Introduction to Wood and Natural Fiber Composites

by Stokke, Douglas D.; Wu, Qinglin; Han, Guangping; Stevens, Christian V.

• ISBN13: 9780470710913
• ISBN10: 0470710918
• Edition: 1st
• Format: Hardcover
• Copyright: 2013-12-31
• Publisher: Wiley

Summary

Over the past two decades, there has been a shift in research and industrial practice, and products traditionally manufactured primarily from wood are increasingly combined with other nonwood materials of either natural or synthetic origin. Wood and other plant-based fiber is routinely combined with adhesives, polymers, and other "ingredients" to produce composite materials.

Introduction to Wood and Natural Fiber Composites draws together widely scattered information concerning fundamental concepts and technical applications, essential to the manufacture of wood and natural fiber composites. The topics addressed include basic information on the chemical and physical composition of wood and other lignocellulosic materials, the behavior of these materials under thermocompression processes, fundamentals of adhesion, specific adhesive systems used to manufacture composite materials, and an overview of the industrial technologies used to manufacture major product categories. The book concludes with a chapter on the burgeoning field of natural fiber-plastic composites.

Introduction to Wood and Natural Fiber Composites is a valuable resource for upper-level undergraduate students and graduate students studying forest products and wood science, as well as for practicing professionals working in operational areas of wood- and natural-fiber processing.

For more information on the Wiley Series in Renewable Resources, visit www.wiley.com/go/rrs

Topics covered include: 

• Overview of lignocellulosic material, their chemical and physical composition
• Consolidation behavior of wood and fiber in response to heat and pressure
• Fundamentals of adhesion
• Adhesives used to bond wood and lignocellulosic composites
• Manufacturing technology of major product types
• Fiber/plastic composites

Author Biography

Douglas D. Stokke
Department of Natural Resource Ecology and Management, Iowa State University, Ames, USA

Qinglin Wu
School of Renewable Natural Resources, Louisiana State University AgCenter, Baton Rouge, USA

Guangping Han
College of Material Science and Engineering, Northeast Forestry University, Harbin, China

Series Editor
Christian Stevens
Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium

Table of Contents

Series Preface xi

Preface xiii

Acknowledgments xv

1 Wood and Natural Fiber Composites: An Overview 1

1.1 Introduction 1

1.2 What Is Wood? 1

1.3 Natural Fibers 2

1.3.1 Fibers 2

1.3.2 Lignocellulosic Materials 4

1.3.3 Worldwide Lignocellulosic Fiber Resources 4

1.3.4 Wood as a Teaching Example 5

1.4 Composite Concept 6

1.4.1 Composites Are Important Materials 6

1.4.2 What Is a Composite? 7

1.4.3 Taxonomy of Matrix Composites 7

1.4.4 Laminar Composites 9

1.4.5 Taxonomy of Wood and Natural Fiber Composites 10

1.4.6 Composite Scale 12

1.5 Cellular Solids 13

1.5.1 Natural and Synthetic Cellular Solids 13

1.5.2 Relative Density 14

1.6 Objectives and Organization of This Book 15

References 16

2 Lignocellulosic Materials 19

2.1 Introduction 19

2.2 Chemical Composition of Lignocellulosic Materials 19

2.2.1 Polymers: Structure and Properties 19

2.2.2 Lignocellulose 20

2.2.3 Cellulose 21

2.2.4 Hemicelluloses 28

2.2.5 Lignin 31

2.2.6 Extractives and Extraneous Materials 34

2.3 The Woody Cell Wall as a Multicomponent Polymer System 35

2.3.1 Skeletal Framework Polymers 35

2.3.2 Reinforced Matrix Theory 36

2.3.3 Cell Wall Ultrastructure 36

2.3.4 Cell Wall Structure Dictates Physical Properties 38

2.3.5 Cell Wall Structure from Molecular to Anatomic Level 39

2.4 Anatomical Structure of Representative Plants 40

2.4.1 Plant Cell Walls Are Not Solitary Entities 40

2.4.2 Structure of Grain Crop Stems 42

2.4.3 Structure of Herbaceous Biomass Crop Stems 45

2.4.4 Structure of Bast Fiber Stems 46

2.4.5 Structure of Woody Monocotyledons 49

2.4.6 Wood 52

2.5 Comparison of Representative Plant Stems 57

2.6 Cellular Solids Revisited 57

References 57

3 Wood as a Lignocellulose Exemplar 61

3.1 Introduction 61

3.2 Wood as a Representative Lignocellulosic Material: Important

Physical Attributes 61

3.3 Moisture Interactions 61

3.3.1 Moisture Content 62

3.3.2 Hygroscopicity 63

3.3.3 States of Water in Wood 69

3.3.4 Capillary or Free Water 72

3.3.5 Shrinking and Swelling due to Moisture Flux 72

3.4 Density and Specific Gravity of Wood 74

3.4.1 Density 74

3.4.2 Specific Gravity of Wood 76

3.5 Wood: A Cellular Solid 79

3.5.1 Relative Density of Wood 79

3.6 Mechanical Properties 80

3.6.1 Compression Strength 80

3.6.2 Compression Strength of Wood versus Relative Density 82

3.6.3 Mechanical Properties in Context 83

3.7 Wood Is the Exemplar: Extending Principles to Other Plant Materials 83

References 83

4 Consolidation Behavior of Lignocellulosic Materials 85

4.1 Introduction 85

4.2 Synthetic Crystalline and Amorphous Polymers 85

4.2.1 Polyethylene 86

4.2.2 Polystyrene: Isotactic, Syndiotactic, and Atactic 86

4.2.3 Degree of Crystallinity, Revisited 87

4.2.4 Thermal Softening of Amorphous Polymers: Glass Transition

Temperature, Tg 88

4.3 Glass Transition Temperature of Wood Polymers 89

4.3.1 Glass Transition Temperature of Wood Polymers: Empirical Data 90

4.3.2 Kwei Equation: Modeling Tg of Wood Polymers 95

4.4 Viscoelastic Behavior of Lignocellulosic Materials 97

4.4.1 Time–Temperature Superposition 97

4.4.2 Viscoelasticity in Mechanical Systems 98

4.4.3 Stress and Strain 99

4.4.4 A Trampoline Analogy 100

4.4.5 Hysteresis 101

4.4.6 A Classic Model of Viscoelastic Stress Relaxation:

Maxwell Body 101

4.4.7 Lignocellulosic Materials Are Viscoelastic 104

4.5 Heat and Mass Transfer 104

4.5.1 Hot Pressing Parameters 104

4.5.2 Thermodynamics 101 105

4.5.3 Thermodynamics of Water 106

4.5.4 Mass Transfer: Moisture Vapor Movement 108

4.5.5 Heat Transfer: Conduction 109

4.5.6 Heat Transfer: Convection 110

4.5.7 Internal Mat Conditions 111

4.6 Consolidation Behavior: Viscoelasticity Manifested During

Hot Pressing 112

4.6.1 Response of a Viscoelastic Foam to Compression 112

4.6.2 Viscoelastic Response of Lignocellulosic Material

to Thermocompression 113

4.6.3 Vertical Density Profile 117

4.7 Press Cycles 119

4.7.1 Effect of Press Closing Time on Development of Vertical

Density Profile 119

4.7.2 Effect of Mat Moisture Content on Face Density 120

4.7.3 Effect of Furnish Density and Compaction Ratio on

Composite Properties 121

4.8 Horizontal Density Distribution 123

4.8.1 In-Plane Density Variation 123

4.8.2 Thickness Swelling 124

References 125

5 Fundamentals of Adhesion 129

5.1 Introduction 129

5.2 Overview of Adhesion as a Science 129

5.2.1 A Brief History of Adhesion Science 129

5.2.2 Adhesive Bonding 130

5.2.3 Adherend 131

5.2.4 Adhesive 131

5.2.5 Adhesive Joint 131

5.2.6 Marra’s Concept of Bond Anatomy 132

5.2.7 Contemporary Concept of Bond Anatomy 132

5.2.8 Scale of Adhesive Bond Interactions 134

5.3 Adhesion Theories 136

5.3.1 Overview of Adhesion Theories 136

5.3.2 Mechanical Adhesion 137

5.3.3 Specific Adhesion 138

5.4 Surface Interactions 143

5.4.1 Surface Interactions Are Critical Determinants of Adhesion 143

5.4.2 Surface Energy of Liquids and Solids 143

5.4.3 Wetting Phenomenon 148

5.5 Work of Adhesion: Dupr´e Equation 152

5.6 Lignocellulosic Adherends 153

5.6.1 Adhesive Resin–Substrate Interactions 153

5.6.2 Adhesion as a Surface Phenomenon 153

5.6.3 Lignocellulosic Adherends Present Challenges to Adhesion 154

5.6.4 Wood Adherend Variables 155

5.6.5 Mechanisms of Wood Bonding 164

5.6.6 Durable Wood Adhesive Bonds 165

References 166

6 Adhesives Used to Bond Wood and Lignocellulosic Composites 169

6.1 Introduction 169

6.2 The Nature of Wood Adhesives 169

6.2.1 Most Wood Adhesives Are Organic Polymers 170

6.2.2 Molecular Weight, Viscosity, Gel Time, and Tack Are Important

Attributes of Polymeric Adhesive Resins 170

6.3 Adhesives Used to Bond Wood and Other Natural Fibers 175

6.3.1 Classification of Adhesives by Origin 175

6.3.2 Classification of Adhesives by Structural Integrity and

Service Environment 175

6.3.3 Classification of Adhesives by Response to Heat 177

6.4 Amino Resins 178

6.4.1 Urea Formaldehyde Resins 179

6.4.2 Melamine Formaldehyde Resins 183

6.5 Phenolic Resins 184

6.5.1 Resoles (Resols) 184

6.5.2 Novolacs (Novolaks) 186

6.5.3 Comparison of Key Attributes and Uses of Resoles

and Novolacs 187

6.6 Resorcinol Resins 188

6.6.1 Synthesis 189

6.6.2 Cure Chemistry 189

6.6.3 Phenol-Resorcinol-Formaldehyde (PRF) 190

6.7 Polymeric Isocyanate Adhesives 190

6.7.1 Isocyanate Synthesis 190

6.7.2 Isocyanates Used as Wood Adhesives 191

6.7.3 Polyurethane Adhesives 192

6.8 Epoxy Adhesives 193

6.8.1 Synthesis 193

6.8.2 Cure Chemistry 194

6.8.3 Durability of Wood-Epoxy Bonds 195

6.9 Polyvinyl Acetate Adhesives 196

6.9.1 Synthesis 196

6.9.2 Solvent Loss Cure Mechanism 196

6.9.3 Modified PVAc 197

6.10 Hot Melts and Mastics 197

6.10.1 Hot Melts 197

6.10.2 Mastics 198

6.11 Adhesives from Renewable Natural Resources 199

6.11.1 Classes of Natural Materials for Adhesives 199

6.11.2 Lignins in Adhesive Formulation 202

6.11.3 Plant-Derived Tannins as Adhesives 203

6.11.4 Soy Protein Adhesives 204

6.11.5 Animal Protein Adhesives 205

6.11.6 Adhesives Future 206

References 206

7 Technology of Major Wood- and Fiber-Based Composites: An Overview 209

7.1 Introduction 209

7.2 Wood and Natural Fiber Composites as a Material Class 210

7.3 Taxonomy of Adhesive-Bonded Composites Technology 210

7.4 A Generic Process Flow 212

7.5 Technology of Adhesive-Bonded Materials Based on Form of Raw

Material Input 213

7.5.1 Glued-Laminated Timber and Cross-Laminated Timber 213

7.5.2 Plywood, Laminated Veneer Lumber and Parallel

Strand Lumber 215

7.5.3 Technology of Strand Composites 217

7.5.4 Particleboard 218

7.5.5 Medium Density Fiberboard and Hardboard 218

7.6 Laboratory Panel Calculations 219

7.6.1 Material Needs 220

7.6.2 Clamping or Consolidation Pressure 221

7.6.3 Glue Application Rate for Lumber and Veneer Substrates 221

7.7 Measurement Conventions for Production Capacity and Output 222

7.7.1 Measures for Lumber- and Timber-Like Products 222

7.7.2 Measures for Panel Products 224

7.8 Technology of Inorganic-Bonded Materials 225

7.8.1 A Brief History of Inorganic-Bonded Materials 225

7.8.2 Cement-Bonded Materials 227

7.8.3 Gypsum-Bonded Materials 233

References 234

8 Natural Fiber and Plastic Composites 237

8.1 Introduction 237

8.1.1 Synthetic Petrochemical Polymers 237

8.1.2 Bio-Based Polymers 240

8.2 Natural Fibers and Their Temperature-Related Performance 242

8.2.1 Physical, Mechanical, and Chemical Properties 242

8.2.2 Thermal Degradation 243

8.3 Plastic Composite Processing Technology 247

8.3.1 Extrusion: A Fundamental Processing Platform 248

8.3.2 Injection Molding 250

8.3.3 Compression Molding 251

8.3.4 Thermal Forming 252

8.4 Overcoming Incompatibility of Synthetic Polymers and Natural Fibers 252

8.4.1 Introduction 252

8.4.2 Coupling Agents: Definition 253

8.4.3 Coupling Agents: Classification and Function 253

8.4.4 Coupling Agents: Coupling Mechanism 256

8.5 Melt Compounding Natural Fibers and Thermoplastics 257

8.5.1 Challenges for Melt Blending of Natural Fibers 257

8.5.2 Compounding Processes 257

8.5.3 Compounding Principle 258

8.5.4 Melt Rheological Properties 259

8.5.5 Industrial Compounding and Extrusion of WPC 262

8.6 Performance of Natural Fiber and Plastic Composites 263

8.6.1 Mechanical Properties 264

8.6.2 Thermal Expansion Properties 269

8.6.3 Biological Resistance Properties 273

8.6.4 UV Resistance Properties 276

References 280

Index