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AND STRUCTURE PROPERTIES RELATIONSHIPS OF DENSIFIED WOOD Elena V. Kultikova Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in Wood Science and Forest Products Frederick A. Kamke, Chair Charles E. Frazier Audrey G. Zink-Sharp August 30, 1999 Blacksburg, Virginia Keywords: Densified Wood, Tensile Strength, Stiffness Copyright 1999, Elena V. Kultikova STRUCTURE AND PROPERTIES RELATIONSHIPS OF DENSIFIED WOOD Elena V. Kultikova ABSTRACT The objective of this research was to investigate the effect of applied compressive strain in various environments, on the strength and stiffness of compressed wood samples. It is believed that transverse compression of wood at specific conditions of temperature and moisture will result in improved mechanical properties, which can be attributed to increased density and perhaps other physical or chemical changes. Specimens of both mature and juvenile southern pine (Pinus taeda) and yellow-poplar (Liriodendron tulipifera) were compressed radially at three different temperature, and moisture content conditions relevant to the glass transition of wood. Ultimate tensile stress and longitudinal modulus of elasticity were obtained by testing compressed, uncompressed and control samples in tension parallel-to-grain. Strain measurements were performed using laboratory-built clip-on strain gauge transducers. Results of the tensile tests have shown an increase in the ultimate tensile stress and modulus of elasticity after all densification treatments. Scanning electron microscopy was employed for observing changes in cellular structure of densified wood. Existence of the cell wall fractures was evaluated using image processing and analysis software. Changes in cellular structure were correlated with the results of the tensile test. Chemical composition of wood samples before and after desorption experiments was determined by acid hydrolysis followed by high performance liquid chromatography (HPLC). The results of the chemical analysis of the wood specimens did not reveal significant changes in chemical composition of wood when subjected to 160 C, pure steam for up to 8 hours. The results of this research will provide information about modifications that occur during wood compression and will result in better understanding of material behavior during the i manufacture of wood-based composites. In the long run, modification of wood with inadequate mechanical properties can have a significant effect on the wood products industry. Low density and juvenile wood can be used in new high-performance wood-based composite materials instead of old-growth timber. ii ACKNOWLEDGEMENTS I would like to express my sincere appreciation to my advisor Dr. Frederick A. Kamke for his excellent technical guidance, never-ending support, encouragement, and patience throughout my graduate education. One can not wish for a better advisor and teacher. I am also grateful to the other members of my committee, Dr. Chip Frazier and Dr. Audrey Zink-Sharp who served as my teachers and guides during my study at Virginia Tech. Their helpful suggestions and assistance during the course of this project are greatly appreciated. I also would like to acknowledge the support of the USDA National Research Initiative Competitive Grants Program. Special thanks to Dr. George Stern, Dr. Joseph Loferski, Dr. Geza Ifju and others who provided me with the opportunity to study in the United States. This project would not have been possible without extensive assistance of the staff and students of the Department of Wood Science and Forest Products. Many thanks to Harrison Sizemore (Butch), Carlile Price, Jody Jervis, Angie Riegel, Sharon Daley and the members of the Wood Composites Group, Chris Lenth, Mansur Ahmad, and Balazs Zombori. I also would like to thank Andrew Kuti and Mike Lockhart for help with preparing samples for this research. My friends and fellow grad students at Virginia Tech have also been a source of encouragement. I would like to acknowledge the support and friendship of Nicole Robitaille, Marie Laborie, Balazs Zombori, Chris Heine, Alex Salenikovich, Victor Makarov, Vladimir Kochkin, and Olga Stepanova. Special thanks to the friends from International Bible Study Group for their sincere prayer and true friendship in Christ. Finally, but most importantly, I would like to thank my mother, Galina, father, Vasilii, and brother, Alexander, for their love, encouragement and continued support throughout the course of my studies. All my achievements would not be possible without them. iii TABLE OF CONTENTS Abstract.............................................................................................................................i Acknowledgements ........................................................................................................ iii Table of Contents............................................................................................................iv List of Tables...................................................................................................................vi List of Figures ................................................................................................................vii CHAPTER 1. 1.1 1.2 1.3 CHAPTER 2. 2.1 Project Description ..............................................................................1 Introduction ...........................................................................................1 Technical Objectives .............................................................................1 Rationale and Significance .................................................................... 1 Literature Review ................................................................................3 Densified Wood.....................................................................................3 2.1.1 Background................................................................................3 2.1.2 Wood Stabilization ....................................................................4 Influence of High temperature and Steam Pressure on Wood................6 2.2.1 Viscoelastic Behavior of Amorphous Polymers in Wood ..........6 2.2.2 Compression of Cellular Materials ............................................8 References .............................................................................................9 Effect of Densification on Tensile Strength and Stiffness Parallel to the Grain ..........................................................................12 Introduction .........................................................................................12 Background .........................................................................................12 Experimental .......................................................................................13 3.3.1 Materials ..................................................................................13 3.3.2 Methods ...................................................................................14 Results and Discussion ........................................................................24 Conclusions .........................................................................................29 References ...........................................................................................30 Effect of Densification on Wood Structure ......................................53 Introduction .........................................................................................53 Background .........................................................................................53 Experimental .......................................................................................55 4.3.1 Materials ..................................................................................55 4.3.2 Methods ...................................................................................55 Results and Discussion ........................................................................56 Conclusions .........................................................................................57 References ...........................................................................................57 2.2 2.3 CHAPTER 3. 3.1 3.2 3.3 3.4 3.5 3.6 CHAPTER 4. 4.1 4.2 4.3 4.4 4.5 4.6 iv CHAPTER 5. 5.1 5.2 Effect of Densification on Chemical Composition of Wood............59 Introduction .........................................................................................59 Experimental .......................................................................................59 5.2.1 Materials ..................................................................................59 5.2.2 Methods ...................................................................................60 Results and Discussion ........................................................................60 Conclusions .........................................................................................61 References ...........................................................................................61 Summary ............................................................................................63 5.3 5.4 5.5 CHAPTER 6. APPENDIX A: Calculations of the Pump Pressure...................................................64 APPENDIX B: Statistical Analysis.............................................................................65 APPENDIX C: Images of Undensified and Densified Wood Specimens..................84 VITA.............................................................................................................................136 v LIST OF TABLES Summary of compression levels and environments by specimen type ..................31 Environmental conditions and number of replications for densification treatments (420 total specimens) ...........................................................................31 3.3 Average data for specific gravity and moisture content (control samples) ............32 3.4 Average data for ovendry specific gravity before (G orig) and after (G) each densification treatment and for the change in specific gravity ( G) ......................33 3.5 Average moisture content before and after each densification treatment...............34 3.6 Time used for each densification treatment, in minutes, and temperature inside the samples at each step of the densification process, C. .....................................34 3.7 Average moisture content of the tensile test specimens, % ...................................35 3.8 Average grain angle measured in the narrowest portion of the tensile test specimens, (degrees)..........................................................................................36 3.9 Mean and coefficient of variation (COV) for ultimate tensile stress and tensile modulus, and mean for ovendry specific gravity of the samples tested in tension parallel-to-grain.....................................................................................................37 3.10 Mean and coefficient of variation (COV) for specific ultimate tensile stress and specific tensile modulus, and mean for ovendry specific gravity of the samples tested in tension parallel-to-grain.............................................................38 5.1 Composition of wood samples (southern pine, aspen, yellow-poplar) before and after desorption experiment ............................................................................62 3.1 3.2 vi LIST OF FIGURES 2.1 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21 3.22 3.23 3.24 3.25 3.26 Typical stress-strain curve characterizing a cellular material in compression..........9 Test specimen, showing location of thickness measurements................................14 Tg of lignin vs. moisture content (by Kwei eguation) and environmental conditions..............................................................................................................15 Tension parallel-to-grain test specimen.................................................................18 Details of CET ......................................................................................................19 Details of the sample test fixture ...........................................................................20 Effect of grain angle on the tensile, bending and compression strength of timber ....................................................................................................................22 Distribution of the stresses on a plain oriented at degrees to uniaxial load ........23 Hydraulic press .....................................................................................................39 A diagram of the pressurized sorption apparatus...................................................40 Tensile test setup ...................................................................................................41 An image of the tensile test specimen illustrating grain angle measurement .........42 Average ultimate tensile stress, N/mm2, of mature southern pine samples tested in tension parallel-to-grain ....................................................................................43 Average tensile modulus, N/mm2, of mature southern pine samples tested in tension parallel-to-grain ....................................................................................43 Average specific ultimate tensile stress, N/mm2, of mature southern pine samples tested in tension parallel-to-grain.............................................................44 Average specific tensile modulus, N/mm2, of mature southern pine samples tested in tension parallel-to-grain ..........................................................................44 Average ultimate tensile stress, N/mm2, of juvenile yellow-poplar samples tested in tension parallel-to-grain ..........................................................................45 Average tensile modulus, N/mm2, of juvenile yellow-poplar samples tested in tension parallel-to-grain ....................................................................................45 Average specific ultimate tensile stress, N/mm2, of juvenile yellow-poplar samples tested in tension parallel-to-grain.............................................................46 Average specific tensile modulus, N/mm2, of juvenile yellow-poplar samples tested in tension parallel-to-grain ..........................................................................46 Average ultimate tensile stress, N/mm2, of mature yellow-poplar samples (3mm) tested in tension parallel-to-grain...............................................................47 Average tensile modulus, N/mm2, of mature yellow-poplar samples (3mm) tested in tension parallel-to-grain ..........................................................................47 Average ultimate specific tensile stress, N/mm2, of mature yellow-poplar samples (3mm) tested in tension parallel-to-grain .................................................48 Average specific tensile modulus, N/mm2, of mature yellow-poplar samples (3mm) tested in tension parallel-to-grain...............................................................48 Average ultimate tensile stress, N/mm2, of mature yellow-poplar samples (4mm) tested in tension parallel-to-grain...............................................................49 Average tensile modulus, N/mm2, of mature yellow-poplar samples (4mm) tested in tension parallel-to-grain ..........................................................................49 Average specific ultimate tensile stress, N/mm2, of mature yellow-poplar samples (4mm) tested in tension parallel-to-grain .................................................50 vii 3.27 Average specific tensile modulus, N/mm2, of mature yellow-poplar samples (4mm) tested in tension parallel-to-grain...............................................................50 3.28 Average change in specific gravity of mature southern pine specimens after all densification treatments.........................................................................................51 3.29 Average change in specific gravity of mature yellow-poplar specimens after all densification treatments.........................................................................................51 3.30 Average change in specific gravity of juvenile yellow-poplar specimens after all densification treatments.........................................................................................52 4.1 Cross sections of compressed Douglas-fir flakes. (a) Elastic collapse (160x), (b) Fractures in cell walls caused by extreme buckling (250x)..............................54 B1 Interaction Plot: Mean Ultimate Stress vs. Treatment at three levels of strain.......67 B2 Interaction Plot: Mean Ultimate Stress vs. Treatment at two levels of species ......67 B3 Interaction Plot: Mean Tensile Modulus vs. Treatment at three levels of strain. ...70 B4 Interaction Plot: Mean Specific Ultimate stress vs. Treatment at three levels of strain .................................................................................................................72 B5 Interaction Plot: Mean Specific Ultimate Stress vs. Treatment at two levels of species...............................................................................................................72 B6 Interaction Plot: Mean Specific Modulus vs. Treatment at three levels of strain ...75 B7 Interaction Plot: Mean Specific Modulus vs. Treatment at two levels of species ..75 B8 Interaction Plot: Mean Change in Specific Gravity vs. Treatment at three levels of strain .......................................................................................................78 B9 Interaction Plot: Mean Change in Specific Gravity vs. Treatment at two levels of species.....................................................................................................78 B10 Interaction Plot: Mean Change in Specific Gravity vs. Strain at two levels of species...............................................................................................................79 B11 Interaction Plot: Mean Change in Specific Gravity vs. Strain at two levels of types of wood....................................................................................................79 C1 SEM micrograph of juvenile yellow-poplar (control)............................................85 C2 SEM micrograph of juvenile yellow-poplar (control)............................................85 C3 SEM micrograph of compressed juvenile yellow-poplar (TRT1)..........................86 C4 SEM micrograph of compressed juvenile yellow-poplar (TRT1) showing buckling of the cell wall in the radial direction .....................................................86 C5 SEM micrograph of compressed juvenile yellow-poplar (TRT1) showing an elastic collapse of the vessel walls caused by extreme buckling .......................87 C6 SEM micrograph of uncompressed juvenile yellow-poplar (TRT1)......................87 C7 SEM micrograph of compressed juvenile yellow-poplar (TRT1)..........................88 C8 SEM micrograph of compressed juvenile yellow-poplar (TRT1) showing failure in the cell wall............................................................................................88 C9 SEM micrograph of compressed juvenile yellow-poplar specimen (TRT1) showing elastic collapse of the vessel wall............................................................89 C10 SEM micrograph of compressed juvenile yellow-poplar (TRT2)..........................89 C11 SEM image of compressed juvenile yellow-poplar (TRT2) showing interior progressive cell wall collapse ................................................................................90 C12 SEM micrograph of compressed juvenile yellow-poplar (TRT2) showing elastic collapse of the vessel walls.........................................................................90 C13 SEM micrograph of uncompressed juvenile yellow-poplar (TRT2)......................91 viii C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 C28 C29 C30 C31 C32 C33 C34 C35 C36 C37 C38 C39 C40 C41 C42 C43 C44 C45 C46 C47 C48 C49 SEM micrograph of uncompressed juvenile yellow-poplar (TRT2) ......................91 SEM micrograph of compressed juvenile yellow-poplar (TRT3).........................92 SEM micrograph of compressed juvenile yellow-poplar (TRT3).........................92 SEM micrograph of compressed juvenile yellow-poplar (TRT3).........................93 SEM micrograph of compressed juvenile yellow-poplar (TRT3) showing plastic yielding caused by extreme buckling .........................................................93 SEM micrograph of uncompressed juvenile yellow-poplar (TRT3)......................94 SEM micrograph of uncompressed juvenile yellow-poplar (TRT3)......................94 SEM micrograph of compressed juvenile yellow-poplar (TRT3).........................95 SEM micrograph of compressed juvenile yellow-poplar (TRT3) showing buckling if the ray and the vessel wall...................................................................95 SEM micrograph of control mature yellow-poplar (4mm) ....................................96 SEM micrograph of compressed mature yellow-poplar (4mm), TRT1, showing multiple fractures in the cell walls.........................................................................96 SEM micrograph of compressed mature yellow-poplar (4mm), TRT1, showing failure caused by extreme buckling .......................................................................97 SEM micrograph of compressed mature yellow-poplar (4mm), TRT1, showing multiple fractures and vessel collapse ...................................................................97 SEM micrograph of uncompressed mature yellow-poplar (4mm), TRT1..............98 SEM micrograph of uncompressed mature yellow-poplar (4mm), TRT1..............98 SEM micrograph of compressed mature yellow-poplar (4mm), TRT1..................99 SEM micrograph of compressed mature yellow-poplar (4mm), TRT1, showing cell wall collapse in radial direction ......................................................................99 SEM micrograph of compressed mature yellow-poplar (4mm), TRT1, showing multiple fractures in the cell walls.......................................................................100 SEM micrograph of compressed mature yellow-poplar (4mm), TRT1, showing collapse of the vessel walls and fractures in fiber tracheids.................................100 SEM micrograph of compressed mature yellow-poplar (4mm), TRT1................101 SEM micrograph of uncompressed mature yellow-poplar (4mm), TRT1............101 SEM micrograph of uncompressed mature yellow-poplar (4mm), TRT1............102 SEM micrograph of uncompressed mature yellow-poplar (4mm), TRT1............102 SEM micrograph of compressed mature yellow-poplar (4mm), TRT2................103 SEM micrograph of compressed mature yellow-poplar (4mm), TRT2, showing elastic collapse of the vessel walls.......................................................................103 SEM micrograph of compressed mature yellow-poplar (4mm), TRT2, showing separation of the fiber tracheids...........................................................................104 SEM micrograph of uncompressed mature yellow-poplar (4mm), TRT2............104 SEM micrograph of uncompressed mature yellow-poplar (4mm), TRT2............105 SEM micrograph of compressed mature yellow-poplar (4mm), TRT2................105 SEM micrograph of compressed mature yellow-poplar (4mm), TRT2................106 SEM micrograph of compressed mature yellow-poplar (4mm), TRT2................106 SEM micrograph of uncompressed mature yellow-poplar (4mm), TRT2............107 SEM micrograph of uncompressed mature yellow-poplar (4mm), TRT2............107 SEM micrograph of compressed mature yellow-poplar (4mm), TRT3................108 SEM micrograph of compressed mature yellow-poplar (4mm), TRT3................108 SEM micrograph of compressed mature yellow-poplar (4mm), TRT3................109 ix C50 C51 C52 C53 C54 C55 C56 C57 C58 C59 C60 C61 C62 C63 C64 C65 C66 C67 C68 C69 C70 C71 C72 C73 C74 C75 C76 C77 C78 C79 C80 C81 C82 C83 C84 C85 C86 SEM micrograph of uncompressed mature yellow-poplar (4mm), TRT3............109 SEM micrograph of uncompressed mature yellow-poplar (4mm), TRT3............110 SEM micrograph of compressed mature yellow-poplar (4mm), TRT3................110 SEM micrograph of compressed mature yellow-poplar (4mm), TRT3, showing multiple fractures in the cell walls.......................................................................111 SEM micrograph of compressed mature yellow-poplar (4mm), TRT3................111 SEM micrograph of uncompressed mature yellow-poplar (4mm), TRT3............112 SEM micrograph of uncompressed mature yellow-poplar (4mm), TRT3............112 SEM micrograph of compressed mature yellow-poplar (3mm), TRT1................113 SEM micrograph of compressed mature yellow-poplar (3mm), TRT1................113 SEM micrograph of compressed mature yellow-poplar (3mm), TRT1, showing brittle fractures in the cell walls...........................................................................114 SEM micrograph of compressed mature yellow-poplar (3mm), TRT1, showing buckling of the ray and elastic collapse of the vessel walls .................................114 SEM micrograph of compressed mature yellow-poplar (3mm), TRT1................115 SEM image of uncompressed mature yellow-poplar (3mm), TRT1 ....................115 SEM micrograph of uncompressed mature yellow-poplar (3mm), TRT1............116 SEM micrograph of compressed mature yellow-poplar (3mm), TRT2................116 SEM micrograph of compressed mature yellow-poplar (3mm), TRT2................117 SEM micrograph of compressed mature yellow-poplar (3mm), TRT2, showing separation between the fiber tracheids.................................................................117 SEM micrograph of uncompressed mature yellow-poplar (3mm), TRT2............118 SEM micrograph of uncompressed mature yellow-poplar (3mm), TRT2............118 SEM micrograph of compressed mature yellow-poplar (3mm), TRT3................119 SEM micrograph of compressed mature yellow-poplar (3mm), TRT3, showing elastic bending of the ray and the vessel walls .....................................119 SEM micrograph of compressed mature yellow-poplar (3mm), TRT3................120 SEM micrograph of compressed mature yellow-poplar (3mm), TRT3................120 SEM micrograph of uncompressed mature yellow-poplar (3mm), TRT3............121 SEM micrograph of uncompressed mature yellow-poplar (3mm), TRT3............121 SEM micrograph of mature southern pine, control..............................................122 SEM micrograph of mature southern pine, control..............................................122 SEM micrograph of mature southern pine, control..............................................123 SEM micrograph of compressed mature southern pine, TRT1 ............................123 SEM micrograph of compressed mature southern pine, TRT1 ............................124 SEM micrograph of compressed mature southern pine, TRT1 ............................124 SEM micrograph of compressed mature southern pine, TRT1, showing multiple fractures in earlywood tracheids............................................................125 SEM micrograph of compressed mature southern pine, TRT1, showing cracks in the walls of latewood tracheids ............................................................125 SEM micrograph of compressed mature southern pine, TRT1, multiple fractures in earlywood tracheids..........................................................................126 SEM micrograph of compressed mature southern pine, TRT1, showing failure of earlywood tracheids .............................................................................126 SEM micrograph of uncompressed mature southern pine, TRT1 ........................127 SEM micrograph of uncompressed mature southern pine, TRT1 ........................127 x C87 SEM micrograph of compressed mature southern pine, TRT2 ............................128 C88 SEM micrograph of compressed mature southern pine, TRT2 ............................128 C89 SEM micrograph of compressed mature southern pine, TRT2, showing separation between earlywood tracheids .............................................................129 C90 SEM micrograph of compressed mature southern pine, TRT2, showing multiple cracks in the tracheids walls ..................................................................129 C91 SEM micrograph of compressed mature southern pine, TRT2 ............................130 C92 SEM micrograph of compressed mature southern pine, TRT2 ............................130 C93 SEM micrograph of uncompressed mature southern pine, TRT2 ........................131 C94 SEM micrograph of uncompressed mature southern pine, TRT2 ........................131 C95 SEM micrograph of compressed mature southern pine, TRT3 ............................132 C96 SEM micrograph of compressed mature southern pine, TRT3 ............................132 C97 SEM micrograph of compressed mature southern pine, TRT3 ............................133 C98 SEM micrograph of compressed mature southern pine, TRT3, showing elastic collapse of the earlywood tracheids..........................................................133 C99 SEM micrograph of compressed mature southern pine, TRT3 (mostly elasic collapse) .......................................................................................134 C100 SEM micrograph of uncompressed mature southern pine, TRT3 ........................134 C101 SEM micrograph of uncompressed mature southern pine, TRT3 ........................135 C102 SEM micrograph of compressed mature yellow-poplar (fully densified). ...........135 xi

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