P for 15 minutes at 125 psi were decided upon for the f i n a l pressing of the boards. Although a 15-minute cure was probably longer than necessary for this temperature, i t was maintained to insure complete cure. Conversations with authorities of Monsanto Canada Limited confirmed t h i s . 29 Table II. Amount of Delamination Occurring in 4- By 4-inch Samples of Overlaid Particle Board After 3 Cycles of a 4-Hour Soak and 20-Hour Dry at 95\u00C2\u00B0F Press conditions (% delamination) Type Glue Spread 110\u00C2\u00B0P for 160\u00C2\u00B0P for 245\u00C2\u00B0F for (lb. per M 20 min.at 15 min.at 7 min. at sq.ft. 125 p s i 125 p s i 125 p s i S.G.L.) A 50 - 0 . 0 0 . 0 40 2.2 0 . 0 0 . 0 60 3 . 8 B 30 - 0 . 0 40 9.6 0 . 0 0 . 0 60 8 . 7 0 . 0 Table III. Thicknesses of Boards and Veneer Before and After Pressing Type Thickness Boards (in.) Single Thickness Veneer (in.) Combined B+2V (in.) Thickness After Pressing(in.) A 0.380 0.052 0.484 0.461 B 0 . 3 8 4 0 .052 0.488 0.469 C 0.372 0.052 0.476 0.466 D 0 .386 0 .052 0.490 0.471 E 0.374 0 .052 0.478 0.458 P 0.373 0 .052 0.477 0.465 30 F i n a l lay-up As noted above, i t was decided to use press conditions of 160\u00C2\u00B0F at 125 p s i f o r 15 minutes f o r the f i n a l pressing. Minimum assembly time was 3 minutes. Maximum assembly time was 15 minutes, hut t h i s was not c r i t i c a l since the time involved i n feeding the press was n e g l i g i b l e . An Interwood glue-spreading machine was employed to d i s t r i b u t e the adhesive on the boards (Figure 2). This machine was e l e c t r i c a l l y driven, and capable of spreading a double glue l i n e . The r o l l e r s of the machine were chain-driven, with accurate mechanism f o r r a i s i n g and lowering them. Accurate glue spread of 4-0 pounds per thousand square feet single glue l i n e was also obtainable, and was c o n t r o l l e d throughout the lay-up. Pre-weighed paper was attached to extra sheets of hoard and a f t e r passing through the spreader t h i s paper was again weighed to determine spread on top and bottom r o l l e r s . New adhesive was c o n t i n u a l l y added to prevent foaming. The 24\u00E2\u0080\u0094 by 4-8-inch boards were put through the r o l l e r s of the glue spreader. Veneer, with the apparent loose side toward the adhesive, was placed under and over the hoard. A Berthelsen hydraulic hot-plate press was used to cure the adhesive (Figure 3). This press was equipped with 54\u00E2\u0080\u0094 hy 5 4 -inch platens, continuously heated hy c i r c u l a t i n g o i l . Temperature checks on the upper and lower platens before Figure 3 . Berthelsen Oil-heated Hot-press f o r Bonding Veneer to P a r t i c l e Boards 32 pressing i n d i c a t e d no deviation from the desired 160\u00C2\u00B0F which was set on the machine c o n t r o l s . A maximum pressure of 400 p s i was capable of being exerted over the entir e p l a t e n area, or a t o t a l maximum pressure of 1,666,400 pounds. Press p l a t e s were of f a b r i c a t e d s t e e l with precision-ground working surfaces. The press was f u l l y automatic; a pre-set constant pressure was maintained f o r each press load. A f t e r the required 15-minute cycle the press automatically opened. Both an extra board and a section of plywood were o v e r l a i d before the f i n a l operation was begun. A f t e r pressing, the panels were dead-stacked f o r 24 hours to insure complete f l a t n e s s . 33 TEST METHODS AND PROCEDURES At the completion of the dead-stacking period, t e s t specimens were cut from each o v e r l a i d and non-overlaid panel as shown i n Figure 4-. This c u t t i n g arrangement allowed the maximum number of t e s t s and the required number of specimens i n each t e s t . Testing was di v i d e d into four phases: glue-l i n e shear t e s t s , other strength t e s t s , moisture t e s t s , and accelerated aging. The s i z e and number of specimens f o r each t e s t are shown below. Size of Number of Test Specimen ( i n . ) Specimens Cl u e - l i n e shear dry 1 by 3# 5 wet 1 by 5 Tension p a r a l l e l to surface 0 j, p a r a l l e l ^ , 2 by 12_T 3 perpendicular'' 2 hy 12 3 S t a t i c bending p a r a l l e l 3 by 14- 3 perpendicular 3 by 14- 3 L a t e r a l n a i l resistance 2 by 10 3 Nail-withdrawal resistance 3 by 3 6 Dimensional change p a r a l l e l to grain d i r e c t i o n (length of panel) 2 hy 12 1 perpendicular to gra i n d i r e c t i o n (width of panel) 2 hy 12 1 p Grain of veneer overlay p a r a l l e l to length of t e s t specimen. ^ Grain of veneer overlay perpendicular to length of t e s t specimen. k Necked down to a 1-inch width over c e n t r a l 4- inches. 34 Test Size of Number of Specimen ( i n . ) Specimens Warping 12 by 12 2 Accelerated aging 3 by 6 3 Moisture content and s p e c i f i c g r a v i t y 2 by 2 3 Glue-line shear Glue-line shear specimens were cut according to s p e c i f i c a t i o n s f o r preparing plywood g l u e - l i n e shear samples (3). Specimens were prepared so that shear was applied over a one-inch-square area. Testing was done on a plywood g l u e - l i n e t e s t i n g machine owned by Monsanto Canada Limited. Rate of loading was 600 to 1000 pounds per minute. Specimens were tested i n the dry and wet conditions. Preparation of the wet specimens consisted of a 48-hour soak i n water at room temperature, an 8-hour dry at 145\u00C2\u00B0P, followed by 2 cycles of a 16-hour soak and 8-hour dry, then another 16-hour soak. Specimens were tested when wet. Load to f a i l u r e and percentage of g l u e - l i n e , board, or veneer f a i l u r e were recorded. Mechanical t e s t s other than g l u e - l i n e shear These t e s t s included s t a t i c bending, t e n s i l e strength p a r a l l e l to the surface, l a t e r a l n a i l r e s i s t a n c e , and nail-withdrawal r e s i s t a n c e . For ease of a p p l i c a t i o n and f o r comparison of values, the t e s t i n g methods, with the exception of the l a t e r a l n a i l resistance t e s t , followed 35 Legend.: 1. g l u e - l i n e s h e a r s amples 2. s t a t i c b e n d i n g 3. t e n s i o n p a r a l l e l 4. l a t e r a l n a i l r e s i s t a n c e 5. n a i l w i t h d r a w a l 6 . d i m e n s i o n a l change i n l e n g t h and t h i c k n e s s 7. w a r p i n g ' 8. m o i s t u r e c o n t e n t and s p e c i f i c g r a v i t y 9 . a c c e l e r a t e d a g i n g g * o o OJ F i g u r e 4. G u t t i n g P l a n o f 2- by 4 - f o o t N o n - o v e r l a i d and \u00C2\u00A5'eneer-overlaid B o a r d s a n d Plywood 36 those suggested by the Wood P a r t i c l e Board Committee (28). Det a i l e d information of specimen size and t e s t i n g procedure are given i n ASTM s p e c i f i c a t i o n 1037 D ( 1 ) . Average moisture content of a l l specimens at time of t e s t i n g was 8.0 percent. Moisture content was determined by the oven-dry method; three 2 - hy 2-inch samples were randomly selected from each hoard. These samples were also used to determine s p e c i f i c g r a v i t y . T e n s i l e strength t e s t s were made on a Baldwin Southwark 60 ,000 pound, hydraulically-operated, u n i v e r s a l t e s t i n g machine. S i x specimens were cut from each type of ov e r l a i d and non-overlaid board. Rate of loading was 0.04 inches per minute. In order to evaluate d i r e c t i o n a l properties within both the non-overlaid board and the ov e r l a i d board, three specimens were cut with t h e i r length 5 p a r a l l e l to the length^ of the board, and three specimens with t h e i r long dimension perpendicular to the length of the board. Results are reported i n Appendix A, and a s t a t i s t i c a l a n a l ysis of the data i s presented i n Appendix B. F l e x u r a l strength t e s t s were made on a T i n i u s Olsen 2 0 , 0 0 0 pound u n i v e r s a l t e s t i n g machine (Figure 5 ) . ^ For the non-overlaid hoards the length or longest d i r e c t i o n of a 4- hy 8-foot board r e f e r s to the 'machine d i r e c t i o n * . For the o v e r l a i d hoards, length r e f e r s to the l o n g i t u d i n a l d i r e c t i o n of the grain of the veneer. In t h i s study, grain of the veneer was p a r a l l e l to machine d i r e c t i o n of the hoards. 38 Specimens were cut according to a span-to-depth ratio of 24 to 1 (28). Each specimen was 3 inches i n width, with a span of 12 inches and a length of 14 inches. Specimens were centre-loaded at the rate of 0.24 inches per minute. This speed depended on unit rate of fibre strain and was calculated from the following formula (28): Z L 2 N = ~ , where N = rate of moving head, i n inches per minute, Z = unit rate of fibre strain, in inches per inch of outer fibre length per minute (0.005), L = span, i n inches, and d = thickness of specimen i n inches. The rounded portion of the loading block of the machine had a diameter equal to Vfi times that of the thickness of the specimen, or 3/4 inch. Deflection readings were taken every 50 pounds of load on the high-strength specimens and every 20 pounds on the low-strength specimens. Maximum load was recorded. Load and deflection at proportional limits were visually interpolated from load-deflection curves drawn for each sample. Deflections were read from the machine head. 3 9 Modulus of rupture and modulus of e l a s t i c i t y were cal c u l a t e d f o r each specimen from the following formulae (28): R = 223E\u00C2\u00AB and 2bd^ p L 3 E = 1 , where 4hd 3Y R = modulus of rupture, i n p s i , E = modulus of e l a s t i c i t y , i n p s i , P - maximum load, i n pounds, L = length of span, i n inches, h = width of specimen, i n inches, d = thickness of specimen, i n inches, P^ = load at proportional l i m i t , i n pounds, and Y = center d e f l e c t i o n at proportional l i m i t , i n inches. Load-deflection curves were constructed and the strength (modulus of rupture) and s t i f f n e s s (modulus of e l a s t i c i t y ) c a lculated. T y p i c a l curves are shown i n Pigure 6. Por the m u l t i - l a y e r hoard and the plywood, the strength and s t i f f n e s s terms should he c a l l e d the 'apparent moduli of rupture and e l a s t i c i t y ' since the foregoing equations apply to homogeneous materials. Por comparative purposes i t was convenient to use these equations when c a l c u l a t i n g values f o r a l l specimens. Values and s t a t i s t i c a l analyses are presented i n Appendices C through P. 40 4 0 Q Figure 6. Typical Load-deflection Curves. Curve Number 1 represents particle board ('C^ with grain direction of veneer overlay parallel to span direction. Curve Number 2 Is same non-overlaid board with long direction of board parallel to'span direction. 41 For l a t e r a l n a i l resistance, a t e s t was devised which simulated actual loading conditions f o r n a i l movement when i n s e r v i c e , f o r example, i n wall paneling. In t h i s t e s t the end of a 2 - hy 1 0 -inch specimen was n a i l e d to a 2 - hy 4-inch stud clamped on the base of the T i n i u s Olsen t e s t i n g machine. N a i l type was 2 # -inch common, as prescribed by the National B u i l d i n g Code (19) f o r wall sheathing. For the same type of n a i l i n g the Housing and Home Finance Agency (10) recommend a 2-inch n a i l . The n a i l was driven i n so that i t s head was f l u s h with the surface of the specimen. Tension was applied at r i g h t angles to the d i r e c t i o n of the n a i l . This apparatus i s shown i n Figure 7\u00C2\u00AB Load was applied at the rate of 0 . 2 5 inches per minute (28). Results are reported i n Appendix G and a s t a t i s t i c a l analysis of the data i s presented i n Appendix H. The nail-withdrawal t e s t was also made on the T i n i u s Olsen universal t e s t i n g machine. A 2-inch n a i l was driven perpendicular to the surface of the 3 - by 3-inch sample, and 1/2 inch of the n a i l was l e f t protruding from the hoard. Specimens were adequately supported during n a i l i n g . A stop-device was constructed around the support to prevent the n a i l from being driven i n past the 1 / 2-inch mark. Testing was made a f t e r n a i l s had remained i n samples f o r 72 hours. Figure 8. Nail-withdrawal Test Assembly 43 The t e s t i n g apparatus i s shown i n Figure. 8. Load was applied at the rate of 0.06 inch per minute (28). Average values and range of values f o r each hoard and a s t a t i s t i c a l a n a l y sis are shown i n Appendices I and J . P h y s i c a l t e s t s Specimens used to measure warping and dimensional change were f i r s t conditioned f o r two weeks at a r e l a t i v e humidity of 75 percent and temperature of 68\u00C2\u00B0F. A f t e r t h i s i n i t i a l conditioning the specimens were measured then reconditioned f o r two more weeks at a r e l a t i v e humidity of 25 percent and temperature of 65\u00C2\u00B0F- This second conditioning was done to induce warping and dimensional change i n the panels. Linear measurements were taken on the l a s t three days of each conditioning period. Specimens were wrapped i n p l a s t i c bags when being t r a n s f e r r e d from the humidity cabinet f o r measurements to insure no moisture l o s s or pick-up. Testing was d i v i d e d into two phases: measurement of warping and measurement of dimensional change. Warp was measured as t w i s t , cup, and bow. Twist was the maximum devia t i o n of the fourth corner of the panel with the other corners held f l a t . Cup was measured as the maximum deviation from the plane surface perpendicular to the face g r a i n (across the machine-direction on the non-overlaid boards), and bow as the maximum deviation p a r a l l e l to the face g r a i n ( p a r a l l e l to the machine d i r e c t i o n of the non-overlaid boards). 44 The micro-ground bottom platen of the Berthelsen hot-press was used f o r measuring warp. Four marks were made on the platen f o r the four corners of the panels. Twist was measured by pl a c i n g a stand-mounted d i a l micrometer on one of the corners held f l a t against the platen, then moving the micrometer up the panel to the fourth corner not l y i n g i n the plane. The difference between the f i r s t and second readings was twi s t . Care was taken to insure that the other three corners were held f l a t to the pl a t e n surface. This method i s i l l u s t r a t e d i n Figure 9\u00C2\u00BB Cup and bow were measured i n the same way. For these l a t t e r measurements the micrometer would be moved from a corner held f l a t on the platen to the highest point of cupping or bowing. This method was more accurate than using f e e l e r gauges or a ve r n i e r c a l i p e r . Dimensional change was measured p a r a l l e l to the length and width of each board. Thus, two specimens were cut from each board\u00E2\u0080\u0094one widthwise and one lengthwise. At each of two points approximately 10 inches apart on the centre l i n e of each specimen a small area was rubbed with a grease p e n c i l . A f i n e cross was marked on the centre l i n e with a razor blade at these two points which were l a t e r used as reference points f o r length measurements. The points were numbered A and B. Thickness measurements were made at these two points with a pre-zeroed Ames d i a l micrometer. Thickness measuring apparatus i s shown i n Figure 10. Length measurements were made with a metal r u l e r capable of being read to 0.01 inch. Readings were taken with a magnifying lens (28). Figure 9 \u00C2\u00AB Method Used for Measuring Twist i n Panels. The zeroed d i a l micrometer was placed on one of three corners held f l a t on surface of platen (top photo), then moved to the corner out of plane of the surface (bottom photo). ;ure 10. Thickness Measuring Micrometer Dial Figure 11. Types of Failure Occurring in Tension Parall Samples A, B, and C are particle boards having brash-typ failures: D and E are flake boards having splintering failures. Sample A, i s overlaid particle board with high-tensile strength p a r a l l e l to grain direction of overlay, in contrast to low tensile strength across grain, as i n sample D^. Sample F, represents high tensile strength, splintering failure of overlaid plywood. 47 Accelerated aging This t e s t was incorporated to determine the amount of veneer delamination, checking, and roughening, and to note e f f e c t of hoard d i s i n t e g r a t i o n . The t e s t was modified somewhat from that suggested hy the Wood P a r t i c l e Board Committee (28). Because of i t s s e v e r i t y on the urea-formaldehyde bonded hoards, the steaming phase of the aging cycle was omitted. As w i l l he further explained, even t h i s modified c y c l i n g t e s t was too severe. Specimens were subjected to s i x cycles of accelerated aging, one cycle of which consisted of the f o l l o w i n g : 1. Immersion i n water at room temperature f o r 4 hours. 2. Storage i n r e f r i g e r a t o r at 30\u00C2\u00B0F f o r 20 hours. 3. Heating i n dry a i r at 145\u00C2\u00B0P f o r 4 hours. 4. Immersion i n water at room temperature f o r 4 hours. 5. Heating i n dry a i r at 145\u00C2\u00B0F f o r 16 hours. 4-8 DISCUSSION OF RESULTS Thicknesses of the hoards before and after pressing are shown i n Table III. Thicknesses for the 3/8-inch hoards ranged from 0.374- to 0.386 inches; plywood thickness was 0.373* Boards A, B, and E had large variations i n thickness, deviating as much as 0.018, 0 . 0 1 3 , and 0.022 inches, respectively. A l l other hoards had tolerances within 0.003 inch. Thickness of panels after pressing was smaller than the combined thicknesses of boards and veneer before lay-up. This decrease i n thickness after pressing was possibly caused hy a small amount of compression i n the boards and veneer during pressing. Glue-line shear Results of this shear test are shown in Table IV. Glue-line fa i l u r e in both dry and wet tests was limited to boards B and C. Board B had 50 percent glue-line failure when tested dry and 10 percent when tested wet. Board C had 10 percent glue-line f a i l u r e when tested both wet and dry. Glue-line fa i l u r e , where i t did occur, was on hoards having the highest specific gravity, namely hoards B and C. It i s possible that because of the denser surfaces of these 49 Table IV. Glue-line Sheat Test Tested Dry Tested Wet Type Load (lb) Glue % Failure Veneer Core Load (lb) Glue % Failure Veneer Core A 67 0 30 70 46 0 0 100 B 93 50 20 30 76 10 20 70 C 91 10 30 60 71 10 20 70 D 81 0 10 90 53 0 0 100 E 82 0 15 85 68 0 0 100 F 75 0 40 60 91 0 5 95 Each value average of 5 specimens. Table V. Analysis of Variance for Glue-line Shear Test Source of Variance Boards (B) Treatment (T) Error Total Correction Degrees of Freedom 5 1 5 11 1 Sum of Squares 1,190 588 595 2,373 66,603 Mean Squares 238 588 119 F 2 . 0 0 0 N.S 4.941 N.S N.S. Not significant at the 5% level. 50 two boards a poor glue bond may have r e s u l t e d during pressing. Surface hardness therefore appeared to influence glue bond. Board A, composed of eastern white pine p a r t i c l e s with a small percentage of hark, had the lowest shear values. Boards D and E were midway i n strength value. When tested dry, some of the f a i l u r e occurred i n the veneer. When tested wet, the p a r t i c l e - t o - p a r t i c l e bonds were weakened and most of the f a i l u r e occurred i n the board core. A l l shear values of the boards decreased when tested wet except those of the plywood. The breaking strength of the o v e r l a i d plywood increased from 75 to 91 p s i following the cold-water soak. Because of the greater t e n s i l e strength of the Douglas f i r p l i e s i n the plywood, much of the wood f a i l u r e i n dry shear was i n the overlay veneer. The grain of the veneer overlay was p a r a l l e l to the grain of the face p l i e s of the plywood. In general, the urea-formaldehyde adhesive used to bond the veneer to the hoards was s a t i s f a c t o r y when the boards were l a i d up according to the press conditions employed here. Although an analysis of variance (Table V) ind i c a t e d no s i g n i f i c a n t d i f f e r e n c e s between boards, or between dry and wet shear values, there was a d e f i n i t e decrease i n values from the dry to the wet condition with the exception noted above of the plywood. Both shear values and wood f a i l u r e i n the veneer decreased when the samples were tested wet because of the weaker board core. Soaking tended to e f f e c t a d e t e r i o r a t i o n of the board core. .51 Tension p a r a l l e l to length and width of surface Values f o r tension p a r a l l e l to the surface are shown i n Table VI. The range of values and analysis of variance of the main e f f e c t s and i n t e r a c t i o n s are given i n Appendices A and B. Overlaid boards had s i g n i f i c a n t l y higher values than non-overlaid hoards. Of the o v e r l a i d hoards, grain d i r e c t i o n was the most s i g n i f i c a n t f a c t o r a f f e c t i n g t e n s i l e strength. The wood veneer, being very high i n t e n s i l e strength p a r a l l e l to the g r a i n , had the e f f e c t of increasing t e n s i l e strength of the panels. Wood (veneer) has a low t e n s i l e strength perpendicular to the grain d i r e c t i o n , and i n general the o v e r l a i d boards had lower t e n s i l e strengths than non-overlaid boards when tested i n t h i s d i r e c t i o n . On t h i s basis i t appears that p a r t i c l e and f l a k e boards have higher t e n s i l e strength than wood across the grain. The veneer overlay tended to minimize d i f f e r e n c e s between boards. Differences between boards, o v e r l a i d and non-overlaid, were s i g n i f i c a n t at the 5 percent confidence l e v e l . A 'studentized T' t e s t was performed and the r e s u l t s i n d i c a t e d that the plywood panels had s i g n i f i c a n t l y higher t e n s i l e strength values than a l l other boards. Non-overlaid boards A and B, of the p a r t i c l e type, were s i g n i f i c a n t l y lower than a l l other hoards, and board D, composed of f l a k e s , had the highest t e n s i l e strength. Boards C and E had t e n s i l e strength values midway between the others. .52 Table VI. A. Summary of Mechanical Properties of Non-overlaid Board Type Tension Modulus Modulus \u00E2\u0080\u00A2 L a t e r a l N a i l -P a r a l l e l o f ' of N a i l * Withdrawal (p s i ) Rupture E l a s t i c i t y Resistance Resistance (psi) (M p s i ) ( l b ) (lb) A p a r a l l e l 670 1 ,030 193 25 perpend. 640 1,010 193 120 B p a r a l l e l 960 1,970 356 32 perpend. 860 1,510 280 160 C p a r a l l e l 1,440 2 ,320 368 30 perpend. 1 ,270 2,070 367 190 D p a r a l l e l 2,600 3 ,920 548 46 perpend. 2 ,590 3,770 548 210 E p a r a l l e l 1,190 3,430 690 30 perpend. 1,190 2,520 544 180 P p a r a l l e l 5 ,570 14 ,190 1,635 31 perpend. 570 2,700 226 230 B. Summary of Mechanical Properties of Overlaid Board Type Tension Modulus Modulus L a t e r a l N a i l -P a r a l l e l of of N a i l * Withdrawal (ps i ) Rupture E l a s t i c i t y Resistance Resistance (p s i ) (M p s i ) (lb) (lb) A p a r a l l e l perpend. 3,680 590 8,120 1,100 1,166 261 205 40 B p a r a l l e l perpend. 4,130 1,010 8,940 1,610 1,045 188 220 59 C p a r a l l e l perpend. 4 , 3 9 0 1 ,300 8,850 1,810 1,137 322 190 46 D p a r a l l e l perpend. 5,140 2,270 9,400 3,230 977 396 200 54 E p a r a l l e l perpend. 4 , 0 2 0 1,060 8,240 1,680 1,062 275 195 33 F p a r a l l e l perpend. 7,490 3,060 10,830 2,490 1,384 119 210 30 * Specimens were p u l l e d so that shear was at r i g h t angles to d i r e c t i o n of face veneer. 53 Although d i f f e r e n c e s were not s i g n i f i c a n t , hoards A, B, and C had higher t e n s i l e strength values p a r a l l e l to the long d i r e c t i o n of the hoard than perpendicular to i t . T e n s i l e strength values f o r hoards D and E i n both d i r e c t i o n s were s i m i l a r . Boards composed of f l a k e s had higher t e n s i l e strength values than those composed of p a r t i c l e s . These find i n g s are i n agreement with those of Turner (24) and Kl a u d i t z , who found that bonding strength increased with p a r t i c l e s i z e . Small p a r t i c l e s require more adhesive hinder per u n i t area. Furthermore, large, t h i n f l a k e s are more compressible, i n s u r i n g a b e t t e r surface-to-surface contact during bonding. Plywood had the highest t e n s i l e strength with two p l i e s p a r a l l e l to the d i r e c t i o n of t e s t i n g ; these values were much lower when one p l y was p a r a l l e l to the d i r e c t i o n of t e s t . Overlaying with veneer increased t e n s i l e strength i n both d i r e c t i o n s , hut because of the normal arrangement of the p l i e s the di f f e r e n c e s were not minimized as they were with the boards. Cross grain i n the core p l y of the plywood accounted f o r the low value i n tension perpendicular to the length of the grai n of the face p l y . Types of f a i l u r e s are i l l u s t r a t e d i n Figure 11. Wood P a r t i c l e Board Handbook, p. 182. 54 Static bending Modulus of rupture. Values for moduli of rupture are shown in Table VI, and the range of values and the analysis of variance i n Appendices C and D. Like tensile strength, grain direction of the veneer was the most significant factor. Differences between hoards were not significant, hut based on a wider interpretation of data, some conclusions could he drawn. The veneer overlay increased strength values of the hoards from 140 to 690 percent when tested p a r a l l e l to the grain. Veneer overlaying also minimized the differences between boards. Moduli of rupture values for overlaid board with direction of grain perpendicular to the span, with the exception of boards A and B, were lower than the values for the non-overlaid board. Wood veneer with the grain at right angles to the span contributed no strength to the board because of the lower fibre stress i n tension across the grain on the bottom, on convex surface, of the specimen under test. Because of the increased moment of i n e r t i a without a corresponding increase i n strength, calculated values for the overlaid board were lower than those of the non-overlaid hoard. Strength of the veneer perpendicular to the grain was less than the strength of the boards. Again, strength of the hoards increased with particle size; non-overlaid boards D and E had the highest 55 strength values i n bending. Board D was the highest. Board A had the lowest values f o r ultimate strength i n bending. Non-overlaid plywood with the face grain p a r a l l e l to the span had the highest strength i n bending. With the face p l i e s perpendicular to the span, strength values f o r the non-o v e r l a i d and o v e r l a i d plywood were higher than those of both the non-overlaid and o v e r l a i d boards, with the exception of board D. Modulus of rupture decreased f o r the o v e r l a i d plywood, presumably because of the lower bending strength of the overlay veneer and the larger c r o s s - s e c t i o n a l area involved. Although not s i g n i f i c a n t i n the 'studentized T' t e s t , a l l boards had higher strength values i n the long d i r e c t i o n of the board. Modulus of e l a s t i c i t y . Values f o r moduli of e l a s t i c i t y , or s t i f f n e s s , are shown i n Table VI, and the range of values and analysis of variance i n Appendices E and E, r e s p e c t i v e l y . Grain d i r e c t i o n was the most s i g n i f i c a n t f a c t o r a f f e c t i n g s t i f f n e s s of the o v e r l a i d boards. When tested p a r a l l e l to the grain of the veneer, s t i f f n e s s values, with the exception of plywood, were increased from 54 to 500 percent. Again, the veneer tended to equalize d i f f e r e n c e s between boards. Board A, having a low s t i f f n e s s value, had a higher value a f t e r overlaying than a l l other boards. 56 S t i f f n e s s values of o v e r l a i d board decreased over those of non-overlaid hoard when tested perpendicular to the grain of the veneer. Board A was an exception i n t h i s case. The reason f o r the lower values was that the cr o s s - s e c t i o n a l areas increased without a corresponding increase i n strength properties of the veneer. F u j i i (6) found the same r e s u l t s when t e s t i n g the a f f e c t of d i f f e r e n t overlays on p a r t i c l e boards. The formula used i n c a l c u l a t i n g modulus of e l a s t i c i t y i s based on an i s o t r o p i c material of rectangular cross-section. As discussed, f o r the plywood and the m u l t i -l a y e r hoards, the s t i f f n e s s values should be considered as the 'apparent moduli of e l a s t i c i t y 1 , since f o r comparative purposes the c a l c u l a t i o n s were based on the rectangular c r o s s - s e c t i o n a l areas of the material. Non-overlaid boards A, B, and C were s i g n i f i c a n t l y lower i n s t i f f n e s s than boards D, E, and F. Flakeboards had higher values than the p a r t i c l e boards. This increase i n strength f o r the flake boards i s discussed i n the section under t e n s i l e strength. S t i f f n e s s decreased i n the over l a i d ' plywood because of the lower bending strength, or f i b r e s t r e s s , of the P h i l i p p i n e mahogany veneer. As i n bending, the diff e r e n c e s i n strength values between p a r a l l e l and perpendicular d i r e c t i o n s of the plywood were large because of the o r i e n t a t i o n of the p l i e s . 57 Values were higher i n the l o n g i t u d i n a l d i r e c t i o n of the hoard. Prom a review of the t e n s i l e strength, ultimate strength i n bending, and s t i f f n e s s p r o p e r t i e s , i t i s under-standable that the wood elements might tend to orient themselves somewhat i n a l o n g i t u d i n a l d i r e c t i o n as they f a l l . onto the mat during the manufacturing process. L a t e r a l n a i l resistance This t e s t was done with the idea of d u p l i c a t i n g l a t e r a l n a i l movement forces on a panel i n actual s e r v i c e , f o r example, when used as wall paneling. Values are given i n Table VI, with ranges and the analysis of variance shown i n Appendices G and H. Although no s i g n i f i c a n t d i f f e r e n c e s were apparent i n the analysis of variance, conclusions were formulated from the type of f a i l u r e of the board. Shearing stresses from the n a i l movement were at r i g h t angles to the grain of the veneer of the o v e r l a i d boards, and at r i g h t angles to the machine d i r e c t i o n of the non-overlaid boards. The overlay increased l a t e r a l n a i l resistance f o r hoards A, B, ami E, but d i d not increase the resistance f o r plywood. On the o v e r l a i d boards the n a i l bent or was being p u l l e d out from the stud a f t e r maximum load was reached at from between 200 to 220 pounds. No rupturing occurred around the n a i l on the o v e r l a i d boards. Non-overlaid hoards A, B, C, and E a l l f a i l e d hy a rupturing of the wood elements 58 around the n a i l . Boards f a i l e d by a combination of tension and shear. An example of t h i s type of f a i l u r e i s shown i n Figure 7\u00C2\u00BB Board D d i d not f a i l ; as i n the plywood and the o v e r l a i d boards, the n a i l bent and p u l l e d out from the stud. Boards A and B had the lowest values i n l a t e r a l n a i l resistance, with loads of 120 and 160 pounds, r e s p e c t i v e l y . Again, overlaying minimized d i f f e r e n c e s between boards. L a t e r a l n a i l resistance of the non-overlaid boards depended on t h e i r composition. Nail-withdrawal resistance Values f o r nail-withdrawal resistance are given i n Table VI, and values f o r range and the analysis of variance are shown i n Appendices I and J. Overlaying the boards had a s i g n i f i c a n t e f f e c t on withdrawal values. With the exception of plywood, nail-withdrawal resistance increased f o r a l l boards. The higher values f o r the over-l a i d board can be explained i n two ways: 1) the increased holding area against the n a i l , and 2) the prevention by the veneer of f i b r e break-away from around the bottom of the board as the n a i l was driven through. Of the non-overlaid? boards, the m u l t i - l a y e r board E and plywood had the lowest r e s u l t s ; however, these d i f f e r e n c e s were not s i g n i f i c a n t at the 5 percent confidence l e v e l . 59 Nail-withdrawal resistance i s generally c o r r e l a t e d with s p e c i f i c g r a v i t y . In these r e s u l t s the hoards with the lowest values also had the lowest d e n s i t i e s . Board A again had the lowest resistance values. In a study such as t h i s , because of the wide range of values f o r each board (Appendix I) and the varying composition of each hoard, i t i s d i f f i c u l t to make d e f i n i t e conclusions r e l a t i n g to n a i l -withdrawal resistance being c o r r e l a t e d with s p e c i f i c g r a v i t y . D r i v i n g the n a i l perpendicular to the surface of the board i s d i f f i c u l t . A n a i l driven at a s l i g h t angle from the normal w i l l tend to have a higher withdrawal resistance (14-). This f a c t o r might have contributed to the wide range of values. I t i s important to note that withdrawal resistance of the hoards was comparable to that of plywood. For more r e l i a b l e r e s u l t s the number of r e p l i c a t e s should be increased. Dimensional change Results of dimension change t e s t s are shown i n Table VII. Dimensional change of p a r a l l e l samples corresponds to change i n length of the e n t i r e board, and perpendicular change r e f e r s to change i n the width of the board. Average decrease i n thickness of the non-overlaid boards i n going from 75 to 25 percent r e l a t i v e humidity was 5^1 percent, and 4 . 5 percent f o r the non-overlaid plywood. For the o v e r l a i d hoards and plywood, these values were 4.0 percent and 3 .7 percent, r e s p e c t i v e l y . Overlaying tended to decrease 60 Table VII. Dimensional Change i n Thickness and Length of Panels Between 75 and 25 Percent Rela-t i v e Humidity Non-overlaid Overlaid Type Thickness (in) (%) Length (in) (%) Thickness (in) (%) Length ( i n ) (%) A p a r a l l e l perpend. 0.16 0.15 * 4.6 0.04 0.03 0.38 0.28 0.15 0.16 3.5 0.02 0.04 0.19 0.38 B p a r a l l e l perpend. 0.20 0.18 5.6 0.04 0 . 0 2 0.38 0.19 0.16 0.17 3.8 0.00 0.04 0.00 0.37 C p a r a l l e l perpend. 0.19 0.17 5.4 0.03 0.02 0.28 0.19 0 .17 0.18 4.1 0 . 0 1 0 . 0 3 0.09 0.35 D p a r a l l e l perpend. 0.21 0.21 6.1 0.02 0.02 0.20 0.20 0.21 0.16 4.3 0.00 0.03 0.00 0.28 E p a r a l l e l perpend. 0.13 0.14 4.0 0.02 0.02 0.19 0 .19 0.16 0 .17 4.0 0.01 0.02 0.09 0.18 F p a r a l l e l perpend. 0.13 0.20 4.5 0.00 0.03 0.00 0.28 0.16 0.16 3.7 0.01 0.03 0.10 0.29 Ave. dimensional change f o r Ave. dimensional change f o r plywood Ave. dimensional change f o r Ave. dimensional change f o r plywood non-overlaid boards 5*1% non-overlaid boards and 5.0% o v e r l a i d boards 3*9% o v e r l a i d boards and 3.9% Average of p a r a l l e l and perpendicular measurements. 61 dimensional change i n thickness. I t i s possible the veneer acted as a b a r r i e r , or slowed moisture pick-up i n the specimens. I f the specimens had been conditioned f o r a longer period i t i s possible that the change i n thickness f o r the o v e r l a i d and non-overlaid boards would have been more nearly equal. The non-overlaid hoards A, B, and C had s l i g h t l y l a r g e r shrinkage values i n length than i n width. Plywood had n e g l i g i b l e shrinkage i n length because of the small l o n g i t u d i n a l shrinkage component of the two face p l i e s . Any r a d i a l swelling of the centre ply.cwould be r e s t r a i n e d by the two face p l i e s . Widthwise i n the plywood, however, the r a d i a l shrinkage of the face p l i e s was r e s t r a i n e d only s l i g h t l y by the l o n g i t u d i n a l shrinking of the centre p l y . The dimensional change i n length and width was equal f o r hoards D and E. Overlaying tended to reduce the i s o t r o p i c shrinking properties of the boards. Shrinking lengthwise i n the o v e r l a i d boards was decreased because of the r e s t r a i n i n g a c t i o n of the veneer due to i t s small component of l o n g i t u d i n a l shrinkage. However, shrinkage i n width increased because of the large r a d i a l shrinkage component of the veneer. Overlaying the plywood tended to increase shrinkage. With the non-overlaid plywood the centre p l y was r e s t r a i n i n g two p l i e s , but when o v e r l a i d , the centre p l y was r e s t r a i n i n g four p l i e s , hence the increased shrinkage. 62 Boards A and E had the smallest dimensional change i n thickness. These two hoards also had the lowest s p e c i f i c g r a v i t y . However, because of the complex nature of the boards, i t i s d i f f i c u l t , w ithin the scope of t h i s study, to cor r e l a t e s p e c i f i c g r a v i t y with percent dimensional change. Variables enter in t o the make-up of the board, such as r e s i n amount, effectiveness of r e s i n f i l m , p a r t i c l e s i z e , and amount of wax a d d i t i v e s , which influence the amount of dimensional change. Warping Amount of twist, cup, and how occurring i n the panels at 75 and 25 percent r e l a t i v e humidity i s shown i n 7 Table VIII. Generally, warping' at 75 percent and at 25 percent r e l a t i v e humidity was approximately the same. Overlaying the boards decreased warping and minimized di f f e r e n c e s between boards. Plywood panels, both o v e r l a i d and non-overlaid, exhibited more warp than the boards. Of the hoards, A had the l a r g e s t amount of twist, cup, and bow. Board B had a large amount of warp at 25 percent r e l a t i v e humidity. Board E had no warping when ov e r l a i d , and very l i t t l e when not o v e r l a i d . The remainder of the hoards had varying amounts of warp f a l l i n g between Refers to twist, cup and how. 63 Table VIII. Warping i n Panels at 75 and 25 Percent Relative Humidity-Type Twist (0.001 in.) Cup (0.001 in.) Bow (0.001 in.) Non-overlaid 75% 25% d i f f . 75% 25% d i f f . 75% 25% d i f f A 85 85 0 38 25 7 24 50 26 B 0 25 25 8 10 2 0 15 15 C 0 5 5 3 6 3 5 7 2 D 10 24 14 7 0 7 5 3 2 E 0 23 23 0 5 5 0 0 0 P 165 16 149 15 9 4 5 7 2 Overlaid A 0 0 0 8 21 13 0 0 0 B 0 6 6 13 14 1 4 2 2 C 5 2 3 0 0 0 2 10 8 D 5 0 5 2 0 2 0 0 0 E 0 0 0 0 0 0 0 0 0 P 93 10 83 12 12 0 7 0 7 64 these two. Differences, where they occurred, d i d not appear to follow a d e f i n i t e trend. When the panels went from 75 to 25 percent r e l a t i v e humidity, warping decreased i n some samples and increased i n others. The warping i n plywood i n several instances reversed i t s e l f . T h e o r e t i c a l l y , plywood constructed of p l i e s placed s y m e t r i c a l l y about the n e u t r a l axis should have shrinkage of the face p l i e s equally r e s t r a i n e d by the centre p l y , and no warping should take place. However, dif f e r e n c e s i n thickness between p l i e s and v a r i a t i o n s i n grain d i r e c t i o n and density within the p l i e s of the plywood accounted f o r the large amount of warp. Warping i n the boards can be ascribed to f i n e s that have f a l l e n or s e t t l e d to the bottom of the mat during formation i n the manufacturing process r e s u l t i n g i n a non-homogeneous mass. Furthermore, non-homogeneity of p a r t i c l e s i z e can cause differences i n swelling or shrinking, r e s u l t i n g i n warp i n the panel. P a r t i c l e and f l a k e boards are composed of small elements of wood. Wood shrinks to a n e g l i g i b l e degree i n the l o n g i t u d i n a l d i r e c t i o n as compared to l a r g e r shrinkage i n i t s r a d i a l and tangential d i r e c t i o n s . By p l a c i n g these wood elements across each other at random as i s done i n board manufacture, the large r a d i a l and tangential shrinkage components are r e s t r a i n e d by the small l o n g i t u d i n a l movement of the adjacent p a r t i c l e s . Generally, 65 boards are constructed with the l o n g i t u d i n a l d i r e c t i o n of the f i b r e s mainly oriented p a r a l l e l to the plane of the panel, hence thickness swelling i s not r e s t r a i n e d . Accelerated aging No delamination of the veneer occurred a f t e r s i x cycles of t h i s t e s t , but i n t e r n a l d e t e r i o r a t i o n of the board core was prevalent. Because of the subjective nature of t h i s t e s t , comparisons between boards were d i f f i c u l t to make. A l l d e t e r i o r a t i o n was i n the board where p a r t i c l e - t o - p a r t i c l e or f l a k e - t o - f l a k e adhesion was l o s t a f t e r repeated cycles of the t e s t . Samples were inspected during each phase of every c y c l e . In the f i r s t c y c l e , boards A and B were the f i r s t to open i n the core, followed by board E. After.'its i n i t i a l d e t e r i o r a t i o n , board E d i d not become appreciably worse with each cycle as d i d most of the other boards. A f t e r s i x cycles board A had almost completely opened i n the centre. Board B was next. The remainder of the boards had about the same degree of d e t e r i o r a t i o n i n the core. Appearance of the boards a f t e r four and s i x cycles i s shown i n Figure 12. Roughness and t w i s t i n g of the veneer corresponded to the amount of core opening; the more the core opened from l o s s of adhesion the more the face veneer would t w i s t . Checking was absent on the veneer of a l l boards, but was 66 pronounced on the surface of the o v e r l a i d plywood samples. This was because the face veneer was not placed at r i g h t angles to the face p l y of the plywood. I f t h i s had been the case, presumably checking would have been s u b s t a n t i a l l y decreased. The overlay and face p l i e s of the plywood, i f placed at r i g h t angles to one another would exert r e s t r a i n i n g action on each other during moisture content changes. In commercial p r a c t i c e , the overlay veneer would be placed with i t s grain d i r e c t i o n p a r a l l e l to the grain d i r e c t i o n of the face p l i e s of the plywood. The a l t e r n a t i v e i s to have s p e c i a l l y constructed plywood where the grain d i r e c t i o n of the overlay i s at r i g h t angles to the grain d i r e c t i o n of the face p l i e s of the plywood. Boards composed of p a r t i c l e s appeared to undergo more d e t e r i o r a t i o n than those composed of f l a k e s . The p a r t i c l e boards had more f a i l u r e because of the large amount of surface area f o r the r e s i n binder to cover e f f e c t i v e l y as compared to the r e l a t i v e l y small amount of surface area of the f l a k e board. Figure 12. Accelerated Aging Samples. Type of d e t e r i o r a t i o n i n board core a f t e r four cycles i s shown i n top photo, and a f t e r s i x cycles, i n bottom photo. >3 68 CONCLUSIONS AND RECOMMENDATIONS The following conclusions have been made from t h i s study: 1. Urea-formaldehyde adhesive was s a t i s f a c t o r y when bonding P h i l i p p i n e mahogany veneer to p a r t i c l e and f l a k e board. Glue-line f a i l u r e was minimal and occurred only on hoards of high density. 2. Overlaying the board with veneer increased t e n s i l e strength p a r a l l e l to the surface, ultimate strength i n bending, and s t i f f n e s s i n the d i r e c t i o n of the grain of the veneer, but generally decreased these properties perpendicular to the d i r e c t i o n of the grain of the veneer. 3. Boards composed of fla k e s had higher strength properties than those composed of p a r t i c l e s . Overlaid plywood had s l i g h t l y higher strength values than the ov e r l a i d boards. 4-. Veneering tended to minimize d i f f e r e n c e s i n both warping and strength properties between the boards. Nail-withdrawal resistance and l a t e r a l n a i l r esistance were also increased. 69 5. Although not s i g n i f i c a n t i n analyses of variance, there were small di f f e r e n c e s i n strength properties between the length and width d i r e c t i o n s of most boards. 6. Veneering decreased warping but d i d not appreciably a f f e c t dimensional change i n thickness and width \"of the panels. Dimensional change i n length of the boards was decreased by the veneer. Plywood exhibited more warping than the boards. 7. No delamination of the veneer occurred a f t e r accelerated aging. Roughness and twist of veneer was r e l a t e d to amount of d e t e r i o r a t i o n i n the board core. P a r t i c l e boards dete r i o r a t e d more r e a d i l y than the f l a k e boards. 8. Board A, composed of eastern white pine, had the lowest values i n p h y s i c a l and mechanical t e s t s . Board D of the f l a k e type and board E of the m u l t i - l a y e r type had the highest values, and boards B and C were intermediate. Prom an analysis of the t e s t procedures and subsequent r e s u l t s , the following recommendations have been formulated: 1. In evaluating p a r t i c l e boards f o r use as p a r t i t i o n s or w a l l paneling, i t might be advisable to use l a r g e r sized samples when measuring warp. For 70 intensive study, a more accurate device to measure deviation from the plane surface also needs to he incorporated. 2. To measure dimensional change, a d i a l micrometer r i g i d l y mounted on a metal base would be more accurate than the method used here (28). More replicates should he taken for warping and dimensional change measurements. 3. As used in this study, the la t e r a l n a i l resistance test was not as satisfactory as might be desired. It did show differences between non-overlaid hoards but was not effective, on overlaid boards. For evaluation of n a i l resistance at varying distances from the edge of the board, the method described in ASTM 1037 D (1) i s recommended. 4-. Because of the wide range of values i n the n a i l -withdrawal test, more replicates should be used. 71 BIBLIOGRAPHY 1. 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Wood P a r t i c l e Board Committee. No date. Recommended t e s t i n g procedures f o r wood p a r t i c l e hoard. Nat. Wood Mfg. Assoc. Chicago. 22 pp. 74 APPENDICES A. Tension P a r a l l e l to Surface of Non-overlaid and Overlaid Boards and Plywood B. Analysis of Variance of Tension P a r a l l e l to Surface as Affected by Overlay and Grain D i r e c t i o n C. Modulus of Rupture of Non-overlaid and Overlaid Boards and Plywood D. Analysis of Variance of Modulus of Rupture as Affected by Overlay and Grain D i r e c t i o n E. Modulus of E l a s t i c i t y of Non-overlaid ahd Overlaid Boards and Plywood P. Analysis of Variance of Modulus of E l a s t i c i t y as Affected by Overlay and Grain D i r e c t i o n G. L a t e r a l N a i l Resistance of Non-overlaid and Overlaid Boards and Plywood H. Analysis of Variance of L a t e r a l N a i l Resistance as Af f e c t e d by Veneer-overlay I. Nail-withdrawal Resistance of Non-overlaid Boards and Plywood J . Analysis of Variance of Nail-withdrawal Resistance as A f f e c t e d by Veneer-overlay Appendix A. Tension Para l l e l to Surface of Non-overlaid and Overlaid Boards and Plywood Type Non-overlaid Overlaid mean(psi) range (psi) mean(psi) range (ps: A par a l l e l 670 610- 750 3680 3650-3750 perpend. 640 \u00E2\u0080\u00A2620- 650 590 570- 610 B pa r a l l e l 960 830-1040 4130 3850-4410 perpend. 860 840- 890 1010 1000-1030 C para l l e l 1440 1380-1490 4390 4230-4544 perpend. 1270 1190-1330 1300 1280-1330 D par a l l e l 2600 2570-2600 5140 4990-5300 perpend. 2590 2300-2880 2270 2110-2500 E pa r a l l e l 1190 1120-1270 4020 3500-4400 perpend. 1190 1140-1210 1060 970-1160 F pa r a l l e l 5570 5200-6250 7490 6670-8450 perpend. 570 2 5 0 - 730 3060 2410-3740 Appendix B. Analysis of Variance of Tension Parallel to Surface as Affected by Overlay and Grain Direction Source of Variance Boards (B) Treatment (T) Grain direction (G) BxT BxG TxG BxGxG Total Corr. Degrees of Freedom 5 1 1 5 . 5 1 5 23 1 Sum of Squares 221,041 143,995 257,716 6,833 84,062 84,609 26,082 824,338 1,386,723 Mean Squares 44,208 143,995 257,716 1,367 16,812 84,609 5,219 8 .475** 27,606 * * * 49.409 0.262 3,223 16.221 significant at the lev e l . * * : * * * significant at the 1% le v e l , significant at the 0.1% level. Appendix C. Modulus of Rupture of Non-Overlaid and Overlaid Boards and Plywood Type Non-overlaid Overlaid mean(psi) range(psi) mean(psi) range(psi) A p a r a l l e l 1030 960- 1080 8120 7930- 8490 perpend. 1010 950- 1040 1100 1090- 1120 B p a r a l l e l 1970 1910- 2000 8940 8470- 9350 perpend. 1510 1510- 1510 1610 1440- 1690 C par a l l e l 2320 2210- 2390 8850 8720- 9041 perpend. 2070 1970- 2120 1810 1800- 1820 D p a r a l l e l 3920 3870- 4030 9400 9270- 9480 perpend. 3770 3420- 3990 3230 2980- 3370 E p a r a l l e l 3430 3420- 3510 8240 8170- 8340 perpend. 2520 2310- 2650 1680 1540- 1770 P par a l l e l 14-190 13380-14940 10830 10280-11260 perpend. 2700 1640- 3660 2490 2080- 2750 Appendix D. Analysis of Variance on Moduli of Rupture As Affected by Overlay and Grain Direction Source of Degrees of Sum of Mean Variance Freedom Squares Squares P Boards (b) 5 571,574 114,315 2.830, Treatment (T) 1 278,641 278,641 6.899. Grain * direction (G) 1 1,269,600 1,269,000 31.436 BxT 5 205,758 41,152 1.019 BxG 5 342,301 68,460 1.695* BxGxT 5 201,937 40,387 9.H3 Total 23 3,237,844 Corr. 1 4,747,262 * significant at 5% l e v e l . ** significant at 1% lev e l . Appendix E. Modulus of E l a s t i c i t y of Non-Overlaid and Overlaid Boards and Plywood Type Non-overlaid Overlaid mean(lOpsi) range (lOpsi) mean(10p si) range(10p; A pa r a l l e l 193 193- 193 1166 1166-1166 perpend. 193 193- 193 261 258- 262 B pa r a l l e l 356 356- 356 1045 1037-1062 perpend. 280 280- 280 188 188- 188 C pa r a l l e l 368 368- 368 1137 1137-1137 perpend. 367 367- 367 322 322- 322 D p a r a l l e l 598 598- 598 997 997- 997 perpend. 598 598- 598 396 393- 399 E p a r a l l e l 690 6 9 0 - 690 1062 950-1122 perpend. 544 399- 617 275 210- 315 P p a r a l l e l 1635 1475- 1867 1384 935-1609 perpend. 226 191- 278 119 111- 132 Appendix P. Analysis of Variance of Moduli of E l a s t i c i t y As Affected by Overlay and Grain Direction Source of Variance Boards (B) Treatment (T) Grain direction (G) BxT BxG TxG BxTxG Total Corr. Degrees of Freedom 5 1 1 5 5 l 5 23 1 Sum of Squares 411,602 230,880 1,933,473 310,124 736,461 554,496 182,254 4,359,298 8,580,104 Mean Squares 82,320 230,880 1,933,473 62,025 147,292 . 554,496 36,451 F 2.258 6.334 53.043 1 .702 4.041, 15.212 significant at the le v e l . * * * significant at the 0.1% l e v e l . Appendix G. L a t e r a l N a i l Resistance of Non-overlaid and Overlaid Boards and Plywood m Non-overlaid Overlaid Load- -, Load- Type Load- Load Type Mean(lb) x Range (lb) F a i l u r e Mean (lb) Range(lb) F a i l u r e A 120 110-135 * 205 205-205 * * B 160 125-175 * 220 195-250 * * C 190 180-210 * 190 180-210 * * * D 210 195-225 * * * 200 160-220 ** * E 180 165-200 * 195 185-215 * * P 230 210-245 * * * 210 205-225 * * * * board f a i l e d around n a i l e i t h e r in.shear, tension, or a combination of these. ** n a i l bent. *** n a i l bent and was being p u l l e d out of stud. each value the average of 4 r e p l i c a t e s . Appendix H. Analysis of Variance of L a t e r a l N a i l Resistance as Affec t e d by Veneer Overlay Source of Variance Boards (B) Treatment (T) Er r o r T o t a l Degrees of Freedom 5 1 5 11 Sum of Squares 37.0 14.0 43.7 446.8 Mean Squares 7-40 14.00 8.74 F 0.847 1.602 Appendix I. Wail-withdrawal Resistance of Non-overlaid and Overlaid Boards and Plywood Type Non-overlaid Overlaid Load-Mean(lb) 1 Load-Range(lb) Load-Mean(lb) Load-Range(lb) A 25 23-27 40 31-54 B 32 19-40 59 49-70 C 30 21-40 46 34-63 D 46 39-54 54 42-67 E 30 20-40 33 28-36 P 31 25-41 30 24-34 1 Each value the average of 6 r e p l i c a t e s . Appendix J. Analysis of Variance on Nail-withdrawal Resistance as Af f e c t e d by Veneer-Overlay Source of Variance Degrees of Freedom Sum of Squares Mean Squares P Boards (B) 5 Treatment (T) 1 E r r o r 5 T o t a l 11 Correction 1 658.0 385-3 256.7 1,300.0 17,328.0 131.6 385-3 51.3 2.56 7.51* s i g n i f i c a n t at the 5% l e v e l . "@en . "Thesis/Dissertation"@en . "10.14288/1.0106045"@en . "eng"@en . "Forestry"@en . "Vancouver : University of British Columbia Library"@en . "University of British Columbia"@en . "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en . "Graduate"@en . "Comparative evaluation of some physical and mechanical properties of veneer-overlaid and non-overlaid particle board"@en . "Text"@en . "http://hdl.handle.net/2429/39899"@en .