Lignin and Lignans as Renewable Raw Materials: Chemistry, Technology and Applications

Topics covered include:

 Structure and physicochemical properties
 Lignin detection methods
 Biosynthesis of lignin
 Isolation methods
 Characterization and modification of lignins
 Applications of modified and unmodified lignins
 Lignans: structure, chemical and biological properties
 Future perspectives

Series Preface

Preface xiii

Acronyms xvii

List of Symbols xxi

Part One Introduction 1

1 Background and overview 3

1.1 Introduction 3

1.2 Lignin: economical aspects and sustainability 4

1.3 Structure of the book 5

References 8

Part Two What is lignin? 9

2 Structure and physicochemical properties 11

2.1 Introduction 11

2.2 Monolignols, the basis of a complex architecture 12

2.3 Chemical classification of lignins 15

2.4 Lignin linkages 19

2.5 Structural models of native lignin 22

2.6 Lignin–carbohydrate complex 37

2.7 Physical and chemical properties of lignins 44

References 48

3 Detection and determination 53

3.1 Introduction 53

3.2 The detection of lignin (colour–forming reactions) 53

3.3 Determination of lignin 59

3.4 Direct methods for the determination of lignin 61

3.5 Indirect methods for the determination of lignin 65

3.6 Comparison of the different determination methods 72

References 75

4 Biosynthesis of lignin 81

4.1 Introduction 81

4.2 The biological function of lignins 82

4.3 The shikimic acid pathway 82

4.4 The phenylpropanoid pathway 85

4.5 The biosynthesis of lignin precursors (the monolignol specific pathway) 86

4.6 The dehydrogenation of the precursors 92

4.7 Peroxidases and laccases 92

4.8 The radical polymerisation 95

4.9 The lignin–cabohydrate connectivity 109

4.10 Location of lignins (cell walls lignification) 111

4.11 Lignins from hybrids 112

4.12 Differences between Angiosperm and Gymnosperm lignins 115

References 119

Part Three Sources and Characterization of Lignin 127

5 Isolation of lignins 129

5.1 Introduction 129

5.2 Methods for lignin isolation from wood and grass for laboratory purposes 130

5.3 Commercial lignins 143

References 154

6 Functional and spectroscopic characterization of lignins 161

6.1 Introduction 161

6.2 Elemental analysis and empirical formula 161

6.3 Determination of molecular weight 163

6.4 Functional group analyses 167

6.5 Frequencies of functional groups and linkage types in lignins 176

6.6 Characterization by spectroscopic methods 182

6.7 Raman spectroscopy 186

References 195

7 Chemical characterization and modification of lignins 207

7.1 Introduction 207

7.2 Characterization by chemical degradation methods 207

7.3 Other chemical transformations of lignins 238

7.4 Other chemical modifications of lignins 247

7.5 Thermolysis (pyrolysis) 249

7.6 Biochemical transformations of lignins 250

References 252

Part Four Lignins Applications 267

8 Applications of modified and unmodified lignins 269

8.1 Introduction 269

8.2 Lignin as fuel 272

8.3 Lignin as a binder 273

8.4 Lignin as chelant agent 275

8.5 Lignin in biosciences and medicine 276

8.6 Lignin in agriculture 278

8.7 Polymers with unmodified lignin 279

8.8 Other applications of unmodified lignins 288

8.9 New polymeric materials derived from modified lignins and related biomass derivatives 294

8.10 Polymers derived from chemicals obtainable from lignin decomposition 304

8.11 Other applications of modified lignins 305

References 308

9 High–value chemical products 313

9.1 Introduction 313

9.2 Gasification: syngas from lignin 315

9.3 Thermolysis of lignin 316

9.4 Hydrodeoxygenation (hydrogenolysis) 317

9.5 Hydrothermal hydrolysis 319

9.6 Chemical depolymerisation 321

9.7 Oxidative transformation of lignin 324

9.8 High–value chemicals from lignin 328

References 335

Part Five Lignans 339

10 Structure and chemical properties of lignans 341

10.1 Introduction 341

10.2 Structure and classification of lignans 341

10.3 Nomenclature of lignans 346

10.4 Lignan occurrence in plants 349

10.5 Methods of isolation of lignans from plants 354

10.6 Structure determination of lignans 356

10.7 The chemical synthesis of lignans 357

References 387

11 Biological properties of lignans 401

11.1 Introduction 401

11.2 Biosynthesis of lignans 402

11.3 Metabolism of lignans 413

11.4 Plant physiology and plant defence 418

11.5 Podophyllotoxin 422

11.6 Biological activity of different lignan structures 435

References 466

Part Six Outcome and Challenges 491

12 Summary, conclusions, and perspectives on lignin chemistry 493

12.1 Sources of lignin 493

12.2 On the structure of lignin 494

12.3 Biosynthesis and biological function 495

12.4 Applications of lignin 495

12.5 Lignans 497

12.6 Perspectives 498

References 499

General index 500

Author index 501