Poly(lactic acid)

RAFAEL A. AURAS, Professor, School of Packaging, College of Agriculture & Natural Resources, Michigan State University, USA. LOONG-TAK LIM, Professor, Department of Food Science, University of Guelph, Canada. SUSAN E. M. SELKE, Professor Emeritus, School of Packaging, College of Agriculture & Natural Resources, Michigan State University, USA. HIDETO TSUJI, Professor, Department of Applied Chemistry and Life Science, Toyohashi University of Technology, Japan.

List of Contributors xix

Preface xxiii

Author Biographies xxvii

Part I Chemistry and Production of Lactic Acid, Lactide, and Poly(Lactic Acid) 1

1 Production and Purification of Lactic Acid and Lactide 3
Wim Groot, Jan van Krieken, Olav Sliekersl, and Sicco de Vos

1.1 Introduction 3

1.2 Lactic Acid 4

1.2.1 History of Lactic Acid 4

1.2.2 Physical Properties of Lactic Acid 4

1.2.3 Chemistry of Lactic Acid 4

1.2.4 Production of Lactic Acid by Fermentation 5

1.2.5 Downstream Processing/Purification of Lactic Acid 8

1.2.6 Quality/Specifications of Lactic Acid 10

1.3 Lactide 10

1.3.1 Physical Properties of Lactide 10

1.3.2 Production of Lactide 11

1.3.3 Purification of Lactide 13

1.3.4 Quality and Specifications of Polymer-Grade Lactide 14

1.3.5 Concluding Remarks on Polymer-Grade Lactide 16

References 16

2 Aqueous Solutions of Lactic Acid 19
Carl T. Lira and Lars Peereboom

2.1 Introduction 19

2.2 Structure of Lactic Acid 19

2.3 Vapor Pressure of Anhydrous Lactic Acid and Lactide 19

2.4 Oligomerization in Aqueous Solutions 20

2.5 Equilibrium Distribution of Oligomers 21

2.6 Vapor–Liquid Equilibrium 23

2.7 Density of Aqueous Solutions 25

2.8 Viscosity of Aqueous Solutions 25

2.9 Summary 26

References 26

3 Industrial Production of High-Molecular-Weight Poly(Lactic Acid) 29
Anders Södergård, Mikael Stolt, and Saara Inkinen

3.1 Introduction 29

3.2 Lactic-Acid-Based Polymers by Polycondensation 30

3.2.1 Direct Condensation 31

3.2.2 Solid-State Polycondensation 32

3.2.3 Azeotropic Dehydration 33

3.3 Lactic Acid-Based Polymers by Chain Extension 34

3.3.1 Chain Extension with Diisocyanates 34

3.3.2 Chain Extension with Bis-2-Oxazoline 36

3.3.3 Dual Linking Processes 36

3.3.4 Chain Extension with Bis-Epoxies 36

3.4 Lactic-Acid-Based Polymers by Ring-Opening Polymerization 37

3.4.1 Polycondensation Processes 37

3.4.2 Lactide Manufacturing 37

3.4.3 Ring-Opening Polymerization 39

References 40

4 Design and Synthesis of Different Types of Poly(Lactic Acid)/Polylactide Copolymers 45
Ann-Christine

Albertsson, Indra Kumari Varma, Bimlesh Lochab, Anna Finne-Wistrand, Sangeeta Sahu, and Kamlesh Kumar

4.1 Introduction 45

4.2 Comonomers with Lactic Acid/Lactide 47

4.2.1 Glycolic Acid/Glycolide 47

4.2.2 Poly(Alkylene Glycol) 48

4.2.3 δ-Valerolactone and β-Butyrolactone 51

4.2.4 ε-Caprolactone 51

4.2.5 1,5-Dioxepan-2-One 52

4.2.6 Trimethylene Carbonate 52

4.2.7 Poly(N-Isopropylacrylamide) 52

4.2.8 Alkylthiophene (P3AT) 53

4.2.9 Polypeptide 53

4.3 Functionalized PLA 54

4.4 Macromolecular Design of Lactide-Based Copolymers 55

4.4.1 Graft Copolymers 57

4.4.2 Star-Shaped Copolymers 59

4.4.3 Periodic Copolymers 60

4.5 Properties of Lactide-Based Copolymers 62

4.6 Degradation of Lactide Homo-and Copolymers 63

4.6.1 Drug Delivery from Lactide-Based Copolymers 64

4.6.2 Radiation Effects 65

References 65

5 Preparation, Structure, and Properties of Stereocomplex-Type Poly(Lactic Acid) 73
Neha Mulchandani, Yoshiharu Kimura, and Vimal Katiyar

5.1 Introduction 73

5.2 Stereocomplexation in Poly(Lactic Acid) 73

5.3 Crystal Structure of sc-PLA 74

5.4 Formation of Stereoblock PLA 75

5.4.1 Single-Step Process 75

5.4.2 Stepwise ROP 76

5.4.3 Chain Coupling Method 77

5.5 Stereocomplexation in Copolymers 79

5.5.1 Stereocomplexation in Random and Alternating Lactic Acid or Lactide-Based Polymers 79

5.5.2 sc-PLA–PCL Copolymers 80

5.5.3 sc-PLA–PEG Copolymers 80

5.6 Stereocomplex PLA-Based Composites 81

5.7 Advances in Stereocomplex-PLA 82

5.8 Conclusions 83

References 83

Part II Properties 87

6 Structures and Phase Transitions of PLA and Its Related Polymers 89
Hai Wang and Kohji Tashiro

6.1 Introduction 89

6.2 Structural Study of PLA 89

6.2.1 Preparation of Crystal Modifications of PLA 89

6.2.2 Crystal Structure of the α Form 91

6.2.3 Crystal Structure of the δ Form 92

6.2.4 Crystal Structure of the β Form 93

6.2.5 Structure of the Mesophase 94

6.3 Thermally Induced Phase Transitions 95

6.3.1 Phase Transition in Cold Crystallization 95

6.3.2 Phase Transition in the Melt Crystallization 95

6.3.3 Mechanically Induced Phase Transition 96

6.4 Microscopically-viewed Structure-Mechanical Properties of PLA 98

6.5 Structure and Formation of PLLA/PDLA Stereocomplex 100

6.5.1 Reconsideration of the Crystal Structure 100

6.5.2 Experimental Support of P3 Structure Model 103

6.5.3 Formation Mechanism of Stereocomplex 104

6.6 PHB and Other Biodegradable Polyesters 106

6.6.1 Poly(3-Hydroxybutyrate) (PHB) 106

6.6.2 Polyethylene Adipate (PEA) 109

6.7 Future Perspectives 110

Acknowledgements 110

References 110

7 Optical and Spectroscopic Properties 115
Isabel M. Marrucho

7.1 Introduction 115

7.2 Absorption and Transmission of UV–Vis Radiation 115

7.3 Refractive Index 118

7.4 Specific Optical Rotation 119

7.5 Infrared and Raman Spectroscopy 119

7.5.1 Infrared Spectroscopy 120

7.5.2 Raman Spectroscopy 125

7.6 1H and 13C NMR Spectroscopy 127

References 131

8 Crystallization and Thermal Properties 135
Luca Fambri and Claudio Migliaresi

8.1 Introduction 135

8.2 Crystallinity and Crystallization 136

8.3 Crystallization Regime 140

8.4 Fibers 142

8.5 Commercial Polymers and Products 144

8.6 Degradation and Crystallinity 146

Acknowledgments 148

References 148

9 Rheology of Poly(Lactic Acid) 153
John R. Dorgan

9.1 Introduction 153

9.2 Fundamental Chain Properties from Dilute Solution Viscometry 154

9.2.1 Unperturbed Chain Dimensions 154

9.2.2 Real Chains 154

9.2.3 Solution Viscometry 155

9.2.4 Viscometry of PLA 156

9.3 Processing of PLA: General Considerations 158

9.4 Melt Rheology: An Overview 159

9.5 Processing of PLA: Rheological Properties 160

9.6 Conclusions 165

Appendix 9.A Description of the Software 166

References 166

10 Mechanical Properties 169
Mohammadreza Nofar, Gabriele Perego, and Gian Domenico Cella

10.1 Introduction 169

10.2 General Mechanical Properties and Molecular Weight Effect 170

10.2.1 Tensile and Flexural Properties 170

10.2.2 Impact Resistance 171

10.2.3 Hardness 172

10.3 Temperature Effect 172

10.4 Relaxation and Aging 173

10.5 Annealing 174

10.6 Orientation 176

10.7 Stereoregularity 179

10.8 Self-Reinforced

PLA Composites 180

10.9 PLA Nanocomposites 180

10.10 Copolymerization 181

10.11 Plasticization 181

10.12 PLA Blends 182

10.13 Conclusions 186

References 186

11 Mass Transfer 191
Uruchaya Sonchaeng and Rafael Auras

11.1 Introduction 191

11.2 Background on Mass Transfer in Polymers 193

11.3 Mass Transfer Properties of Neat PLA Films 194

11.3.1 Mass Transfer of Gases 194

11.3.2 Mass Transfer of Oxygen 199

11.3.3 Mass Transfer of Water Vapor 201

11.3.4 Mass Transfer of Organic Vapors 203

11.4 Mass Transfer Properties of Modified PLA 205

11.4.1 PLA Stereocomplex and PLA Blends 206

11.4.2 PLA Nanocomposites 207

11.4.3 Other PLA Modifications 207

11.4.4 PLA in Other Forms 207

11.5 Final Remarks 208

Acknowledgments 208

References 208

12 Migration and Interaction with Contact Materials 217
Herlinda Soto-Valdez and Elizabeth Peralta

12.1 Introduction 217

12.2 Migration Principles 217

12.3 Legislation 218

12.4 Migration and Toxicological Data of Lactic Acid, Lactide, Dimers, and Oligomers 219

12.4.1 Lactic Acid 219

12.4.2 Lactide 224

12.4.3 Oligomers 225

12.5 EDI of Lactic Acid 226

12.6 Other Potential Migrants from PLA 227

12.7 Conclusions 227

References 228

Part III Processing and Conversion 231

13 Processing of Poly(Lactic Acid) 233
Loong-Tak Lim, Tim Vanyo, Jed Randall, Kevin Cink, and Ashwini K. Agrawal

13.1 Introduction 233

13.2 Properties of PLA Relevant to Processing 233

13.3 Modification of PLA Properties by Process Aids and Other Additives 235

13.4 Drying and Crystallizing 237

13.5 Extrusion 239

13.6 Injection Molding 241

13.7 Film and Sheet Casting 245

13.8 Stretch Blow Molding 249

13.9 Extrusion Blown Film 251

13.10 Thermoforming 252

13.11 Melt Spinning 254

13.12 Solution Spinning 258

13.13 Electrospinning 261

13.14 Filament Extrusion and 3D-Printing 265

13.15 Conclusion: Prospects of PLA Polymers 266

References 267

14 Blends 271
Ajay Kathuria, Sukeewan Detyothin, Waree Jaruwattanayon, Susan E. M. Selke, and Rafael Auras

14.1 Introduction 271

14.2 PLA Nonbiodegradable Polymer Blends 272

14.2.1 Polyolefins 272

14.2.2 Vinyl and Vinylidene Polymers and Copolymers 279

14.2.3 Rubbers and Elastomers 285

14.2.4 PLA/PMMA Blends 287

14.3 PLA/Biodegradable Polymer Blends 289

14.3.1 Polyanhydrides 289

14.3.2 Vinyl and Vinylidene Polymers and Copolymers 289

14.3.3 Aliphatic Polyesters and Copolyesters 297

14.3.4 Aliphatic–Aromatic Copolyesters 303

14.3.5 Elastomers and Rubbers 305

14.3.6 Poly(Ester Amide)/PLA Blends 307

14.3.7 Polyethers and Copolymers 307

14.3.8 Annually Renewable Biodegradable Materials 309

14.4 Plasticization of PLA 322

14.5 Conclusions 326

References 327

15 Foaming 341
Laurent M. Matuana

15.1 Introduction 341

15.2 Plastic Foams 341

15.3 Foaming Agents 342

15.3.1 Physical Foaming Agents 342

15.3.2 Chemical Foaming Agents 342

15.4 Formation of Cellular Plastics 343

15.4.1 Dissolution of Blowing Agent in Polymer 343

15.4.2 Bubble Formation 343

15.4.3 Bubble Growth and Stabilization 344

15.5 Plastic Foams Expanded with Physical Foaming Agents 344

15.5.1 Microcellular Foamed Polymers 344

15.5.2 Solid-State Batch Microcellular Foaming Process 345

15.5.3 Microcellular Foaming in a Continuous Process 353

15.6 PLA Foamed with Chemical Foaming Agents 358

15.6.1 Effects of CFA Content and Type 358

15.6.2 Effect of Processing Conditions 359

15.7 Mechanical Properties of PLA Foams 360

15.7.1 Batch Microcellular Foamed PLA 360

15.7.2 Extrusion of PLA 361

15.7.3 Microcellular Injection Molding of PLA 362

15.8 Foaming of PLA/Starch and Other Blends 362

References 363

16 Composites 367
Tanmay Gupta, Vijay Shankar Kumawat, Subrata Bandhu Ghosh, Sanchita Bandyopadhyay-Ghosh, and Mohini Sain

16.1 Introduction 367

16.2 PLA Matrix 367

16.3 Reinforcements 368

16.3.1 Natural Fiber Reinforcement 368

16.3.2 Synthetic Fiber Reinforcement 370

16.3.3 Organic Filler Reinforcement 370

16.3.4 Inorganic Filler Reinforcement 371

16.3.5 Laminated/Structural Composites 372

16.4 Nanocomposites 374

16.5 Surface Modification 375

16.5.1 Filler Surface Modification 375

16.5.2 Compatibilizing Agent 376

16.5.3 Composite Surface Modification 377

16.6 Processing 377

16.6.1 Conventional Processing 377

16.6.2 3D Printing 378

16.7 Properties 379

16.7.1 Mechanical Properties 379

16.7.2 Thermal Properties 382

16.7.3 Flame Retardancy 382

16.7.4 Degradation 383

16.7.5 Shape Memory Properties 383

16.8 Applications 384

16.8.1 Biomedical Applications 385

16.8.2 Packaging Applications 387

16.8.3 Automotive Applications 387

16.8.4 Sensing and Other Electronic Applications 388

16.9 Future Developments and Concluding Remarks 390

References 390

17 Nanocomposites: Processing and Mechanical Properties 411
Suprakas Sinha Ray

17.1 Introduction 411

17.2 Nanoclay-Containing PLA Nanocomposites 412

17.3 Carbon-Nanotubes-Containing PLA Nanocomposites 414

17.4 Graphene-Containing PLA Nanocomposites 416

17.5 Nanocellulose-Containing PLA Nanocomposites 417

17.6 Other Nanoparticle-Containing PLA Nanocomposites 418

17.7 Mechanical Properties of PLA-Based Nanocomposites 419

17.8 Possible Applications and Future Prospects 421

Acknowledgment 422

References 422

18 Mechanism of Fiber Structure Development in Melt Spinning of PLA 425
Nanjaporn Roungpaisan, Midori Takasaki, Wataru Takarada, and Takeshi Kikutani

18.1 Introduction-Fundamentals of Structure Development in Polymer Processing 425

18.2 High-speed Melt Spinning of PLLAs with Different d-Lactic Acid Content 426

18.2.1 Wide-angle X-ray Diffraction 426

18.2.2 Birefringence 427

18.2.3 Differential Scanning Calorimetry 428

18.2.4 Modulated-DSC and Lattice Spacing 429

18.3 High-speed Melt-Spinning of Racemic Mixture of PLLA and PDLA 430

18.3.1 Stereocomplex Crystal 430

18.3.2 Melt Spinning of PLLA/PDLA Blend 430

18.3.3 WAXD 431

18.3.4 Differential Scanning Calorimetry 432

18.3.5 In Situ WAXD upon Heating 432

18.4 Bicomponent Melt Spinning of PLLA and PDLA 433

18.4.1 Sheath-Core and Islands-in-the-Sea Configurations 433

18.4.2 Birefringence 434

18.4.3 DSC 434

18.4.4 Post Annealing 435

18.5 Concluding Remarks 436

References 437

Part IV Degradation, Environmental Impact, and End of Life 439

19 Photodegradation and Radiation Degradation 441
Wataru Sakai and Naoto Tsutsumi

19.1 Introduction 441

19.2 Mechanisms of Photodegradation 441

19.2.1 Photon 441

19.2.2 Photon Absorption 442

19.2.3 Photochemical Reactions of Carbonyl Groups 443

19.3 Mechanism of Radiation Degradation 443

19.3.1 High-Energy Radiation 443

19.3.2 Basic Mechanism of Radiation Degradation 444

19.4 Photodegradation of PLA 444

19.4.1 Fundamental Mechanism 444

19.4.2 Photooxidation Degradation 446

19.4.3 High-Energy Photo-Irradiation 447

19.4.4 Photosensitized Degradation of PLA 447

19.4.5 Photodegradation of PLA Blends 449

19.5 Radiation Degradation of PLA 449

19.6 Irradiation Effects on Biodegradability 451

19.7 Modification and Composites of PLA 452

References 452

20 Thermal Degradation 455
Haruo Nishida

20.1 Introduction 455

20.2 Thermal Degradation Behavior of PLLA Based on Weight Loss 455

20.2.1 Diverse Mechanisms 455

20.2.2 Factors Affecting the Thermal Degradation Mechanism 456

20.2.3 Thermal Stabilization 457

20.3 Kinetic Analysis of Thermal Degradation 458

20.3.1 Single-Step Thermal Degradation Process 458

20.3.2 Complex Thermal Degradation Process 459

20.4 Kinetic Analysis of Complex Thermal Degradation Behavior 460

20.4.1 Two-Step Complex Reaction Analysis of PLLA in Blends 460

20.4.2 Multistep Complex Reaction Analysis of Commercially Available PLLA 461

20.5 Thermal Degradation Behavior of PLA Stereocomplex: scPLA 463

20.6 Control of Racemization 464

20.7 Conclusions 465

References 465

21 Hydrolytic Degradation 467
Hideto Tsuji

21.1 Introduction 467

21.2 Degradation Mechanism 467

21.2.1 Molecular Degradation Mechanism 468

21.2.2 Material Degradation Mechanism 479

21.2.3 Degradation of Crystalline Residues 485

21.3 Parameters for Hydrolytic Degradation 488

21.3.1 Effects of Surrounding Media 488

21.3.2 Effects of Material Parameters 490

21.4 Structural and Property Changes During Hydrolytic Degradation 498

21.4.1 Fractions of Components 498

21.4.2 Crystallization 498

21.4.3 Mechanical Properties 499

21.4.4 Thermal Properties 499

21.4.5 Surface Properties 500

21.4.6 Morphology 500

21.5 Applications of Hydrolytic Degradation 500

21.5.1 Material Preparation 500

21.5.2 Recycling of PLA to Its Monomer 502

21.6 Conclusions 503

References 503

22 Enzymatic Degradation 517
Ken’ichiro Matsumoto, Hideki Abe, Yoshihiro Kikkawa, and Tadahisa Iwata

22.1 Introduction 517

22.1.1 Definition of Biodegradable Plastics 517

22.1.2 Enzymatic Degradation 517

22.2 Enzymatic Degradation of PLA Films 519

22.2.1 Structure and Substrate Specificity of Proteinase K 519

22.2.2 Enzymatic Degradability of PLLA Films 519

22.2.3 Enzymatic Degradability of PLA Stereoisomers and Their Blends 520

22.2.4 Effects of Surface Properties on Enzymatic Degradability of PLLA Films 521

22.3 Enzymatic Degradation of Thin Films 525

22.3.1 Thin Films and Analytical Techniques 525

22.3.2 Crystalline Morphologies of Thin Films 525

22.3.3 Enzymatic Adsorption and Degradation Rate of Thin Films 526

22.3.4 Enzymatic Degradation of LB Film 526

22.3.5 Application of Selective Enzymatic Degradation 529

22.4 Enzymatic Degradation of Lamellar Crystals 530

22.4.1 Enzymatic Degradation of PLLA Single Crystals 530

22.4.2 Thermal Treatment and Enzymatic Degradation of PLLA Single Crystals 532

22.4.3 Single Crystals of PLA Stereocomplex 533

22.5 Recent Advances in Characterization of Enzymes that Degrade PLAs Including PDLA and Related Copolymers 534

22.5.1 αβ-Hydrolase 535

22.5.2 Lipases and Cutinase-Like Enzymes 535

22.5.3 Polyhydroxyalkanoate Depolymerases 536

22.5.4 Enhancement of Biodegradability of PLAs 536

22.5.5 Control of Enzymatic Degradation of PLAs 537

22.6 Future Perspectives 537

References 537

23 Environmental Footprint and Life Cycle Assessment of Poly (Lactic Acid) 541
Amy E. Landis, Shakira R. Hobbs, Dennis Newby, Ja’Maya Wilson, and Talia Pincus

23.1 Introduction to LCA and Environmental Footprints 541

23.1.1 Life Cycle Assessment 541

23.1.2 Uncertainty in LCA 542

23.2 Life Cycle Considerations for PLA 542

23.2.1 The Life Cycle of PLA 542

23.2.2 Energy Use and Global Warming 544

23.2.3 Environmental Trade-Offs 544

23.2.4 Waste Management 545

23.2.5 End of Life 546

23.3 Review of Biopolymer LCA Studies 546

23.3.1 Cradle-to-Gate and Cradle-to-Grave LCAs 546

23.3.2 End-of-Life LCAs 547

23.4 Improving PLA’s Environmental Footprint 553

23.4.1 Agricultural Management 553

23.4.2 Feedstock Choice 554

23.4.3 Energy 554

23.4.4 Design for End of Life 555

References 555

24 End-of-Life Scenarios for Poly(Lactic Acid) 559
Anibal Bher, Edgar Castro-Aguirre, and Rafael Auras

24.1 Introduction 559

24.2 Transition from a Linear to a Circular Economy for Plastics 559

24.3 Waste Management System 561

24.4 End-of-Life Scenarios for PLA 564

24.4.1 Prevention and Source Reduction 565

24.4.2 Reuse 566

24.4.3 Recycling 566

24.4.4 Biodegradation 569

24.4.5 Incineration with Energy Recovery 572

24.4.6 Landfill 573

24.5 LCA of End-of-Life Scenario for PLA 574

24.6 Final Remarks 575

References 575

Part V Applications 581

25 Medical Applications 583
Shuko Suzuki and Yoshito Ikada

25.1 Introduction 583

25.2 Minimal Requirements for Medical Devices 583

25.2.1 General 583

25.2.2 PLA as Medical Implants 584

25.3 Preclinical and Clinical Applications of PLA Devices 585

25.3.1 Fibers 585

25.3.2 Meshes 588

25.3.3 Bone Fixation Devices 589

25.3.4 Micro-and Nanoparticles, and Thin Coatings 595

25.3.5 Scaffolds 597

25.4 Conclusions 598

References 598

26 Packaging and Consumer Goods 605
Hayati Samsudin and Fabiola Iñiguez-Franco

26.1 Introduction: Polylactic Acid (PLA) in Packaging and Consumer Goods 605

26.2 Food and Beverage 606

26.2.1 Evolution of PLA in the Food and Beverage Market 606

26.2.2 Growing Interest in PLA Serviceware 607

26.3 Distribution Packaging 612

26.4 Other Consumer Goods : Automotive 613

26.5 Other Consumer Goods 613

26.6 Challenges and Final Remarks 614

References 615

27 Textile Applications 619
Masatsugu Mochizuki

27.1 Introduction 619

27.2 Manufacturing, Properties, and Structure of PLA Fibers 619

27.2.1 PLA Fiber Manufacture 619

27.2.2 Properties of PLA Fibers and Textile 619

27.2.3 Effects of Structure on Properties 620

27.2.4 PLA Stereocomplex Fibers 621

27.3 Key Performance Features of PLA Fibers 621

27.3.1 Biodegradability and the Biodegradation Mechanism 621

27.3.2 Moisture Management 623

27.3.3 Antibacterial/Antifungal Properties 623

27.3.4 Low Flammability 624

27.3.5 Weathering Stability 624

27.4 Potential Applications 625

27.4.1 Geotextiles 625

27.4.2 Industrial Fabrics 625

27.4.3 Filters 626

27.4.4 Towels and Wipes 626

27.4.5 Home Furnishings 627

27.4.6 Clothing and Personal Belongings 627

27.4.7 3D-Printing Filament 628

27.5 Conclusions 628

References 628

28 Environmental Applications 631
Akira Hiraishi and Takeshi Yamada

28.1 Introduction 631

28.2 Application to Water and Wastewater Treatment 631

28.2.1 Application as Sorbents 631

28.2.2 Application to Nitrogen Removal 633

28.3 Application to Methanogenesis 637

28.3.1 Anaerobic Digestion 637

28.3.2 Methanogenic Microbial Community 637

28.4 Application to Bioremediation 638

28.4.1 Significance of PLA Use 638

28.4.2 Bioremediation of Organohalogen Pollution 638

28.4.3 Other Applications 639

28.5 Concluding Remarks and Prospects 640

Acknowledgments 641

References 641

Index 645