Biopolymers: Environmental Applications 9783110998726

Table of contents :
Cover
Half Title
Also of interest
Biopolymers: Environmental Applications
Copyright
Contents
List of contributing authors
1. General overview of biopolymers: structure and properties
1.1 Introduction
1.2 Classes of biopolymers
1.2.1 Biopolymers of animal origin and their applications
1.2.1.1 Chitosan
1.2.1.2 Collagen
1.2.1.3 Gelatin
1.2.1.4 Hyaluronic acid
1.2.1.5 Keratin
1.2.2 Biopolymers of plant origin and their applications
1.2.2.1 Alginate
1.2.2.2 Carrageenan
1.2.2.3 Cellulose
1.2.2.4 Guar Gum
1.2.2.5 Gum Arabic
1.2.2.6 Pectin
1.2.2.7 Xylan
1.2.3 Biopolymers of microbial origin and their applications
1.2.3.1 PHA
1.2.3.2 Pullulan
1.2.3.3 Levan
1.2.3.4 Dextran
1.2.3.5 PHB (polyhydroxybutyrate)
1.2.3.6 Bacterial cellulose
1.2.3.7 Curdlan
1.2.3.8 Xanthan gum
1.3 Structure of biopolymers
1.3.1 Bead model of biopolymers
1.3.2 Electronic structure
1.3.3 Molecular structure
1.3.4 Photonic structure
1.4 Properties of biopolymers and biopolymer composites
1.4.1 Brittleness and ductility properties
1.4.2 Characteristic temperature/Thermal properties
1.4.3 Chemical properties
1.4.4 Creep and fatigue properties
1.4.5 Dynamic mechanical thermal properties
1.4.6 Fibre mechanical properties
1.4.7 Flexural properties dynamic mechanical thermal properties
1.4.8 Impact properties
1.4.9 Physical properties
1.4.10 Tensile properties
1.4.11 Toughness and hardness properties
1.4.12 Tribological properties
1.5 Conclusions
References
2. Progress and prospects of biopolymers production strategies
2.1 Introduction
2.1.1 Bibliometric analysis
2.2 Production of biopolymers from algae
2.2.1 Solvent extraction of biopolymer
2.2.2 Biopolymer production using ultrasound extraction (UBE)
2.2.3 Microwave-assisted extraction (MAE) of biopolymer
2.2.4 Subcritical water extraction (SCWE) of biopolymer
2.3 Polymers produced by bacteria
2.3.1 Biosynthesis of bacterial polyhydroxyalkanoates (PHA)
2.3.2 Bacterial cellulose (BCs)
2.3.3 Bacterial production and recovery of hybrid biopolymers
2.4 Other strategies for biopolymers production
2.5 Synthetic biology strategies for biopolymer synthesis
2.6 Prospects and conclusion
References
3. Modern analytical approach in biopolymer characterization
3.1 Introduction
3.2 Bibliographic study
3.3 Characterization of biopolymers
3.4 Microscopy methods
3.4.1 Optical microscopy
3.4.2 Laser scanning confocal microscopy (LCSM)
3.4.3 Electron microscopy
3.4.4 STM (scanning tunneling microscope) and SPM (scanning probe microscopy)
3.4.5 Differential dynamic microscopy (DDM)
3.5 Spectroscopy methods for characterizing biopolymers
3.5.1 X-ray diffraction analysis (XRD)
3.5.2 Fourier transform-infrared spectroscopy (FTIR)
3.5.3 Raman spectroscopy
3.6 Recent research on biopolymers characterization by analytical techniques
3.7 Conclusions
References
4. Biodegradable polymers – research and applications
4.1 Introduction
4.2 Biodegradable versus non-biodegradable polymers
4.2.1 Commercially available important biodegradable polymers based on their market value and properties
4.3 Methods and the factors affecting biodegradation of the polymers
4.4 Recent market trends and challenges for biodegradable polymers production
4.5 Industrial production status and commercialized products
4.6 Metabolic engineering tools to increase the production of biodegradable polymers
4.7 Recent applications of the biodegradable polymers
4.7.1 Application in packaging industry
4.7.2 Application in the electronics industry
4.7.3 Application in agriculture industry
4.7.4 Application in automotive industry
4.7.5 Application in biomedical industry
4.7.6 Application in field of aquaculture
4.7.7 Application in construction industry
4.8 Conclusions
References
5. Biopolymers as a versatile tool with special emphasis on environmental application
5.1 Introduction
5.2 Synthesis and characterization of biopolymer composites
5.3 Environmental application of biopolymers and biopolymer composites
5.3.1 Hazardous contaminants removal
5.3.2 Water/wastewater treatment
5.3.3 Biopolymer (nano) composites
5.3.4 Bio-energy
5.3.5 Cost analysis
5.4 Future prospects
5.5 Conclusions
References
6. Development of biopolymers from microbes and their environmental applications
6.1 Introduction
6.1.1 Biosynthetic pathway and regulation of microbial biopolymers
6.1.1.1 Synthesis of high molecular weight biopolymers
6.1.1.2 Bacterial synthesis of exopolysaccharides
6.2 Microbial biopolymers and its metabolic engineering
6.2.1 Technological advancements in metabolite engineering
6.2.2 Production of novel bio-based polymers using synthetic biology and metabolic engineering (ME)
6.2.3 Comparison of microbial biopolymer over synthetic polymer
6.2.3.1 Biodegradability
6.2.3.2 Economic aspects
6.2.3.3 Life cycle assessment (LCA)
6.3 Environmental impacts
6.4 General production of biopolymers using microorganisms
6.4.1 Xanthan
6.4.2 Levan
6.4.3 Pullulan
6.4.4 Dextran
6.4.5 PHA
6.4.6 PHB
6.4.7 Biosurfactant
6.4.8 Gellan
6.4.9 Hyaluronate production
6.4.10 Cellulose production
6.5 Factors affecting the production of microbial biopolymers
6.6 Recent approaches in separation and purification of microbial biopolymers
6.7 Environmental applications of microbial biopolymers
6.8 Global market value of microbial biopolymers
6.9 Bottlenecks and future perspectives of microbial biopolymers
6.10 Conclusions
References
7. Plant-based biopolymers for wastewater pollutants mitigation
7.1 Introduction
7.1.1 Need for plant-based biopolymers and their importance
7.2 Plant-based biopolymers for the treatment of pollutants
7.2.1 Cellulose
7.2.2 Carrageenan
7.2.3 Starch
7.2.4 Alginate
7.2.5 Xylan
7.2.6 Inulin
7.2.7 Pectin
7.2.8 Tragacanth
7.3 Mechanism of pollution removal using Biopolymers
7.3.1 Adsorption
7.3.2 Flocculation
7.3.3 Bridge formation
7.3.4 Electrostatic patches
7.4 Plant-based biopolymers for the mitigation of xenobiotic compounds
7.5 Advantages and disadvantages of biopolymers
7.5.1 Advantages of biopolymers
7.5.2 Disadvantages of biopolymers
7.6 Conclusions
7.7 Summary
References
8. Animal sourced biopolymer for mitigating xenobiotics and hazardous materials
8.1 Introduction
8.2 Xenobiotics and its effect on environment
8.3 Animal source-based biopolymers
8.4 Animal sourced biopolymers for the mitigation of xenobiotic and hazardous chemicals
8.4.1 Collagen
8.4.2 Chitosan
8.4.3 Gelatin
8.4.4 Keratin
8.4.5 Silk fibroin and wool
8.4.6 Other sources
8.5 Summary and future prospects
References
9. Biopolymer based membrane technology for environmental applications
9.1 Introduction
9.2 Membrane production methods
9.2.1 Selective membrane surface morphology
9.3 Biopolymeric membranes
9.3.1 Membrane derived by bacterial fermentation
9.3.2 Membranes based on biopolymers derived from vegetable sources
9.3.3 Membranes based on biopolymers derived from animal sources
9.4 Environmental applications of biopolymeric membranes
9.4.1 Heavy metal removal
9.4.2 Dye removal
9.4.3 Herbicides and pesticides removal
9.4.4 Water filtration
9.4.5 Water treatment
9.4.6 Green hydrogen
9.4.7 Enhancing soil characteristics
9.4.8 Construction sector
9.4.9 Merits and demerits of biopolymeric membranes
9.4.9.1 Merits
9.4.9.2 Demerits
9.5 Conclusion
References
10. Biopolymeric composite materials for environmental applications
10.1 Introduction
10.2 Production strategies and characterization of biopolymers-based composites (macro/micro/nano level)
10.3 Application of biopolymer-based composites
10.3.1 Biopolymer composite with macro particles
10.3.2 Biopolymer composite with microparticles
10.3.3 Biopolymer composite with nanoparticles
10.4 Benefits and limitations on the usage of biopolymers composites in environmental remediation
10.5 Future perspectives
10.6 Conclusions
References
Index

Citation preview

Jeyaseelan Aravind and Murugesan Kamaraj (Eds.) Biopolymers

Also of interest Physical Chemistry of Polymers A Conceptual Introduction Sebastian Seiffert,  ISBN ----, e-ISBN ----

Silicon-Based Polymers and Materials Jerzy J. Chruściel,  ISBN ----, e-ISBN ----

Superabsorbent Polymers Chemical Design, Processing and Applications Sandra Van Vlierberghe, Arn Mignon (Eds.),  ISBN ----, e-ISBN ----

Handbook of Biodegradable Polymers Catia Bastioli (Ed.),  ISBN ----, e-ISBN ----

Physical Sciences Reviews e-ISSN -X

Biopolymers Environmental Applications Edited by Jeyaseelan Aravind and Murugesan Kamaraj

Editors Prof. Jeyaseelan Aravind Saveetha Institute of Medical and Technical Sciences (SIMATS) Department of Bio-Engineering Tamil Nadu Saveetha Nagar Thandalam, Chennai-602105 India [email protected] Dr. Murugesan Kamaraj SRM Institute of Science and Technology Department of Biotechnology Bharathi Salai Ramapuram, Chennai-600089 India [email protected]

ISBN 978-3-11-099872-6 e-ISBN (PDF) 978-3-11-098718-8 e-ISBN (EPUB) 978-3-11-098723-2 Library of Congress Control Number: 2023937071 Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the internet at http://dnb.dnb.de. © 2023 Walter de Gruyter GmbH, Berlin/Boston Cover image: RecycleMan / iStock / Getty Images Plus Typesetting: TNQ Technologies Pvt. Ltd. Printing and binding: CPI books GmbH, Leck www.degruyter.com

Contents List of contributing authors

XI

Vasuki Sasikanth, Bhuvaneswari Meganathan, Thirumalaisamy Rathinavel, Sindhu Seshachalam, Harini Nallappa and Brindha Gopi 1 General overview of biopolymers: structure and properties 1 1.1 Introduction 2 1.2 Classes of biopolymers 4 1.2.1 Biopolymers of animal origin and their applications 6 1.2.2 Biopolymers of plant origin and their applications 8 1.2.3 Biopolymers of microbial origin and their applications 11 1.3 Structure of biopolymers 11 1.3.1 Bead model of biopolymers 12 1.3.2 Electronic structure 13 1.3.3 Molecular structure 14 1.3.4 Photonic structure 15 1.4 Properties of biopolymers and biopolymer composites 16 1.4.1 Brittleness and ductility properties 17 1.4.2 Characteristic temperature/Thermal properties 17 1.4.3 Chemical properties 18 1.4.4 Creep and fatigue properties 18 1.4.5 Dynamic mechanical thermal properties 18 1.4.6 Fibre mechanical properties 1.4.7 Flexural properties dynamic mechanical thermal properties 19 1.4.8 Impact properties 19 1.4.9 Physical properties 20 1.4.10 Tensile properties 20 1.4.11 Toughness and hardness properties 20 1.4.12 Tribological properties 22 1.5 Conclusions 23 References

1

18

Sowmya Hari, Karthiyayini Ramaswamy, Uma Sivalingam, Ashwini Ravi, Suresh Dhanraj and Manjunathan Jagadeesan 29 2 Progress and prospects of biopolymers production strategies 29 2.1 Introduction 31 2.1.1 Bibliometric analysis 32 2.2 Production of biopolymers from algae 34 2.2.1 Solvent extraction of biopolymer 35 2.2.2 Biopolymer production using ultrasound extraction (UBE)

VI

2.2.3 2.2.4 2.3 2.3.1 2.3.2 2.3.3 2.4 2.5 2.6

Contents

Microwave-assisted extraction (MAE) of biopolymer 36 37 Subcritical water extraction (SCWE) of biopolymer 38 Polymers produced by bacteria 39 Biosynthesis of bacterial polyhydroxyalkanoates (PHA) 41 Bacterial cellulose (BCs) 42 Bacterial production and recovery of hybrid biopolymers 43 Other strategies for biopolymers production 44 Synthetic biology strategies for biopolymer synthesis 47 Prospects and conclusion 48 References

Gunasekaran Priya, Natarajan Shanthi, Sundaramoorthy Pavithra, Soundararajan Sangeetha, Subbiah Murugesan and Shanmugasundaram Shyamalagowri 55 3 Modern analytical approach in biopolymer characterization 56 3.1 Introduction 57 3.2 Bibliographic study 59 3.3 Characterization of biopolymers 61 3.4 Microscopy methods 62 3.4.1 Optical microscopy 62 3.4.2 Laser scanning confocal microscopy (LCSM) 62 3.4.3 Electron microscopy 3.4.4 STM (scanning tunneling microscope) and SPM (scanning probe 64 microscopy) 65 3.4.5 Differential dynamic microscopy (DDM) 66 3.5 Spectroscopy methods for characterizing biopolymers 66 3.5.1 X-ray diffraction analysis (XRD) 67 3.5.2 Fourier transform-infrared spectroscopy (FTIR) 68 3.5.3 Raman spectroscopy 3.6 Recent research on biopolymers characterization by analytical 68 techniques 71 3.7 Conclusions 72 References Mahajan Megha, Murugesan Kamaraj, Thirumullaivoyal G. Nithya, Shanmugaselvam GokilaLakshmi, Pugazh Santhosh and Balasubramanian Balavaishnavi 77 4 Biodegradable polymers – research and applications 78 4.1 Introduction 79 4.2 Biodegradable versus non-biodegradable polymers 4.2.1 Commercially available important biodegradable polymers based on their 80 market value and properties 84 4.3 Methods and the factors affecting biodegradation of the polymers

Contents

4.4 4.5 4.6 4.7 4.7.1 4.7.2 4.7.3 4.7.4 4.7.5 4.7.6 4.7.7 4.8

VII

Recent market trends and challenges for biodegradable polymers 85 production 88 Industrial production status and commercialized products Metabolic engineering tools to increase the production of biodegradable 90 polymers 92 Recent applications of the biodegradable polymers 92 Application in packaging industry 93 Application in the electronics industry 93 Application in agriculture industry 94 Application in automotive industry 95 Application in biomedical industry 95 Application in field of aquaculture 96 Application in construction industry 96 Conclusions 97 References

Suresh Babu Palanisamy 5 Biopolymers as a versatile tool with special emphasis on environmental 101 application 101 5.1 Introduction 103 5.2 Synthesis and characterization of biopolymer composites 105 5.3 Environmental application of biopolymers and biopolymer composites 106 5.3.1 Hazardous contaminants removal 106 5.3.2 Water/wastewater treatment 109 5.3.3 Biopolymer (nano) composites 110 5.3.4 Bio-energy 113 5.3.5 Cost analysis 113 5.4 Future prospects 114 5.5 Conclusions 114 References Krishnanjana Nambiar, Saravana Kumari P, Dheeksha Devaraj and Murugan Sevanan 6 Development of biopolymers from microbes and their environmental 119 applications 120 6.1 Introduction 122 6.1.1 Biosynthetic pathway and regulation of microbial biopolymers 126 6.2 Microbial biopolymers and its metabolic engineering 126 6.2.1 Technological advancements in metabolite engineering 6.2.2 Production of novel bio-based polymers using synthetic biology and metabolic 126 engineering (ME) 129 6.2.3 Comparison of microbial biopolymer over synthetic polymer

VIII

6.3 6.4 6.4.1 6.4.2 6.4.3 6.4.4 6.4.5 6.4.6 6.4.7 6.4.8 6.4.9 6.4.10 6.5 6.6 6.7 6.8 6.9 6.10

Contents

Environmental impacts 131 131 General production of biopolymers using microorganisms 132 Xanthan 132 Levan 133 Pullulan 133 Dextran 133 PHA 134 PHB 134 Biosurfactant 134 Gellan 135 Hyaluronate production 135 Cellulose production 135 Factors affecting the production of microbial biopolymers Recent approaches in separation and purification of microbial 137 biopolymers 139 Environmental applications of microbial biopolymers 139 Global market value of microbial biopolymers 139 Bottlenecks and future perspectives of microbial biopolymers 142 Conclusions 143 References

Krishnan Harshan, A. Prashanth Rajan, Danie Kingsley, Rahul Amin Sheikh, Jemima Aashmi and Anand Prem Rajan 147 7 Plant-based biopolymers for wastewater pollutants mitigation 148 7.1 Introduction 148 7.1.1 Need for plant-based biopolymers and their importance 149 7.2 Plant-based biopolymers for the treatment of pollutants 151 7.2.1 Cellulose 152 7.2.2 Carrageenan 153 7.2.3 Starch 154 7.2.4 Alginate 154 7.2.5 Xylan 154 7.2.6 Inulin 155 7.2.7 Pectin 155 7.2.8 Tragacanth 157 7.3 Mechanism of pollution removal using Biopolymers 157 7.3.1 Adsorption 157 7.3.2 Flocculation 157 7.3.3 Bridge formation 157 7.3.4 Electrostatic patches 158 7.4 Plant-based biopolymers for the mitigation of xenobiotic compounds

Contents

7.5 7.5.1 7.5.2 7.6 7.7

Advantages and disadvantages of biopolymers 158 Advantages of biopolymers 158 Disadvantages of biopolymers 159 Conclusions 159 Summary 160 References

IX

158

Vipendra Kumar Singh, Priya Gunasekaran, Medha Kumari, Dolly Krishnan, and Vinoth Kumar Ramachandran 8 Animal sourced biopolymer for mitigating xenobiotics and hazardous 165 materials 165 8.1 Introduction 167 8.2 Xenobiotics and its effect on environment 168 8.3 Animal source-based biopolymers 8.4 Animal sourced biopolymers for the mitigation of xenobiotic and hazardous 169 chemicals 169 8.4.1 Collagen 171 8.4.2 Chitosan 172 8.4.3 Gelatin 172 8.4.4 Keratin 173 8.4.5 Silk fibroin and wool 173 8.4.6 Other sources 173 8.5 Summary and future prospects 175 References Vardhana Janakiraman, Srinivasarao Sowmya and Mani Thenmozhi 9 Biopolymer based membrane technology for environmental 181 applications 181 9.1 Introduction 183 9.2 Membrane production methods 183 9.2.1 Selective membrane surface morphology 187 9.3 Biopolymeric membranes 187 9.3.1 Membrane derived by bacterial fermentation 188 9.3.2 Membranes based on biopolymers derived from vegetable sources 189 9.3.3 Membranes based on biopolymers derived from animal sources 190 9.4 Environmental applications of biopolymeric membranes 190 9.4.1 Heavy metal removal 194 9.4.2 Dye removal 195 9.4.3 Herbicides and pesticides removal 196 9.4.4 Water filtration 196 9.4.5 Water treatment

X

9.4.6 9.4.7 9.4.8 9.4.9 9.5

Contents

Green hydrogen 197 198 Enhancing soil characteristics 199 Construction sector Merits and demerits of biopolymeric membranes 202 Conclusion 202 References

201

Anil Kumar Moola, Muhil Raj Prabhakar, Baishali Dey, Balasubramanian Paramasivan, Sita Manojgyna Vangala, Ramya Jakkampudi and Selvam Sathish 207 10 Biopolymeric composite materials for environmental applications 208 10.1 Introduction 10.2 Production strategies and characterization of biopolymers-based composites 210 (macro/micro/nano level) 214 10.3 Application of biopolymer-based composites 215 10.3.1 Biopolymer composite with macro particles 217 10.3.2 Biopolymer composite with microparticles 218 10.3.3 Biopolymer composite with nanoparticles 10.4 Benefits and limitations on the usage of biopolymers composites in 220 environmental remediation 222 10.5 Future perspectives 222 10.6 Conclusions 223 References Index

229

List of contributing authors Jemima Aashmi School of BioSciences and Technology Vellore Institute of Technology Vellore India E-mail: [email protected] Balasubramanian Balavaishnavi Department of Biochemistry College of Science and Humanities SRM Institute of Science and Technology Kattankulathur Tamil Nadu 603203 India Dheeksha Devaraj Department of Biotechnology Karunya Institute of Technology and Sciences Deemed to be University Coimbatore India Suresh Dhanraj Department of Microbiology Vels Institute of Science Technology and Advanced Studies (VISTAS) Chennai 600117 Tamil Nadu India Shanmugaselvam GokilaLakshmi Department of Biochemistry College of Science and Humanities SRM Institute of Science and Technology Kattankulathur Tamil Nadu 603203 India Brindha Gopi Department of Biotechnology Sona College of Arts and Science Salem 636 005 India

https://doi.org/10.1515/9783110987188-201

Priya Gunasekaran Department of Biotechnology College of Science and Humanities SRM Institute of Science and Technology Ramapuram Chennai Tamil Nadu India Sowmya Hari Department of BioEngineering Vels Institute of Science Technology and Advanced Studies (VISTAS) Chennai 600117 Tamil Nadu India Krishnan Harshan School of BioSciences and Technology Vellore Institute of Technology Vellore India Manjunathan Jagadeesan Department of Biotechnology Vels Institute of Science Technology and Advanced Studies (VISTAS) Chennai 600117 Tamil Nadu India E-mail: [email protected] Ramya Jakkampudi Department of Chemistry Services Excelra Knowledge Solutions Uppal Hyderabad 500039 India E-mail: [email protected]

XII

List of contributing authors

Vardhana Janakiraman Department of Biotechnology Vels Institute of Science Technology and Advanced Studies (VISTAS) Pallavaram Chennai 637001 Tamil Nadu India Murugesan Kamaraj Department of Biotechnology Faculty of Science and Humanities SRM Institute of Science and Technology Ramapuram Campus Chennai 600089 Tamil Nadu India Danie Kingsley School of BioSciences and Technology Vellore Institute of Technology Vellore India Dolly Krishnan Secretary cum Founder Director Research Wing Brainology Scientific Academy of Jharkhand Ranchi Jharkhand India Medha Kumari Brainology Research Fellow Neuroscience and Microplastic Lab Brainology Scientific Academy of Jharkhand Ranchi Jharkhand India Saravana Kumari P Department of Microbiology Rathnavel Subramaniam College of Arts and Science Coimbatore India Bhuvaneswari Meganathan Department of Biotechnology Sona College of Arts and Science Salem 636 005 India

Mahajan Megha Department of Biochemistry College of Science and Humanities SRM Institute of Science and Technology Kattankulathur Tamil Nadu 603203 India Anil Kumar Moola Department of Entomology College of Agriculture Food and Environment Agriculture Science Centre North University of Kentucky Lexington KY USA E-mail: [email protected] Subbiah Murugesan P.G. and Research Department of Botany Pachaiyappas College Chennai 600030 Tamil Nadu India Harini Nallappa Department of Biotechnology Sona College of Arts and Science Salem 636 005 India Krishnanjana Nambiar Department of Biotechnology Karunya Institute of Technology and Sciences Deemed to be University Coimbatore India Thirumullaivoyal G. Nithya Department of Biochemistry College of Science and Humanities SRM Institute of Science and Technology Ramapuram Campus Kattankulathur Tamil Nadu 603203 India E-mail: [email protected]

List of contributing authors

Suresh Babu Palanisamy Department of Biotechnology Saveetha School of Engineering Saveetha Institute of Medical and Technical Sciences (SIMATS) Thandalam Chennai 602105 Tamil Nadu India E-mail: [email protected] Sundaramoorthy Pavithra Department of Biotechnology Bannari Amman Institute of Technology Sathyamangalam 638401 Tamil Nadu India Muhil Raj Prabhakar Baishali Dey and Balasubramanian Paramasivan Department of Biotechnology & Medical Engineering National Institute of Technology Rourkela Odisha 769 008 India E-mail: [email protected] Gunasekaran Priya Department of Biotechnology Faculty of Science and Humanities SRM Institute of Science and TechnologyRamapuram Campus Chennai 600089 Tamil Nadu India A. Prashanth Rajan Department of Biotechnology Karunya Institute of Technology & Sciences Coimbatore India Anand Prem Rajan School of BioSciences and Technology Vellore Institute of Technology Vellore India E-mail: [email protected]

XIII

Vinoth Kumar Ramachandran Department of Biotechnology College of Science and Humanities SRM Institute of Science and Technology Ramapuram Chennai Tamil Nadu India E-mail: [email protected] Karthiyayini Ramaswamy Department of Botany Avinashilingam Institute for Home Science and Higher Education for Women Coimbatore 641043 Tamil Nadu India Thirumalaisamy Rathinavel Department of Biotechnology Sona College of Arts and Science Salem 636 005 India E-mail: [email protected] Ashwini Ravi PG Department of Biotechnology Dwaraka Doss Goverdhan Doss Vaishnav College (Autonomous) Chennai 600106 Tamil Nadu India Soundararajan Sangeetha P.G. and Research Department of Zoology Pachaiyappas College Chennai 600030 Tamil Nadu India Pugazh Santhosh Department of Biochemistry College of Science and Humanities SRM Institute of Science and Technology Kattankulathur Tamil Nadu 603203 India

XIV

List of contributing authors

Vasuki Sasikanth Department of Biotechnology Sona College of Arts and Science Salem 636 005 India Selvam Sathish Department of Biotechnology Bharathidasan University Tiruchirappalli Tamil Nadu 620 024 India E-mail: [email protected] Sindhu Seshachalam Department of Biotechnology Sona College of Arts and Science Salem 636 005 India Murugan Sevanan Department of Biotechnology Karunya Institute of Technology and Sciences Deemed to be University Coimbatore India E-mail: [email protected] Natarajan Shanthi P.G. and Research Department of Botany Pachaiyappas College Chennai 600030 Tamil Nadu India Rahul Amin Sheikh School of BioSciences and Technology Vellore Institute of Technology Vellore India Shanmugasundaram Shyamalagowri P.G. and Research Department of Botany Pachaiyappas College Chennai 600030 Tamil Nadu India E-mail: [email protected]

Vipendra Kumar Singh School of Biosciences and Bioengineering Indian Institute of Technology Mandi VPO Kamand Mandi Himachal Pradesh India Uma Sivalingam PG Department of Biotechnology Dwaraka Doss Goverdhan Doss Vaishnav College (Autonomous) Chennai 600106 Tamil Nadu India Srinivasarao Sowmya Department of Chemistry Vels Institute of Science Technology and Advanced Studies (VISTAS) Pallavaram Chennai 637001 Tamil Nadu India Mani Thenmozhi Department of Biotechnology Vels Institute of Science Technology and Advanced Studies (VISTAS) Pallavaram Chennai 637001 Tamil Nadu India E-mail: [email protected] Sita Manojgyna Vangala Department of Chemistry Services Excelra Knowledge Solutions Uppal Hyderabad 500039 India E-mail: [email protected]

Vasuki Sasikanth, Bhuvaneswari Meganathan, Thirumalaisamy Rathinavel*, Sindhu Seshachalam, Harini Nallappa and Brindha Gopi

1 General overview of biopolymers: structure and properties Abstract: Biopolymers are synthesized from a biological origin under natural phenomenon especially during their growth cycle, in the form of polymeric substances that portrays excellent properties such as flexibility, tensile strength, steadiness, reusability, and so on. The amalgamated form of two or more biopolymers leads to the formation of “biocomposites” with novel applications. Several mechanisms were identified for the effective production of biopolymers from diverse life forms such as microbial origin plant and animal origin. Based on their origin, biopolymer differs in their structure and functions. Biopolymers are preferred over chemically synthesized polymers due to their biodegradability and their impact on the environment. Biopolymers play a pivotal role in pharmaceutical industries. The biopolymers could be employed for, the administration of medicine as well as regenerative medicine to reach minimal immunogenicity and maximum pharmacological expressivity in a treated individual. Based on their properties biopolymers were exclusively used in medical devices, cosmaceuticals, and confectionaries, it is also used as additives in food industries, bio-sensors, textile industries, and wastewater treatment plants. Ecological support is of utmost concern nowadays due to the ever-expanding ramification over the planet by usage of plastic as packaging material, turning up scientists and researchers to focus on biodegradable biopolymer utilization. The miscibility-structural-property relation between every biopolymer must be focused on to improve the better environment. Specific biopolymers are designed for the betterment of agrarian and commoners of society. Advanced structural modifications, properties of biopolymers, and applications of biopolymers to achieve a greener environment were discussed in this chapter. Keywords: agrarian; biocomposites; biopolymer; pharmaceutical.

1.1 Introduction Biopolymer is an organic polymer derived from natural living organisms such as plants, animals, and microbial sources. Biopolymers can degrade completely at accelerated

*Corresponding author: Thirumalaisamy Rathinavel, Department of Biotechnology, Sona College of Arts and Science, Salem, 636 005, India, E-mail: [email protected] Vasuki Sasikanth, Bhuvaneswari Meganathan, Sindhu Seshachalam, Harini Nallappa and Brindha Gopi, Department of Biotechnology, Sona College of Arts and Science, Salem, 636 005, India As per De Gruyter’s policy this article has previously been published in the journal Physical Sciences Reviews. Please cite as: V. Sasikanth, B. Meganathan, T. Rathinavel, S. Seshachalam, H. Nallappa and B. Gopi “General overview of biopolymers: structure and properties” Physical Sciences Reviews [Online] 2023. DOI: 10.1515/psr-2022-0214 | https://doi.org/10.1515/9783110987188-001

2

1 General overview of biopolymers

rates. They break down into simple substances such as CO2, methane or H2O that are easily found in the environment by synthetic actions of microbes [1]. Structural units of biopolymers are amino acids, sugars, polysaccharides, proteins, and nucleotides [2]. Biopolymers are appearing to hold great business prosperity because of their elasticity, employability, and tough nature. The chemical and pharmaceutical industries share a major advantage in using these biopolymers [3]. Plant source includes cellulose, pectin, and xylan. The animal source includes chitosan, collagen, keratin, and gelatin [4]. Polymers are now derived from microbial sources as well which include polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), and bacterial cellulose (BC). Chemically synthesized polymer is polylactide [PLA]. The most predominant and useful biopolymers are starch, cellulose, chitin, collagen, keratin, PHA, PHB, BC, and PLA. Biopolymers production rate estimated to become a 14.92 billion dollar industry by the financial year 2023. The biocomposites hike up the mechanical properties of biopolymers by 60% by their reactive structural modification. Starch is an environment-friendly material. Starch can replace the use of synthetic polymers in the plastic industry. Starch is a heterogeneous material comprised of two types of polymers namely amylase and amylopectin. Naturally occurring starch exists in granulated form. Amylose is a polysaccharide made of D-glucose monomers. 1, 4 alpha glycoside bonds connect the amylase whereas 1, 6 alpha glycoside bonds links the amylopectin. Due to their structural difference their properties also differ greatly. Amylose is more crystalline while amylopectin is readily digestible because of its branching. Amylopectin has a branched structure such that most short chains of 1, 4-linked anhydrous units as in amylase and 4–5% branching point with 1, 6 linkages frequently occurring at every 20–30 glucose units, which forms a major component of starch.

1.2 Classes of biopolymers Cellulose is the most abundantly occurring biopolymer which is found in the cells of plants. Cellulose has been widely used as a biocomposite in many fields. Cellulose has the most unique structure compared with others. Cellulose is also made up of D-glucose subunits. Cellulose has beta orientation while others have alpha orientation. The hydroxyl group of cellulose is placed overhead the level of sugar (glucose ring). Cellulose is crystalline and it has a white powdery appearance. Cellulose in plant cells is in the form of cellulose micro fibrils. Chitin is an ample biopolymer next to cellulose. Deacetylation of chitin gives chitosan. It is a positively charged polysaccharide. Arthropods like shrimps, crabs, lobsters, and insects have chitin in their exoskeleton. The fibrous crystalline state is the native form of chitin. It is extensively used in drug delivery, antimicrobial agents and also in food industry.

1.2 Classes of biopolymers

3

Collagen is extensively used in the biomedical industry. It is the major structural compound of the skins and hides of animals. Collagen exists in fibrous form thus it provides mechanical assistance and organizational structure to the connective tissues of our body. Native collagen structure is triple helical alpha domains. These chains have Lhanded amino acid sequence polyproline. Approximately there are more than 30 types of collagens. Type I collagen consists of an N-terminal propeptide, middle collagen domain, and C-end pro-peptide. It appears in bones, tendons, and organs. Type II collagen forms a basis of hyaline cartilage, it includes articular cartilages. It forms a homotrimer with alpha 1 chains and it occupies 50% of protein in cartilage region. They are articulated into fibrils. Type III collagen is a major structural component of large blood vessels, uterus etc. Interaction with platelets of blood for clotting the blood and acting as an important signaling molecule during wound healing are the two major functions of type III collagen. Type IV collagen is an important component of cell adhesion, migration, proliferation, and cell differentiation. It provides mechanical stability for cells. Type V collagen is also called as fibrilar collagen. It is usually found in hair and nails. Type V collagen constitutes bone matrix, interstitial cell of muscles lungs and placenta [5]. Keratin is a member of the fibrous protein family. Its intricate structure like a nanofibre lattice structure acts as a barrier in our epithelial cells. Based on order keratin is classified into alpha and beta keratin. α-keratin is profoundly found in nails and α/β-keratin is found in the carapace of turtles. Keratin is a natural source of nitrogen and is used as fertilizer. Keratin structure is dependent on the amino acid constitution. Keratin has a strong and stable structure, so it is insoluble in water, acids, alkali, and solvents. Keratin protects the epithelial cells and strengthens skin and internal organs [6]. PHA is an agreeable polymeric substance that is derived from many microorganisms that act as a renewable carbon resource. A wide range of bacteria can hold these polymer substances in their body as a storehouse of energy and carbon sources in cases of nutrition deficiency. PHAs are used as fabrication material for absorbable medical supplies such as meshes, implants, sutures, etc. [2]. PHB is a family of PHA biopolymers that is built up by a variety of microorganisms [7]. PHB can be used as a conventional product for many petroleum-derived plastics. PHB is biocompatible in nature [8]. Bacterial cellulose (BC) which is similar to plant cellulose and has the same molecular formula is a sustainable natural nanomaterial. Functional BC has been produced in large quantities for performing various scientific inventions by combining various properties like synergetic effects, optical, magnetic, catalytic properties, and bioactivities. PLAs are the best replacement for most petro polymers [9]. PLAs are synthesized from lactic acid through various processes to create an environment-friendly polymer. It was first used in the medical and packing industries. Tissue engineering a vastly growing field uses PLA and its copolymers. PLAs are the most optimistic polymers in the form of renewable resources [10, 11]. Biopolymers are classified upon many bases with different scales. Based on their source they are classified into three classes such as animals, plants and microbes.

4

1 General overview of biopolymers

1.2.1 Biopolymers of animal origin and their applications 1.2.1.1 Chitosan Chitosan is a natural polysaccharide and second most abundant biopolymer next to cellulose [12, 13]. Chitosan has characteristics of high bioactive, rapid degradability, polyelectrolyte action [14], high absorbing flexibility, antimicrobial activity [15], high muco-adhesive, low immunogenicity, and nontoxic [16]. Chitosan also carries the property of blood clot formation, antioxidant, antitumor [17]. Chitosan is derived from chitin when deacetylation reaches approximately 50% [18]. The applications of chitosan were as follows: Chitosan has a specific property that inhibits the formation of bacterial plaque [19]. It also acts as an inducing agent for healing ulcers and infections [20]. Chitosan helps to promote osteogenesis [21]. Chitosan plays the main role in column chromatography to isolate lectin [22]. Chitosan acts as a suppressor of tumor cells in mice by activating the peritoneum [23]. Chitosan helps in the coating of fruits and vegetables [24]. Production of antimicrobial packing and nanofilms in the food industry [25]. Chitosan is used in ligament tissue building [26]. Its specific property of water sorptivity, oxygen permeability [27], blood coagulation, and cytokine induction enhance scaffolding material [28]. Chitosan has wide applications in the field of biomedical industry [29], food industry [30], biosensors, bone tissue engineering, cosmetic industry, and textile industry [31]. 1.2.1.2 Collagen Collagen is a proteinaceous molecule synthesized by fibroblast originating from reticulum cell or pleuripotent cells [32]. It is a primary structural material of vertebrates and body protein found in connective tissues, tendons, bones, and cartilages [33]. It is mainly derived from animal species such as cattle bones and bovine [34]. Collagen has the characteristic nature of easy absorbability, low antigenicity, high tensile strength, biodegradability, and high affinity with water [35]. Applications of collagen is widely used in tissue engineering, hydrogel and sponges in dressing severe burns and wounds [36]. Collagen-based nanoparticles cytotoxic agent acts as parenteral carriers which execute antimicrobial property [37]. Collagen plays a main role in cultured skin transportation, substituting osteoinductive activity, skin replacement and tissue engineering, and acting as carriers for inducing protein in bones [38]. Collagen is responsible for tissue management and coagulation in vital organs such as the liver and spleen [39]. A combination of collagen and hyaluronic acid is used to repair mimic bones [40]. Collagen is also used in food packing industries [41]. Biomedical applications of collagen include gene delivery, collagen shields, protein delivery, and vascular tissue engineering [42]. Collagen has the property of high tensile strength and low extensibility which helps in tissue arrangement.

1.2 Classes of biopolymers

5

1.2.1.3 Gelatin Gelatin is a derived product of native collagen by partial hydrolysis. Gelatin consists of all essential amino acids except tryptophan and water-soluble proteinaceous substance. The source of gelatin is from different types of collagens hides, pig skin, fish, and cattle bones. Gelatin has the characteristic nature of form emulsifying and wetting. It has a high surface active property [43]. Applications of gelatin were as follows: Gelatin acts as an emulsifier in the pharmaceutical and food packing industry. Grafting of cardiac tissues and cardiac skin damages is done by imposing insoluble gelatin. A combination of gelatin with other biopolymers is used to repair bone degeneration and native cardiac tissues. Its specific property of adhesive and high surface active nature enhance stem cell therapy. Gelatin is also used for hair growth and quality. Its unique property of foam hydrogel enhances many applications such as tissue engineering, gene transfection, bone regeneration, cosmetic surgery, and recovery of sports injuries and wound dressing. Gelatin is used in the production of antimicrobial edible film. Fish-derived gelatin has high benefits and advantages in drug delivery. Extraction of high metals and dyes from wastewater can be obtained using gelatin. Gelatin’s major application is in the pharmaceutical industry as an emulsifying and wetting agent. Gelatin with yeast is incorporated in wine and beer production [44]. Effective healing of a skin wound using epidermal growth factor (EGF) microsphere incorporated with gelatin, without any foreign body reaction. Gelatin is also used in commercial products such as bath salts, hair sprays, facial creams and sunscreen due to its gelling and stabilizing properties. Gelatin is used as a microsphere for cell transplantation carriers. In the field of microbiology gelatin act as a hair filter to analyze hair-borne microorganisms. Gelatin is also used in the forensic department as gel lifters to trace finger impressions. 1.2.1.4 Hyaluronic acid Hyaluronic acid is found in extracellular matrix and cartilages of mammals and then in various fluid of body. The source of hyaluronic acid is vitreous humor of the eye, synovial fluid and umbilical tissue of higher animals. Hyaluronic acid is a linear polysaccharide and its classification is based on D-glucuronicacid and N-acetyl D-glucosanine constituent [45]. Hyaluronic acid exhibit distinctive properties such as water retaining high loading capacity, high viscosity, soluble in water, and mucoadhesive polysaccharide [46]. Applications of gelatin were as follows: Hyaluronic acid commonly excels in various drug delivery systems such as ocular, nasal, parental, and protein based drug delivery [47]. It acts as rejuvenating agent and used in soft tissue contouring treatment [48]. Hyaluronic acid helps to fill deep wrinkles and scars in skin [49]. Hyaluronic acid is used to repair tissues of brain and nerve with other biopolymer. Dressing agent of burnt wound, surgical wound deep scars which are done by hyaluronic acid. In the field of cosmetics, hyaluronic acid or hyaluronic based hydrogel are used to align lip shape and facial line [50].

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1 General overview of biopolymers

1.2.1.5 Keratin Keratin is a protein based biopolymer found in hair, horns, nail, skin, scales, beaks hooves, feathers, and claws of animals from different species. Basically there are two types of keratin, primary and secondary keratin. Keratin source are from cytoplasmic epithelia of humans, animals and birds. It provides many applications due to its physical and chemical property [51]. Keratin is a protein derived biopolymer which helps in waste water management. Keratin is fibrous material which is insoluble in water and organic solutions, which in turn fabrication development from animal fiber, nanofiber, and keratin films [52]. Keratin does important applications in drug delivery system and tissue engineering [53].

1.2.2 Biopolymers of plant origin and their applications 1.2.2.1 Alginate Alginate is a polymer that is found in nature, they are negatively charged polysaccharide which has good biodegradability, bioabsorbable, and less toxicity [54]. Alginate is found in brown algae by bringing out an alkaline solution from organic acid [55]. The most unique feature of alginate is that it contains a carboxylate group in them which make the ability to withstand in presence of divalent cations like Ca2+ and Mg2+ [56, 57]. Alginate combined with amino acids, proteins, fatty acids, and other microelements has wide application in many fields of industrial places in biomedical, agriculture, and pharmaceuticals [58, 59]. It has wide range property as it can take different forms of membranes, fibers, hydrogel, and capsules [60]. 1.2.2.2 Carrageenan Carrageenan is an anionic linear polysaccharide that originated from red algae (Rhodophyceae) by the method of hot alkaline extraction. They consist of continuous units of 3,6-and hydrate galactose and galactose [61]. Carrageenan is classified into different types based on their origin and state into different types, they are: – Kappa (κ): It consists of one sulfate group in each polysaccharide. They are inflexible or flexible and thermo reversible. – Iota (i): It consists of two sulfate groups in each polysaccharide. They form double helix transformation to gel in water. – Lambda (λ): It consists of three sulfate groups in each polysaccharide. They have a non-gelling property and are soluble in hot water [62].

1.2 Classes of biopolymers

7

1.2.2.3 Cellulose Cellulose is a commonly found polysaccharide in the environment and they are majorly found in the plant, which is the polymer of glucose [52]. Cellulose is known as micro fibril or fibril due to its structure that has hydrogen bonds between its hydroxyl groups in inter molecule and intra-molecule [53]. 1.2.2.4 Guar Gum Guar gum is extracted from embryo sac of cluster bean (originated from plant). It is linear polymer of β-D-mannose. They are branched and linked with diequatorial linkers. Guar gum shows different kinds of properties compostable, water-hating nature, stability, and film forming ability. Guar Gum are non-ionic have applications in tissue engineering and also act as carrier in transport of drug [54–56]. 1.2.2.5 Gum Arabic Gum Arabic is sticky dry secretion from stem of Senegal gum. It is polysaccharide which is acidic in nature made up of arabinose, rhamnose, galactose, and glucuronic acid [63]. In early stages of medical field gum arabic is used as lining in inflamed surfaces and internal lining of intestinal skin inflammation [64]. Gum Arabic possesses different kinds of properties decreases absorption of glucose, increase fecal secretion, increase bile acids which make the ability to change physiological state of human in positive way [59]. 1.2.2.6 Pectin Pectin is heteropolysaccharide which are found in most of the terrestrial plants common extraction of pectin is done from citrus peel, apple, and woody plants. It is soluble in water and has high tendency to hydrate [65]. Pectin widely plays a vital role in biomedical field for treating over eating, used as binding agent in tablet formation, and specific drug delivery, and some pectin show in vitro immunological response, it also induced in tissue engineering [61]. 1.2.2.7 Xylan Xylan is a hemicellulose material which is found in annual plants and cell walls of cereals for example lignocelluloses is one of major producer of xylan [66]. Extraction of xylan is done using bamboo leaves, brown sea weed, wheat, and corn stack. Characteristic features of xylan which has high viscosity, biocompatibility, non-antigenicity, biodegradability, and adhesive nature [67]. This type of plant biopolymer has numerous applications in the field of drug delivery [68], lowering blood cholesterol, decrease insulin

8

1 General overview of biopolymers

response, xylan plays role in the treatment of liver disorder, it also involves in immune stimulating process, wound dressing, tissue repair mechanism, anticoagulant agent, and executes antimicrobial effect [69].

1.2.3 Biopolymers of microbial origin and their applications 1.2.3.1 PHA PHA is a widely used bio-based polymer creating a potent role in the production of energy. Such PHA could fix major issues such as shortage of petroleum, reduction in emission of CO2 thereby protecting our environment. The PHB can be synthesized via crops, domestic wastewater, and activated sludge. PHA can be used as a basic substrate for the production of biofuel. Still, PHA was under research for preparation at minimal cost so that it could be used as a substitute for already available biodiesel, ethanol and fossil fuels. P3HB (Poly-3-Hydroxybutyrate) has largely used FAME biofuels made out of PHAs, still more research work should be intensified to explore FAME biofuel via the esterification process [70]. Commercialization of such biofuels should be considered to create awareness among people. 1.2.3.2 Pullulan Aureobasidium pullularia is a black yeast-fungus generally known as pullulans and exhibits enzymatic activity like invertase, transferase and proteolytic enzyme. It is a universal solvent soluble polysaccharide with a high molecular weight of about 10,000–400,000 kDa. Pullulans can be produced in a medium comprising heteropolysaccharides or any complex carbohydrate sources. It is a natural form of glucan containing maltotriose units combined in a linear model with alpha 1, 6 glycosidic linkages with glucose residue ending with a trisaccharide [71]. 1.2.3.3 Levan Levan is a polysaccharide found in extracellular membranes. It is a non-toxic and bioactive polymer. Levan can be synthesized both from plant and microbial origins. It is a carbohydrate polymer comprising fructoses connected by 2, 6-glycosidic linkages. Bacillus subtilis is a primary microorganism to synthesize microbial kinds of levan. Other microbes such as Bacillus polymyxa, Aerobacter levanicum, Streptococcus, and Corynebacterium were also involved in the synthesis of levan-polysaccharide [72, 73]. It possesses a potent industrial-based application such as thickening agents and encapsulators for drug delivery systems and it is also used as an alternative for a few petrochemicals.

1.2 Classes of biopolymers

9

1.2.3.4 Dextran Dextran is a bioactive polymer. It was first utilized by Scheibler in the year 1874. This levo rotator carbohydrate possesses an empirical formula of C6H10O6 that helps in stabilizing cane and beet sugars. Dextran was formed by Leuconostoc mesenteroides as a fermented product in cane sugar and sugar beets. They are produced extracellular. It forms a linear polymer of alpha 1, 4 and 1, 6 glycosidic linkages [74]. It is soluble in a common universal solvent and found its usage in the food industry, packing industry, and pharma-based companies. 1.2.3.5 PHB (polyhydroxybutyrate) Ralstonia eutropha is the primary producer of polyhydroxybutyrates (PHB) few microbial species producing PHBs were Alcaligens, Azotobacter, Nocardia, Pseudomonas, and Rhizobium [75]. These microbes synthesize PHB as a poly-β-hydroxybutyrate polymeric compound which is a storage form of energy source in nature. It is found that this PHB is finding its extensive use in drug delivery and biodegrading thermal plastic in the United Kingdom. It also serves as a good alternative for plastic in the packaging industry. 1.2.3.6 Bacterial cellulose Bacterial cellulose is a nanofiber bioactive material extracted from monocyte bacterial pieces of machinery, which uses the chemical energy derived from renewable substrates. Bacterial cellulose is produced at extracellular matrix and it is obtained in its pure form. BC was used in the pulp and paper industry, concrete, cosmetics, and biosensor applications. It helps in wound healing and wound dressing, CDD (conventional dry dressing), and oncology treatment. Bacterial cellulose synthesis is a multifaceted process that involves two important mechanisms including uridine phosphoglucose synthesis and glucose polymerization into a linear unbranched beta-1-4 glycosidic linkage by cellulose synthase. Bacterial cellulose-pellicles are also used in the temporary treatment of skin burns as well as dermal injuries. It is also used in preparing electro chromic dyes. In electronic companies, it is used for the production of OLEDs [76]. 1.2.3.7 Curdlan Curdlan is a linear form of glucan. It is synthesized by the fermentation of Alcaligens faecalis (myogenic culture). Curdlan gets its name from the property it possesses. Curdlan forms curd-like material when it is subjected to heat. It is a neutral compound comprised of 1–3, beta-glycosidic linkages without any branched structures. It is soluble in alkaline medium and insoluble in water. It also shows a unique helical nature that forms gels easily; this gel exhibits potent pharmacological properties. Curdlan founds its potent

10

1 General overview of biopolymers

usage as a gel in nanodrug encapsulation and it gradually releases bioactive agents in immunological systems. This pharmaceutically important compound is being used to treat oncological cells, wound healing, and microbial growth inhibitors. 1.2.3.8 Xanthan gum Xanthan gums can form a high colloidal solution even at lower concentrations. This property makes it more special for making hydrocolloids, emulsions, etc., This xantham gum is synthesized by a microbe called Xanthomonas campestris by simple carbohydrate fermentation followed by alcoholic precipitation drying and milling process. Xanthan gum founds its extensive use in oil recovery as the controlling agent of motility, in hole drilling type of operating systems, to improvise suspension capacity of drilled mud and it is also used in gels to enhance volumetric effectiveness [77, 78]. Biopolymer characteristics, applications from different origin presented in Table 1.1.

Table .: Types of biopolymers, characteristics, and its applications. Origin

Name of bioploymer

Characteristics

Applications

Animal

Chitosan

High mucoadhesive, low immunogenicity, nontoxic, and gel-forming ability [] Easy absorbability, low antigenicity, high tensile strength, biodegradability, and high affinity with water [] Emulsifying and wetting agent, high surface active property []

Antioxidant, antitumor []

Collagen

Plant

In tissue engineering, hydrogel, and sponges in dressing severe burns and wounds [] Gelatin Emulsifier in pharmaceutical and food industry, grafting of cardiac tissues, tissue engineering, bone regeneration and wound dressing [] Hyaluronic acid Water retaining capacity, high loading Drug delivery system (ocular, nasal, capacity, high viscosity, soluble in water, protein based), used to fill deep wrinand mucoadhesive [] kles and scars in skin, align lip and facial line [] Keratin Fibrous material which is insoluble in Manufacturing bandages and scaffolds, water and organic solutions waste water management, drug delivery system, and tissue engineering [] Alginate Biodegradability, bio absorbable and Biomedical, agriculture, and pharmaless toxic [] ceuticals [, ] Carrageenan Flexible or inflexible, thermo reversible Used in medical field and form double helix transformation to gel in water [] Guar gum Compostable, water hating nature, sta- Tissue engineering and act as carrier in ble, and film forming ability [–] transport of drug [–]

1.3 Structure of biopolymers

11

Table .: (continued) Origin

Name of bioploymer

Characteristics

Pectin

Soluble in water and high tendency to hydrate []

Xylan

Microbes Levan

Dextran Bacterial cellulose Curdlan

Xanthan gum

Applications

Biomedical field for treating over eating, binding agent in tablet, drug delivery, invitro immunological response, and tissue engineering [] High viscosity, biocompatibility, Drug delivery, lowering blood cholesnon-antigenicity, biodegradability, and terol, decrease insulin response, adhesive nature [] immune stimulating process, wound dressing, tissue repair mechanism, anticoagulant agent, and antimicrobial effect [] Non-toxic and bioactive [, ] Thickening agent, alternative for petrochemicals and encapsulators for drug delivery systems Bioactive, soluble in common universal Food industry, packing industry, and solvent [] pharma based companies Produced at extracellular matrix and Paper industry, concrete, cosmetics, obtained in pure form [] biosensor applications, and treatment of skin burns and dermal injuries [] Forms curd like material when subUsed as gel in nano drug encapsulation, jected to heat, soluble in alkaline mebioactive agents in immunological sysdium, and insoluble in water tems, treat oncological cells, wound healing, and microbial growth inhibitors Form high colloidal solutions at lower Used in oil recovery, in hole drilling type concentrations [, ] of operating systems, improve suspension capacity of drilled mud and in gels to enhance volumetric effectiveness [, ]

1.3 Structure of biopolymers The recent trend of creating sustainable matters in different zones like drugs, and agriculture is also helpful for this industry to grow. Various observers are interested to modify the structures of biopolymers which will have greater efficiency and for producing novel polymers. Polymers combined with organic materials will eventually reduce the production of chemically synthesized polymers. Biopolymers are biodegradable, nano-composites, harmless, pure and intact materials [79].

1.3.1 Bead model of biopolymers The structure of biopolymers has been a content of examination ever since it was created. There are various methods to determine the structure of biopolymers, but the X-ray

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1 General overview of biopolymers

diffraction technique is the most successful one. It does not reveal the structure of crystalline matter and that of substances in solution. Dynamic light scattering, transient electric nuclear magnetic resonance, and centrifugation are some of the techniques to determine polymeric properties. The building of molecular models is not possible with the help of hydrodynamic properties found by performing the above-mentioned methods. Various experiments have been made to get the arbitrary shape of the model which is called as bead model in which the shape is an assembly of spheres with radius and positions. Bead size is selected depending on the molecular size. Irremediable transport characteristics of macromolecules developed by Kirk Wood are the basis for this method. The present bead model form is a result of various researchers. Smaller biopolymers were not created because of their high cost. Bloomfield and Garcia were the ones who modified amino acids in the form of larger domains by which the bead number was reduced to tens. Recent developments have found new methods to construct the bead models of macromolecules of biology. Garcia de la Torre put forth a solution for DNA Fragments that is each bead corresponding to a single nucleotide. The mixed model shows the design of 8 smaller amino acids which indicates a sphere while the others are arranged as partially coinciding arrangements. One group has 10 atoms in the larger group of amino acids [80].

1.3.2 Electronic structure The knowledge of the electronic structure of biopolymers such as DNA and proteins is very much needed to know about various physical and chemical properties. They are large molecules and their order is episodic. DNA-B is helix and has two anti-parallel nucleotide sequences and protein has amino acid groups which are formed as beta pleated sheets or alpha-helical structures. To find out the electronic structures of proteins and DNA one has to follow the steps in Figure 1.1. The energy gap values of homo polypeptides range from 8 to 329 eV. These energy gaps need to be insulated as it reduces the correlation effect. The band of a polypeptide (a splitting effect is caused) is much slim than that of homo polypeptides. Periodic multicomponent polypeptides have the largest band gaps and it has insulating properties. Neither banding nor hoping is possible in this case. For maintaining electro neutrality in polynucleotide sodium ions have been added to each of the phosphate groups, sodium ions will not only interact with the phosphate group but also interacts with the entire DNA molecule. A large gap in bands has been observed which excludes the property of intrinsic conductivity. The most reliable model is the aperiodic protein model when compared to periodic ones because the energized localization of amino acid residue depend on the E-environment of residue whereas in a periodic models the electronic environment keeps on changing thereby shifting energy positions. Intrinsic conductivity is not possible in periodic and a periodic polypeptide chains and DNA because of their

1.3 Structure of biopolymers

13

Figure 1.1: Steps to find out the electronic structure of proteins.

huge energy gaps whereas extrinsic conduction is possible [81]. The electronic structure, its charge transferring properties has to be studied in order to unveil the biological potency for nanotechnology oriented applications.

1.3.3 Molecular structure Biopolymers are the ‘building blocks of nature’, found in all living organisms, it may be of animal, microbial, or vegetable origin. Biopolymers include proteins (polymers of amino acids), genetic material (polymers of nucleic acids), glycoforms (carbohydrates and glycosylated molecules), metabolites, and other structural molecules. Almost these are all biopolymers existing in long chain or branched chain polymers in variety of molecular structures [82]. Sporopollenin is a substance that is naturally present in the shells of a plant. It is the most dissent material in the organic world. It is made of a cross-linked polymer. It is high in resistance to chemical degradation. The main steps to finalize the structure of sporopollenin is exine of sporopollenin can be built up by aliphatic biopolymer it can be constructed totally as an aromatic biopolymer it can be as an aliphatic or an aromatic biopolymer. Recent research report revealed that thermic decimation of sporopollenin, wherein the first stage of the degradation undergoes below 500° where removal of hydrogen and oxygen atom takes place, and the second stage is above 500° when aromatic compounds are formed. Recently Li and his colleagues put forth a general molecular structure of pine sporopollenin using high-energy ball milling and nuclear magnetic resonance (NMR) techniques. Ball milling of lignin and pollen grains leads to alteration of its native form and can synthesize new compounds. Sporopollenin is highly stable and insoluble. A more energetic TOF SIMS secondary ion was bombarded. This broke every C–C bond of the

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1 General overview of biopolymers

precursor ions. The tandem MS imaging showed the presence of ions. These ions are characteristic of diacylglycerol. Fatty acids that were identified which has an extra terminal group in their structure. This confirms the fatty acids forming polyhydroxy acid containing three oxygen atoms. Based on the biomedical application of the sporopollenin exine is exhibit as spherical dendrimers which is used as a microcapsule [83].

1.3.4 Photonic structure Biological photonic structures could prevent light scattering, propagation, and emission via hierarchical structures. Naturally, derived polymers are ubiquitous. They are produced by plants, animals, and microorganisms. Biopolymers photonic structure, natural source optical mechanisms are given below: Cellulose-chiral pneumatic structures, gratings-fruits, flowers-chiral photonic crystals, diffraction gratings, chitin-chiral pneumatic structures, multilayered structure, disordered networks-insect cuticles/wings, and mollusk shells-chiral photonic crystals. Natural polymers offer various advantages that are the unique amalgamation of optical and mechanical properties which are important for applications in the real world such as renewability, diverse interfacial chemistries, biocompatibility, and controlled thermal properties (Figure 1.2) [84]. Most of the biopolymers are highly clear in the visible range. Natural materials can efficiently absorb sunlight and convert it to chemical energy. Photonic substances obtained from these natural polymers are helpful in environmentally amiable and tenable energy collection and conversion. Colors from conventional chemicals or biological stains show little dissipative loss. Biophotonic structures can create a spectrum of candescent, deep, and eternal colors. These are useful for security where marks of authentication are needed. This is cost-effective, and material needs are significantly reduced. Biopolymers and its selective applications are presented in Figure 1.3 [85].

Figure 1.2: Importance of photonic structure of Biopolymers.

1.4 Properties of biopolymers and biopolymer composites

15

Figure 1.3: Biopolymers and its selective applications.

1.4 Properties of biopolymers and biopolymer composites Biopolymers are polymers of biomolecules composed of long chain monomeric units which are joined together by covalent bonds. They have a complex molecular assembly

16

1 General overview of biopolymers

which gives them a well defines three-dimensional structure [86]. Plastics have been replaced by natural biopolymers to create a resource-friendly environment [87]. Materials derived from biopolymers are sustainable and renewable and prove an excellent performance with a low-carbon print. Biopolymers have acquired special interest as they can replace several of the items we use every day that are made from petroleum. Various factors like the degree of polymerization, types of additives and concentration of additives show a difference in the properties of biopolymers. Electro active biopolymers [EABP] possess electronic and ionic conductivity which gives the possibility to replace other synthetic materials. Examples of biopolymers that show a wide range of electrical conductivity include starch, cellulose, chitosan, and pectin [88]. The properties of biopolymers are classified as relative, synthesizing and component properties. Relative attributes represent the permeability, solubility, and density of the polymer. Synthesizing properties include quality parameters like viscosity, optical purity, stability, and mechanical properties. Component aspects are the combination of relative and synthesizing attributes related to the function and performance of the polymer [89]. Properties of biopolymer presented in Figure 1.4.

1.4.1 Brittleness and ductility properties A biopolymer composite is regarded to be brittle or ductile if it cracks under load with or without prominent distortion. Ductile biopolymers acquire more energy and deform before breakage whereas fragile biopolymers break [90]. Some polymers like polystyrene are breakable and do not distort before complete breakage, but tend to when they are reinforced with natural fibers to produce a biopolymer composite. The fragile and malleable properties of the biocomposites were examined through impact testing [91]. Polylactic acid can be shapeless or a mixture of both crystalline and amorphous based on

Figure 1.4: Properties of biopolymers.

1.4 Properties of biopolymers and biopolymer composites

17

their stereochemistry. The amorphous PLAs transition from a hard and brittle state to a rubbery or viscous state occurs when the glass transition temperature exceeds the normal range. Below the transition temperature polylactic acid will behave as glass with the ability to deform at elevated temperature and load until it is brought to its transition temperature. At a temperature, lower than the transition temperature, polylactic acid behaves as a brittle biopolymer. The ductile-to-brittle transition is referred to as the immediate drop in the absorbed energy due to impact load [92].

1.4.2 Characteristic temperature/Thermal properties The dominant factor that determines the thermal properties of biopolymer and biopolymer composites are thermal stability and thermal conductivity. Lignin is used as a thermosetting material as it has intra and intermolecular bonding and acts as thermoplastic. It is included as a blend and co-polymers with other polymers due to its thermal instability. Some factors like glass transition temperature, melting temperature, thermal degradation rate, the heat of fusion, and stability play an important role in biopolymers analysis [93]. The flexibility of amorphous polymers is reduced when they are cooled below a characteristic transition temperature called the glass transition temperature (Tg). In the case of flax-reinforced biopolymers, the application temperature must be relatively low because when flax is exposed to high temperatures; it results in degradation [94]. These factors or parameters are determined using differential scanning calorimeter (DSC) and thermo gravimetric analysis (TGA) [95]. Banana has nearly 62% of cellulosic fibers thus it is used as fiber reinforcement to produce biopolymers. The Thermo gravimetric Analysis (TGA) was performed on the biopolymer composite synthesized from resorcinol – para-nitro aniline – urea formaldehyde with banana fiber. The spectrometric and Friedman Technique kinetic study showed an increased crystalline nature of biocomposites and the waste from the banana plant played an important role in the better thermal stability which is useful in various applications [96].

1.4.3 Chemical properties Chemical properties like optical purity and molecular mass of the biopolymer composites affect the mechanical strength of biopolymer composites like polylactic acid. With increasing molecular weight, the tensile strength and modulus of elasticity also increase. Since polyhydroxyalkanoates have short-length monomers, they have low stretching ability and can easily tear. The synthesis of biopolymers is quite tedious as the decomposition temperature is lower than the melting temperature. So, it directs to break under the application of heat which reduces the molecular mass of the biopolymer composite [97].

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1 General overview of biopolymers

1.4.4 Creep and fatigue properties Creep is the slow permanent time-dependent deformation caused due to mechanical stress. Fatigue refers to the cyclic damage caused due to repeated material handling. Fatigue properties are influenced by the structure and shape of biopolymer composites [98]. Creep properties of fiber-reinforced composites reveal that the modulus of creep of wood fiber polypropylene composites is reduced at elevated temperatures. The formation of cracks occurs as microscopic cracks which transform into a risky stage leading to the complete failure of the biopolymer composites.

1.4.5 Dynamic mechanical thermal properties Dynamic mechanical thermal analysis (DMTA) regulates the heat deflection temperature (HDT) of biopolymers. The storage modulus, loss modulus, and damping values are the functions of temperature at 3 °C/min. The thermal properties were found to be decreased by adding plasticizer but from DMTA analysis, an increase in storage modulus and enhanced softening of biopolymer occurred from 50 to 60 °C [67]. DMTA may give information regarding the storage modulus, E′, the loss modulus, E″, and the dampening (tan δ) as a function of the temperature [99].

1.4.6 Fibre mechanical properties The biopolymer composites strengthened with natural fibers show various mechanical attributes required for a variety of aspects. Major mechanical properties include tensile, hardness, toughness, ductility, brittleness, and thermal properties. Various properties like the chemistry and physical properties of natural fibers and biopolymers, composite processing techniques, fiber loading concentration, copolymerization, and plasticization affect the mechanical strength of biopolymers. The presence of a waxy substance also impacts the mechanical strength which affects the adherence and wetting of biopolymers [100].

1.4.7 Flexural properties dynamic mechanical thermal properties Flexural property is the mechanical characterization test that determines deformability. Flexural stiffness depends on Young’s modulus and the moment of inertia of the material. The biopolymer composites with wood and fiber reinforcement show a high Young’s modulus. The modulus of elasticity and flexural strength of biopolymer composites along the length can be elevated by increasing the fiber content [101]. Swapan et al. studied and inquired about the flexural properties of 30 wt% hemp-fiber strengthened thermoplastic polylactic acid produced by the compression molding method. The decrease in flexibility

1.4 Properties of biopolymers and biopolymer composites

19

is due to kinking which is referred to as weak spots. This causes stress concentration in the composite. Thus, by boosting the quantity of fiber, the quantity of weak spots increases which lowers the flexibility of biopolymers. The surface chemical treatment of the fibers improved the flexibility and the elasticity because of the interaction between the surface-treated fibers and polymer than others that are not chemically treated [102].

1.4.8 Impact properties The impact property of a material is the capacity to withstand fracture under applied pressure. Various factors like the type of fiber and biopolymer, size of the particle, adhesion, and specimen condition influence the impact properties of biopolymer composites. PLA composites reinforced with bamboo fiber showed decreased impact strength and to increase the same, the fibers are altered by saline treatment. After this treatment, the impact strength of the composite increased up to 33% [103]. Usually, impact tests are performed on composites, not on fibers as composites can resist fracture under sudden impact. Thermo set resins have less impact resistance owing to the formation of covalent chemical bonds between the polymers. In general, thermoplastic polymers like thermoplastic polypropylene (PP) have good impact strength than thermosetting resins. The compounds which provide a chemical bond between two dissimilar materials (coupling agents) are generally involved to enhance the impact strength of the biopolymers. The impact strength can be improved by improving the adhesion between PP and bio fiber using coupling agents like maleic anhydride. For some thermoplastics like polylactic acid (PLA), the addition of flax fibers did not improve the impact strength.

1.4.9 Physical properties The physical property of biopolymers such as density shape, melting, boiling points and viscosity are depends on contact of biopolymers with water molecules with respect to change in the interior structure by making them humidity sensitive [104]. Swelling of the hydrophilic biopolymers α area is created by adsorbed molecules. Density is an important parameter as higher density values suggest higher transportation costs and implementation of the materials becomes easy and less dangerous. PLA (polylactic acid), PHB (polyhydroxy butyrate), and PCL (polycaprolactone) seem to be the best alternatives in the case of flax reinforcement since they can produce lighter composites. Targeting a less dense material can be the cause for choosing flax to strengthen the composite: its density is 1.45 g/cm3 which is lesser than the density of glass fiber reinforcement (2.54 g/cm3). The crucial property is the water uptake or water content of the biopolymer composites. In the case of the biopolymer composites absorption of moisture is considered a drawback as relocation of water through the biopolymer can disturb the polymer fiber combination

20

1 General overview of biopolymers

thus lessening the whole strength of the biopolymer composites. When it comes to flax reinforcement, it is more considerable since flax absorbs considerable amounts of water leading to swelling which leads to a drop in the strength of the composite. Thus, it is required to alter the flax content to lower its water-taking capacity. An additional physical attribute is the time of degradation which is expected to be short as possible. If the biopolymer has a very low time of degradation, it may decrease the corrosion resistance of the biopolymer.

1.4.10 Tensile properties Tensile tests are the most commonly used tests for deciding the structure and mechanical aspects of biopolymers. To amplify the tensile properties of biopolymer composites, fibers are added to the biopolymer matrix as fibers have higher stiffness and strength than biopolymers. Modulus of elasticity is defined as the ratio between stress and strain which is also called stiffness. The toughness and modulus of elasticity vary corresponding to the type of fiber and biopolymer. Viscose fibers have the lowest tensile strength and modulus. Lyocell and modal fibers have good tensile strength and modulus [105]. By adding approximately 10 wt% of coconut fiber, polyhydroxy butyrate (PHB) is produced, which enhanced its tensile property and lengthens the composite. Properties of different biopolymers presented in Table 1.2.

1.4.11 Toughness and hardness properties The toughness and hardness properties of biopolymer composites depend on their sturdiness and malleability. The capacity to take up the energy and distort without any damage is known as the toughness of the biopolymer composite [109]. The fracture toughness is the ability of a composite containing a crack to resist fracturing. The toughness of a biopolymer composite is determined by examining the ability of the material to withstand any collision. The capability of the biopolymer to withstand permanent distortion when a force is applied is called hardness. Various aspects like rigidness, toughness, malleability, and plasticity affect the hardness of a biopolymer composite [110]. Hardness tests were performed on areca nut fiber-based composites; these composites hold hardness numbers in the range of 20–25. When the areca nut fibers were reacted with the base, the hardness rose to 35. Hardness tests are also performed on sisal, cotton and bamboo-reinforced biopolymer composites.

1.4.12 Tribological properties The study of the abrasion and wear performance of the two mating surfaces is called tribology. The friction and wear of a biopolymer composite are amplified by the addition

21

1.4 Properties of biopolymers and biopolymer composites

Table .: Properties of biopolymers. Biopolymer

Properties

References

Cellulose acetate

Biodegradable High elongation property High resistivity High gloss and flexibility Soluble in acetone and in acids Removes dyes easily Easy to compost and incinerate Easily bind with plasticizer Superior rheological and viscoelastic properties Low melting point  °C Easily degraded by the enzyme lipases Semi crystalline in nature Biocompatible with co-polymers Melting point –  °C Specific heat − . kJ K− kg− It has fair chemical resistance to dilute acids, alcohols, greases and oils, and poor chemical resistance to alkalis Izod impact strength  J m− Tensile modulus – . GPa Tensile strength –  MPa Melting point –  °C PLA is soluble in dioxane, benzene (Hot), and tetrahydrofuran It is a crystalline biopolymer with Tg (glass transition temperature) –  °C It possesses high surface energy Izod impact strength – . It is highly brittle in nature It has low thermal property High degree of crystallinity Young’s modulus (. GPa)

[]

Polycaprolactone (PCL)

Polyhydroxyvalerate (PHV)

Polylactic acid (PLA)

Poly(alkylenealkanoate)s (PBS)

[]

[]

[]

[, ]

of natural fibers [111]. No other polymer except nylons is used in its native state as they provide less rate of wear with optimum friction coefficient. Therefore, most of the polymers are modified by adding fillers that can either increase or decrease the friction and decrease the wear rate of a biopolymer composite [112]. Polytetrafluoroethylene (PTFE) is a self-lubricating polymer that is made wear resistant by strengthening it with hard filler like metals or strong fiber such as carbon or glass fibers. The filler strengthens the matrix of polymer which increases the wear resistance to a certain extent. Whereas non-abrading fibers like cotton and aramid promote the formation of thin film on the counter surface which helps in lowering the wear of the biopolymer composite.

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1 General overview of biopolymers

Two commonly used wear and friction test procedures are pinon discard dry and rubber wheel. Pinon disc involves sliding wear along with a constant contact area. Lubrication has an important role in the tribology of biopolymers. Lubricants like aqueous-based, oil-based and improved properties were used to lessen the wear and abrasion between the surface of biopolymer materials. Water and solid-based lubricants were most commonly and popularly used in polymer tribology. One of the most successful lubricants was developed by Hummer’s method by blending aqueous-based polyethyleneimine with reduced graphene oxide (PEI-RGO). Various tribometers used to study the abrasion and wear aspects of the composites include twin Disc, ring on a ring, four ball pin on disc, ring on the ring, block on the ring, bouncing ball, ring on the ring, and ball on the disc. Ascribed to its reliability, pin on disc instrument is most commonly used.

1.5 Conclusions Costs of producing biopolymers are higher compared to oil based plastics, but the development in this field of business has profoundly decreased the cost of making. Plants that are critical for proffering bio-based polymers are planted near the zones important of rural and urban areas of the nation to reduce the shipment costs. The new applications in agronomy, foods, cosmetics, and therapeutics could in a near future, accentuate the effort of research for their development. They could be used as substitute for environmental pollutant controlling agent as a reinforced rubber. The amalgamated organic modifications and size reduction property enhances the filler and matrix mixture adhesion thereby increasing the performance of polysaccharide. With the help of available genomic data and activity-dependent screening, the scientists have developed auto phosphorylating enzyme from bacterium which is a common lab contaminant. They could derive a kind of expressed bacterial enzyme from microbe, purified it and discovered that it could produce a contemporary polysaccharide known as acholetin similar to the chemical composition of chitin polymer. Due to the incredible properties of futuristic microbial polysaccharides evolve; we need to get streamlined for projecting up by commercialization of such products thereby balancing the improvementation of original structures by balanced development both in cost wise and production wise. Current unstable methods of extracting microbial peptides or polysaccharides must be stabilized by optimizations. The main issue in new polysaccharide commercialization is the sorting process of new superior biopolymers in comparison to classical polymers. Very few polymers are made available in market yet there is way long to get explored about published or patented biopolymers. Patented polymers might be used in food industries as well as packaging industries. Likewise biopolymers set a new era of research in various industrial and biotechnological industries.

References

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Sowmya Hari, Karthiyayini Ramaswamy, Uma Sivalingam, Ashwini Ravi, Suresh Dhanraj and Manjunathan Jagadeesan*

2 Progress and prospects of biopolymers production strategies Abstract: In recent decades, biopolymers have garnered significant attention owing to their aptitude as an environmentally approachable precursor for an extensive application. In addition, due to their alluring assets and widespread use, biopolymers have made significant strides in their production based on various sources and forms. This review focuses on the most recent improvements and breakthroughs that have been made in the manufacturing of biopolymers, via sections focusing the most frequented and preferred routes like micro-macro, algae apart from focusing on microbials routes with special attention to bacteria and the synthetic biology avenue of biopolymer production. For ensuring the continued growth of the global polymer industry, promising research trends must be pursued, as well as methods for overcoming obstacles that arise in exploiting the beneficial properties exhibited by a variety of biopolymers. Keywords: biopolymer; composition; extraction; synthesis; yield.

2.1 Introduction Chemical polymers and their mixtures have been the standard choices for many industries; however, due to their toxicity to living things, introducing these nonbiodegradable compounds into the ecosystem and food chain has prompted worrisome concerns. Therefore, scientists worldwide continue to look for cheaper and more effective replacements for existing materials. One such endeavor is developing and deploying biopolymer-based materials in engineering applications. Biopolymers are increasingly used in favor of petrochemical plastics due to their many advantages over

*Corresponding author: Manjunathan Jagadeesan, Department of Biotechnology, Vels Institute of Science, Technology and Advanced Studies (VISTAS), Chennai, 600117, Tamil Nadu, India, E-mail: [email protected] Sowmya Hari, Department of BioEngineering, Vels Institute of Science, Technology and Advanced Studies (VISTAS), Chennai, 600117, Tamil Nadu, India Karthiyayini Ramaswamy, Department of Botany, Avinashilingam Institute for Home Science and Higher Education for Women, Coimbatore, 641043, Tamil Nadu, India Uma Sivalingam and Ashwini Ravi, PG Department of Biotechnology, Dwaraka Doss Goverdhan Doss Vaishnav College (Autonomous), Chennai, 600106, Tamil Nadu, India Suresh Dhanraj, Department of Microbiology, Vels Institute of Science, Technology and Advanced Studies (VISTAS), Chennai, 600117, Tamil Nadu, India As per De Gruyter’s policy this article has previously been published in the journal Physical Sciences Reviews. Please cite as: S. Hari, K. Ramaswamy, U. Sivalingam, A. Ravi, S. Dhanraj and M. Jagadeesan “Progress and prospects of biopolymers production strategies” Physical Sciences Reviews [Online] 2023. DOI: 10.1515/psr-2022-0215 | https://doi.org/10.1515/9783110987188-002

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traditional plastics. These include biodegradable, non-polluting, environmentally benign, and commercially valuable. Using these biopolymers as an alternative to synthetic plastics could have significantly fewer harmful environmental effects and reduce the energy needed to produce the same amount of plastic. In addition, biopolymers have captured a significant niche in commercial avenues due to their compatible and ecologically benign nature [1–3]. Biopolymers are a diverse, flexible class of ingredients created from organic and natural origin, and most of these polymers originate from plants; however, some are derived from animals or bacteria [4]. Biopolymer synthesis that complements waste management has also received much interest because of its inherent sustainability. Chitin, chitosan, PHA, cellulose, hydroxyapatite, and pectin are some of the most widely used biopolymers. Microbial polymers, PHA in particular, stand out among biopolymers of interest because they biodegrade entirely without producing harmful byproducts [5]. However, the high cost of manufacturing biopolymers of microbial origins limits their usage, despite their usefulness in many contexts [6]. In order to combat this problem, agro-industrial waste, such as agricultural residues [7, 8] food waste, and industrial waste, is being used as a commercially exploitable substrate for increasing microbial biopolymer synthesis [9, 10]. Polyesters, polyamides, and polysaccharides are microbial biopolymers that can be successfully created from pure cultures, mutants chosen from the lab, or genetically engineered organisms. Protein and metabolic engineering have been inspired to create custom biopolymers with modified features that can be used as a renewable source due to the comprehension of microbial biopolymer production and its restrictions. The manufacture of commercially valuable customized biopolymers that serve as highvalue commodities for several applications, including environmental considerations, is facilitated by the genetic alteration of biopolymer-producing microbes [11, 12]. Bacterial biopolymers are used as a buffer against environmental stresses. Microbial biopolymers are critical for pathogenicity and biofilm growth and are categorized into capsular, storage, and extracellular polysaccharides based on biochemical processes [13]. All kinds of microorganisms, both natural and engineered genetically, can produce biopolymers like polylactic acid (PLA), polyhydroxyalkanoate (PHA), polysaccharide, carboxylic acid, and butanediol. Systems biology and metabolic engineering methods improve the performance of biopolymers and their precursor molecules [14]. One interesting alternate method for making biopolymers could be via microalgae and cyanobacteria. The research benefit centers on the fact that these microalgae can develop and amass a range of valuable elements in both lean and non-lean substrates, unlike purely heterotrophic microorganisms. Additionally, it has been noted that many species build up intracellular polyesters as a form of energy storage. However, there are still many challenges to productivity and overall process costs. A biorefinery strategy could overcome the comparatively slow rates of biomass output and the buildup of intracellular algal biopolymers. Further, microalgae could use effluent as a resource of nutrients, lowering their impact on the environment and production costs [15–17].

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This review offers a thorough summary of the efficient production of various biopolymers from biobased substrates, focusing on the source and avenue of production via algal, bacteria, or semi-synthetic streams, including enzyme-supported means of creation of biopolymers.

2.1.1 Bibliometric analysis A technique for examining a topic’s research structure and trends is bibliometric analysis. Research on biopolymer production articles indexed in Scopus bibliometric databases is examined. The “TITLE-ABS-KEY (biopolymers AND production)” keyword search was restricted to the years 2020–2022. According to the search results, 661, 911, 777 documents were published in 2020, 2021, and 2022, respectively. Among 2000 total documents displayed in the search, 1424 documents are research-based which is evidence of the continuous progress of research in the production of biopolymers. Based on this search India, China, Brazil, the United States, and Italy are the top 5 countries that contributed to the documents related to biopolymers production. Bibliometrix R-Tool [18], a recent R package that enables a more thorough bibliometric study by applying specific tools for both bibliometric and scientometric quantitative research, is used to examine the obtained data. The generic function summary is used in Table 2.1 to summarize the major findings of the bibliometric investigation. It presents the most important information about the bibliographic data frame as well as numerous tables, such as top publications per number of citations, yearly scientific production, most prolific nations, most valuable authors, most appropriate sources, complete citations by country, and so on. Figure 2.1a depicts the conceptual structure map of the keywords created using the multi-dimensional scaling (MDS) approach. The MDS method is based on the concurrent rate of occurrence of keywords. Huge data sets with several variables are reduced into two- or three-dimensional structures, with the plane distance between keywords indicating their similarity. The keyword’s proximity to the cluster’s focal point reflects its importance, whereas narrow topics are on the cluster’s perimeter. Biopolymers, sustainable development, biosynthesis, genetics, metabolism, hydrolysis, fermentation, bacteria, substrates, biomass, and metabolic engineering are some of the keywords linked with the biopolymer production subject that emerged in the MDS picture. Figure 2.1b depicts the worldwide cooperation based on the document search. The blue tint of the map represents worldwide research collaboration. The pink border separating the states also indicates the level of engagement of the authors. It’s interesting to see how the countries with the most papers on biopolymer production have partnered in this way. This bibliometric study reveals the global need, progress, and growing interest in biopolymer manufacturing research.

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Table .: Generic function summary of bibliometrix analysis obtained for the Scopus database search. Description Key info regarding data Duration Resources (Journals, Books, etc) Articles Yearly progress rate % Paper mean age Median citations per article Citations Manuscript contents Keywords plus (ID) Author’s keywords (DE) Authors Authors Authors of single-authored paper Authors association Single-authored papers Co-authors per article Global co-authorships % Article categories Scientific article Book Book chapter Conference document Conference review Data paper Editorial Erratum Note Review Short survey

Results :   . . . , ,     . .           

2.2 Production of biopolymers from algae There are basically three techniques used for the synthesis of biopolymers, according to a study of the literature [10]. Figure 2.2 displays the biosynthesis processes for the biopolymers. The three main methods of producing biopolymers from microalgae are: producing biopolymeric-based substances within each microalgae cell; blending microalgae biomass with other additives to improve biopolymer assimilation; and synthesizing biopolymeric products by using microbes fermented with green microalgae biomass [15, 19]. Enzymes from microalgae are used in addition to the conventional biopolymer synthesis routes to convert green biomass with a microalgal orientation into biopolymer

2.2 Production of biopolymers from algae

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Figure 2.1: MDS analysis (a) and Country collaboration map (b) from bibliometrix analysis.

biosynthesis. The globe over, microalgae-produced polysaccharides are widely used. In order to produce biopolymers, it is therefore imperative to increase the economic feasibility of microalgae-based biorefineries and work with microalgae biomass that is derived from wastewater. Microalgae-based biorefineries guarantee cost savings, reduce

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Figure 2.2: Production methods of biopolymer from algae.

carbon emissions, create a circular bioeconomy, and could be able to maintain overall environmental sustainability [15, 19]. The removal of pollutants from wastewater medium is frequently improved when the development of microalgae is restricted. Consequently, there is a strong need for a future culture strategy to enhance the synthesis of biopolymers. In order to increase the biopolymer content while significantly reducing costs, it is expected that effluents rich in carbon and nitrogen will be coupled with the growing system and microalgae’s metabolic pathways. In addition to nutritional supplies, light illumination is a significant environmental factor that affects how much cell biomass increases and how much biopolymers are produced by microalgae [20]. To guarantee that the biopolymer is properly extracted from the interior of the cells, many approaches are utilized during extraction. Some of these processes include destabilization and/or cellular disruption, separating the biomass from the culture media, recovering the biopolymer, and purifying. Some of the methods utilised for PHA extraction include the use of organic solvents, supercritical fluids, biological digestion (enzymes), mechanical methods including high-pressure homogenization and ultrasound, combined mechanical and chemical procedures, and investigations of spontaneous release of biopolymers. Organic solvent extraction is the most used method of extraction because it is easy to use, degrades little, and yields products with a high level of purity [21].

2.2.1 Solvent extraction of biopolymer A number of organic solvents have been used to produce biopolymers from green microalgae biomass [22]. Even while additional chemical reagents are required, the solvent-based

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extraction method is simpler and requires less downstream processing than total fermentation. As may be observed, methanol, glycerol, sodium hypochlorite, and chloride of potash are the most often utilized solvents. PHB can be extracted using sodium hypochlorite and chloroform with claimed performances of up to 60% [15]. Six microalgae strains in total will have their biopolymer synthesis yield performance evaluated. The biopolymer yield proficiency was addressed by the cyanobacterial strains Synechocystis sp., Nostoc sp., and Porphyridium purpureum at around 204, 323, and 83 mg/L, respectively [23]. Since they function just as well as halogenated solvents while being less expensive, non-chlorinated solvents like cyclohexanone and butyrolactone hold great potential as non-toxic, environmentally friendly solvents. Although considerable PHA recovery results from PHB extraction with cyclohexanone, the procedure appears to be temperature-sensitive [24]. In an effort to completely replace organic solvents, ionic liquids are also recommended as extraction solvents. By processing wet or dry biomass with 1-Ethyl3-methylimidazolium diethyl phosphate at moderate temperatures, up to 60% of the biopolymer components can be recovered. The practicality of the procedure is increased by highlighting the potential for recovering the ionic liquid [25]. Ionic liquids act like ordinary organic solvents because of the electrically charged ions in their salt solutions [26]. Moreover, the creation of two separate phases composed of either two different polymers or a polymer plus an inorganic salt dissolved in water is required for the aqueous two-phase extraction method (ATPE) [27]. Ethylene oxide-propylene oxide/sodium chloride, ethylene oxide-propylene oxide/ammonium sulphate, and polyethylene glycol/potassium phosphate are among the PHA-related mixtures of dissolved components in ATPEs [27, 28]. Temperature, the quantity of dissolved compounds, the time of the extraction, and other variables all affect how quickly the bioplastics recover. Due to its nontoxicity and scalability at a low operational cost, this method is deemed technically and economically suitable as the primary extraction process as well as a pretreatment step. The adjustment of physicochemical properties may result in the improvement of biopolymers. The types of microalgae used in the extraction process, as well as a number of mechanical procedures including sifting, filtering, and centrifugation, all have a significant impact on the extraction process [29]. In order to avoid time-wasting research and the monotony of unit operations, microalgae are often examined on how well they produce bioproducts. To make biopolymers, the best microalgae will be used.

2.2.2 Biopolymer production using ultrasound extraction (UBE) Typically, UBE procedures rely on the cavitation phenomena that are created by ultrasound pulses. Cavitation causes turbulence, which causes microparticles in the biomass of microalgae to collide and become distressed. In most cases, the ultrasound radiation is converted into vibrational energy that contributes to disrupting the cell walls of the microalgae. Because of this, the transfer rate is increased, making it possible to extract bio-based polymers from microalgae [30]. In order to extract carrageenan from

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Chondrus crispus, Torres et al. [31] used UBE. They reported that the ideal extraction parameters were an extraction time of 34.7 min; a maximum power of 1130 W with an ultrasonic amplitude of 79.0%; and a solid-liquid ratio of 2.1 g/100 g. Maximum carrageenan yields (44.3%) and viscoelastic modulus (925.9 Pa) were seen in the dependent variables, which also had the lowest gelling temperatures (38.7 °C). The few benefits of ultrasound-mediated extraction over conventional methods include a notable reduction in the amount of time needed to remove biopolymers (from hours to minutes), the elimination of the need for membrane separation processes, the ability to conduct extraction at room temperature without affecting yield, and reduced environmental impact and material losses [32]. When compared to the traditional approach, the extraction yield from ultrasound-assisted extraction was 33% greater. Under various operating parameters and ideal circumstances, sulfated polysaccharides were extracted from red algae, Jania rubens, and green algae, Ulva lactuca, using both conventional and UBE [33]. The findings showed that 4 h of ultrasonic extraction produced the highest yields of both red and green algae. Similarly to this, Flórez-Fernández et al. [34] minimized the use of harmful chemicals by isolating alginate from the same Sargassum muticum using an ultrasound-assisted extraction method. Alginate was extracted from S. muticum using an ultrasound method that required a 4x faster extraction time than the traditional method. Temperature, ultrasound frequency, and the duration of the sonication all have an impact on the isolation process. According to information published by Flórez-Fernández et al. [34], the maximum sonication time influences better biopolymer extraction from microalgae biomass. Additionally, increasing the frequency of ultrasound waves helps microalgae produce more biopolymers.

2.2.3 Microwave-assisted extraction (MAE) of biopolymer Biopolymers are present in every microalgae cell and may be distinguished using MAE. It is believed to be ecologically benign to use green biomass to develop necessary products. There are several advantages associated with such microwave-mediated extraction because of how microwave irradiation affects ions and dipoles [35, 36]. A rapid and consistent procedure, the use of solvents sparingly, and little to no work are just a few benefits. Less time is spent on trials. By valorizing the C. crispus (Rhodophyta) wastes generated during industrial extraction of hybrid carrageenan using MAE in a specified temperature range (140–200 °C) and microwave processing conditions (160 °C, 5 min), it is possible to recover about 10% of semi-refined hybrid carrageenan [37]. With the use of the microwave, Mastocarpus stellatus, a red algae, was removed from a hybrid carrageenan biopolymer, resulting in greater extraction yields [36]. The ideal conditions were found to be 150 °C for 6 min for the predicted biopolymer yields. The increase in temperature contributed to the effectiveness of biopolymers. In order to obtain hybrid carrageenans with a range of viscoelastic properties, microwave hydro diffusion and gravity were employed. If this approach is used instead of the standard

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one, time could be saved. The yields for the recovered hybrid carrageenans and bioactive fractions were equivalent to those from red algae using conventional techniques, according to Barral-Martnez et al. [38]. Moreover, the commercial significance of microwave-based extraction is connected to the lack of syneresis of biopolymeric gels. It may be fruitful to develop a few novel strategies for reaching high productivity and technological economic competency in addition to continuing research on electromagnetic wave-based biopolymer synthesis.

2.2.4 Subcritical water extraction (SCWE) of biopolymer SCWE is an emerging technique for removing bioactive substances from the biomass of microalgae. The water will pressurize the well throughout this procedure at a lower pressure than the critical pressure, which is less than 22.12 MPa, and at a higher temperature than the boiling point, up to 647.14 K [39]. The use of cutting-edge extraction methods to separate biopolymers from microalgae biomass has significantly increased recently. Comparing this method to traditional extraction techniques reveals many advantages. Instead of using chemicals, water is employed as a solvent. High product yield, decreased energy consumption, and quicker reaction times are just a few benefits of SCWE. They demonstrated an innovative technique for using the SCWE to get rid of the fucoidan biopolymer from Saccharina japonica, according to Saravana et al. [40]. It has been noted that the traditional extraction approach had a poor removal efficacy of 2.47% whereas the isolation of fucoidan in the presence of this water extraction method addressed it as improved efficiency of 4.85%. To precipitate crude fucoidans using Himanthalia elongata, SCWE produced a liquid phase that was used to extract alginates with a variety of viscoelastic properties [41]. The experiment was conducted in a pressurized reactor with continuous stirring, a temperature of 160 °C, and a ratio of 1:30 (w/w) algae: water. The reactor was then rapidly cooled to separate the liquid and solid phases by vacuum filtering. The ionic liquid is added to this subcritical water extraction method to improve biopolymer dissolution and increase removal efficiency. Ionic liquids provide many advantages over various organic solvents, including better thermal efficiency, increased durability, improved stability, low vapor pressure creation, and others [39, 40]. A different study used deep eutectic solvents and subcritical water extraction to extract the biopolymer from S. japonica [40]. With regard to the removal of alginate (28.1%) and fucoidan (14.93%) from S. japonica, the created technique demonstrated a high level of productivity and efficiency when compared to other traditional methods. The highest results were obtained at a hydrothermal treatment temperature of 130 °C during the isolation of hybrid carrageenans from M. stellatus red seaweed utilizing SCWE operating in a wide range of thermal settings (70–190 °C). Eco-friendly SCWE technology may be a wise choice for creating biopolymers that may be of interest to sectors including the pharmaceutical, cosmetics, and food industries.

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2.3 Polymers produced by bacteria Organic wastes from agricultural, domestic, and industrial processes contain a range of carbon and nitrogen sources and microelements. These byproducts can thus create cheap synthetic media for microbial growth and polymer production. Some bacteria, including Azotobacter and Pseudomonas are capable of producing alginate in the form of exopolysaccharides [42]. Exopolysaccharides have potential uses in wastewater treatment with biorefinery approaches. As a result of the harnessing of exopolysaccharides, pollutants are removed, and high-value products, including nutraceutical compounds, proteins, and fatty acids, may be separated [43]. Gram-positive bacteria like Sarcina ventriculi produce cellulose less frequently than gram-negative bacteria like Komagataeibacter, Acetobacter, Archomobacter, Azotobacter, Agrobacterium, Alcaligenes, Rhizobium, Salmonella, and Pseudomonas. Several Komagataeibacter species are renowned for synthesizing cellulose most cleanly and effectively of any known bacteria [44, 45]. Transmembrane protein-producing bacteria subsequently self-assemble the cellulose chains into ribbon-like threads that are 40–80 nm wide and 3–8 nm thick. Hydrogen bonds between and inside molecules make up the majority of the interactions in this relationship. As a result of the ribbons’ entwining, a nanoporous network with a macroscopic topology resembling a gelatinous membrane is formed [45]. Suppose bacteria are grown utilizing a static method, which causes the creation of a membrane at the air/liquid interface. In that case, they benefit from having access to oxygen, protection from the elements, and moisture management [46]. Bacterial Cellulose membranes have several remarkable characteristics, including a high level of crystallinity and highly polymerized glucan chains. These traits confer superior mechanical properties (tensile strength between 200 and 2000 MPa and Young’s modulus between 15 and 138 GPa) and thermal stability. BC membranes, in contrast, are naturally occurring hydrogel with a great capacity to store water (99% of its weight is water). Although many Komagataeibacter species have unique growth needs, Hestrin-Schramm medium (HS), a synthetic medium made up of glucose, peptone, yeast extract, citric acid, and Na2HPO4, is frequently employed for the generation of bacterial cultures (BC). Although BC yields in HS-fed cultures are good, the expense of employing this technique climbs significantly [47]. The commercialization of BC products is still in its early stages [42]. However, scientists are researching new strategies to establish affordable growth environments and may have discovered the solution for agricultural leftovers. Hydrolysates of maize stalk and wheat straw, molasses, distillery effluent fluids, effluent from the refining of soybean oil, peels, and leftovers from the manufacture of fruit juices (citrus, apple, tomato, grape, pineapple, and watermelon) [48, 49]. As anticipated, the yield of BC varies according to the residual products used. More study is required to identify an appropriate platform for efficient large-scale production with the concurrent

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benefit of agricultural waste recycling. A few of the numerous applications for BC include water purification and wastewater treatment [42]. The heteropolysaccharide xanthan, also called xanthan gum (XG), has a glucose backbone chain and monomers joined by β-(1–4) bonding, similar to cellulose. In contrast, the glucan backbone of XG bears a residue of glucuronic acid connected to two mannose units in the XG side chain at position C-3. The polymer’s alternate glycosylation of half the side chain residues gives it an anionic quality [50]. The solutions exhibit pseudoplastic fluid properties such as viscosity even at low XG concentrations, stability at low pH, and high ionic strength. Hot and cold water may dissolve XG [50, 51]. Xanthomonas campestris is the most prominent of the few Xanthomonas species that generate XG as an exopolysaccharide. The high cost of the culture medium needed for X. campestris’s growth and polymer synthesis using glucose and sucrose as carbon sources are the major restrictions. Researchers investigated the feasibility of synthesizing low-cost media from various wastes to support the circular economy. Molasses, whey, fruit peels and juice, coconut shell, lignocellulosic residues, and kitchen trash have all been discovered to make culture media that promotes the effective synthesis of XG [52–54]. The selected list of biopolymers synthesized by different bacteria are summarized in Table 2.2.

2.3.1 Biosynthesis of bacterial polyhydroxyalkanoates (PHA) Biodegradable PHAs polymers are often synthesized in nature by microorganisms in the form of insertion bodies; these structures serve as storage materials within asexual cells [2, 82]. PHA is favored among biopolymers due to its low environmental impact, renewable precursor molecule, and wide range of biochemical applications. PHA typically comprises 600–35,000 [R]-hydroxy fatty acid monomer units. Research into modifying existing PHA molecules, improving the biopolymer’s physiochemical properties, and using genetically engineered organisms to create a PHA biopolymer with modified functional groups has led to the identification of nearly 150 distinct PHA molecules to date, and this number is expected to rise [83]. Bacterial fermentation typically makes PHA molecules of lipids or carbohydrates to create a linear polyester molecule. PHA molecules may be found in the microsomes and mitochondria of eukaryotic cells and bacteria like Escherichia coli, Azotobacter vinelandii, and Bacillus subtilis. Affordably sourced PHA was tested by Aljuraifani et al. [84], who isolated it from Pseudomonas sp. using a variety of rice bran, date, and soy molasses as economic carbon sources. For rice bran molasses, the optimal concentration for PHA formation was 15 g/L (w/v); for soy molasses, it was 20 g/L (w/v); and for glucose molasses, the optimal concentration was 10 g/L (w/v). This finding inferred that the higher PHA production attained using a soy molasses as a carbon source. A team engaged Haloferax mediterranei to produce a PHA yield of 55.6% using 2%–5% (w/v) soy molasses as the carbon precursor molecule. Ali et al. [85] investigated a different method for generating bioplastic using a bacterial strain obtained from readily available soil and organic garbage. PHB may

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Table .: Selected biopolymers and its bacterial sources. Biopolymer

Microorganism

Dextran

Leuconostoc mesenteroides AA Lactobacillus plantarum DM Leuconostoc strains Leuconostoc sp. Lactobacillus sp. Leuconostoc mesenteroides Lactobacillus sanfranciscensis Lactobacillus reuteri Streptococcus salivarius Streptococcus mutans Lactobacillus satsumensis Lactobacillus reuteri Streptococcus mutans JC, Leuconostoc citreum CW Lactobacillus reuteri  Lactobacillus kefiranofaciens ZW Lactobacillus kefiranofaciens ATCC  Pediococcus parvulus . Weissella confusa Lactococcus lactis Lactococcus lactis Leuconostoc mesenteroides subsp. dextranicum Leuconostoc citreum Lactobacillus plantarum Lactobacillus satsumensis Lactobacillus kefiranofaciens Lactobacillus kefiranofaciens Lactobacillus satsumensis Streptococcus thermophilus Cupriavidus necator DSM  Bacillus cereus SPV Alcaligenes latus Alcaligenes latus DSM

Alternan Mutan Levan

Inulin

Kefiran β-D-Glucan β-Glucan Dextran D

Kefiran α-Glucans Hyaluronic acid PHA, PHB (polyhydroxybutyrate)

References [, ] [] [, ] [–]

[, ]

[–] [] [] [, –]

[, , ] [] [, ] [–]

be separated and purified from microbial biomass with a maximum yield of 74 mg/L using a process known as sodium hypochlorite chloroform extraction [86]. PHAs may be extracted and precipitated from the cellular biomass using several solvents, including acetone, methanol, and ethanol. Because of their resistance to environmental stress, PHA and PHB molecules are often synthesized in large quantities as an intracellular inclusion from the dry biomass of roughly 90% of the cell. PHA is successfully extracted from the cellular biomass of many microorganisms, including Ralstonia eutropha, Alcaligenes latus, and Pseudomonas oleovorans, which account for 50–80% of

2.3 Polymers produced by bacteria

41

PHA synthesis [87]. With Bacillus sp., it is possible to mass manufacture PHA components via either growth or nongrowth mechanisms, marking a significant advance in the industrial use of polymeric substances [88]. The majority of researchers support utilising E. coli as the model organism for enhancing PHA synthesis by genetically modifying wild strains [89]. In some strains of E. coli, lactose serves as the main precursor carbon source for the production of PHA. It is possible to use the economically significant whey protein as a lactose source for carbon consumption by manipulating the pha operon, which generates PHA. Lactose cannot be used as a carbon source by all yeast strains; examples include XL1-Blue, JM, and DH5a. As a consequence, the genetically modified wild-type strain E. coli GCSC6576 (pSYL107) would preferentially utilise lactose for the large-scale synthesis of PHA molecules in the fed-batch system, producing 79% PHA molecules with a higher dry cell biomass weight (87 g/L). By adjusting the period of PHA synthesis, the genetically modified E. coli strain GCSC6576 (pSYL107) boosted PHA production with an 80% increase in dry cell mass. The DNA from the Cupriavidus necator and A. latus species has been spliced together to form the pha operon. The studies effectively produced PHB yields of 80.5%, demonstrating the efficiency of strain CGSC4401, with a dry cell mass weight of 119.5 g/L, as a producer of PHB. Squillaci et al. [90] looked into the halophilic archaeon Haloterrigena turkmenica’s capacity to make pigments and PHAs in a lab setting. Batch fermentation was used by Osman et al. [91] to investigate biopolymer production by Microbacterium sp. WA81 was found capable of producing the polymer at a concentration of around 18 mg/L. In this case, the produced polymer was isolated, purified, and characterized; it was found to have a low molecular weight, which is an advantageous feature. Molasses, whey, and crushed sesame were all tested as possible medium components to enhance output by the bacterial isolate while keeping production costs down. The optimal ratio of molasses, whey, and crushed sesame was 9.21, resulting in a massive increase in polymer production up to 660 mg/L. The amount of polymer generated increased by more than 250% when this method was used to bioreactor culture, reaching 2.5 g/L. Kundu et al. [92] examined the production of PHA by various microorganisms, offering a comprehensive look at how these nonselective bacteria use cheaper carbon-rich substrates.

2.3.2 Bacterial cellulose (BCs) Agro-industrial waste and byproduct stream sustainably as feedstock for bacterial cellulose (BC) production. Thin stillage (TS) from the rice winery business can be added to the HS medium to help Gluconacetobacter xylinus grow and generate BC. The findings show that adding TS lowers G. xylinus’s rate of lowering sugar intake, starting with a high BC conversion yield. ABE fermentation effluent and wastewater from the company that processes candied jujubes make good raw materials for BC manufacture. Vazquez et al. [93] observed high BC production when studying BC production utilizing wine

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leftovers or glycerol leftovers from biodiesel as inexpensive carbon sources. According to Rani et al. [94] BC was produced by Gluconacetobacter sp. at the air-liquid interface during the viticulture of grapes. A subsequent study reveals that grape medium yields BC of higher quality than HS in yield and mechanical qualities. The province of British Columbia can also grow plants from a range of fruit juices, konjac powder, maple syrup, and wheat straw, according to tests undertaken by different teams in the past. The production of BC may also be boosted by supplementing the culture medium with substances including lignosulfonate, organic acids, vitamin C, sodium alginate, single sugar-linked glucuronic acid-based oligosaccharide (SSGO), and vitamin C. By including reinforcement materials or altering the culture conditions while growing bacteria, in situ modification is performed. Several additives are used as part of the ex-situ modification procedure in the BC polymer matrix. These modifications change the morphological, physicochemical, and mechanical properties of the BC composite. Many studies based on its in-situ and ex-situ change have been published to broaden the usage of BC in a variety of fields [95]. One of the worst types of environmental contamination, oil spills, significantly negatively affect the ecological system. Tetraethoxysilane hydrolyzes BC, resulting in BC@SiO2 networks with good separation performance for separating surfactantstabilized O/W and W/O emulsions have been produced by a team of researchers. Methyl orange (MO), methylene blue (MB), and rhodamine 6G are examples of organic dyes that can be eliminated using polydopamine (PDA)/BC membranes (R6G). When cellulose nanofibers from wood, bacteria, and algae are dried and pyrolyzed, the chars are ideal for absorbing oils and adsorbing dyes. In addition, BC-based nanocomposite and BC-silver nano prisms can kill E. coli cells and clean water contaminated with pesticides that include chlorides, including endosulfan [96–99].

2.3.3 Bacterial production and recovery of hybrid biopolymers Bacterial cellulose membranes are modified utilising inorganic components to create hybrid organic-inorganic composites. Inorganic compounds including titanium dioxide, silver, montmorillonite clay, and silica may be absorbed by the BC matrix. The resulting composites have enhanced mechanical, chemical, and antimicrobial properties [100, 101]. Recently, the electrostatic coupling of Chit was enhanced by using oxidised BC. The final structure is a self-assembling nanocomposite sponge-like structure that exhibits outstanding stability and rapid and efficient procoagulant activity [102]. Hydrophobic BC aerogels (HBCAs) with low density (6.77 mg/cm3), large surface area (169.1 m2/g), and high porosity (99.6%) are produced by surface-modifying BC aerogels with trimethylchlorosilane and freeze-drying. The trimethylsilylation process lowers the surface energy of cellulose nanofibers while preserving their threedimensional web-like microstructure at water/air contact angles up to 146.5°.

2.4 Other strategies for biopolymers production

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The HBCAs, as prepared, demonstrated remarkable mass absorption capabilities (185 g/g) for various oils and organic solvents. The bioplastic is often mixed with more than one molecule with different physiochemical characteristics, employing various ways during the synthesis phase to produce PHB hybrid systems. Due to their multifunctional qualities, the resultant composites are good candidates for various applications. The scientists created immobilized PHB matrices modified with CaCO3 layers to create piezoelectric hybrids. This technique must be improved if it is to compete with synthetic polymers and produce high yields for a range of applications [103]. A culture medium for the synthesis of bioplastics may be produced more cheaply by employing food and agricultural wastes, according to a few research investigations. This method allows for the efficient production of PHB from materials such as corn-steep alcohol, cheese whey, rice, wheat bran, molasses, starchy wastewaters, cooking oil, glycerol waste, and fruit and brewer’s wastewater [104–106]. The usage of PHB is promoted in a variety of industries, including the ones of food, building, transportation, agriculture, biotechnology, pharmaceuticals, and biomedicine (Yeo et al. 2018).

2.4 Other strategies for biopolymers production In recent years, there has been a rise in interest in using bioelectrochemical systems (BES) for treating wastewater. Recovering useful chemicals, fuels, and power while simultaneously treating garbage is possible using BES [107]. Many valuable chemicals and products are made using BES technology, which is applied on low-cost substrates [108]. The generation of PHAs in a microaerophilic microenvironment at the biocathode of BES was reported by Srikanth et al. [109]. PHA synthesis was initiated in BES at the biocathode due to low levels of dissolved oxygen (DO) as a backup mechanism for re-oxidizing Nicotinamide adenine dinucleotide (NAD) [110]. The biofilm that forms on the anode and acts as the bio-anode and produces PHB and other compounds like amino acids and lactic acids from organic substrates was described by Pham et al. [111]. Microbes in the anode oxidize organic materials and generate biopolymers, as indicated by Pant et al. [112]. Microbes are encapsulated and cemented as a matrix of biopolymers in a thick layer of biopolymers affixed as a biofilm on the surface. The effectiveness of electron transmission in BES is primarily affected by the composition of biopolymers and the presence of a wide variety of microorganisms [113]. In 2010, researchers Behera et al. [114] found that when biofilm thickness increased, power output decreased. Recent advances in BES have shown the utilization of biocathode to boost electrogenesis activity via PHA-related cathode synthesis [115]. In their study of the BES’s efficacy, Srikanth et al. [109] treated synthetic wastewater to generate 512 mV of electricity and accumulate PHA at a rate of roughly 19% dry cell weight. In addition, BES’s cathode

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and anode chambers used enhanced cultures derived from activated sludge and an anaerobic digester. In BES, PHB synthesis has been linked to biomass synthesis. Between 3 and 50% of BES’s electrons are utilized to produce PHB. Dissolved oxygen and an absence of electron donors have been linked to PHB buildup [116]. Depending on the microaerophilic circumstances, microorganisms that accumulate PHA might serve as electron acceptors in the cathode. The advantages of this approach to BES include simultaneous energy generation, waste treatment, and biopolymers production through a single fermentation process [117].

2.5 Synthetic biology strategies for biopolymer synthesis Figure 2.3 [118] shows the overview of biosynthetic pathways to polymers. A powerful inhibitor of glucosamine (GlcN) synthase and glucosamine (GlcN) breakdown, glucosamine 6-phosphate (GlcN-6-P) controls the accumulation of GlcN inside cells. One of the challenges facing microbial production in the biosynthesis of GlcN and N-acetylglucosamine is this feedback inhibitory activity (GlcNAc). GlcNAc and are potential candidates for microbial biosynthesis because to their susceptibility to functionalization via the amine group and subsequent use in the polymerization into chitin and chitosan. Both GlcN and GlcNAc are composed of glucose moieties, but GlcN’s C2 hydroxyl is connected to an amino group, whereas GlcNAc’s amino group is acetylated. Chitin from shellfish has long been subjected to strong acid hydrolysis in order to form amino polysaccharides and subsequent biopolymers [118]. In recent years, several additional hosts, including E. coli, B. subtilis, and Saccharomyces cerevisiae, have been able to produce GlcN and its derivatives. The synthesis of GlcNAc transferase and the deletion of nagE, a GlcNAc transporter, increased the GlcN titer in E. coli to 17 g/L. The transcriptional strength of the GlcNAc synthesis module has been strengthened by improved expression of the glucosamine synthase and glucosamine acetyltransferase. Acidic by-products were removed by inhibiting ldh from the lactate synthesis pathway and pta from the synthetic acetate pathway. Deng et al. used a two-stage fed-batch culture, glucosamine synthase overexpression (GlmS), catabolic gene inactivation, and fed-batch fermentation to overproduce GlcN in E. coli at titers as high as 110 g/L. By producing synthetic short regulatory RNAs and the Hfq protein, which is designed to inhibit glycolysis by targeting pfk and peptidoglycan production by targeting glmM, Liu et al. [119] employed a dynamic metabolomics method to raise GlcNAc titers in a 3 L fed-batch bioreactor to 31.65 g/L. They found that the main impediment to the pathway’s productivity is a futile cycle between N-acetylglucosamine6-phosphate (GlcNAc-6-P) and GlcNAc, which is caused by the high energy demands of ATP phosphorylation and dephosphorylation.

2.5 Synthetic biology strategies for biopolymer synthesis

Figure 2.3: Overview of biosynthetic routes to biopolymers (Reproduced from Anderson et al. [118] Published by Elsevier Ltd under the terms of the creative commons CC-BY license).

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Eliminating the problematic glucokinase increases ATP generation and restores normal cell growth, which doubles GlcNAc output. S. cerevisiae was used to test for GlcNAc over-producers using a synthetic suicide riboswitch that limited growth in response to GlcN-6-P. A mutant version of glutamine-fructose-6-phosphate transaminase (GFA1) and a haloacid dehalogenase-like phosphatase (HAD) were screened and demonstrated to be very effective as a result of the growth-coupled circuit [119–121]. A change in GFA1 expression, the first and rate-limiting step in chitin formation, was also found in the mutant, as well as overexpression of Protein phosphatase YqaB, which is specialised for converting GlcNAc-6-P to GlcNAc. When GlcNAc was created by reducing glycolytic flow by disrupting pfk-2, shake flask fermentation produced titers of 1.2 g/L when fed glucose and 1.8 g/L when given galactose. Glycolysis was slowed down under galactose feeding by the removal of pfk-2, allowing gluconeogenesis to begin and galactose to be used as the only carbon source. One of the challenges to microbial production in the biosynthesis of GlcN and GlcNAc is the feedback inhibitory effects of GlcN-6-P, a strong inhibitor of GlcN synthase and GlcN degradation, which restricts the development of GlcN inside the cell. In culture broth, it is difficult to produce large titers because aminosugars can substitute for other carbon and nitrogen sources. This necessitates the employment of a recovery technique during fermentation. In order to maintain growth and production in balance, UDP-N-acetylglucosamine (UDPGlcNAc), the sugar donor for the synthesis of N-acetylated chitooligosaccharide, the precursor for the biosynthesis of peptidoglycan, is typically kept at high intracellular concentrations in developing bacterial cells. Aminosugars with free amino groups are unstable in an aqueous solution because GlcN may spontaneously rearrange and dimerize to form derivatives such fructosazine, D-arabinose, and pyrazine in an aqueous solution with a neutral pH. Bio-polymerization can therefore prevent degradation issues. There are exciting possibilities when GlcN and GlcNAc overproduction strategies are combined for subsequent bio-polymerization. Traditional sources of purified HA include umbilical cords and rooster combs. Streptococcus zooepidemicus, a naturally occurring producer, has been used to create a low-cost bacterial fermentation method [122, 123]. B. subtilis, L. lactis, and Pichia pastoris have all been shown to synthesize HA. Hyaluronan (HA) is manufactured in bacteria from UDP-glucuronic acid (UDP-GlcUA) and UDP-GlcNAc by a single enzyme complex called hyaluronan synthase (HAS). UDP-GlcUA and UDP-GlcNAc exist naturally as part of cell wall production, which directly competes with HA synthesis. The resultant HA polymers’ average molecular weight and chain length are strongly influenced by the relative quantity of precursors and HAS. This results in increased amounts of fermentation products, such as lactic acid, which inhibits HA synthesis in anaerobically fermenting bacteria (S. zooepidemicus). Production in anaerobic conditions often ceases at around 3 g/L in bacteria sensitive to low DO, such as B. subtilis. This bottleneck in B. subtilis was conquered by regulating the production of hyaluronidase, which decreased the culture’s molecular weight and viscosity in exchange for a decrease in chain size. Heterologous expression of the HA pathway in anaerobictolerant Corynebacterium glutamicum with deletion of lactate dehydrogenase led to the

2.6 Prospects and conclusion

47

accumulation of 21 g/L HA with a mass in the middle of the range. A recombinant suicide plasmid introduced into S. zooepidemicus inhibited the organism’s native hyaluronidase expression, resulting in 9 g/L of a more complex polymer [124–127].

2.6 Prospects and conclusion Biopolymers have attracted much interest as a possible material source due to their low environmental impact and wide availability. The current information suggests that biopolymers have a remarkable potential to resist degradation over time. Biopolymers have the potential to outperform their synthetic counterparts in several ways, including biocompatibility, biodegradability, and environmental friendliness. However, numerous obstacles remain in their commercialization and widespread manufacturing. The biggest challenge ahead is the high price of the fermentation substrate in the case of intracellular biopolymers like PHA and cellulose. The toxicity of chemical extraction is a primary worry, and the high expense of solvent extraction and downstream processing of the polymers is a close second. Widely utilized biopolymers such as PHA, cellulose, chitosan and chitin, hydroxyapatite, and pectin have drawbacks such as permeability, moisture, short lifespan, and susceptibility to environmental exposure. Another issue with biopolymers’ potential as a long-term replacement for synthetic materials is their weak mechanical strength and lackluster physical qualities. Because of their superior material qualities, bio-composites are a viable alternative to the materials mentioned above in various fields, including the automotive, civil construction, food packaging, and medical industries. Increasing biopolymer manufacturing using efficient methods is crucial to the sector’s long-term health and the widespread use of the materials. The greatest strategy to decrease production costs may be incorporating waste valorization into biopolymer synthesis or extraction. Low product yield is a persistent issue, but it can be permanently fixed by genetic modification of the genes responsible for PHA synthesis and the creation of integrated methods for PHA manufacturing. Biopolymers have a lot of potential applications, and growth might be sped up by creating green methods for extracting polymers and optimizing the process variables for optimal product recovery. Improving biopolymer research as a replacement for synthetic polymers and as a sustainable green alternative is crucial in light of the pressing need to preserve the health and stability of the planet’s soil, water, and living species.

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40. Saravana PS, Cho YN, Woo HC, Chun BS. Green and efficient extraction of polysaccharides from brown seaweed by adding deep eutectic solvent in subcritical water hydrolysis. J Clean Prod 2018;198:1474–84. 41. Flórez-Fernández N, Domínguez H, Torres MD. Functional features of alginates recovered from Himanthalia elongata using subcritical water extraction. Molecules 2021;26:4726. 42. Horue M, Berti IRR, Cacicedo ML, Castro GR. Microbial production and recovery of hybrid biopolymers from wastes for industrial applications-a review. Bioresour Technol 2021;340:125671. 43. Murujew O, Whitton R, Kube M, Fan L, Roddick F, Jefferson B, et al. Recovery and reuse of alginate in an immobilized algae reactor. Environ Technol 2021;42:1521–30. 44. Moniri M, Moghaddam AB, Azizi S, Rahim RA, Ariff AB, Saad WZ, et al. Production and status of bacterial cellulose in biomedical engineering. Nanomaterials 2017;7:257. 45. Picheth GF, Pirich CL, Sierakowski MR, Woehl MA, Sakakibara CN, de Souza CF, et al. Bacterial cellulose in biomedical applications: a review. Int J Biol Macromol 2017;104:97–106. 46. Horue M, Cacicedo ML, Castro GR. New insights into bacterial cellulose materials: production and modification strategies. Int J Adv Med Biotechnol 2018;1:44–9. 47. Gorgieva S, Trček J. Bacterial cellulose: production, modification and perspectives in biomedical applications. Nanomaterials 2019;9:1352. 48. Hussain Z, Sajjad W, Khan T, Wahid F. Production of bacterial cellulose from industrial wastes: a review. Cellulose 2019;26:2895–911. 49. Kumar V, Sharma DK, Bansal V, Mehta D, Sangwan RS, Yadav SK. Efficient and economic process for the production of bacterial cellulose from isolated strain of Acetobacter pasteurianus of RSV-4 bacterium. Bioresour Technol 2019;275:430–3. 50. Patel J, Maji B, Moorthy NSHN, Maiti S. Xanthan gum derivatives: review of synthesis, properties and diverse applications. RSC Adv 2020;10:27103–36. 51. Elella MHAA, Goda ES, Gab-Allah MA, Hong SE, Pandit B, Lee S, et al. Xanthan gum-derived materials for applications in environment and eco-friendly materials: a review. J Environ Chem Eng 2021;9:104702. 52. Gondim TS, Pereira RG, Fiaux SB. Xanthan gum production by Xanthomonas axonopodis pv. mangiferaeindicae from glycerin of biodiesel in different media and addition of glucose. Acta Sci Biol Sci 2019;41:e43661. 53. da Silva JA, Cardoso LG, de Jesus Assis D, Gomes GVP, Oliveira MBPP, de Souza CO, et al. Xanthan gum production by Xanthomonas campestris pv. campestris IBSBF 1866 and 1867 from lignocellulosic agroindustrial wastes. Appl Biochem Biotechnol 2018;186:750–63. 54. Zhang S, Wang J, Jiang H. Microbial production of value-added bioproducts and enzymes from molasses, a by-product of sugar industry. Food Chem 2021;346:128860. 55. Aman A, Siddiqui NN, Qader SAU. Characterization and potential applications of high molecular weight dextran produced by Leuconostoc mesenteroides AA1. Carbohydr Polym 2012;87:910–5. 56. Das D, Goyal A. Characterization and biocompatibility of glucan: a safe food additive from probiotic Lactobacillus plantarum DM5. J Sci Food Agric 2014;94:683–90. 57. Bounaix MS, Gabriel V, Morel S, Robert H, Rabier P, Remaud-Siméon M, et al. Biodiversity of exopolysaccharides produced from sucrose by sourdough lactic acid bacteria. J Agric Food Chem 2009;57: 10889–97. 58. Leemhuis H, Pijning T, Dobruchowska JM, van Leeuwen SS, Kralj S, Dijkstra BW, et al. Glucansucrases: three-dimensional structures, reactions, mechanism, α-glucan analysis and their implications in biotechnology and food applications. J Biotechnol 2013;163:250–72. 59. Zannini E, Waters DM, Coffey A, Arendt EK. Production, properties, and industrial food application of lactic acid bacteria-derived exopolysaccharides. Appl Microbiol Biotechnol 2016;100:1121–35. 60. Öner ET, Hernández L, Combie J. Review of levan polysaccharide: from a century of past experiences to future prospects. Biotechnol Adv 2016;34:827–44. 61. Patel S, Majumder A, Goyal A. Potentials of exopolysaccharides from lactic acid bacteria. Indian J Microbiol 2012;52:3–12.

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Gunasekaran Priya, Natarajan Shanthi, Sundaramoorthy Pavithra, Soundararajan Sangeetha, Subbiah Murugesan and Shanmugasundaram Shyamalagowri*

3 Modern analytical approach in biopolymer characterization Abstract: Biopolymers have received a lot of interest recently, and academic and industrial research on biopolymers has been refocused. These biopolymers comprise naturally occurring substances as well as artificial substances created from naturally occurring monomers. Plastics have the potential to be replaced by biopolymers because they are hazardous to the environment and rely on nonrenewable resources like petroleum for production. Due to the overwhelming interest in biopolymers, characterization tools and processes have emerged as crucial components in biopolymer research to examine and enhance the characteristics and functionality of materials based on biopolymers. When evaluating the performance of these bio-nanocomposites, using the right tools for characterization is crucial. This review concentrated on highlevel analytical methods for characterizing biopolymers, biopolymer-based composites, and their derivatives structurally, physically, and chemically. The most common analytical instrument methods based on microscopy (Optical, laser scanning confocal, scanning tunneling, scanning probe, differential dynamic, scanning, and transmission electron) and spectroscopy (Fourier transform infrared, X-ray diffraction, and Raman). The use of these tools for characterization in current research studies is also highlighted in order to demonstrate how the biopolymer under study might be used in various applications. Keywords: analysis; analytical; biopolymer; characterization; instruments; properties.

*Corresponding author: Shanmugasundaram Shyamalagowri, P.G. and Research Department of Botany, Pachaiyappas College, Chennai, 600030, Tamil Nadu, India, E-mail: [email protected] Gunasekaran Priya, Department of Biotechnology, Faculty of Science and Humanities, SRM Institute of Science and Technology- Ramapuram Campus, Chennai, 600089, Tamil Nadu, India Natarajan Shanthi and Subbiah Murugesan, P.G. and Research Department of Botany, Pachaiyappas College, Chennai, 600030, Tamil Nadu, India Sundaramoorthy Pavithra, Department of Biotechnology, Bannari Amman Institute of Technology, Sathyamangalam, 638401, Tamil Nadu, India Soundararajan Sangeetha, P.G. and Research Department of Zoology, Pachaiyappas College, Chennai, 600030, Tamil Nadu, India As per De Gruyter’s policy this article has previously been published in the journal Physical Sciences Reviews. Please cite as: G. Priya, N. Shanthi, S. Pavithra, S. Sangeetha, S. Murugesan and S. Shyamalagowri “Modern analytical approach in biopolymer characterization” Physical Sciences Reviews [Online] 2023. DOI: 10.1515/psr-2022-0216 | https://doi.org/10.1515/9783110987188-003

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3.1 Introduction Recent trends have seen natural biopolymers take the place of synthetic polymers as a result of increased research interest in sustainable environments. They can be divided into microbial biopolymers, chemically synthesized biopolymers, and naturally synthesized biopolymers. Due to their equal performance to synthetic polymers in terms of performance, configuration, and applications, biopolymers, and their composites were introduced to the market using technological improvements [1]. Additionally, biopolymers can be changed by adding characteristics that affect how they function [2]. The substantial volume of plastic garbage being generated is strongly resisted by these organic compounds made from natural sources. Plastic packaging is neither biodegradable nor renewable, which has sparked resurgence in interest in biopolymer-based packaging alternatives. These biopolymers include those made chemically from naturally occurring monomers like lactic acid, proteins, starches, cellulose, starches, and other polysaccharides, as well as those that are produced naturally. These bio-based polymers are already starting to be sold commercially [3]. Biopolymers have attracted a lot of interest from both industry and academia because they have material features suited for a variety of industrial and medical uses. The main drivers of interest in and growth in the use of biopolymers as commonplace products are their reusability, biodegradability, and frequently, biocompatibility [4]. These innovative natural analogs can be used in food, medical, pharmaceutical, and environmental applications due to their simplicity of handling, dependability, and chemistry [5]. Furthermore, the supply of petroleum is running out quickly and it is not a renewable resource. Traditional plastics, or products made of petroleum-based polymers, are still essential to daily living, but because they are not biodegradable and consequently build up in the environment, there is rising worry about their effects on the environment. Biopolymers made from renewable resources, therefore, have an edge over manufactured, nonrenewable polymers in the market. To compete in the market against synthetic polymers derived from oil, biopolymers, and commodity items based on them must lower their production costs. Utilizing biopolymers, which are plentiful and inexpensive to extract from the source material, as the primary component of biopolymeric products can be a wise first step in mitigating cost-related concerns [4]. Biopolymer networks in biology, like the cross-linked bundles (or fibers) of collagen and fibrin in the extracellular matrix (ECM), act as the medium for the transmission of numerous biochemical/biomechanical cues that control cell motility, differentiation, proliferation, and apoptosis. They also support the mechanical function of cells. The management and metabolism of healthy organs as well as the delivery of medications to tumor tissues depend heavily on the absorption and diffusion of different macromolecules in networks comprised of biopolymers. The configuration and microstructure of the network, particularly the intricate pore space between the

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fibers, greatly influence these biological processes. In order to quantitatively comprehend the biological processes, an acquaintance with the active transportation and mechanical possessions of biopolymer networks is therefore essential [6]. The creation, characterization, use, and applications of biopolymers and their composites are covered in a number of review publications [7]. Both fundamental polymer science and practical engineering of polymeric systems are still driven by the requirement to characterize dynamic processes and features. Modern study on the emergence of diverse classes of materials has led to the need for adequate characterization in order to gain knowledge of their intricate morphology and structure and identify the best uses for them. Microscopy techniques belong to a group of multipurpose techniques that are frequently employed for the detailed examination and comprehension of materials at high magnification levels. The utilization of microscopic tools for their study has been a tremendous help in assisting researchers’ innate drive to comprehend these natural wonder materials, especially with the rising attention on biopolymers in recent years [8]. In a similar vein, describing the dynamics of polymer molecules and materials has long been accomplished by the use of radiation scattering (light, X-rays, and neutrons) [9]. Numerous researchers have looked at the transport characteristics and microstructure of biopolymer networks [8]. However, a thorough analysis of the numerous analytical methods used to characterize the structural properties of bio-nanocomposites is lacking. In order to evaluate the performance of biopolymers, choosing the right technique for their characterization is essential. Thus, the current review’s main objective is to compile the most popular methods for characterizing biopolymers.

3.2 Bibliographic study Bibliometric analysis was undertaken to follow the development of scientific output in a certain area, a bibliometric search of worldwide research output on a given set of keywords, such as “biopolymer + Characterization,” from 2013 to 2022 in a Scopus database. Figure 3.1 shows the Scopus database investigation for the research outcome. The keyword “TITLE-ABS-KEY (biopolymer AND characterization) Limit to 2013–2022” is found in 3221 documents in the database. A maximum number of documents (623) was published in that in 2021 and the year-wise progression is given in Figure 3.1a. The majority of publications (2640) are within the article type, followed by reviews (208) and conference papers (193) (Figure 3.1b). India, the United States, and China are the top 3 countries that released 700, 461, and 408 key documents, respectively, out of the total documents in the time period of 2013–2022 (Figure 3.1c). The comprehensive bibliometric analyses for the Scopus dataset (first 2000 documents among 4147) obtained are performed using open-source bibliometrix R-package (Version 3.0.5) [10]. The instrument’s names were found to be in the position of the top 25 keywords (Figure 3.2a) and the co-occurrence mapping of keywords highlighting the instrument names

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(Figure 3.2b) emphasized the importance of characterization in biopolymer research. The method and effectiveness of document search are significantly influenced by the selection of appropriate and pertinent keywords. The keyword acts as a crucial link that sets the information sources apart from the enormous selection of publications.

Figure 3.1: Bibliometric analysis of documents as per Scopus database. The document information was retrieved using the keyword “TITLE-ABS-KEY (biopolymer AND characterization)” in the Scopus database for the period of 2013–2022 (data as of 02/11/2022). (a) Data as per documents for year-wise; (b) data as per documents type; (c) data as per Top 10 country.

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Figure 3.2: Bibliometrix R-analysis of keywords. (a) Most relevant words, and (b) co-occurrence map for the dataset obtained for the keyword “TITLE-ABS-KEY (biopolymer AND characterization)” in the Scopus database.

3.3 Characterization of biopolymers Based on the previously mentioned characteristics, the natural or synthetic polymers produced utilizing various techniques and resources were thoroughly characterized, making them acceptable for use in culinary and medical applications. Following characterization, the characteristics were assessed for their biodegradability and environmental friendliness in accordance with ASTM standards to ensure they met the

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required quality criteria [11]. The relative, synthesizing, and component properties of biopolymers can be used to categorize their characteristics. The term “relative properties” refers to the fundamental and innate characteristics of a polymer that are independent of its structure and chemical makeup. The study’s polymer’s density, solubility, transparency, and permeability are all represented by relative qualities. The quality parameters of viscosity, optical purity, mechanical qualities, stability, and molecular weight are connected to synthesis attributes. Component properties are a combination of the first two features and relate to how well the biopolymer performs and functions [1]. A variety of microscopic and spectroscopic methods were used to characterize the biopolymers (Figure 3.3). Melting, boiling point, density, shape, and viscosity are the primary physical characteristics connected with biopolymers and biopolymer composites. It has been discovered that the internal structure of biopolymers is altered by the interaction of water molecules, making them more susceptible to moisture. Melt blending was used to study two biocomposite systems based on poly (l-lactic acid) (PLLA) with lignin serving as a filler and PEG serving as a plasticizer. The inclusion of polyethylene glycol was shown to provide the PLLA biocomposite more flexibility and stiffness [12]. In the majority of the aforementioned applications, several cutting-edge techniques for converting triglyceride oils into polymers and monomers have been used. In contrast to these materials, nanocellulose is a more recent type of nanomaterial that is widely employed because of its comparatively superior physical and chemical properties. Such nanoparticles have the ability to change the surface chemistry of the integrated material, as well as certain favorable properties including high flexibility, improved strength, low density, and therefore lower ultimate weight [13]. The process of extraction has a significant impact on the physical characteristics of the finished products [14].

Figure 3.3: Techniques used for the characterization of biopolymers.

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Thermal stability and thermal conductivity are the two most crucial factors in determining a biopolymer’s thermal characteristics. Thermal analysis of biomaterials makes extensive use of process variables such as stability, thermal degradation rate, glass transition, melting and crystallization temperature, the heat of fusion, and crystallinity degree. Differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA), which demonstrated better moisture, chemical, and heat resistance of polymers, can be used to measure these parameters [15]. In comparison to other materials, polymers have more complicated molecule structures, which makes it difficult to currently grasp how molecular interaction affects mechanical qualities. The glass transition temperature (Tg), which is a crucial element in polymer mechanical characteristics, is well understood. At temperatures above and below their Tg, polymers deform using several methods. For “glassy” polymers below Tg, the polymer chains are essentially frozen in place, and only tiny strains (usually 5%) can be accommodated elastically, during which the spacing between the polymer chains barely changes [16]. To ascertain mechanical qualities, a variety of procedures may be applied. Tensile testing is a reliable technique in which the two ends of a tensile model are fixed in a tensile testing machine and pulled apart. There are numerous additional popular methods for evaluating mechanical properties outside tensile testing, including compression, bending, and shear tests. According to Gleadall [16], they are all similar in that they all quantify the force necessary to cause deformation or failure. The diameter and surface roughness of the fibers have a big impact on how wettable the fiber is with the matrix and how strong the composites are mechanically [17]. The type and quantity of waxy substance in natural fibers affect their wettability by water, which is measured using the contact angle [18]. With the use of pycnometer experiments utilizing toluene and a genuine density analyzer, the density of the fiber is investigated (helium pycnometer). Additionally, ASTM D3800 M uses the Archimedes method and hexane [19]. Optical characteristics must be determined for their industrial use as coatings, glazing agents, plastics, and transparent materials. Protection from UV rays and lipid oxidation is essential for maintaining food quality. Transparency, color, light absorption/transmission polarizability, absorption coefficient, dielectric, and refractive index are the most crucial optical properties that have been the subject of research studies [7]. Prior to the development of conducting polymers (conjugate polymers), polymers were supposed to be electrical insulators; however, these organic polymers possess distinctive electrical and optical properties that are comparable to those of inorganic semiconductors [20].

3.4 Microscopy methods Currently, a wide range of characterization techniques is available to evaluate and characterize materials. Giving a full understanding of the structure and property correlations, these techniques help identify the end-use applications of biopolymers.

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Microscopy techniques stand out among these because they can analyze the shape and chemical composition, among other factors [8].

3.4.1 Optical microscopy Due to its simplicity and minimal sample preparation requirements, optical microscopy has long been used in biopolymer research to evaluate materials. Size, shape, uniformity, void content, failure analysis, and quality control can all be observed using optical microscopy [21]. An optical microscope provides a wider perspective of the filler distribution worldwide in the sample than other approaches because it can see the filler dispersion in composites on a greater scale. Analyzing the dry fiber diameter as a function of total polymer concentration and calculating the average fiber diameter using microscopy images and a computer image analyzer, it has been successfully used to assess the uniformity of poly(“ε-caprolactone)/chitosan blend fibers to be used in tissue engineering [22].

3.4.2 Laser scanning confocal microscopy (LCSM) LCSM has some benefits over traditional wide-field optical microscopy since it can reduce or even remove background noise from the focus plane and can take several optical sections of thick specimens. Any out-of-focus light source from specimens with a thickness greater than the local focus plane is eliminated using spatial filtering techniques. This method can provide images from samples prepared for it that are superior to those produced by traditional fluorescence microscopy, but it is unable to produce images with nanoscale resolution [23]. The investigation of DTAF-labelled cellulose nanofibrils (CNF) embedded into coumarin 30 (C30) labeled polyethylene (PE) matrix was effectively conducted using LCSM in conjunction with Förster resonance energy transfer (FRET) [24]. A deep learning-based segmentation method for confocal laser scanning microscopy pictures of biopolymer networks was presented by Asgharzadeh et al. [25]. Their deep neural network segmented pictures of filamentous temperature-sensitive Z proteins from chloroplasts of Physcomitrella patens, a moss, with a dice score of 0.88 using encoder–decoder network architecture.

3.4.3 Electron microscopy In the fields of science and industry, scanning electron microscopy (SEM) is one of the most adaptable, notable, and well-liked procedures. It is a type of electron microscopy that scans the samples with a high-energy electron beam to produce an image with a high level of resolution and magnification. When the electrons on the sample interact with the electron beam from the electron cannon, specific indications concerning the

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surface topography are created. The signals from the secondary and backscattered electrons, which include data about the material, are analyzed to produce the SEM images. This method offers a wealth of details on the materials being examined, such as elemental composition, surface morphology, and crystallinity [26]. Since many years ago, EM has been extensively utilized to investigate and analyze biopolymer systems in order to learn more about their structure, morphology, size, shape, surface modifications, wear and tear, etc. Biopolymers, biopolymer-aided nanoparticles, biopolymer nanoparticles, biopolymer fibers, and biopolymer nanocomposites have all been the subject of important SEM research [27–29]. SEM micrographs are a crucial tool for comprehending the morphology of various starch kinds. Sujka and Jamroz [30] investigated how ultrasounds affected the morphological and practical characteristics of starches from different sources, including native maize, rice, wheat, and potato starch suspended in either water or ethanol. Native starch molecules displayed a distinctive granular structure. Despite some surface fissures, the starches maintained their initial morphological behavior and structure during the ultrasonic treatments. A variation of the standard SEM known as field emission scanning electron microscopy (FESEM) offers images with a higher resolution and a wider energy range. The employment of a field emission gun as an electron generation device in FESEM is one of the primary distinctions between it and SEM. As a result, it is possible to analyze samples at low potentials and enhance spatial resolution. FESEM has already been successfully employed in place of SEM to generate high-resolution pictures of biopolymer systems [31]. Saleh and Rana [32] used FESEM as a method to describe the impact of surface-modified biopolymer swelling control and the rheological properties of clay. The ability of the styrene-modified cellulose to block the shale material’s nanopores was demonstrated in their investigation using FESEM analysis. Styrenemodified cellulose is forced onto the shale surface and blocks the surface pores as a result of the positive differential pressure between the water-based mud and the shale material. In the study by Ghasemi et al. [33], FESEM pictures of three-component (chitosan, sodium alginate, and polyvinyl alcohol) hydrogels with various percentages of mesoporous Ag2O/SiO2 nanoparticles were captured. The FESEM image clearly showed the increase in the number of nanoparticles, demonstrating that when the proportion of nanoparticles in the hydrogel structure increases, the hydrogel’s porosity also increases. Additionally, the mesoporous Ag2O/SiO2 three-dimensional structure has greatly improved the hydrogel’s contact surface with the outside world. One of the most potent microscopes on the market today, the transmission electron microscope (TEM), is utilized as an analytical tool to examine and view objects at the nanoscale. With resolutions below 0.5 Å, high-resolution transmission electron microscopy (HRTEM) is a type of TEM that makes it easier to image specimens at the atomic level and makes it possible to examine the atomic structure of the materials. In the research of biopolymer-assisted nanoparticle production, HRTEM has proven to be a valuable tool for examining the crystal planes of nanoparticles, the crystal structure of

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cellulose, nanocomposites, and even the molecular orientations of biopolymers [8]. The crystallographic analysis method known as Selected Area Electron Diffraction (SAED) is frequently used in conjunction with TEM. With a parallel electron beam source, the majority of TEM apparatus can perform SAED analysis, which yields diffraction patterns as a result of the electron beam being scattered by the sample lattice. In order to learn more about the crystalline structure of biopolymers, SAED has been applied in the investigation of such materials [34]. Ma et al. [35] used TEM analysis to investigate the curcumin carrier created by electrostatic interactions between chitosan and carboxymethylated corn fiber gum (CMCFG). Through TEM investigation, it was revealed that no spherical structure was generated when chitosan or CMCFG have combined with curcumin alone. In contrast, when CMCFG and chitosan-curcumin complexes were combined, spherical particles with high dispersity and uniform size were produced (mass ratio at 2:1). Although their sizes were smaller (163.585 nm), the intricacies of the particles could be observed in the enlarged TEM image, which showed that they were types of solid spherical particles with clearly defined borders.

3.4.4 STM (scanning tunneling microscope) and SPM (scanning probe microscopy) SPM is a series of various distinctive techniques that can image atoms as well as nanoscale structures and surfaces [36]. Various interactions are investigated and evaluated depending on the probe sensors being used, and the type of SPM being utilized is determined by the interactions being monitored between the probe and the sample surface. For instance, scanning tunneling microscopy (STM) measures the electric current flowing between the sample surface and probe, whereas atomic force microscopy (AFM) deals with the electrostatic forces, chemical force microscopy (CFM) measures chemical interactions and magnetic force microscopy (MFM) measures magnetic forces, and so forth [37]. The family of SPMs includes a wide range of techniques; in this article, the main approaches employed in the biopolymer sector are covered. The molecular structure of the xanthan biopolymer produced by various distinct strains of Xanthomonas campestris was analyzed using AFM, which has also been used to determine the differences in the molecular structure of the biopolymers [38]. In the characterization of cellulose [39], chitosan [40], and other biomaterials, CFM has demonstrated its value in the investigation of biomaterial and biopolymer areas. Triethoxysilyl N-propyl gluconamide was used to functionalize the silicon nitride cantilever probes used by Lee et al. [41] to assess the cellulose in biomass samples using CFM. The examination of magnetic biocomposites is the extent of MFM’s application in biopolymer systems. The MFM offers information concerning the dispersion and encapsulation of the magnetic nanoparticles inside the biopolymer matrix due to external magnetic fields having no response to biopolymers [42]. The 3D image of AFM showed layer-by-layer assembly of inter molecules at 310-nm resolution in a study of

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response surface methodology model to optimize the concentration of agar, alginate, and carrageenan for the improved properties of biopolymer film [43]. The characterized smooth surface has a more functional application of biopolymers. A scanning tunneling microscope (STM) is a non-optical microscope that scans over a sample surface at regular intervals using an electric probe tip. STM relies on the concept of the quantum mechanical phenomena known as tunneling, which happens when an electron’s wavelike characteristics allow them to pass through a barrier that, in theory, it should not be able to. STM has also been employed in research on cellulose crystalline fibrils [44], methylcellulose surface modification [45], and biocomposites [46], among other things. In their study of the surface modification of methylcellulose/cobalt nitrate polymer electrolytes by H2S, Abdullah et al. [45] found that the surface roughness of the samples increased after H2S treatment. The investigation of basic structures, morphology, molecular structure, surface properties, chemical composition, topography, microstructure, and interfaces all depend heavily on these microscopic techniques. They also include details about how nanoparticles are distributed, intercalated, aggregated, and exfoliated inside the composites. Special attention is required while interpreting these photos, though. The final structures shown in the photographs can be significantly influenced by the intrinsic properties of the materials, analysis methodologies, and sample preparation techniques. Biopolymers can change or become impaired when exposed to the electron beams used in electron microscopes. The results might not be accurate if these changes are not considered while evaluating the photographs [8].

3.4.5 Differential dynamic microscopy (DDM) There are many similarities between the evolution of light scattering measurements in former times and DDM, a new method for characterizing dynamical processes in polymers. But the fact that DDM can combine Fourier-space analysis with real-space imaging data offers several clear benefits. Based on these advancements, DDM has the potential to join scattering techniques as a crucial and useful tool for the characterization of polymeric systems and materials [9]. The use of DDM in biological polymers and systems has grown at a particularly rapid rate. Studies using DDM microrheology on the development of hyaluronic acid networks monitored the dynamics’ evolution throughout both physical and chemical gelation [47]. Several recent researches have used DDM to focus on the involvement of different elements and processes in the dynamics and mechanics of cytoskeletal networks involving actin and microtubule assemblies as a step toward more intricate and natively structured biomaterials. For instance, recent multichannel fluorescent DDM experiments [48] revealed that microtubules play a crucial role in regulating the ballistic motion and contractile forces connected to the myosin-driven activity of reconstituted cytoskeletal networks.

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In particular, converting real-space images to the Fourier domain enables one to analyze ensemble-level statistical information encoded in the entire image while still maintaining the real-space representation to help with analysis [49]. Fourier-domain analysis of imaging data has emerged in the last decade as a potential way to combine the benefits of microscopy experiments and scattering measurements, while potentially avoiding some of their respective limitations. A particularly potent and adaptable Fourier-domain analysis technique for examining material dynamics using video microscopy data is differential dynamic microscopy (DDM) [50]. The popularised description of DDM as “dynamic light scattering on a microscope” has inspired researchers to apply the method to obtain dynamic information accessible to scattering measurements in a variety of contexts accessible to microscopy experiments [9].

3.5 Spectroscopy methods for characterizing biopolymers 3.5.1 X-ray diffraction analysis (XRD) Highly crystalline, semi-crystalline, microcrystalline, or amorphous polymers are just a few of the different types of polymers that can exist. All three types of polymers can exist in the same polymer sample. According to research, mechanical qualities including compression, tensile strength, buckling, and creep are known to be impacted by the existence and relative quantity of various forms, which rely on how the polymer was created and treated. Consequently, it is crucial to precisely determine the degree of crystallinity. In order to determine the degree of crystallinity for semi-crystalline, amorphous polymeric, and composite materials—which can be deduced from the appearance of the XRD pattern—polymer scientists utilize XRD. Polymers can be molded and extruded, and they can be treated into fibers and films. In both crystalline and noncrystalline materials, each of these processes has the ability to orient the molecules, and diffraction can be used to detect the orientation. Through the Hermans orientation function, our professionals determine the crystallographic orientation primarily using XRD patterns. Borax, which has previously been utilized as an intermolecular bond reinforcer, was added to starch to alter its molecular structure, and Franco-Bacca et al. [51] used XRD to analyze the films based on this modification. When it comes to CS film, there are diffraction peaks at 5.62°, 9.67°, 11.46°, 14.27°, 16.92°, 19.53°, 20.45°, 22.12°, 23.98°, 24.45°, and 26.21°. The existence of diffraction peaks at 5.62°, 9.67°, 11.46°, 16.92°, 22.12°, and 23.98° allowed scientists to identify type B starch. Type A starch is distinguished by diffraction peaks at 14.27°, 16.92°, and 23.98° [52]. The V starch polymorph can also be attributed to the diffraction peaks at 7.37°, 8.93°, 9.54°, 12.00°, 19.53°, 22.12°, and 28.64° [53]. Diffraction peaks for isolated chains of amylose and amylopectin were found at

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14.27°, 20.45°, 24.25°, and 26.21° [54]. The starch polymorph composition varies as more borax is introduced, as shown by the diffraction pattern for systems containing both borax and starch. A second diffraction peak at 5.99° can be seen in the diffraction pattern for 0.35Bx-CS; this peak may be related to a less hydrated structure as a result of the addition of borax.

3.5.2 Fourier transform-infrared spectroscopy (FTIR) The analytical technique known as FTIR is useful and trustworthy for identifying polymers and evaluating the quality of plastic products. The spectrum created when a plastic material absorbs infrared light—typically in the mid-infrared region—gives a characteristic “fingerprint” that may be used to quickly screen and test samples for a variety of applications. It is crucial to establish the identity of the materials and evaluate their quality since the quality of the polymeric materials used during manufacture determines the quality and performance of plastic products. Scientists perform quick and accurate identification studies for samples of all types of polymer materials and all sizes, including pellets, parts, opaque samples, fibers, powders, wire coatings, and liquids, by using both reflectance and transmission sampling approaches that are suitable for polymer analysis and comparison against spectral databases. Our polymer experts can implement quality control assessments of the materials used by monitoring any changes in the infrared spectra of a sample and a reference sample. Additional FTIR studies can be used if differences are found to better understand the potential contamination. The molecular spectroscopy methods offered by Intertek laboratories, including TGA, DRIFTS, FTIR/TGA, nuclear magnetic resonance (NMR), GC/MS, LC/MS, UV/Vis spectroscopy, near-infrared spectrometer, and Raman scattering, are frequently combined with infrared spectroscopy. Incorporating FTIR with these methods yields useful further information about the molecular structure of polymer molecules. When combined with other analytical methods, FTIR can be incredibly successful in identifying unknown plastics and polymeric compounds. The fingerprint region of the spectrum, which lies in the bandwidth between 3279 and 1030 cm−1, is where the polysaccharides found in okra mucilage, which is a biopolymer, are found. Additionally, the broad-spectrum peak at 3279 cm−1 in their FTIR data, which indicates the existence of aromatic sugar with O–H as the primary functional groups, indicated the characteristic of the polysaccharide made up of galactose, rhamnose, and galacturonic acid. Another feature of the band at 2938 cm−1 is the methyl C–H bonding connected to benzene rings. The band at 2942 cm−1 corresponds to the characteristic C–H stretching in cellulose and hemicellulose components. The C–O stretching band in complex polysaccharide spectra was assigned a wavelength of 1245 cm−1, whereas the C–O–C group was given a wavelength of 1030 cm−1, showing the existence of aromatic bonds found in galactose, galacturonic acid, and rhamnose. The

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“anomeric area” (950–750 cm−1) and the “sugar region” (1200–950 cm−1) are two spectral regions for polysaccharides that are crucial for structural characterization [55].

3.5.3 Raman spectroscopy Raman spectroscopy is a characterization method that finds bond vibrations that alter a molecule’s capacity to polarise light. As a result, it is a non-destructive method that may be used to examine both polymers and their additives. In general, by using a set of reference spectra known as “fingerprints,” Raman spectra can be utilized for identifying purposes. These spectra can reveal details about the molecular makeup and identity of the polymer under investigation. Raman microspectroscopy provides details on the molecular makeup of a sample and has been extensively utilized to describe biopolymers like collagen, silk-fibroin, or biopolymer composites, which are also suitable for 3D bioprinting [56]. The choice of a specific biopolymer or biopolymer composite has an impact on optical properties as well as printability, mechanical properties, and cell viability [57]. This impact was shown in-depth scans of various bioink formulations and may make it more difficult to analyze by microscopic techniques. Bioinks were assessed in accordance with their sensitivity to identify biological features on a biopolymer backdrop after optical penetration depth characteristics [58]. The researchers used a Gaussian function as a test to analyze the spectral contour breakdown of demineralized spongiosa samples using Raman spectroscopy. In the range of 750–2050 cm−1, the average coefficient of correlation (R2) between the recovered and input spectra was 0.99, suggesting almost perfect agreement [59]. Raman spectroscopy, contact angle, and interfacial tension studies were all used by Li et al. [60] to show that the complex formed in TBOC 4% had a stronger emulsifying ability than TBOC 6%. TBOC stands for high total biopolymer concentrations.

3.6 Recent research on biopolymers characterization by analytical techniques In recent years, several polymer-based studies including biopolymers and biopolymer composites are carried out around the world. In that diverse analytical instrumentations are employed for the characterization of biopolymers, biopolymer composites, and biopolymer degradation process, etc. Aziz et al. [61] used electrochemical impedance spectroscopy to evaluate the electrochemical behavior of the produced samples (EIS). To ascertain the potential stability and main charger carrier transport of the polymer electrolyte, the linear sweep voltammetry (LSV) and transference number measurement (TNM) techniques were each used. Utilizing cyclic voltammetry (CV), the constructed electrical double-layer capacitor’s (EDLC) performance was examined.

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Specific capacitance (SC), equivalent series resistance (ESR), efficiency, energy density (ED), and power density (PD) density were all identified as crucial characteristics. Glycerol has been found to be an effective plasticizer for enhancing ionic conductivity and capacitance behavior. The direct current electrical conductivity of the films was assessed using electrical impedance spectroscopy (EIS), and the electrolyte with the maximum glycerol inclusion also had the highest ionic conductivity (8.57 10−4 S/cm). The compatibility of SC with the electrolyte components has been examined using FTIR spectroscopy. The shift and alteration in the FTIR peaks’ intensities served as evidence of the interactions’ degree. At scan speeds of 50 mV/s, the CS of the built EDLC was measured and found to be 41.11 F/g despite initial Ed and Pd values of 15.56 Whkg−1 and 750 Wkg−1, respectively. It was calculated and found that the ionic transference number (tion) is 0.956, confirming the dominance of ionic conduction in the electrolyte system. The breakdown voltage of the polymer electrolyte was found to be 2.09 V. Tsiklin et al. [59] aimed to investigate the biocompatibility and microstructural characteristics of demineralized human spongiosa Lyoplast® (Samara, Russian Federation). SEM, micro-computed tomography, Raman spectroscopy, and proteomic analysis were used to examine the graft’s microstructural and biochemical characteristics. Furthermore, fluorescence microscopy and cell cultures were used to assess the graft’s ability to adhere to cells. Microstructural examination of the graft showed that all cellular debris and bone marrow components had been completely removed, revealing its hierarchical porosity structure. The proteomic study also supported the preservation of extracellular proteins including collagen, which both promote and hinder cell adhesion, proliferation, and differentiation. By adding NaCl salt, pectin loses some of its semicrystalline characteristics and becomes more amorphous, as observed by X-ray diffraction analysis and XRD deconvolution technique [62]. Investigation of FTIR and FTIR deconvolution revealed that the addition of NaCl caused complexation and an increase in free ions. The shifting of pectin’s UV absorbance band illustrates the produced polymer electrolytes’ optical characteristics. The electrons’ passage from the valence band to the conduction band caused the optical bandgap of the pectin polymer electrolyte to drop from 3.13 eV to 2.98 eV. Dielectric constant measurements were made on these films between 303 and 373 K in the frequency range of 42–106 Hz [62]. A variety of starches were examined by Warren et al. [63] using FTIR, wide angle XRD, NMR, 13C cross-polarization/magic angle spinning (CP/MAS), and DSC. These starches included native wild type, modified, amorphous, and extruded starches (both in dry and hydrated states). Due to C–C, C–O, and C–OH stretching and bending, the FTIR of starches showed distinctive peaks in the region 1200–1000 cm−1. Additionally, they discovered that the DSC enthalpy ranged from 0 to 17.6 J/g, with the mean enthalpy of the entire set of starch sample samples being 9 J/g. Similar results were obtained using 13C CP/MAS, where each starch sample had a total helical order with a mean helical order of 30% ranging from 4% to 49%. XRD was used to measure relative crystallinity and it was discovered that the starches had a crystallinity range of 0%–51% and a mean of 25.8%.

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Malviya et al. [64] characterize Tamarindus indica derived Tamarind gum polysaccharide (TGP) to assess its potential for biological applications. The powder is freeflowing and has good flowability, as evidenced by the results of the Hausner ratio, Carr’s index, and angle of repose measurements, which were 0.94, 6.25, and 0.14, respectively. When the gum’s purity was checked using chemical testing for several phytochemical components, only carbohydrates were discovered to be present. According to the swelling index, which was discovered to be 87 ± 1%, TGP has a good water intake capacity. It was discovered that the pH of the 1% gum solution was neutral, measuring about 6.70 ± 0.01. Total, sulfated, acid-insoluble, and water-soluble ash values were discovered to be 14.00 1.00%, 13.00 0.05%, 14.04 0.57%, and 7.29 0.06%, respectively. The existence of alcohol, amines, ketones, and anhydride groups was confirmed by the IR spectra. The SEM analysis showed that the particle is spherical in shape and irregular and that the contact angle was 90°, indicating excellent wetting and good spreading of liquid over the surface. A prominent exothermic peak at 350 °C revealed by DSC analysis demonstrates the material’s crystalline structure. TGP has acceptable qualities, according to the results of the investigated properties, and can be utilized as an excipient to create dosage forms for biomedical purposes. SEM and synchrotron-based 2D chemical mapping FTIR analysis demonstrated that PLA with 4% pectin by weight which was synthesized by Satsum et al. [65] had the best dispersion. Furthermore, in situ synchrotron-based wide-angle X-ray scattering demonstrated that the synthesized pectin not only helps PLA crystallize but also acts as a reinforcing material to enhance mechanical properties (SR-WAXS). According to the SR-WAXS data, the crystallization rate and crystallinity were at their highest levels at 8% w/w pectin addition. Few recent research works which utilized the characterization techniques for biopolymer composites are summarized in Table 3.1. Table .: Recent research works utilized characterization techniques for biopolymer composites. S.No Title

Characterization Reference



CLSM SEM TGA XRD FTIR FESEM XRD FTIR DSC FTIR TGA









Development and characterization of biopolymers films mechanically reinforced with garlic skin waste for the fabrication of compostable dishes Preparation and characterization of solid biopolymer electrolytes based on polyvinyl alcohol/cellulose acetate blend doped with potassium carbonate (KCO) salt Synthesis and characterization of dextran, poly (vinyl alcohol) blend biopolymer electrolytes with NHNO, for electrochemical applications

Extraction of the bacterial extracellular polysaccharide FucoPol by membrane-based methods: Efficiency and impact on biopolymer properties Chemical design and characterization of cellulosic derivatives conXRD taining high-nitrogen functional groups: Towards the next generation SEM of energetic biopolymers FTIR NMR

[]

[]

[]

[]

[]

3.7 Conclusions

71

Table .: (continued) S.No Title

Characterization Reference



SEM DSC FTIR FTIR

 

Physicochemical and thermal characterization of poly (-hydroxybutyrate-co--hydroxybutyrate) films incorporating thyme essential oil for active packaging of white bread Synthesis and characterization of starch-based bioplastics using varying plant-based ingredients, plasticizers, and natural fillers Properties and characterization of lignin nanoparticles functionalized in macroalgae biopolymer films



Bulgur bran as a biopolymer source: production and characterization of nanocellulose-reinforced hemicellulose-based biodegradable films with decreased water solubility



Development and characterization of cornstarch-based bioplastics packaging film using a combination of different plasticizers



Fabrication and characterization of antimicrobial biopolymer films containing essential oil-loaded microemulsions or nanoemulsions



Characterization of novel biopolymer blend mycocel from plant cellulose and fungal fibers XPS, SEM, DSC, and nanoindentation characterization of silver nanoparticle-coated biopolymer pellets







Simultaneous biosynthesis of bacterial polyhydroxybutyrate (PHB) and extracellular polymeric substances (EPS): process optimization and scale-up Structural elucidation and cytotoxic analysis of a fructan-based biopolymer produced extracellularly by Zymomonas mobilis KIBGE-IB

FTIR TGA Microscopy SEM TGA DSC FTIR FTIR XRD SEM TGA SEM AFM FTIR Light microscope SEM FTIR SEM DSC XPS FTIR FESEM EDX AFM FTIR NMR XRD

[]

[] []

[]

[]

[]

[] []

[]

[]

CLSM, Confocal laser scanning microscopy; TGA, Thermogravimetric analysis; SEM, Scanning Electron Microscopy; FTIR, Fourier Transform Infrared; DSC, Differential Scanning Calorimetry; NMR, Nuclear Magnetic Resonance; FESEM, Field Emission Scanning Electron Microscopy; XPS, X-ray Photoelectron Spectroscopy; EDX, Energy dispersive X-ray spectroscopy; XRD, X-ray diffraction; AFM, Atomic Force Microscopy.

3.7 Conclusions Numerous uses of biopolymers are found in food, medicine, agriculture, the environment, and other branches of analytical chemistry. Therefore, crucial components of biopolymer research are the analytical methods that show the properties of biopolymers. Analytical methods that quickly and accurately show the structural quirks of

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these biopolymers are a must for the realization of this scenario. Due to their complex composition and structural structure, most biopolymers are difficult to analyze well from a chemical and physical standpoint. Such a sample needs to be thoroughly characterized using a variety of analytical techniques. Sophisticated instruments of microscopy and spectroscopy are employed widely in biopolymer research to reveal their internal and external properties. However, each instrumental analysis has advantages and disadvantages to some extent, which can be overcome by the combinations of multiple instruments or characterized the material in detail with multiple analyses. The continuous progress and development in the instrumentation and technology will be expected to resolve the issues with the existing limitations and provide new solutions for biopolymer characterization in the future. Acknowledgments: The authors acknowledge all those involved to support this paper.

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Mahajan Megha, Murugesan Kamaraj, Thirumullaivoyal G. Nithya*, Shanmugaselvam GokilaLakshmi, Pugazh Santhosh and Balasubramanian Balavaishnavi

4 Biodegradable polymers – research and applications Abstract: The major concern in ecology we are facing in this era of modernization is environmental pollution due to non-biodegradable plastics. Because of its low cost, readily available nature, light weight, corrosion resistance, and added additives, it is adaptable and suitable for a wide range of applications. But the problem is that most of the petroleumbased plastics are not recyclable. Recycling and degradation of plastics are time-consuming and also release harmful chemicals, which pose a great threat to the environment. It is the need of the modern era to focus on the production of biodegradable and eco-friendly polymers as alternatives to these plastics. Nowadays, plant-based polymers are coming onto the market, which are easily degraded into soil with the help of microorganisms. However, commercialization is less due to its high production costs and the requirement for large agricultural lands for production, and their degradation also necessitated the use of special composting techniques. It is urgently needed to produce good quality and a high quantity of biodegradable polymers. The microorganisms are often searched for and screened from the carbon-rich and nutrient-deficient environment, but the commercial value of the polymers from microorganisms is very costly. Moreover, the currently explored microbes like Ralstonia eutropha, Aspergillus eutrophus, Cupriavidus necator, etc. are producing polymers naturally as a carbon reserve. But the quality as well as quantity of production are low, which means they cannot meet our requirements. So, the main aim of this chapter is to focus on the wide applications of different biodegradable polymers from plants, animals and even microbes and recent advancements in their production and improvement of biopolymers to increase their quality and quantity from natural sources, as well as their applications in packaging, the medical field, aquaculture, and other various fields for the commercialization of the product.

*Corresponding author: Thirumullaivoyal G. Nithya, Department of Biochemistry, College of Science and Humanities, SRM Institute of Science and Technology - Ramapuram Campus, Kattankulathur, Tamil Nadu 603203, India, E-mail: [email protected] Mahajan Megha, Shanmugaselvam GokilaLakshmi, Pugazh Santhosh and Balasubramanian Balavaishnavi, Department of Biochemistry, College of Science and Humanities, SRM Institute of Science and Technology, Kattankulathur, Tamil Nadu 603203, India Murugesan Kamaraj, Department of Biotechnology, Faculty of Science and Humanities, SRM Institute of Science and Technology - Ramapuram Campus, Chennai 600089, Tamil Nadu, India As per De Gruyter’s policy this article has previously been published in the journal Physical Sciences Reviews. Please cite as: M. Megha, M. Kamaraj, T. G. Nithya, S. GokilaLakshmi, P. Santhosh and B. Balavaishnavi “Biodegradable polymers – research and applications” Physical Sciences Reviews [Online] 2023. DOI: 10.1515/psr-2022-0217 | https://doi.org/10.1515/9783110987188-004

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Keywords: biodegradable; biopolymers; eco-friendly; plant-based polymers; polyhydroxyalkanoates; sustainable.

4.1 Introduction Plastics and polymers are vital materials for our everyday existence. In today’s world, plastics are ubiquitous, and we cannot imagine our lives without them. Overall plastics production and consumption were assessed to have increased to more than 400 million metric tonnes by 2022 and were expected to rise up to 600 million metric tonnes by 2050 due to modernization and industrialization [1]. Plastic trash presents significant danger by stifling and starving untamed life, appropriating non-local and possibly unsafe life forms, and retaining harmful synthetic compounds in the environment. No doubt, plastics are very beneficial to us, but their fate in the environment is of utmost concern for our society. The major concern in ecology we are facing in this era of modernization is environmental pollution due to non-biodegradable plastics. Because of its low cost, readily available nature, light weight, corrosion resistance, and added additives, it is adaptable and suitable for a wide range of applications. But the problem is that most of the petroleum-based plastics are non-recyclable [2–4]. Recycling and degradation of plastics are time-consuming and also release harmful chemicals, which pose a great threat to the environment. Around 200 million metric tonnes of waste plastic enter the seas and oceans each year, killing an estimated one million aquatic animals [1, 5, 6]. Not only this, over the past decades, the incineration and burning of plastics has caused the release of harmful dioxins and carbon dioxide into the atmosphere, which leads to many potent diseases in living organisms, including cancer, respiratory, reproductive, and immunological disorders in humans [7]. The creation of biodegradable and environmentally acceptable alternatives to these plastics should be the primary priority in the present period, not only to safeguard our mother earth but also for the benefit of human and animal health. These plastics are choking innocent creatures as well as clogging drains. Nowadays, plant-based biopolymers are in vogue, which are easily degraded into soil with the help of microbes. Thinking of plants as a renewable resource for plastics is unbelievable, but it is true that plants are used for manufacturing biobased biodegradable plastics. However, commercialization is limited due to high production costs and the requirement for large agricultural land [8]. Even the technology for producing biodegradable plastic has not advanced to the point where industries can produce an eco-friendly alternative to plastics at a price equal to that of conventional plastic. So, it is the need of the time to produce good quality as well as a high quantity of bioplastics, and the microorganisms are a good choice for the production of cost-effective bioplastics that are degradable in nature and readily available in the microorganisms naturally as a carbon reserve [9]. But the quality as well as quantity of production are low, which means they cannot meet our requirements. So, the main aim of this chapter is to highlight the status and challenges of increasing the production of biodegradable polymers. The

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success of biodegradable plastic depends directly on the evolution of a cost-effective production technology coupled with large market demand. This chapter discusses the recent advancements in the production and improvement of biopolymers from natural sources to increase their quality and quantity, as well as their applications in packaging, the medical field, construction, automobiles, aquaculture, and other various fields for the commercialization of the product.

4.2 Biodegradable versus non-biodegradable polymers The polymers are made up of repeated units of a specific kind of monomer. They can be natural or synthetic polymers. Biodegradable polymers are degraded into smaller subunits over time by the process of hydrolysis or enzymatic reactions by microorganisms, and even other composting methods are also available that help them to degrade easily. On the other hand, non-biodegradable polymers are not able to degrade because of their hydrophobic nature, and this is the main reason for the plastic pollution all over the world [10]. These plastics can be broken down into microplastics over time due to environmental conditions and the action of microorganisms, but they remain in the water bodies, aquatic wildlife, animals, and birds and have even been reported in human blood [10, 11]. The production of plastics from renewable sources is advisable these days to reduce the carbon footprint in the environment and also to reduce marine pollution due to plastic accumulation in water bodies and animals, which is a great threat not only to animals and the environment but also to humans. Even some biodegradable polymers are only partially biodegradable; they are only referred to as “biobased” since they are made from biomass, which is a natural renewable resource. Although many biopolymers are biobased but not biodegradable, such as polyethylene Furanoate (PEF), bio-polypropylene (bio-PP), polytrimethylene terephthalate (PTT), bio-polyethylene terephthalate (bio-PET), bio-polyethylene (bioPE), and bio-polyamides (bio-PAs), there is still debate or confusion regarding their full biodegradability. Various other examples are discussed in Table 4.1 based on their source of origin: either some are biobased or others are non-biobased, i.e., made up of non-renewable petroleum sources [10–12]. Not only microorganisms but many other factors are involved in the complete degradation of the biopolymers, such as other abiotic factors such as light, temperature, mechanical stress, degradation time, etc. Also, the chemical degradation method is also used these days to convert these polymers into carbon dioxide and biomass. The basic steps involved in biodegradation are the formation of a film, i.e., biodeterioration, and then depolymerization with the help of extracellular enzymes, followed by bio assimilation by microbes and mineralization into simpler products [13–15]. No doubt, biodegradable polymers are the future of the green economy, but a lot of improvements and

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Table .: Commonly used biodegradable and non-biodegradable polymers based on their source of origin. Source of origin

Biodegradable polymers

Non-biodegradable polymers

Bio based polymers (made up of renewable sources)

Thermoplastic starch, cellulose, chitin, chitosan, corn zein, wheat gluten, soy protein, zymosan, lentinan, dextran, mannan, collagen, gelatin, whey protein, waxes, surfactants, polyhydroxyalkanoates, polyhydroxybutyrate, poly e-caprolactones, polylactic acid, polyglycolic acid, polyvinyl oxyalkanoates, silk, nylon -nylon  Polycaprolactones, polybutylene succinate, polybutylene succinate adipate, polylactic acid copolymers, polyglycolic acid copolymers, polyvinyl alcohol, polyvinyl acetate

Hyaluronic acid, pullulan, carbopol, poly(ethylene glycol), poly(ethylene oxide), bio-PE (polyethylene), bio-PP (polypropylene), bio-PET (polyethylene terephthalate), bio-PA (polyamide), bio-PTT (polytrimethylene terephthalate)

Non-biobased polymers (made up of non-renewable sources)

Linear High density polyethene (HDPE), branched low density polyethene (LDPE), ultra-high molecular weight polyethylene (UHMWPE), poly (tetrafluoroethylene)-PTFE (Teflon)

cost-efficient technology still have to be developed for their efficient use in the market [13, 15]. A lot of industries all over the world are based on biodegradable polymers, but still only one percent of total non-biodegradable plastics production (around more than 370 million metric tonnes per year) is currently used in the market in various fields.

4.2.1 Commercially available important biodegradable polymers based on their market value and properties In the market these days, many types of biopolymers are available based on the nature of the raw material and their degradability properties. Biopolymers are polymers that are produced from either plants, animals, or microorganisms, either naturally or through chemical production. The polymers that are produced naturally by living organisms are lipids, polysaccharides, proteins, polyhydroxyalkanoates, lactic acid, etc., which exhibit the same properties as conventional non-biodegradable polymers. These polymers have potential enough to replace petroleum-based plastics, but they have certain limitations. These biobased polymers are classified as biodegradable biopolymers and non-biodegradable biopolymers based on their production criteria and degradation properties [12, 14]. Synthetic biopolymers are chemically synthesized from nonrenewable sources (petroleum products), but the monomeric unit is derived from natural sources, which may be plant, animal, or microbial sources. These are more popular due to their mechanical properties that are similar to those of conventional plastics. These polymers can be hydrolyzed or have a carbon backbone. Based on the backbone, there are many types such as PLA (polylactide), PCL (polycaprolactone), PGA (polyglycolide), polyamides, polyurethane, polyanhydrides, polyvinyl alcohol, polyvinyl

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acetate, etc. [16, 17]. Most of the demand and usage of synthetic biopolymers is in the packaging and biomedical industries because they make food stable by increasing shelf life and, most importantly, are easily compostable. Among synthetic biopolymers, PLA and PGA have the largest market shares as compared to other synthetic polymers, as they have great optical transparency properties [18]. However, PLA’s poor barrier properties to oxygen and water vapor, combined with its amorphous nature, limit its market use. On the other hand, PGA is the most attractive biodegradable synthetic polymer because of its good barrier properties and high crystallinity [19, 20]. There are many properties that need to be checked and analyzed, such as crystallinity, melting temperature, tensile strength, chain orientation, optical transparency, etc., before any biopolymers can be commercialized. These properties are based on the nature of the monomer and the side chain group of the structure of the polymer. PLA composites are widely used as they are blended with other bioplastics to improve their structural properties [20]. PBS is another biopolymer made up of succinic acid and 1,4-butanediol that is more flexible than PLA and PGA. Its higher elongation rate and around 35% crystallinity make it superior to any other biopolymers, especially in food packaging applications [20, 21]. Apart from that, many other synthetic biopolymers are in use in the construction and electronics industries, such as polyacrylates, polyphosphoesters, polyanhydrides, polyethylene fumarate, etc. These are derived chemically from petroleum sources, and in their production process, many additives are used, which are responsible for the addition of some additional groups in their structure, which makes their structural properties complex and hence may affect their degradability efficiency [21]. Some of the synthetic biopolymers are non-biodegradable in nature. Natural biopolymers are derived from natural renewable sources, i.e., plants, animals, and microorganisms, and even some of the polymers are of human origin, such as hyaluronic acid and chondroitin sulphate [17]. These polymers can be the proteins, polysaccharides, and lipid molecules present inside living organisms and may be formed in their later stages of the life cycle. They are formed by the polymerization reactions that take place inside the cell using specific enzymes, and specific genes are responsible for their production. Mostly all natural biopolymers can be mineralized into simpler products after composting and, hence, are biodegradable in nature. Plant based polymers are extracted from plants either in the form of proteins and polysaccharides. Biodegradable plastics currently used in the market are mainly of plant origin. Nowadays, plant-based biopolymers are in vogue, which are easily degraded into soil with the help of microbes. Thinking of plants as a renewable resource for plastics is unbelievable, but it is true that plants are used for manufacturing biobased biodegradable plastics. However, commercialization is limited due to high production costs and the requirement for large agricultural land [8]. Even the technology for producing biodegradable plastic has not advanced to the point where industries can produce an eco-friendly alternative to plastics at a price equal to that of conventional plastic. So, it is the need of the time to produce good quality as well as a high quantity of bioplastics, and the microorganisms are a good choice for the production of cost-effective bioplastics that are degradable in nature

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and readily available in the microorganisms naturally as a carbon reserve. However, both the quality and quantity of production are inadequate to meet our needs. Plantbased starches and corn-based polymers are in high demand in the market, but they also require special composting technology. With the advancement of nanotechnology, nowadays nanofibers or nanocomposites are replacing the normal biopolymers [22]. A promising class of materials for the manufacture of skin wound dressings that can combat bacteria on the mending system is regular polymers. In this regard, gelatin, a hydrophilic polysaccharide found in plant cell walls, and zein, a liquor-dispersible protein from corn, were combined to generate a bio composite. Additionally, glycerol was introduced while working on the mechanical exhibits [23]. The results showed the incredible potential of this plant-based biomaterial as medication delivery frameworks for the treatment of various diseases. This biocomposite is also easily degradable, and antimicrobial assays revealed that it is resistant to three microbes, namely Escherichia coli, Staphylococcus aureus, and Candida albicans. Additionally, the biocompatibility was confirmed in vitro with essential human dermal fibroblasts via MTS measurements and cell morphology assessments. Animal-based polymers are extremely popular right now and have several uses in the medical field. They can be either carbohydrates or proteins or lipids obtained from animals. Their use in the market is constrained due to their inferior tensile strength and other mechanical characteristics to plant-based biopolymers. However, due to their inherent biodegradability, they have advanced more in terms of drug delivery systems inside the body. Animal-based polymers are in significant demand across all industries, including biomedicine. In the medical field, chitin, chitosan, fibrin, and collagen are increasingly frequently employed for a wide range of purposes, including drug delivery systems, stunting, transplantation procedures, and more [15, 24]. There is also advancement in the field of meniscal tissue engineering and regeneration medicine because of the use of animal-based biocompatible, biodegradable, and cytocompatible biopolymers. For example, collagen, gelatin, and agarose, due to their good mechanical properties and thermal stability, are widely used in tissue regeneration procedures. These are flexible to process and also undergo various chemical modifications with time. However, their only limitation is a lack of immunogenicity and cell adhesion, which limit their use in some cases [25]. Apart from this, elastin, albumin, and casein polymers are also used in various biomedical applications, refer Figure 4.1 for various applications of biopolymers available commercially. Also, hyaluronic acid and chondroitin sulphate of human origin are very costly biopolymers and recently have been reported in various transplantation procedures but still experience certain limitations in their use, which limits their commercialization [26]. Many compostable and biodegradable plastics have been developed using plants, animals, and synthetic biomaterials these days. But each polymer and biomaterial have its own advantages and disadvantages. PLA (polylactic acid) and starch-based polymers are widely developed by the bioplastics industry and derived from renewable resources like corn, potatoes, sugars, etc. [23, 27]. But they have certain limitations and are more

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Figure 4.1: Commercial uses of biopolymers available in the market “reproduced from Aya Samir et al. (2022) with CC BY-NC permission” [28].

costly than bioplastics, which also require special recycling techniques. For example, PLA is biodegradable in industrial composting conditions only. Polyhydroxyalkanoates (PHAs) are the new and emerging field of biopolymers of microbial origin produced by many bacteria as a secondary reserve carbon metabolite that is 100% biodegradable [29]. PHAs are produced industrially using sugars and fatty acids as a substrate for bacterial growth. Furthermore, they are compatible with a green economy because they can be made from non-fossil fuel resources and have properties similar to or resembling conventional plastics. The most important PHA family member is polyhydroxy butyrate (PHB). PHB is produced inside the bacterial cell when there is an excess of carbon and a nutritional limitation [27]. Numerous sources demonstrate that a wide range of bacteria, including Alcaligene eutrophus, Azotobacter beijierinckia, Pseudomonas oleovorans, Rhizobium sp., and Bacillus sp., manufacture PHAs as a reserve carbon source primarily to safeguard themselves from stressful environments [30]. In the natural environment, microorganisms’ breakdown of PHB clearly and fully results in carbon dioxide and water. Only this biopolymer is completely biodegradable when used in a natural environment. Many efforts were made to reduce production costs by identifying bacterial lines that could develop and produce PHB from less expensive source materials and by improving fermentation conditions for PHB production. In terms of renewable natural bioplastics, bio monomers are critical because they determine the final polymer structure and purity, which are necessary to assess the potential of the polymers or their copolymers and enable product excretion from cells, which simplifies downstream recovery and purification [31]. The most famous example of a naturally occurring bio monomer is polyester poly (lactic acid), or PLA, which is created by the

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polymerization of L- (+)-lactic acid. A number of microorganisms, including filamentous fungi and lactic acid bacteria, naturally create L-lactic acid as a byproduct of fermentation [30, 33]. PHB and other PHA made by bacteria have sufficiently high molecular masses to have polymer properties that are very similar to those of common plastics, such as polypropylene. PHB copolymers can be produced which may result in the creation of polymers comprising 3-hydroxyvalerate (3HV) or 4-hydroxybutyrate monomers by co-feeding substrates. A polymer called three-hydroxybutyrate-co-3-hydroxyvalerate, which is less stiff and more brittle than PHB, is created when 3HV is incorporated into PHB. The feedstock affects the composition of the final PHA [30, 33].

4.3 Methods and the factors affecting biodegradation of the polymers Biodegradation of biopolymers depends on many factors, i.e., environmental conditions, substrate or nutrients availability for the growth of polymer degrading microorganisms, duration time and most important the nature of monomer present in the polymer, molecular weight of the polymer, and the degree of crystallinity [31]. There are many controlling factors which is listed in Table 4.2, responsible for the partially or complete degradation of the polymers. Microorganisms are usually responsible for biodegradation process as they secrete enzymes on to the surface of biopolymers which results in adsorption of the enzyme and then hydrolysis of the complex bonds takes place [32]. The enzymes like PE synthases, cellulases, esterase, cutinase, etc. are released during the process which results in mineralization of the bioplastics into carbon dioxide, water and the biomass. Some bioplastics after degradation may release methane gas especially petrochemical-based bioplastics [31, 32]. Biodegradation to small molecules must take place outside of the microorganism because the substrate (the biopolymer that needs to be degraded) is frequently too large to be taken up. The most significant biodegradation processes for biopolymers, such as the hydrolysis of ester bonds to liberate the monomers, are carried out by extracellular enzymes that are excreted by microorganisms. A portion of the substrate is cut off by the Table .: Factors affecting biodegradation of biopolymers []. Factors affecting biodegradation process Environmental conditions Abiotic factors Biotic factors Temperature, pH, Mois- Hydrophobicity, Extracellular ture, UV radiation enzymes, Nutrients, biosurfactants

Physical properties of polymers Molecular weight, size and shape, crystallinity, functional groups, cross-linking, blend, copolymers, additives

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extracellular enzyme’s active site, which interacts with it to create a complex. This more minute, soluble component can enter the bacteria. Endoenzymes within the organism further digest the chemicals [34]. Abiotic activities, such as photodegradation and chemical hydrolysis under hot, acidic, or basic conditions, take place concurrently with biotic processes to physically and chemically degrade the material. Abiotic and biotic degradation processes can also interact; for instance, mechanical deterioration might make a polymer more susceptible to enzymatic deterioration, speeding up biotic degradation. Mechanical degradation can also result via the actions of meso- and micro-fauna, such as earthworms that break up litter and mix it in with the mineral soil [35]. Therefore, both biotic and abiotic processes control the overall rate of degradation of organic material. Glycoside hydrolases, a wide class of enzymes that catalyze the hydrolysis of glycosidic bonds, are primarily responsible for degrading starch. Long starch polymers are first split into shorter fragments by the enzyme amylase. Several enzymes that specialize in hydrolyzing glycosidic bonds, including amylase, glucoamylase, and glucosidase, hydrolyze these fragments. Numerous soils have been shown to contain starch hydrolyzing enzymes, and bacteria like Bacillus circulans, Klebsiella pneumonia, and Aspergillus oryzae produce a range of enzymes that can break down starch [35, 36]. The degradation process will start on the very first day and will take several weeks or even a year in some cases, depending on the enzyme and environmental conditions [37]. Trichoderma reesei and Phanerochaete chrysosporium are two cellulose-degrading fungi that are extensively used for the process of cellulose degradation and moreglucosidases are produced by P. chrysosporium than by T. reesei, and acidic conditions are optimum for the degradation process. Also, Laetisaria arvalis is a fungus that produces both Lytic polysaccharide monooxygenases (LPMOs) and hydrolytic enzymes, making it more efficient in degrading cellulose [38]. The degradation rate of the cellulose polymer will also depend on environmental factors and soil conditions. It will vary from 31 days to 495 days. Specific enzymes are involved in the degradation of specific biopolymers. For example, lignin peroxidase is used for lignin-based polymer degradation [39], PHA (polyhydroxyalkanoates) is degraded with the help of PHA depolymerases [40], etc.

4.4 Recent market trends and challenges for biodegradable polymers production The world produces 390 million tonnes of plastic waste per annum which is belief to double by 2035. Because of increasing environmental concerns/legislative pressure for plastics waste and rapid increases in the cost of petroleum, there is a need of development of “environmentally friendly” materials called Biopolymers.

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Europe dominated the global market for biopolymers which result in the expansion of the fresh green food sector there as shown in Figure 4.2. Additionally, the market is growing faster due to the growing use of biopolymers in packaging applications. However, it is anticipated that the high cost of biopolymers will put a brake on market expansion throughout the anticipated forecast period. The size of the global biopolymers market was estimated at USD 13.7 billion in 2021 and is anticipated to reach USD 35.25 billion by 2030, growing at a projected CAGR of 11.07% from 2022 to 2030 (refer Figure 4.3). By region, Europe had the biggest revenue share in 2021, with about 43.5% (refer Figure 4.2). By product, the biobased PET market accounted for around 57% of total revenue in 2021 [41, 42]. The packaging sector, which accounted for the greatest proportion of the global biopolymers market in 2021 as depicted in Figure 4.5, is anticipated to expand at a CAGR of 11.4% from 2022 to 2027 (refer Figure 4.3). Because they extend product shelf life and lower the overall carbon footprint associated with food packaging, biopolymers like polyesters, polylactic acid, polyhydroxy butyrate, and others are often used in packaging. Biopolymer-based films with improved mechanical and optical qualities include those made of polysaccharides and proteins. Because of this, biopolymers are used in packaging for a variety of end uses, including food and beverage, medical and healthcare, and more. As a result of the more opportunities, the use of biopolymers is rapidly expanding in packaging applications, which is speeding up market expansion.

Figure 4.2: Biopolymers market revenue share according to the geographical area in percentage [43].

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Figure 4.3: Biopolymers market size from 2021 to 2030 in USD billion [44].

It is estimated that the worldwide bioplastics market is expanding at a rate of 20–25% annually [45]. They offer benefits including reduced carbon footprint, independence, energy efficiency, and environmental safety. They do, however, have significant drawbacks, such as high costs, recycling, using less raw resources, terminology being misused, and a lack of legislation. There are many different kinds of biopolymers on the market, but it is still unclear how completely they biodegrade because their composting process utilizes certain conditions and commercial hydrolyzation technology. As per current market segment penetration, there is still a lot of scope for segments other than packaging industry which accounts for more than 55% of market share for bioplastics. Only 44% usage of bioplastics are there in bio packaging according to European bioplastics market segment [46, 47]. The main challenges that biopolymer industries are facing are the cost of precursor substrates, yield over substrate rate, volumetric productivity, and the cost of downstream processing. These are only a few of the variables that affect how well a biopolymer production process can be scaled up and if it is economically feasible. While bioengineering attempts to improve the upstream processes (use of inexpensive substrates and greater productivity), bioprocess optimization of the upstream and downstream processes is necessary for scalable and cost-effective production [48]. Another challenge is that biopolymers are extracted from renewable sources in the form of monomers, but their further polymerization process requires various chemical additives and stabilizers to improve the quality of the biopolymer, which affects its biodegradation properties. Despite a significant amount of research and development effort on the production of biopolymers from natural resources, widespread use and commercialization remain a long way off.

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4.5 Industrial production status and commercialized products The market for bioplastics in Europe is anticipated to grow at a CAGR of more than 20.6% between 2022 and 2027 as shown in Figure 4.3. In 2020, the COVID-19 pandemic had a significant impact on the market. However, it is believed that the market has now progressed to pre-pandemic levels. Environmental considerations promoting a paradigm shift and growing demand for bioplastics in flexible packaging are the primary factors driving the market examined over the short time period. However, the availability of less expensive alternatives is probably going to prevent the market from growing. During the projection period, flexible packaging programmes are expected to dominate the global market in terms of volume. Future market opportunities are likely to result from growing use in the electronics industry. Since the biopolymers sector is still in its infancy, it is seeing a lot of innovation. Tapioca, potatoes, maize, rice, and other carbohydrates are used to make the biopolymer known as thermoplastic starch. To create goods that are completely biodegradable, this starch is combined with polymers like polyethylene and polylactic acid (PLA). Because it combines two environmentally friendly components, this biodegradable product is known as an “eco-alloy.” The packaging industry, which accounts for 24% of the rigid packaging market and 19% of the flexible packaging market, is the one that uses this product the most frequently. Additionally, biopolymers are widely utilized by the textile sector (22%) and construction industry (17%) apart from packaging industry [49, 50]. These data demonstrate the expansion of biopolymers in a variety of fields. The market has a wide variety of commercially produced goods. The production of PBAT and agricultural mulch films under the names of the brands Ecoflex and Ecovio has made BASF the top producer of bioplastics. Other than this, there is PLA, a good material utilized in packaging, medicinal applications, and 3D printing. The second-largest producer in the world, Total Energies Corbion, produces about 100,000 tonnes annually. Other important companies involved in the production of biopolymers are depicted in Table 4.3. Biobased polyethylene terephthalate (PET) had the greatest market share across product kinds in 2020, with a share of 56.9% [49]. This is due to the characteristics of biobased PET, such as its capacity to be recycled and degrade naturally. This biopolymer’s composition consists of 30% ethylene glycol generated from plants and 70% terephthalic acid (TPA, derived from fossil). PET made from biobased materials is used to make bottles, bags, cosmetic containers, carpets, sanitary items, foils, and other things. Figure 4.4 shows that not all biopolymers are biodegradable; just a small percentage of them are; the majority are biobased, but special composting procedures are needed to degrade them. Composites made of PBAT, PLA, PHA, PBS, and starch are biodegradable. Through the mineralization process, these polymers are broken down with the support of microbes. Others, however, such as PET, PE, PA, and PTT, which are seeing greater utilization by application in numerous industries, are made from biomass but may not be entirely biodegradable.

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Table .: Popular brands of biopolymers in the market with their applications [, ]. Biopolymer companies

Products

Applications

BASF

PBAT, Mulch films, Chem Cycling PLA

Packaging and Agricultural industry

Bio PBS, Bio PTMG, Durabio

Packaging and Automotive industry

Total energies Corbion Mitsubishi chemical Eastman Futamura

Tritan Renew copolyester Cellulosic film, Nature flex, Improved Marcon Neste Palm oil Nature works PLA (Ingeo brand) Polymateria Life cycle brand Tipa Compostable plastics Biome plastics Bioplastics Danimer Scientific PHA biopolymers

Origin materials Notpla

Ecovative Novomer Cocoon Biotech Cruz Foam Lactips Novoloop Novamont Plantic

D printing and medical applications

Mobile cases , Eyewear, headphones, Textile industry Rigid packaging industry

Aviation biofuels D filaments, Coffee pods and Food industry Cups, Flexible films, Cutlery Packaging industry Packaging industry Additives, aqueous coatings, extrusion coating, extrusion lamination, fibers, film resins, hot melt adhesives, injection molding, thermoforming, and wax replacement polymers PET plastics New polymers and surfactants Seaweed based biopolymers Manufacturing diversified items, such as nets, sachets, alcohol cocktails, lined cardboard, plastic cups, and hot sealable films Mycelium based Skincare, textiles, apparel, and food industry biopolymers Green plastics and polymers Polyols, surfactants, ceramic binders, and thermoplastics Biocompatible silk protein Treatment of osteoarthritis and other degenerative joint disorders Bioplastics from fisheries Consumer packaging, consumer electronics, automotive, waste and BB packaging solutions Water soluble packaging Water-soluble packaging, sustainable packaging, and solutions single-use plastics Thermoplastics Apparel, consumer electronics, automotive, and additive manufacturing Mater-Bi (plant based Films, thermoformed articles, additives, foams, injection biopolymers) molded articles, and extruded articles PLANTIC HP, PLANTIC R Meat, poultry, and dairy packaging sectors

The most widely utilized biopolymer globally is PET, followed by starch composites refer Figure 4.5, but the major issue is their difficult biodegradation process. Only 1% of biopolymers are used globally, and PHA is the only one that is totally biodegradable. Its

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Figure 4.4: Global production capacity of biopolymers in thousand tons according to the type of application “reproduced from report on bioplastics market data 2018 with CC BY-NC permission” [86].

pricey production technique and different features from synthetic plastics are the key causes of its lower level of adaption in other markets. Plastics are widely accessible and less expensive than bioplastics. However, as depicted in Figure 4.5, it only contributes 1% of the market share commercially. The development of bacterial biopolymers and their diverse alternative uses have driven the bio-industrial sector toward the possibility of commercial-scale manufacturing. The widespread use of bioplastics has the potential to solve a number of possible environmental risks by reducing CO2 emissions and ending the need on petroleum for the production of plastics. Table 4.3 discusses the many businesses engaged in the manufacturing of biopolymers from renewable sources, as well as the products they sell and the uses for which they are used.

4.6 Metabolic engineering tools to increase the production of biodegradable polymers For the output and quality of biodegradable polymers to grow, metabolic engineering improvements are now necessary. Poly (-hydroxy fatty acids) are biobased polyesters

4.6 Metabolic engineering tools to increase the production of biodegradable polymers

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Figure 4.5: Global production capacity of bioplastics in 2018–2019 according to the type of biopolymer “reproduced from report on bioplastics market data 2018 with CC BY-NC permission” [86].

that resemble polyethylene and are the result of metabolic engineering of the enzymes involved in the manufacture of polymers. By changing the Pha genes involved in PHA production, medium-chain-length polyhydroxyalkanoates homopolymers are converted into stretchable films [53]. By using enzyme and metabolic engineering, microbial lactatebased polyesters demonstrate translucent and flexible homes, enabling increased manufacturing of biobased polymers. Microbes are now viable factories for generating valuable polymers and/or their precursors from renewable biomass thanks to the discovery of synthetic biology. Recent advances at the chemistry-biology interface have made it possible to create a number of new biopolymers with properties that are significantly different from those of their petroleum-derived equivalents. Exploring practical applications requires a thorough understanding of the biopolymers’ growing structural diversity as well as their material characteristics. The methods used to achieve this goal by metabolic and enzyme engineering are beneficial for a variety of biopolymer applications [54]. To do this, the initial substrate, enzymes, genes, and entire metabolic pathway involved in the cellular production of a particular biopolymer must be identified. The genes responsible for the enhanced production must then be edited or transformed to boost the yield. The substrate involved in the production of biopolymers with in the cell as well as outside the cell plays very important role in the production of desired biopolymers. The monomer for the synthesis of PET, PLA, PBS, PBAT, etc. is obtained by microbial fermentation but the subsequent polymerization process uses petroleum resources.

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Various metabolic engineering tools are used to modify the desired product. This includes heterologous gene expression pathway, optimization of metabolic fluxes, promotor strength, gene number multiplication, deletion of competing pathway, elimination of toxic metabolites, limiting carbon diversion away from the desired pathway, etc. For instance, the recombinant S. cerevisiae strain H131-A3 was engineered to create a lot of ethanol (31.1 g/l), had a high titer (0.41 g/g), and produced xylose at a rapid rate (1.86 g/g/h). The altered strain overexpresses genes from Pichia stipilis xylulose kinase, from Piromyces xylose isomerase, and genes from the non-oxidative pentose phosphate pathway [54]. Even Biobased PET is produced using an engineered strain of Pseudomonas putida that produces cis-muconate from lignin-based catechol was reported by Michael et al. in 2022 [55]. PHA is another biodegradable polymer with numerous uses in the medical and food industries, although its usage is restricted due to its brittle and crystalline character. A lot of genetic engineering work is being done to increase both the quality and quantity. The recombinant strains were designed to evaluate PHA yields with various substrates after new polyhydroxyalkanoates (PHA)-associated genes (phaCp and phaABp) were cloned from Propylenella binzhouense L72T and expressed in E. coli cells for PHA synthesis. Using glucose and propionic acid as substrates, the maximum poly (3-hydroxybutyrate-co3-hydroxy-valerate) (PHBV) yield (1.06 g/l) and cell dry weight (3.31 g/l) were produced in E. coli DH5/ptsG-CpABp [56].

4.7 Recent applications of the biodegradable polymers 4.7.1 Application in packaging industry According to the International Biopolymer Market Status, the biopolymer industry is more thriving in the packaging industry, accounting for more than 70% by application. Biopolymers used in the packaging industry are desirable for preserving food quality. The meals contained within are free of harmful chemical compounds while retaining their freshness [57]. Mechanical properties can also be managed and modified to meet industrial needs. Another important demand for these organic plastics is biodegradable polythene bags. The additives used in plastics cause them to biodegrade when exposed to air, light, or water. When volatile or bioactive molecules are combined with polymeric matrix, the use of cyclodextrins (CDs) in packaging technologies aids in the improvement of their solubility, ensuring the homogeneous distribution of the complexed molecules and preserving them from volatilization, oxidation, and temperature changes. This method is also appropriate for the controlled release of active ingredients and permits the investigation of their relationship with biodegradable polymers with the aim of reducing the harmful environmental effects of food packaging [58, 59]. Starches mixed with biodegradable polymers like Polylactic Acid or polyethylene and heavy metals can be used to make biodegradable bags (PLA). The oxo-biodegradable

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plastic bag series, which uses top-notch additives that break down the polymers more quickly, is another product category that is gaining popularity. Today, a number of product innovators are producing biodegradable or bioplastic-based bags for use in waste collection, composition, and shopping. The polymers of those compostable plastics are entirely natural, and when they decompose, they release carbon dioxide, water, and organic material into the environment. Therefore, compared to conventional plastics, the environmental impact is less. In place of traditional plastics in food packaging, cellulose, starch, chitosan, polylactic acid, and polyhydroxyalkanoates are thought to be suitable substitutes. However, because of their poor performance, difficult processing, and expensive production costs, these biopolymers have a limited commercial application in the food packaging sector [60].

4.7.2 Application in the electronics industry Electronics manufacturing now uses biopolymers, which significantly reduces the amount of plastic waste. Currently, bioplastics and biodegradable polymers are used to make electronic devices including touch screen computer cases, keyboards, earphones, mobile phone cases, loudspeaker cases, laptop cases, gaming console cases, mouse cases, vacuum cleaner cases, etc. In the consumer electronics sector, optimized PLA chemicals are mostly used. Impact resistance, water resistance, stability, high gloss finish, and many other properties were introduced by PLA mixes [61]. The production of electronic devices is constantly expanding, which results in large amounts of digital trash (also known as “E-waste”) being robotically dumped into the environment. Due to the released dangerous chemical compounds, non-biodegradable polymers, and toxic heavy metals, this has serious environmental and ecological consequences. Additionally, as biocompatible polymers are widely employed in biomedical packaging, electronics can be used in implanted biomedical systems. The majority of biodegradable polymers, however, are insufficient for several specific application criteria, such as flexibility, electric conductivity, dielectric properties, fuel, and water vapor barrier. Recent studies have concentrated on the development of nanocomposites by adding nanofillers to biopolymers, in an effort to give them useful properties while keeping strong biodegradability and biocompatibility [62]. Bio nanocomposites therefore have numerous applications in electronic devices.

4.7.3 Application in agriculture industry Aliphatic polyesters, aromatic polyesters, and co-polyesters are the three main types of polymers used commercially in agricultural industry [63]. In terms of both chemical composition and physical characteristics, polyhydroxy alkanoates (PHA) represent the ultimate class of recyclable polymers [64]. The polymer-based products used in agriculture

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are PLA and PBAT with distinctive characteristics and properties that are utilized as pure polymers in blends with various compositions [65]. Polymers made from biomaterials will be a better alternative to those made from petroleum. Since there will not be any collecting of plastic garbage, biodegradation in soil has certain advantages over other degradation techniques like land filling or mechanical recycling [66]. Additionally, it reduces the cost of trash handling. Because many polymers contain solid components and are not water soluble, they cannot be directly destroyed by microorganisms due to their complexity [67]. In other words, this complex is first broken down into monomers with the aid of extracellular enzymes, after which this lower-molecular substance can cross the membrane with the aid of bacteria, after which biomass is formed, and lastly it will go through mineralization and become soil [68, 69]. This procedure increases soil fertility, therefore it also functions as a natural biofertilizer. While polycationic polymers have been used for plant bioengineering, superabsorbent polymeric materials have been used as soil conditioners to reduce the effects of drought. Applications within plants as part of the expanding toolkit for genetically modifying plants to boost productivity and disease resistance complement such activities in the environment [70].

4.7.4 Application in automotive industry The modern automotive sector has seen a number of progressive changes. Many actions had been done to lessen the overall carbon footprint. Environmental conservation initiatives have undoubtedly benefited by switching to fuel-efficient vehicles and cleaner gasoline systems [71]. Plastic goods have played a significant role in the automotive industry. However, there were legitimate worries about the recyclable materials and the growing plastic wastes coming from this area. This is possibly the driving force behind the auto industry’s transition to biopolymers. Biopolymers like PLA, Bio PBS, Bio PTMG, etc. are nowadays extensively used for 3D and 4D printing and the automotive sector also has a huge potential for 4D printing’s capabilities like selfassembly, self-repair, and multifunctionality [72]. In reality, a number of top automakers use biopolymers such bio polyester and bio polyamides. These biopolymers work superbly and are also very beneficial to the environment. These compounds with wonderful qualities and biodegradability have piqued producers’ interest in bioplastics. Biopolymers are used in the production of a variety of automotive components, including the dashboard, interior and exterior features, headliners, sun visors, floor mats, seat cushion covers, and more [73]. The car manufacturers and component suppliers have switched to natural fibre composites out of a desire to find a sustainable alternative to the man-made fibres used in reinforcing composites. Natural fibre composites (NFC) were previously only allowed in non-structural components, but with ongoing, in-depth research, the idea of using NFC in larger structural and exterior parts is quickly growing. Due to their exceptional unique features, such as their excellent thermal and acoustical insulation, vegetable fibres are

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the main source of these fibres used in automobiles. The history of NFC adoption is documented, starting with Henry Ford’s hemp car in 1930 and ending with Polestar’s flax interior panels in 2020 [74].

4.7.5 Application in biomedical industry Due to their intrinsic biocompatibility, biodegradability, and low immunogenicity, biopolymers have a wide range of clinical applications. Tissue engineering, medical implants, wound dressings, and the delivery of bioactive compounds are the top biomedical uses for biopolymers [75]. Biopolymers are a great option for surgical materials as well because of their improved functionality, physical-mechanical qualities, regeneration and adsorption properties, etc. The biomedical sector mostly uses biopolymers such chitosan, alginate, and hyaluronic acid as polysaccharides; collagen, gelatin, and fibroin as proteins; and derivatives of polylactic acid. In many plants, chitosan has an important role in defensive mechanisms and growth regulation. Due to its low toxicity and biocompatibility, it also exhibits antibacterial action. Alginates were utilized in a number of intricate wound dressings. For example, it has antibacterial effects on Gram-positive bacteria like Staphylococcaceae or Bacillus cereus and Gramnegative bacteria like E. coli, Pseudomonas aeruginosa, and Acinetobacter spp. It also has antifungal activity against C. albicans and antiviral effect against Herpesviridae, Flaviviridae, and Togaviridae [76]. Collagen and hyaluronic acids have been shown to aid in the healing process of wounds [77]. Many years ago, silk fibroin from Bombyx mori silkworms was used in medicine. It has been utilized as a suture material because it is a fiber-based material with good mechanical attributes, a high tensile strength, and a high breaking strength.

4.7.6 Application in field of aquaculture The class of biodegradable biopolymers known as polyhydroxyalkanoates (PHA) are manufactured by microorganisms from renewable feedstocks. Because PHA’s characteristics can vary, more research is being done on them to create a variety of useful uses, most notably bioplastics [78]. Poly(3-hydroxybutyrate) (PHB), a common PHA type, has recently been discovered as an efficient biocontrol agent to substitute antibiotics and enhance growth and disease resistance in aquaculture [79]. However, there are a number of difficulties involved in the manufacturing and use of PHB, including the high cost of feedstocks, the high cost of sterilizing, the high energy input harvesting methods, and the toxic extraction and purifying methods. Recirculating Aquaculture System for PHB-Rich Microorganisms (RASPHB) is a revolutionary PHB production and supplementing system. Using chitosan as a bio coagulant, this system combines the synthesis and collection of PHB-rich Zobellella denitrificans ZD1 with the treatment of agro-industrial wastes,

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including aquaculture wastewater/wastes. An aquaculture animal model, brine shrimp Artemia, showed multifunctional effects from chitosan-harvested PHB-rich ZD1 such as bettering growth, survival, immunological response, and modifying gut microbiome [80]. Effects on PHA polymer composition in ZD1 of using various agro-industrial wastes/ wastewaters as substrates [81]. Additionally, bacterial cells that collected fractions of longer PHA monomers along with PHB increased the biocontrol effectiveness by boosting their antipathogenic traits, giving Artemia more energy, and enhancing their ability to survive infections.

4.7.7 Application in construction industry Biopolymers have long been a component of construction materials. Vegetable oil was utilized in lime mortars in Vitruvius’ works. Chinese builders of the great wall employed blood, fish oils, and egg whites as admixtures [82]. The longevity of the biopolymer employed in ancient times shows that biopolymers are still appropriate for use in modern construction material production. It is possible to create biopolymers directly from natural sources or by processing natural ingredients like cellulose, starch, chitin, chitosan, alginates, etc. In the fermentation process, certain microorganisms serve as an excellent source for the manufacture of biopolymers like polyhydroxyalkanoates. They can also be used to make polylactide, bio polyethylene, and polytrimethylene terephthalate [83]. Lignosulfonates have been employed as plasticizing admixtures because they have the capacity to lower the water content and increase the workability of the concrete mix. As an alternative to lignosulfonates, carboxymethyl cellulose and hydroxyethyl cellulose can also be utilized, however their production costs were raised. The flowability and workability of lignin and its derivatives, such as Kraft lignin, are improved by their superior solubility and release properties [84]. Nano silica has received a lot of interest in cement-based composites in recent years because it significantly boosts the cement composites’ compressive strength. Bio-admixtures now play a significant role in the manufacturing of building materials. Biopolymers, particularly microbial biopolymers, will become an increasing trend as a result of the demand for high-quality materials [85].

4.8 Conclusions The fact that biopolymers can help with environmental problems has inspired a great lot of interest among researchers to look into this field. However, a fundamental problem with employing biopolymers is their high cost. Even though there have been several attempts to reduce their production costs, there is still a long way to go before this area is benchmarked. It might be of immediate interest to investigate high value-added applications in therapeutic and surgical settings. Their surface-binding proteins have potential

References

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applications in nanomedicine, including the delivery of drugs. The packaging business is where biopolymers are most frequently used. Future research might concentrate on genetically altering bacterial strains to maximize the synthesis of biopolymers.

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Suresh Babu Palanisamy*

5 Biopolymers as a versatile tool with special emphasis on environmental application Abstract: Water sources are becoming highly unsuited as potable sources due to the presence of impurities and hazardous chemicals. Although there are many conventional methods available, the development of innovative technologies is essential for the treating and recycling of wastewater. Owing to their unique and excellent qualities, polymers have recently seen extensive use across various industries. By joining the monomeric components covalently, biopolymers resemble a more natural alternative to synthetic polymers. The biopolymer and biopolymer composites integrate into many sections of the treatment process easily, making them effective, affordable, and environmentally beneficial. Due to their distinct features, biopolymers can replace traditional adsorbents. The biopolymers and composites discussed in this chapter are ideal adsorbent materials for eliminating contaminants from the environment. Based on their sources, methods of preparation, and uses, biopolymers, and their composites are categorized. This chapter also includes different research perspectives on biopolymers, especially from an ecological and financial standpoint. Keywords: adsorbent; bioenergy; biopolymers; composites; eco-friendly; water treatment.

5.1 Introduction The deterioration of the environment is drastic and unpredictable day by day, owing to surging population, industrialization, and urbanization [1, 2]. Diverse types of hazardous pollutants (both natural and artificial) pose a serious threat to the environment and human health. Some of these harmful contaminants like dyes, pesticides, insecticides, heavy metals, surfactants, etc. are listed as detrimental substances, owing to its ability in inducing gene mutation, neural disorders, gastrointestinal disorders, birth defects, and allergenic reactions [3, 4]. These toxic pollutants directly impact the environment by lowering the oxygen levels and by influencing the retarded growth of biota in land and aquatic environments [5, 6]. The mitigation and elimination of pollutants have attention before the waste discharge and disposal, which opens up new boulevards in the employment of advanced treatment methods [7, 8]. Conventional techniques are not

*Corresponding author: Suresh Babu Palanisamy, Department of Biotechnology, Saveetha School of Engineering, Saveetha Institute of Medical and Technical Sciences (SIMATS), Thandalam, Chennai, 602105, Tamil Nadu, India, E-mail: [email protected]. https://orcid.org/0000-0001-9859-2208 As per De Gruyter’s policy this article has previously been published in the journal Physical Sciences Reviews. Please cite as: S. B. Palanisamy “Biopolymers as a versatile tool with special emphasis on environmental application” Physical Sciences Reviews [Online] 2023. DOI: 10.1515/psr-2022-0218 | https://doi.org/10.1515/9783110987188-005

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promising or noteworthy, due to several limitations such as surplus capital requirements, established infrastructure, and engineering proficiency (Zubair and Ullah, 2021). Advanced treatment methods like advanced oxidation processes (AOPs), ozonation, adsorption, and membrane separation are some of the promising methods with exclusive efficacy. Among these listed techniques, adsorption is found to be more promising in removing pollutants owing to its minimal cost of operation and user friendliness. Still, several efforts have been initiated to develop efficient low-cost adsorbents with enhanced stability for batch process. Biopolymers are biodegradable polymeric materials made up of monomers joined together to form a lengthy chain [9]. Biopolymers are synthesized inside the cell during the microbial growth cycle as a part of their metabolism. The unique attributes of biopolymers derived from organisms seek the attention of researchers universally. Biopolymers are derived mainly from the gamut of biological sources viz. plant biomass, agro-wastes, animals, and microbes. These biopolymers include polysaccharides, fats, nitrogenous bases and proteins. Biopolymers are highly promising competitors for the anthropogenic/artificial polymers and as renewable alternative, owing to its fascinating attributes like abundancy, biocompatibility, biorenewable, environmentally benign nature, and biodegradability. They are broadly categorized into 3 types, viz. natural, microbial, and chemically synthesized biopolymers. Utilization of these biopolymers in plethora of applications including food industries, medical and pharmaceutical industries, and bioremediation are mainly owing to its mechanical, physico-chemical, and biological characteristics. Due to their intrinsic and tunable attributes, scientific community’s focusing on the bulk production of biopolymers [10–12]. In the recent decades, researchers’ attention must develop biodegradable polymers for contaminant mitigation and for universal well-being. This emerging new gen material pave way to new avenues in biopolymers and their composites for commercialization in a wide range of applications such as water purification, petrochemical industries, cosmetics and pharmaceutical industries, food industries, energy storage and conversion devices, and therapeutics [12–14]. Few limitations of biopolymer composites are listed as follows: minimal resistance, prolonged use incompatibility, limited processing ability, and poor mechanical performance also affect the biopolymer and its composites. To overcome these snags, selection of suitable fillers like natural fibers, metal oxides and metal may be selected [15]. Such nanofillers are used to enhance the barrier, mechanical and thermal attributes. Zinc oxide and silver are some of the preferred nanofillers used to synthesize polylactic acid and starch-based bionanocomposites. Biopolymers are produced from subsist monomers using a polymerization reaction, solvent extraction, and by fermentation. Albeit, the techniques used to synthesize biopolymer composites vary from the routine conventional techniques. The filler materials can be augmented into the biopolymers using the stepwise process as listed. Step 1: extrusion solvent casting (blends), Step 2: molding (infusion, resin transfer, compression), Step 3: grafting (stress transference), Step 4: intercalation (continuous

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stirring), and Step 5: electrospinning [16]. The selection of the suitable technique plays a vital role in the physical and mechanical attributes of biopolymer composites. More interestingly, the employed nanoparticles and their shape play a crucial role in determining the attributes of the formed bio-nanocomposites. Based on the geometrical variation, nanoparticulate is classified as nanofibers, nanoparticles, nanorods, nanoplatelets, and nanotubes. Nanoparticles from various industrial and personal care products pollute the water bodies in numerous ways like unprocessed/partially processed industrial effluents, agricultural run offs, and domestic wastewater. These nanoparticles enter the biological system through different ways and it gets transformed into various forms in terrestrial and aquatic biota through physicochemical reactions in a particular environmental setting. Some such notable limitations of nanocomposites have opened up new avenues for the preparation of new bio-nanocomposites. Bio-nanocomposites contain biodegradable materials with promising features to combat against the anthropogenic petroleum-based synthetic polymer composites. These green composites contribute directly in maintaining the economy, environment and technology [16]. Hence, they are considered green assets. Natural biopolymers are mainly derived in the form of polyesters, vinyl polymers, polycarbonates, polyamides, and polysaccharides [3, 18]. These environmentally benign and economic biopolymers are obtained from sustainable and renewable agro-waste materials like pea starch, corn starch, vegetable oil, etc. [17, 19]. Owing to its structural heterogeneity and complexity, it has attracted more attention in a plethora of industrial applications. Makvandi et al. (2020) and Komal et al. (2019) demonstrated the fabrication of biocomposites using banana fibers with polylactic acid in 3 different methods to attain the desirable characteristics. After biocomposites fabrication, attribute evaluation is highly essential to understand the structural and functional complexity. During the scale-up process, expensiveness is reported as the main hitch in biopolymer development during upstream and downstream processing, respectively.

5.2 Synthesis and characterization of biopolymer composites Biopolymer composites are also referred to in varying terms like biocomposites, bionanocomposites, nanobiocomposites, biohybrids, green composites, etc. Even though, biopolymers possess several promising attributes such as low molecular weight, robust barrier performance, and excellent biodegradable capacity. Nevertheless, it requires some unique mechanical qualities in terms of tensile strength, low chemical resistance, short fatigue life, minimal processing capability, and poor durability. To achieve the desirable quality, natural fibers, filler materials, nanofillers with other supporting

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Figure 5.1: Depicts the ingredients required to synthesize the composite, nanocomposite, and bio-nanocomposite.

medium can be mixed into a polymer matrix to produce biocomposites with enhanced efficacy (Figure 5.1). Biocomposites possess inherent intriguing qualities and merits including renewable, sustainable, biodegradable, biocompatible, extraordinary tensile strength owing to the biopolymer’s existence. Using techniques like grafting, interlinking, and nanocomposite bead fabrication, the natural biopolymer efficacy and its performance can be improvised. Moreover, nanostructures have extraordinary surface area, noteworthy chemical reaction ability, surface heterogeneity and surface energy, robust mechanical properties, and minimal power requirements compared to readily available conventional methods and materials [19]. Generally, composite materials with degradable and renewable attributes are considered “green” materials. Some biopolymers derived from natural resources are starch, polyhydroxyalkanoates (PHA), polylactic acid (PLA), lignin, and cellulose acetate. Some polymers derived from synthesis materials, especially from polyvinyl alcohol, aromatic, and aliphatic polyesters are biodegradable, but they are not renewable. Bionanocomposites are categorized based on various characteristics, including size, shape, matrix types, origin, etc. Bio-nanocomposites attain their shape based on the particles used for reinforcement [19, 20]. 1. Elongated particle bio-nanocomposites: To achieve stretchable and elongation behavior, particles like carbon nanotubes and cellulose nanofibrils are added as reinforcement agents to enhance the biomechanical attributes (high aspect ratio). 2. Layered particle-reinforced bionanocomposites: such bionanocomposites can be subcategorized into exfoliated and intercalated nanocomposites, microcomposites, flocculated nanocomposites, and phase-separated nanocomposites. Such polymers are differentiated on the basis of the distribution rate in the matrix, which are also referred as layered polymer nanocomposites. In phase separated or flocculated bionanocomposites, there will no partition owing to the particle–particle interactions

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amid the layers, whereas, in microcomposites, microparticles are distributed in the polymeric matrix. Moreover, intercalated nanocomposites are formed by the intercalation of polymer chains between the nanoparticles formed layers. Such individual layers-based partitions end up in the exfoliated nanocomposites. 3. Particulate bionanocomposites: In this type, selected dimensional particles with low aspect ratios are used as reinforcements to achieve inflammable attributes and to minimize the permeability and production cost of the composites. Hence, these bionanocomposites will exhibit low reinforcing effect.

5.3 Environmental application of biopolymers and biopolymer composites Owing to their minimal carbon foot print performance and plethora of fascinating features, wide range of biopolymers are often considered suitable materials for pollution mitigation. Though, they have few limitations, including poor mechanical attributes, least resistance to reactive chemicals, lack of prolonged durability, short fatigue life, and limited processing ability. To fabricate advanced bio-nanocomposite materials with a gamut of applications, biopolymers are enriched by combining materials like fibers derived from nature, fillers including nanofillers, and other plausible supporting matrices [11]. Natural biopolymer attributes can be obtained through cross linking, grafting, and synthesis of bio-nanocomposite beads. Generally, nanostructures possess robust mechanical properties, maximum surface area, surface energy, prominent chemical reactivity, and least power requirements [21, 22]. These improvised nanocomposite materials exhibit synergistic effects with novel characteristics, which can be utilized for surfeit of environmental applications including wastewater treatment, clean energy, and in bioplastics production. Recent decades authenticate the advances of biopolymer-based nanocomposites fabrication and its utilization in various potential applications from the number of articles published. These enhanced nanocomposites with inimitable structural features and reactive functional groups are utilized for water quality monitoring (real time as well as continuous), which is highly economical with exceptional efficacy in wastewater and water treatment systems. Biopolymer composites incorporated with metal/metal oxide nanoparticles have been widely employed for the pollution mitigation, remediation and treatment of biological sludge, sewage waste generated from municipal and urban areas, slime, and industrial wastewater. Such developed biopolymer compositebased sorbents are considered as highly economical and natural for the mitigation of hazardous dyes and heavy metal pollution. This section covers the highlights the environmental applications of bio-nanocomposites in handling the different types of contaminants and industrial pollutants.

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5.3.1 Hazardous contaminants removal Organic dye pollution is sourced from various industries including paper/pulp, tanning (rubber/leather), personal care products, printing, and textile industries. These complex coloring products possess non-ionic, anionic, and cationic characteristics. Textile industry effluents are rich in high organic content, owing to the usage of a huge volume of non-biodegradable dyes. Several reports have pinpointed the photocatalytic degradation of contaminants like residual organic compounds, dyes, chemicals with nitrogen, etc. Like dyes, wide range of heavy metals including hexavalent chromium, cadmium, lead, nickel, and manganese also pose a serious threat to the ecology and public health. Heavy metal pollution is considered a prime environmental challenge, owing to the wide usage of heavy metals in various industries and their toxicity toward human and aquatic biota.

5.3.2 Water/wastewater treatment Biopolymers and their composites are used in water/wastewater treatment in various ways. The main concern by the environmentalists worldwide is to fabricate sustainable and environmentally benign alternatives to methods employed and materials used to date for contaminant water processing and purification. Customizing the biomaterials and optimizing the process techniques can result in enhanced outcomes in terms of time requirements, efficacy and cost. Moreover, use of biomaterials and their composites reduces the secondary pollution possibility [23]. Prepared algal alginate-based coagulant for treating drinking water. Alike the previous study [24], reported the efficiency of alginate based microporous beads made using titanium oxide. These microbeads exhibited excellent adsorption capacity toward methyl orange and methylene blue dyes with robust stability, facile recovery and recycling features including photocatalytic activity. In [25], Ocinski and team studied the performance of synthesized alginate beads in removing arsenic ions from aqueous solution. Zeng et al. [26] developed a biocompatible ultra-oleophilic membrane using Konjac glucomannan as a cross-linking agent to improvise the efficacy of oil/water separation and other aqueous contaminants like heavy metal ions and polyaromatic dyes. The observed results authenticate the removal efficacy of prepared biopolymer membrane up to 99.9%. Another interesting work reported by [27] demonstrated the efficiency of electrospun nanomembrane made up of polylactic acid (PLA) integrated with β-cyclodextrin fused with polydopamine for removing mixed pollutants. Similarly, for water decontamination, biopolymers are employed in the form of beads and fibers. Arsenic (III) and arsenic (V) metal ions are separated using the developed chitosan goethite bionanocomposite beads [28]. A similar kind of work was reported by [29, 30] experimented the prepared chitosan-based nanocomposites to adsorb arsenic ions from the wastewater. Recent decades corroborated the deployment of nanosorbents/bionanocomposites in various forms in treating water treatment and wastewater treatment, owing to their fabulous attributes and exceptional catalytic efficacy [18, 33]. Table 5.1 list the various biopolymers and their composites employed in water and wastewater treatment exclusively as adsorbents.

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Table .: List of biopolymers and its composites synthesized using different methods for the treatment of water as adsorbents. (Reproduced from [] with permission, copyright © , Elsevier publications). Biopolymer and biopolymer composite as Pollutants (metal ions and dyes) adsorbents as adsorbate Alginate/biochar Alginate/chitosan

Alginate/montmorillonite Alginate/halloysite (Nano) Alginate/magnetic ferrite

Alginate/polyacrylonitrile Alginate/polyaspartate Calcium alginate/orange peel

Calcium alginate/banana peel

Cellulose (amination) cellulose (rise husk)

Nanocellulose (amination)

Cellulose (peanut husk) Cellulose-graft-glycidyl methacrylate Cellulose/acrylonitrile Cellulose-graft-glycidyl methacrylate (amination) Sugarcane bagasse cellulose – amination Chitin Chitosan (amination)

Cd(II) Pb(II) Cu(II) Cd(II) Co(II) Methylene blue Basic red  Methylene blue Pb(II) Basic blue  Basic red  Basic blue  Pb(II) Methylene blue Methyl orange Cu(II) Pb(II) Zn(II) Cu(II) Pb(II) Zn(II) Direct red  Cd(II) Ni(II) Cr(III) Cr(VI) Cu(II)

Acid red  Direct red  Reactive yellow  Cr(VI) Cu(II) Cr(III) Cr(VI) Cu(II) Hg(II) F Reactive black  Reactive blue  Acid red 

Adsorption capacity (mg/g) . . . . . .          . . . . . .  .  . . . . .    . . . . . . .    

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5 Biopolymers as a versatile tool

Table .: (continued) Biopolymer and biopolymer composite as Pollutants (metal ions and dyes) adsorbents as adsorbate Chitosan/alginate Chitosan/calcium alginate Chitosan/cellulose

Chitosan/cotton fibers

Chitosan/graphene oxide(animation) Chitosan/montmorillonite Chitosan/polyurethane

Chitosan/PVC Chitosan/activated clay Chitosan/oil palm Gelatin/chitosan

Guar gum (with amides) Starch-graft-poly acrylic acid

Dialdehyde -aminophenanthroline starch

Oxidized starch

Cu(II) Ni(II) Cu(II) Zn(II) Cr(VI) Ni(II) Pb(II) Hg(II) Cu(II) Ni(II) Pb(II) Cd(II) Au(III) Acid yellow  Congo red Cr(VI) Acid violet  Cd(II) Cu(II) Cu(II) Ni(II) Methylene blue reactive dye RR Congo red Reactive blue  Cd(II) Cr(III) Hg(II) Pb(II)  Reactive blue  Cd(II) Cu(II) Pb(II) Ni(II) Zn(II) Cd(II Cu(II) Ni(II) Zn(II) Cd(II) Cu(II) Pb(II) Zn(II)

Adsorption capacity (mg/g) . . . . . . . . . . . . .  . . . . . . . .  .      . . . . . . . . . . . . .

5.3 Environmental application of biopolymers and biopolymer composites

109

Table .: (continued) Biopolymer and biopolymer composite as Pollutants (metal ions and dyes) adsorbents as adsorbate Succinylated starch

GO-starch (graphene oxide composite) Dithiocarbamate mesoporous starch Starch/acrylonitrile Starch/anamidoxime

Cross-linked amphoteric starch

(Methylation – .%) amino starch

Cross-linked cationic starch (maleic anionic group is .) Cross-linked cationic starch (maleic anionic group is .) Cross-linked cationic starch (maleic anionic group is .) Starch-cross-linked- chitosan Cross-linked starch phosphate carbamates sodium alginate

Sawdust/acrylic acid (carboxylation)

Straw (amination) Xanthan gum (with amides) Zein (amination)

Adsorption capacity (mg/g)

Cd(II) Cu(II) Pb(II) Cd(II) Cr(III) Pb(II) Cr(III) Pb(II) Cr(III) Pb(II) Ni(II) Cr(VI) Cu(II) Pb(II) Pb(II) Cr(VI) Cu(II) Cr(VI)

. . . . . . . . . . . . . . . . . .

Cu(II)

.

Pb(II)

.

Cu(II) Cd(II) Pb(II)

. . . . . . . .   

Cu(II) Ni(II) Cd(II) Acid green  Direct red  Reactive blue 

5.3.3 Biopolymer (nano) composites Several biopolymer composites have been developed based on their intercalation abilities with high molecular weight-based biopolymers in the last 2 decades. Some of the preferred biopolymers are cellulose, starch, chitosan, alginate, gelatin, sacran, and zein [31]. Such smart hybrid materials are highly promising in their gamut of applications, including environmental applications like the removal of oils, pesticides, heavy metals,

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5 Biopolymers as a versatile tool

dyes, and emerging contaminants in aqueous solutions. Additive manufacturing is a recent advancement and emerging technique with surplus promising features. Recent years have corroborated the employment of three-dimensional printing for producing products with tunable qualities like with determined pore structure and porosity, energy efficient, high-resolution products making biocompatible materials, and usage and inclusion of biomaterials, etc. Table 5.2 highlights the wide range of employed 3D printed biopolymer-based products and their environmental applications. Table 5.2 indicates the various 3D printed biopolymer-grafted components for water treatment applications. Figure 5.2 depicts the pros and snags of additive manufacturing techniques in the processing of selected biopolymers for water treatment applications [33]. Orta et al. [43] reported a detailed review on the significance of clay grafted bionanocomposite in environmental pollution mitigation and remediation. In this article, structural and functional properties including physicochemical attributes of the bionanocomposite and the preparation techniques and characterization methodology was discussed in detail. A majority of the clay minerals possess well-defined silicate assemblies (tetrahedral layers and octahedral layers) linked together with oxygen molecules. Such kinds of spatial arrangements will help to classify the clays, based on their characteristics and mineralogical composition.

5.3.4 Bio-energy The conversion of solid biowaste into simpler degradable materials and bioenergy has gained pace in the recent days. Such a methodology is considered the sustainable and environmentally benign alternative to the conventional petrochemical-based materials. In fact, there is a huge need to valorize the abundantly available biowaste generated from agro-industries, food processing units, and municipalities. Employing selected microbes either in the form of pure culture or in consortia or genetically modified will surely help produce biopolymers. Such renewable biopolymers are converted into valuable products in the form of biogas and biohydrogen. Such bioproducts are synthesized either intracellularly or extracellularly, during the biochemical conversion of organic waste by numerous bacterial strains under selected eco-settings. The most successful industrial microbial strains like Alcaligenes latus, Alcaligenes eutrophous, Bacillus sp. Recombinant Escherichia coli, Azotobacter chroococcum, Azotobacter vinelandii, Acotobacter beijerincki, Methylotrophs, Nocardia sp., Rhizobium sp., Pseudomonas sp., etc., are used in the bulk scale production of polyhydroxyalkanoates. To enhance the production of such biodegradable biopolymers from organic waste, the selection of suitable microbial strains, substrates and optimized working conditions are highly essential. As per the literature, it is evident that anaerobic digestion and photolytic fermentation process are highly efficient for making biohydrogen and biogas at a reasonable cost. The combinatorial approach was also found to be promising and novel in synthesizing

Chitosan-diacrylated PluronicF- Polycaprolactone – sodium alginate Sodium alginate-nanoclay-gpoly(acrylic acid) PLA – Cu-metal organic frameworks PLA – carbon black

Alginate

Cellulose acetate (CA)

Adsorption

Monolithic filter Scaffold

Cu (II) removal Amoxicillin removal

Adsorption Adsorption Filtration Demulsification and filtration Filtration Filtration

Cylindrical sorbent Monolithic filter Mesh Mesh Mesh Membrane

Adsorption

Mesh

Pb (II), Cu (II), Cd (II), Scaffold Hg (I) removal Cu (I) removal Various D models (tree, Adsorption algae, plateshape) Pb (II) removal Scaffold Adsorption

Photocatalytic degradation Adsorption

Water treatment mechanism

Printed component

Water treatment application

Malachite green removal Volatile organic compounds removal PLA – iron (III) oxide As (III) removal PLA – dopamine/polystyrene Oil separation nanoparticles PLA – iron powder/hydrogel Oil separation coating CA-ethyl acetate Oil separation CA-polyvinyl alcohol/silica Oil separation nanoparticles

Chitosan-acrylate-based polymer Chitosan – TiO

Chitosan

PLA

Composition

Biocomponent

Gel printing Gel printing

Fused deposition modelling

Fused deposition modelling Fused deposition modelling

Fused deposition modelling

Fused deposition modelling

[]

Fused deposition modelling, D pen, growing robot Gel printing

[] []

[]

[]

[]

[]

[]

[]

[]

[]

References

Gel printing

Gel printing

Stereolithography

Printing method

Table .: D printed bio-based components for water treatment applications (Reproduced from Fijol et al. [] with permission, copyright © , Elsevier publications).

5.3 Environmental application of biopolymers and biopolymer composites

111

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5 Biopolymers as a versatile tool

Figure 5.2: Merits and demerits of additive manufacturing techniques used in processing the selected biopolymers for water treatment applications (Reproduced from Fijol et al. [33], with permission, copyright © 2020, Elsevier publications).

biopolymers, which are used as precursors in the bioplastic manufacturing industries. Some of them are as listed: aliphatic polyesters, polysaccharides, polylactides, polyhydroxanotes, etc. According to [44]; the overall bioenergy production based on anaerobic digestion was reported as 379.769 kWh per year for biomethane. Especially the waste generated from the textile, paper, and cardboard industries is enriched with cellulose. Even, municipal solid waste also possesses some reasonable amount of cellulose, but it is not useful owing to the segregation and separation issues. These cellulose wastes hold high carbon–nitrogen (C/N) ratios around 173/1 to 1000/1 [45]. Owing to its combustible and convertible nature, hydrogen secured a strong place as a clean energy source. Moreover, the production of biohydrogen is almost similar to the biogas production process and the precursors employed in it. Biogas or biohydrogen may be produced by inhibiting the hydrogen using microbes like methanogens and homoacetogens through thermal exposure. Such thermal treatment is not applicable for several spore forming bacterial strains classified under the following species as listed: Thermoanaerobacteriacea, Clostridiaceae, Sporolactobacillaceae, Streptococcaceae, and Lachnospiracae are also employed. Senthil et al. (2022) reported a novel work on synthesizing bioenergy by using the leather waste and its fleshing, blended with graphene oxide, nanocellulose biopolymer, and glycerol. Through chemical polymerization under alkaline condition, the blend was prepared homogenously. The highest energy value observed at 1.2 V was 0.53 mA/cm2.

5.4 Future prospects

113

5.3.5 Cost analysis For any environmental pollution mitigation process, financial requirements, and cost analysis are considered and evaluated. This is a critical step in the remediation and recycling process. For example, in the adsorption process, the overall cost required for the process is considered and evaluated based on the adsorbent employed, its abundancy, and regeneration plausibility. Facile adsorbents prepared from natural biopolymers are exclusive in terms of efficacy for hazardous contaminant remediation. Some researchers have evaluated the expensiveness of chitosan biopolymer adsorbents in the employed remedial process. In General, cost analysis is performed for a raw substrate and its excipients, energy requirements, and finally worker/labor salary. Especially in the production of chitosan, labor and energy costs play a crucial role. The basic raw substrates and other excipients used during formulation covers around 23% and rest of the 70% covers the labor cost of the total cost. Usually, the price of any functionalized or customized products with other essential excipients would be more than the normal cost, owing to the addition of other additives and its grades [46, 50]. Another study demonstrated by [47] highlights the cost analysis for fluoride adsorption using the fabricated biopolymer composites using pectin and alginic acid including few additive analytical grade excipients (i.e., Fe–Al–Ni loaded pectin (PFAN) composite – USD 58.18 per kilogram and for Fe–Al–Ni-loaded alginate (AFAN) composite – USD 67.87 per kilogram) [48]. Analyzed the cost efficacy of the fabricated polyvinyl chloride membranes from waste products with gum Arabic biopolymer exhibited the/least cost in organic matter processing and compared with traditional synthetic membranes. Another recent study reported by [49, 51, 52, 53] demonstrated the efficacy of fabricated starch-based membrane with commercially available synthetic polymer membranes. In this study, chicken feather incorporated with polyethylsulfone membrane exhibited promising chemical oxygen demand (COD) reduction and toxic pollutants up to 30 times when compared with commercially available Nafion membrane.

5.4 Future prospects Biodegradable polymers have become ideal materials for a plethora of sectors like agriculture, medicine, automotive, and packaging industries. These polymers are considered green assets with flexible features to meet out the specific needs. Additionally, biopolymers release/emit negligible amounts of carbon dioxide gas during the production process. Similarly, after utilization also, biopolymers decompose in to organic matter. Compared with synthetic plastics, biodegradable plastics have gained remarkable attention owing to the consumer’s environmental responsibility. Biopolymers can be blended with any flexible filler materials at nanoscale will help mimick the complex native extracellular matrix and attain desired attributes. Biopolymer and its composites

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are highly familiar for contaminant mitigation and recovery. Particularly in oil-spilled sites, biopolymers are employed to boost the performance of oil recovery. Olabode et al. (2020) reported the efficiency of Solanum tuberosum based biopolymer solution as 60% during an oil recovery flooding test. Biopolymers are promising and can be customized as functional stabilizers and enhancers in some geotechnical events. However, more studies must authenticate the tailorable qualities and their feasibility in industrial applications.

5.5 Conclusions Biopolymers are considered an incredible treasure, owing to the low carbon foot print and innumerable unique and tailorable attributes like toxic less, inexpensive, sustainable, renewable, biocompatible, biodegradable, etc., biopolymers, and its composites are used in various applications including environmental remediation. These new-gen green materials exhibit remarkable progress toward establishing a sustainable environment. These natural derived/fabricated green assets play a vital role as a promising alternative and replace anthropogenic polymers with undesirable attributes leading to environmental pollution. Some of these biopolymers are synthesized from biowaste that surpass other sources in terms of sustainability and cost. Proper selection manufacturing technique and addition of appropriate filler/nanofiller materials (organic/inorganic) may enhance the biopolymer attributes to make an exceptional biocomposite/bionanocomposite with desirable features. To achieve the desirable qualities, fabrication techniques like extrusion, grafting and injection-based techniques are employed to improvise the quality and to retain the shelf life and mechanical properties during the manufacturing process. Biopolymers are efficient sorbent materials with exclusive functional attributes, porosity, and surface heterogeneity. Hence, it is widely employed in environmental pollution mitigation. Likewise, biopolymer membranes are also possessing promising attributes with enhanced adsorption efficacy. To improvise the adsorption range furthermore, inclusion of functional additives with biopolymers may be preferred. Apart from their environmental applications, biopolymers are widely used in food, biomedical, pharmaceutical industries, owing to its green attributes. Future scope and its avenues are related to large-scale production of inexpensive biopolymers for industrial, energy, and environmental applications.

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41. Lagalante LA, Lagalante AJ, Lagalante AF. 3D printed solid-phase extraction sorbents for removal of volatile organic compounds from water. J Water Process Eng 2020;35:101194. 42. Xing R, Huang R, Qi W, Su R, He Z. Three-dimensionally printed bioinspired superhydrophobic PLA membrane for oil-water separation. AIChE J 2018;64:3700–8. 43. Fischer S, Thümmler K, Volkert B, Hettrich K, Schmidt I, Fischer K. Properties and applications of cellulose acetate. Macromol Symp 2008;262:89–96. 44. Koh JJ, Lim GJH, Zhou X, Zhang X, Ding J, He C. 3D-printed anti-fouling cellulose mesh for highly efficient oil/ water separation applications. ACS Appl Mater Interfaces 2019;11:13787–95. 45. Li X, Shan H, Zhang W, Li B. 3D printed robust superhydrophilic and underwater superoleophobic composite membrane for high efficient oil/water separation. Sep Purif Technol 2020;237:116324. 46. Orta M, Del M, Martín J, Santos JL, Aparicio I, Medina-Carrasco S, et al. Biopolymer-clay nanocomposites as novel and ecofriendly adsorbents for environmental remediation. Appl Clay Sci 2020;198:105838. 47. Dung TNB, Sen B, Chen CC, Kumar G, Lin CY. Food waste to bioenergy via anaerobic processes. Energy Proc 2014;61:307–12. 48. Zhang P, Zeng G, Zhang G, Li Y, Zhang B, Fan M. Anaerobic co-digestion of biosolids and organic fraction of municipal solid waste by sequencing batch process. Fuel Process Technol 2008;89:485–9. 49. Gkika DA, Liakos EV, Vordos N, Kontogoulidou C, Magafas L, Bikiaris DN, et al. Cost estimation of polymeric adsorbents. Polymers 2019;11:925. 50. Argüelles-Monal WM, Lizardi-Mendoza J, Fernandez-Quiroz D, Recillas-Mota MT, Montiel-Herrera M. Chitosan derivatives: introducing new functionalities with a controlled molecular architecture for innovative materials. Polym 2018;10:1–33. 51. Raghav S, Kumar D. Comparative kinetics and thermodynamic studies of fluoride adsorption by two novel synthesized biopolymer composites. Carbohydr Polym 2019;203:430–40. 52. Aji MM, Narendran S, Purkait MK, Katiyar V. Biopolymer (gum Arabic) incorporation in waste polyvinylchloride membrane for the enhancement of hydrophilicity and natural organic matter removal in water. J Water Proc Eng 2020;38:101569. 53. Nagar H, Aniya V, Saranya C. Economic assessment and application of bio-composite membranes in microbial fuel cell. J Environ Chem Eng 2021;9:106477.

Krishnanjana Nambiar, Saravana Kumari P, Dheeksha Devaraj and Murugan Sevanan*

6 Development of biopolymers from microbes and their environmental applications Abstract: Inventions begin with the invasion of humans and furnish a better livelihood. In some cases, it turns out to be imperative. The environmental issues of using synthetic polymers, including bio-incompatibility, toxicity, high cost, poor hydrophilicity, and pro-inflammatory degradation of byproducts, are increasing the need for and application of eco-friendly, alternative polymeric substances from medicine to biotechnology, which includes the industries of medicine, cosmetics, confectionery, wastewater treatment, etc., as tissue scaffolds, wound dressings, drug packaging material, dermal fillers, moisturising cream, carriers, sun protectants, antiperspirants, and deodorants; gelling agents; stabilisers, emulsifiers, photographic films, etc. Biopolymers are available in different compounds, produced by microbes, plants, and animals, where microbes, for example, Pseudomonas aeruginosa and Kamagataeibacter sucrofermetans, retain these compounds at an exorbitant level, helping them to sustain adverse conditions. Moreover, compared to plant and animal biopolymers, microbial biopolymers are preferred due to their ease of production, design, and processing at an industrial levels. In this regard, polyhydroxyalkanoates (PHA) and poly-3-hydroxybutyrate (PHB) have together attained assiduity for their biodegradable properties and possess similar features as petrochemical-based polymers, commonly synthetic polymers like polyethylene, polypropylene, etc. This attributes to its non-toxic nature, i.e., it behaves eco-friendly by degrading the components through a carbonneutral energy cycle to carbon dioxide and water, which lessens the dependence on petroleum-based polymers. This chapter contemplates the methods to develop biopolymers from microbes and their environmental applications, focusing on the confiscation of heavy metals, organic dyes or oils, etc. Keywords: bioplastics; biopolymers; biosurfactants; environmental application; microorganisms.

*Corresponding author: Murugan Sevanan, Department of Biotechnology, Karunya Institute of Technology and Sciences, Deemed to be University, Coimbatore, India, E-mail: [email protected] Krishnanjana Nambiar and Dheeksha Devaraj, Department of Biotechnology, Karunya Institute of Technology and Sciences, Deemed to be University, Coimbatore, India Saravana Kumari P, Department of Microbiology, Rathnavel Subramaniam College of Arts and Science, Coimbatore, India As per De Gruyter’s policy this article has previously been published in the journal Physical Sciences Reviews. Please cite as: K. Nambiar, S. Kumari P, D. Devaraj and M. Sevanan “Development of biopolymers from microbes and their environmental applications” Physical Sciences Reviews [Online] 2023. DOI: 10.1515/psr-2022-0219 | https://doi.org/10.1515/9783110987188-006

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6.1 Introduction The ever-rising environmental issues have given the concern to develop methods through which the environmental impacts can be controlled. Among these, the development of microbial biopolymers has attained great concern through the time period due to their sustainable characteristics. Among the biopolymer assemblers, microbes can grow in inexpensive carbon, and exorbitant purification methods and can directly induce modifications in their genome to produce desired protein, i.e., produces recombinant protein. The biopolymers produced in the microbes contribute to their virulent properties [1]; at the same time have the potential of ease of biodegradability, effectiveness at extreme conditions, non-toxicity, and eco-friendliness [2]. The functions of these biopolymers include helping them to grow and available at variety of form to use in a wide range of environmental conditions, and biological roles like storing energy, adhesion to the surface, protection, shielding, endurance, and translocation. These are produced depending upon the environmental stimuli and lead to the production of extracellular polymeric substances, also known as exopolysaccharides (EPS) [3], which are important for the formation of biofilms, and arrangement of microbes in a stratified layers of microbial cells in the EPS. Dental plaque caused by Streptococcus mutans and various lactobacilli associated with lesion progression is the most common examples. Hence the EPS production is very vast when compared to the intracellular polymeric substances (IPS). The bacterial pathogen, Staphylococcus aureus produces nuclease and protease that regulates the production of biofilms, wherein, nuclease can have a negative impact on biofilm production hence reducing its therapeutic recalcitrance [4]. Also, nuclease helps in absconding the neutrophil extracellular traps (NETs), which entraps the pathogens that infect the body, causing adverse effects and helping S. aureus to escape phagocytosis. Among the biopolymeric substances [5] like polyamides, polysaccharides, polyphosphates, and polyesters; starch, dextran, alginates, chitosan, cellulose, pullulan, carrageenan, hyaluronic acid, pectin, levan and so on, are mostly studied since they are ubiquitous and found to be non-toxic natural biodegradable biopolymers produced by Absidia glauca, Acetobacter xylinum, Ascophyllum nodosum, Aspergillus niger, Azotobacter sp., Gongronella butleri, Gracilaria sp., Laminaria hyperborea, Leuconostoc mesenteroides, Macrocystis pyrifera, Mucor rouxii, Pleurotus sajor-caju, Pseudomonas sp., etc (Table 6.1). These pave its application in the production of gelling agents, strong chelating agent, absorbent of organic (dyes) and inorganic (heavy metals) materials from water, soil strengthener, and a sealer in concrete cracks, capacitors, in food commodities, photographic films, pharmaceuticals, and in tertiary oil recovery serves as solidifier, stabilizers, thickeners, and emulsifiers [5], a method of extraction of oil from the oil field. They also act as biologically active oligomers with therapeutic applications like the formation of new blood cells (angiogenesis), hindering the tumor, or can induce pro-inflammatory

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Table .: Factors Influencing the process of polymerization. Parameters

Functions

Substrate hitching

Glycosyltransferase enzyme facilitate the attachment/adherence of monomers and progressive polymerization are induced by the lipid-linked oligosaccharides. Monomers are linked by covalent bonds or double bond or epimerization or acetylation to make it tough to break. For example, in P. aeruginosa, the polymerization of the alginate is linked with the tempering of enzymes. A chain-length protein; that controls the degree of polymerization. For example, the chain measurement of O-antigen is smaller in presence of Wzz than in its absence. These possess a role in the polymerization of biopolymer, leading to modifications in its structural organization and molecular mass. For example, accretion of molecular mass of hyaluronate with high substrate concentration. High the amount of synthesis for the substrates eventually reduces the length of polymers.

Coupling of polymerization Wzz protein Substrate concentration Number of copy numbers

mediators, anti-inflammatory substances, tissue scaffolds, wound dressing, drug packaging material, dermal fillers, moisturizing cream, carriers, sun products, antiperspirants and deodorants, and anti-biofilm agents efficiently [6]. These substantiated characteristics of the biopolymers have helped scientists to analyze the multi-protein which was required for the biosynthesis and secretion of biopolymers, the strategic methods for enhancing the production of target biopolymers and in turn to yield better materialistic properties from this modified EPS. The knowledge in genomic sequencing and functional genomics has also paved the way for the need-based, alternative methods in synthesis and mass production of newer biopolymers. The advancements in studies of metabolic engineering directed towards the production of unnatural polymers with unique properties [7, 8]. The commercialization of microbial EPSs is high, hence stating the relationship between biosynthesis mechanisms and the related metabolic pathways to control the cost and which in turn enhances productivity [9]. This chapter deals with biosynthesis, metabolic engineering, production method, and environmental applications in detail in upcoming sessions. The biopolymers cellulose (Acetobacter xylinum, Escherichia Macrocystis pyrifera, coli), alginate (Ascophyllum nodosum, Laminaria hyperborea, Pseudomonas aeruginosa), Chitosan (Azotobacter sp, Absidia sp.), pullulan (A. niger Aureobasidium pullulans Glauca sp., Mucor rouxii, G. butleri, Pleurotus sajorcaju), Carrageenan (rhodophyceae – Gracilaria sp.), gellan (Sphingomonas elodea), dextran (Enteroobacter cloacae, Klebsiella pnuemoniae), lactic acid bacteria (LAB), L. mesenteroides), hyaluronic acid (Streptococcus pyogenes and Bacillus cereus G9241), sialic acid (N-acetyl neuraminic acid (Neisseria meningitides), polyamides (Bacillus anthracis), polyhydroxy alkanoates (Aeromonas hydrophila, Alcaligenes latus, Pseudomonas putida, and Ralstonia eutropha), Polyhydroxy butyrate (Rhodospirillum rubrum

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and Rubrivivax gelatinosus), Poly lactic acid (Lactobacillus delbrueckii, L.cornyniformis), Xanthan (Xanthomonas campestris), acetate (Klebsiella spp.), and hydroxybutanoate (Rhizobium trifolii; R. leguminosarum etc.) are commercially known to produce valuable biopolymers.

6.1.1 Biosynthetic pathway and regulation of microbial biopolymers Microbial biopolymers are chemically polysaccharides, polyamides, polyphosphates, and polyesters. The constituted diversity in polymers with their morphology and other characteristics recruits different enzymes and proteins which are responsible for differences in biosynthesis gene clusters (BGS). The genes regulate and determine the length of chain, assembly of repeat units, polymerization, and export [1, 6, 7]. Genes (for example pha A, pha B, and pha C are used for the synthesis of PHB) encoding the enzymes for the polymerization are clustered in a major operon which will be controlled by potent specific promoters during the entire transcription of BGS [6]. As the first step, these specific enzymes activate the polymer precursors, which are mainly like ADP-Glucose pyrophosphorylase that produce ADP-glucose from nucleotide diphosphate sugars, sugar acids like GDP-mannuronic acid and sugar derivative like UDP-N-acetylglucosamine acting as the direct precursors for the biopolymer synthesis, from Figure (6.1.a–6.1.c). A two-component signal transduction pathway (key mediators of the bacterial signal system), quorum sensing (gene regulation helps in detection and subsequent response to the cell density) which regulates the higher production of 3-oxo-dodecanoy homoserine lactone for biofilm production, alternatively σ factors and anti-σ factors of RNA polymerase, as well as integration of host factor-dependent (IHF – ability to bind DNA and bend the proteins with collateral roles in the structural organization of the DNA and regulates the transcription in Gram-negative bacteria) and cyclic di-GMP-dependent process regulates the transcriptional process in BGS [10]. Environmental stimulus results in mediating responses by activating functionally relevant genes at the transcription level through the transcription factors (TF), where TFs with comprehended sigma (σ) factors are the subunits of RNA polymerases which with the regulatory proteins bind upstream to the genes responsible for the biosynthesis. Anti-σ factors hold to some of the σ factors which are released in response to external stimuli. Overall mechanisms governing the biopolymer synthesis in bacteria recognized as small non-coding RNAs, components of RNA polymerase, regulatory RNA binding proteins, and secondary messengers such as cyclic di-guanosine-mono-phosphate and cyclic di-adenosine mono phosphate that are involved in signal processing and complex regulatory networks [6].

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Figure 6.1: Common production pathways of biopolymer. (a) Production pathway for PHA and PHB, (b) xanthan and (c) hyaluronic acid.

6.1.1.1 Synthesis of high molecular weight biopolymers Commercialization of microbial biopolymers consists of enzymes that can synthesize biopolymers of high molecular mass, where the chemical synthesis is insipid, costly, and the production is possible with low molecular mass raw materials [1, 6]. Many bacterial EPSs have high molecular mass, which can also impact the characteristics of the polymer, pathogenicity, evasion into the host, and medical applications. In organic polymer synthesis, bacterial polysaccharides with high molecular mass have attained great demand as they are microporous and possess high moisture retention property, short gelling capability, and durability in physical conditions. Consider the examples like fucose having a rising demand in the pharmaceutical and nutraceutical industry as a precursor and the precursor of PHA having a role in antibiotic development [11]. Hence, the molecular mass of the biopolymers is determined through the “magnitude of polymerization of monomeric precursors in a polymer”. The factors like substrate hitching, coupling, Wzz protein, substrate concentration, and copy numbers are depicted in Table 6.1. 6.1.1.2 Bacterial synthesis of exopolysaccharides EPS comprises various biopolymers of high molecular mass supplied with a carbon source like glucose, sucrose, etc., under limited conditions. The availability of sugar precursors and enzyme expressivity is modulated by metabolic and physiological parameters. In response to the stimulus, biopolymers are produced intracellularly; on

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subsequent production of biopolymers, these are exported to an exogenous environment, excluding monopolysaccharides like dextran, mutans, and levan are produced and secreted outside the cell by the enzymes, the general biosynthesis of biopolymers are given in Figure 6.1. The enzymes involved the process are located in different sections of the cell and are characterized into based on their function into 4 classes; [1, 7, 9]. The hexokinase and related group of intracellular enzyme that phosphorylates glucose to glucose-6-phosphate (G6P) depicted in Figure 6.1, and has a role in glycolytic pathway also. The group translocating (second group) enzymes, catalyze the efficient switching of monomer to sugar-nucleotide complex. For example, Uridine-5′-diphosphate (UDP)-glucose phosphorylase converts Glu-1-P to UDP-Glu (Figure 6.1.b), one of the key enzymes in EPS pathway. The third group is the glycosyltransferases (GTFs), found in periplasmic membrane of the cell, and facilitates the exporting of sugar nucleotides to a growing biopolymer chain attached to a glycosyl lipid carrier. The fourth group role as a polymerization of macromolecules, found in the periplasmic membrane. General metabolic pathways involved in biopolymers are of four types. The polysaccharide synthesis pathway, mediates the synthesis of dextrans, hyaluronate, and levans since these are less complex and require solitary enzyme. At times, dextrans and levans are synthesized extracellularly by sugar transferases that lead to the conversion of disaccharides to polysaccharides, and this yields energy during the hydrolysis of glycosidic bonds of disaccharides. Wzx/Wzy dependent pathway, in which the polysaccharides like xanthan are synthesized where GTFs assemble as repeating elements with their corresponding linked to lipid carriers, and span across the plasma membrane. Synthase-dependent pathway mediates the synthesis of non-repeated polysaccharides include alginate and cellulose, mediated by multi-protein complexes, include sugar (monomer)-modifying enzymes, polymerases, copolymerase, and secretary subunits. Secretion of modified polysaccharides assisted chemical reactions like acetylation, deacetylation, epimerization, and phosphoethanolamine (pEtN) addition that occur during the translocation of emerging polymers across the membrane [7, 9]. And the ATP-Binding Cassette (ABC) transporter-dependent pathway or Wzx/Wzy independent pathways. These are responsible for the export of a extensive group of oligo-and polysaccharides, especially glycoconjugates and polysaccharides co-polymerase (PCP) [7, 9]. The first three mechanisms, from Table 6.3, activate precursor molecules by corresponding enzymes which in turn produce sugars or sugar acids. The addition of monosaccharides in the extracellular production pathway by disunion of di-or trisaccharides elongates the polymer [12]. Commercially important EPS production and export occur through Wzx/Wzy dependent pathway and ABC transporter pathways, these exports the polymer across the membrane. In the second mechanism Wzy protein is involved in repeating units

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when the activated sugars via GTFs are linked to the lipid carrier. While in mechanism ABC transporter pathway, Wza, Wzb and Wzc genes encodes for outer membrane protein, acid phosphatase and inner membrane tyrosinase respectively for the high level polymerization and surface assembly at the cytoplasmic side of the cell membrane. In the synthase dependent pathway, EPS secretion is independent of the lipid acceptor hence for translocation of the polymer, it is independent of flippase protein [9]. The membrane embedded GTF, a single synthase, performs polymerization followed by translocation, where these assemble homopolymers requiring only a single sugar precursor, for example curdlan or bacterial cellulose [6, 9]. Inner-membrane receptors in Gram-negative (c) bacterial secretion systems such as, in P. aeruginosa alginate production and Gluconacetobacter xylinus cellulose production regulate the polymerization. Regardless of their structural variation, polymerization takes place in the external environment, estimates the uncomplicated method of production as well as is independent of the central carbon metabolic system. Sugar nucleotide precursors produce irregular or regular homo-and heteropolysaccharides through internal biosynthesis and are also involved in the production of the building blocks of cell walls; hence this justifies its importance in growth. The intermediates from the central carbon system are the direct precursors where these along with translocating intermediate molecules for the synthesis of repeating units include sugar nucleotides as nucleoside diphosphate sugars (as ADP-glucose), nucleoside diphosphate sugar acids (GDP-mannuronic acid), and nucleoside diphosphate sugar derivatives (such as UDP-glucose, UDP-N-acetylglucosamine, UDP-galactose, deoxythymidine diphosphate (dTDP)-rhamnose) [13]. These sugars are transported in three different ways that include by the hydrolysis of ATP coupled with the translocation of sugar via the sugar transport, importing by coupled transporting of ions and solutes through phosphoenolpyruvate (PEP) transfer system. The heteropolysaccharide biosynthesis is catalyzed by GTFs depending upon the substrate type, where the uptake of sugar by an active or passive transport mechanism by the organism intracellularly is considered as the initial phase in the synthesis [7, 9]. Subsequently, the sugar nucleotides are formed in the cytoplasm through glycolysis with the catabolism of the substrate. The activated precursor synthesis involves the production of nucleoside diphosphate sugars (NDP-sugars), consequent of sugar phosphorylation. Finally, the EPS is secreted in the cytoplasm for the final sequence in the polymerization of repeated units [14]. GTFs extracellularly synthesize homopolysaccharides, a class of glucansucrase, and are dissimilar to Leloir-type GTFs that exploit sucrose as a donor molecule. These enzymes are responsible for the catalyzing transfer of monosaccharides that generate glycosidic bonds through precursors activated to an acceptor molecule. The energy is released for transferring glycosyl residue and thus is utilized for polysaccharide production.

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6.2 Microbial biopolymers and its metabolic engineering 6.2.1 Technological advancements in metabolite engineering Biopolymers produced were permuted to some other compound depending on their application. These substantiate the importance of designing cell factories for novelbased biopolymer synthesis. The relevant genetic information included the complex cellular, metabolic and experimentation processes. Although, the synthesis is engaged in the complex synthesis process from gene expression to the facilitating enzymes and proteins, key metabolism, and the controlling and signaling system, which leads to the intracellular association or extracellular release through the cell membrane/wall [6]. The industrially relevant cell factories quoted are like E.coli, R. eutropha, P. putida and A. latus are being used for the amalgamation of PHA and PHB [6, 15]. Bacillus subtilis for the mass production of hyaluronate for industrial needs [7, 16]. For the deployment of these miniaturized live factories various techniques are used and a few are listed in Table 6.2.

6.2.2 Production of novel bio-based polymers using synthetic biology and metabolic engineering (ME) For the extensive fabrication of biopolymers, control elements were generalized. A few of the control elements are depicted in Table 6.3. The advancements in the technologies for designing cell factories with synthetic biology, enzyme-mediated alternative production mechanisms, or reformation in biopolymers as well as chemical alterations have helped in the production of novel biopolymers. Genetic level perception has been routed to selective inhibition of virulence factors, which form targets for antimicrobial drugs. This states that the synthesis of biopolymers is related to the central metabolic pathway, which is an integration of carbon, nitrogen, and energy fluxes [6]. Knowledge of proteomics (proteins) and genomics (DNA databases) in combination with in-silico methods helped in understanding the metabolic pathways, functions, enzymes, and regulatory mechanisms. Hence, the MEs aim to intensify substrate and energy flux toward the synthesis of the desired biopolymer. Activated precursor synthesis is a high energyrequiring procedure that depends upon metabolic and primary cell functions. Determination of the redox state of the cell is crucial during amending the metabolic pathways and redirecting the metabolites towards the desired biosynthesis pathway, which is resolved by the factors like electron carriers (NADH and NAD+), oxygen

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Table .: Various metabolic engineering methodologies of biopolymer production. Metabolic Engineering technique

Uses

‘Design-build-test’ engineering technique developed to recreate the desired efficient cell factories. These have higher consistency and low-cost management. The flexible genetic elements involving promoters, ribosome binding site, orthogonal polymerases, terminators, untranslated regions, signal peptides putative stabilization modules, genetic effectors, and protein folding enhancers provide a dynamic platform for tuning the appropriate expression of the gene as well as for production of specific proteins. Bio-oscillators Mimics natural genetic clocks of organisms inducing periodical behavior of the system. Genetic switches (GS) GS are inducible or controllable striking advancements, where the tools such as T polymerase-based expression system, programmable T-based synthetic TFs, RiboTite system and CRISPR-Cas [] allows fine-tuned expression of endogenous or heterologous genes. CRISPR-Cas is used to manipulate several genes while CRISPR interferences redirect the metabolic flux towards the PHA biosynthesis. Toggle switches Stepwise function of ON and OFF. DNA foundries

Rational reprogramming

Inducible system

Biopolymer produced Pullulan nanoparticle and other polysaccharide nanoparticles [].

Glycolytic oscillators for locomotion [] Hyaluronic acid production through microbial cultures through genetic ON & OFF []

For activating capsule biosynthesis operons (CBP) for polysaccharide production (xanthan or glucan etc.) [] This was successfully achieved in Komaga- L-fucose, L-rhamnose are reprogrammed taeibacter rhaeticus iGEM which enhance for immunization []. the amalgamation of cellulosic materials. Broad-host-range derived vector are used in Cyanobacteria for producing renewable low-cost products like energy fuels. Recombinant production of hyaluronate, PHA’s, and poly-glutamic acid (γ-PGA) and cyanophycin are used for the reconstruction of pathways. To accurately control the expression or Xylan induced into microbial cells that can manufacture of desired polymers in degrade chemicals and renewable fuels response to inputs or inducers, light[]. sensing or temperature-sensing sensors are used. One of the examples of photo inducible genes used in E. coli and

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Table .: (continued) Metabolic Engineering technique

Riboswitches

Protospacer –adjacent motif (PAM) Logic plates

FENIX

Uses P. aeruginosa was isolated from Cyanobacteria, a functional light-sensing system. A kind of RNA sequence, which can resize ′ UTR and bring in conformational changes by binding to a ligand that regulates the transcription or translation. The sequence ′-NGG – ′ can follow the target sequence in the CRISPR-Cas system.

Biopolymer produced

csrA gene is regulated by Riboswitches to control glycogen synthesis as well as biofilm formation [].

To transcript various enzymes for oxalate synthesis for the high production Scleroglucan []. Consist of multiple sensors and actuators Xylose and glucose elaboration can be which can perform logical operations. predicted without considering any other factors []. Tagging of a short, hybrid and synthetic Independent regulation of target protein sequence of NIa/SsrA at the C-terminal end and its induction []. of the polypeptide helps in the degradation of the specific sequence.

availability, the uptake of carbon and nitrogen and the kinetics of the enzymes involved [6]. These kinds of control elements should enhance biosynthesis of polymers and not for the cell concentration or by-products. The integration of synthetic biology and ME using automated tools and software has linked high throughput measurements of cellular mass and omics data (the novel comprehensive approach of analysis of genetic or molecular profiles of humans and other microorganisms) and has tremendously advancements in deployment of cell factories and produced products [17, 19]. In-silico methods and computational automation supports synthetic biology and these include, iGEM registry is the availability of biological parts that are tested by the users and used predominantly for developing projects [6], RBS calculator and RBS designer to control over protein expression, COBRA and Cameo, for gene target identification, gene knockout and over expression of gene and macromolecular expression models, for the computation of optimal protein concentration and composition controlling in growing cell [6, 17]. The complex biosynthetic pathway for biopolymers can be analyzed using computational models, and the inter-relative reactions between biosynthesis and metabolism can improve the (bioengineering) strains [6, 17, 20, 21]. In-silico genomescale metabolic flux analysis, ME identified the targets which could enhance the productivity of poly-lactic acid (PLA) and poly(3-hydroxybutyrate-co-lactate). Through these methodologies E. coli strains have also achieved the non-tailor made polymer

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Table .: Control elements for biopolymer production. Control elements

Flux

Hyaluronate precursors – ATP levels

The electron carriers for the hyaluronate production are recycled. Electron transport chain Improved the respiratory electron transport chain, ATP synthesis and nitrate metabolism for the better yield of γ-PGA []. Multiple gene deletions and additions in E. coli Lactate consumption coupled with its conversion to GDP-fucose mediated by blocking the competing colonic acid pathways led to the yield of fucosylated N-acetyllactosamine oligosaccharides. Transcription activator-like effectors (TAL Secreted by Xanthomonas sp., which activates individual effectors) genes upon recognition of plant DNA sequences to aid bacterial infections []. Knocking out specific genes like ackA, ppc, and Replacement of promoters IdhA and acs genes with trc adhE in E. coli promoter which can enhance the PLA production than before [, ]. Introduction of ackA gene from E. coli and P. aer- Investigated by genome-scale metabolic model and its uginosa in P. putida survivability in stressed anaerobic conditions for high production of PHA [, ]. High productivity and expression of eps genes in high salt Drafting genome of Halomonas maura for concentration during stationary state which was found to analyzing the genes responsible for PHA synthesis increase PHA production [, ]. Disruption of alcohol dehydrogenase with gene Required for the improved production of ,-butanediol deletion in Saccharomyces cerevisiae [, ].

production namely poly(lactate-co-glycolate) which consist of a wide range of materialistic characteristics. Rational engineering significantly improvised the vast array of product production in cell factories such as in the development of halophilic bacterium Halomonas smyrnensis AAD6 used for the production of levan, osmoprotectants, Pelexopolysaccharide, and PHAs. Since this tool is cost effective with its sterilization, it just requires a halophilic medium i.e., containing high salt that can prevent the unwanted growth of other prevailing microbes. And in pathway construction, the in silico pathway helps in rapid construction and optimization of multiple gene pathways for higher production.

6.2.3 Comparison of microbial biopolymer over synthetic polymer The comparison can be done on the basis of social, economic and environmental aspects include; biopolymers are biodegradable and emit do not release CO2 during the degradation, whereas synthetic polymers are non-biodegradable and emit high CO2

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during disposal. Synthetic polymers are persistent in nature, non-renewable, obtained from petroleum hydrocarbons by chemical process along with toxic byproducts, easy for further modification, high cost and poor incompatibility. Biopolymers are ecofriendly, renewable, obtained from cheap raw materials, highly specific, and cannot be chemically modified [22]. 6.2.3.1 Biodegradability The change in the chemical structure of degradable biopolymers initiated by the extracellular enzymes secreted by the fungi, bacteria, actinomycetes and yeast. Primarily, microbial enzymes acts on the side chains of the biopolymer and removes the complex structures into simple compounds, which may lead to loss of textural and mechanized properties stipulated by the American Society for Testing Materials (ASTM) and International Standards Organization (ISO). Further biodegradation of biopolymer rendered by the cellular uptake and rapid degradation by naturally occurring Mo’s enzymatic or oxido-reduction reactions, and hydrolytically degradable [19, 23]. Thus, the process of degradation by the Mo’s depends on the polymer. Further complex structures are converted into simple minerals by normal metabolic pathway by the individual microorganism or in synergy. The rate of mineralization depends on the complexity of the biopolymer, presence of other organic factors, physical (abiotic) factors, diversity of microbes, cofactors of the enzymes (ATP, metal ions, vitamins and water). Esterases, lipase, proteases, alkaline phosphatases, lyases, group translocation enzymes, etc. Similarly the mechanical damage and photo degradation in the biopolymer such as shear forces, tension, compression, photoionization, Norrish reactions and Norrish II reactions increases the rate of degradation. Though the biopolymers are synthesized through microbial fermentation, which can substitute synthetic plastics with similar thermosetting and water-resistance characteristics. For example, PHA is produced with nutrient deficiency but is brittle and expensive when used alone. So, blended with polylactic acid (PLA), which complements hydrophobicity to the polymer, whereas chitosan is dissolved in acidic solution before incorporation into biodegradable polymer films [19, 23]. 6.2.3.2 Economic aspects Even though thermoplastics can be recycled and reused, it also poses practical limitations. Hence the recyclability of synthetic polymer is a major issue; also with its poor degradability, causes of its biomagnification problem in the environment. Due to the lack of studies on biopolymer degradation, the economic scale for degradability has not been analyzed. Although, these do not require recycling since they are degradable or compostable; will be decomposed by industrial composting

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under specific conditions. Flash co-pyrolysis (FCP) of biomass and waste biopolymers synergistically improved the pyrolysis and even if the biopolymers enter the plastic industry, FCP is a commercial process opted for short term with high value end products [6, 23]. 6.2.3.3 Life cycle assessment (LCA) A mechanism developed to measure and compare the environmental credentials of the products like biopolymers which include the input and output as the distribution, production phase, use, and final recycling or disposal of the product. The most used system includes cradle-to-gate (CGt) and cradle-to-grave (CGv). CGt involves steps from extraction of raw materials, conversion steps till the product is delivered. Hence CGt is analyzed by material producers. CGv includes CGt, usage and disposal phases [22]. CGt of the biopolymers have impacts in abiotic diminution, global warming, and human toxicity, and ozone layer exhaustion, ecological destruction of freshwater and marine ecosystem, terrestrial ecotoxicity, acidification, photochemical oxidation, and eutrophication [23, 24]. Biopolymers do not cause any of the impacts listed above compared to petroleum-derived polymers like polyethylene, high-molecular mass polyethylene, and low-density polyethylene concerning global warming. With improper end-of-life treatments of biopolymers, they can have higher impacts on the environment when compared to petroleum-derived polymers. Hence better strategies are needed to be developed for being eco-friendly.

6.3 Environmental impacts The disposal of biopolymers with appropriate microbial contents like fungi, bacteria and actinomycetes in the soil helps in proper degradation and yield in with CO2, water, inorganic compounds and indistinguishable level of toxic compounds [19]. The odor emissions of the compost piles can be reduced by blending with compsotable plastics. For example, ammonia as a noxious gas produced during decomposition can be neutralized with the degradation of biodegradable plastics hence reduces the odor [23].

6.4 General production of biopolymers using microorganisms Bacterial metabolite such as, polysaccharides are overwhelmingly diverse due to their specific functional properties, structures and composition. These can be classified based

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on the cellular location as exopolysaccharides (examples like alginate, cellulose, CMC, dextran, galactans, hyaluronic acid, and colonic acid), capsular polysaccharides (examples like K30 antigen, xanthan, gellan) and intracellular polysaccharide (glycogen, PHA, and PHB). EPS biosynthesis is related to the establishment of biofilm growth.

6.4.1 Xanthan The first industrially used biopolymer from Gram-negative phytopathogenic bacteria X. campestris (X. campestris), which is a heteropolysaccharide composed of pentasaccharide. This consists of monomeric units of glucose, mannose, glucose-1-phosphate and glucuronic acid assembled over a polyphenol carrier of phosphate through a set of enzymatic reactions which includes monosaccharide-specific glycosyltransferases, ketal pyruvate transferase and acetyltransferases. Studies of X. campestris on protein expression, peptide-mass fingerprinting or de novo sequencing methods were used to identify the protein functions, pathogenicity and biosynthesis of xanthan [1, 9]. The parameters which influence the production are type of bioreactor and controlled conditions, medium, temperature, pH, and oxygen. The production of xanthan is carried out by inexpensive carbon sources like sucrose, sugarcane molasses and whey. The nitrogen sources like ammonium or nitrate salts are mostly suitable and others like yeast extract, soy meal peptone and soybean whey and it is estimated to have the best production of xanthan using cereal grains. It is important to maintain the optimal pH of 5 or else below this pH can drastically reduce the xanthan produced by the formation of organic acids [15, 25] with accumulation of xanthan. With the proper agitation and aeration at a temperature of 28–30 °C for 100 h, glucose is converted to xanthan.

6.4.2 Levan A naturally occurring polymer formed by D-fructosyl with β-(2–6) linkages between fructose rings, where the polymerization is carried out by levansucrase which catalyzes transfer of fructose residue from sucrose to levan releasing glucose residues. The strains producing levan are H. smyrnensis (H. smyrnensis), Zymomonas mobilis (Z. mobilis), Bacillus subtilis (B. subtilis), Azotobacter vinelandii (A. vinelandii), and Weisella cibaria (W. cibaria). H. smyrnensis was found to have high productivity in sucrose substitutes such as molasses as well as on other cheap biomass resources as a raw materials [9]. A. vinelandii productively produced levan to an amount of 14 g/L by growing on medium which consist of distillery eggs, milk whey permeate, and molasses. While W. cibaria growing in sucrose and lactose as carbon source resulted in 31 g/L of levan [1]; i.e., in stationary phase of quadrupled bioreactor. The culture medium inoculated over the sucrose medium was incubated on rotary shakers at 30 °C for a few days [24]. Being a homopolysaccharide;

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possess properties like high solubility in oil and water, strong gelling property, high biocompatibility and film-forming abilities.

6.4.3 Pullulan A fungal glucan produced by A. pullulans, which is a aliphatic, homopolysaccharide, composed of repeated units of maltose linked by α-1,4-linkages. These are intracellularly synthesized at the cell wall or cell membrane and secreted out to the cell surface which then forms a slimy loose layer [26]. The nitrogen-containing components are required for the biosynthesis of pullulans, where amendment of different concentrations of (NH4)2SO4 had helped in estimating optimal requirements for the production of pullulan [26, 27]. The proteomics studies helped in antioxidant and energy-generating enzymes, also the enzymes concerning the amino acid biosynthesis, glycolysis, glycogen biosynthesis, protein transport and analyzing the transcription when being regulated at limited nitrogen sources, which paved the conversion from glycolysis pathway to the biosynthesis of pullulan [9, 20]. The exhibited characteristics are like excellent solubility in water, slow degradability, high plasticity, non-toxic and excellent film-forming nature.

6.4.4 Dextran A water soluble neutral α glucan secreted extracellularly which consist of repeating linear chains of D-glucopyranosyl linked with α-1,6-linkages, produced by microorganisms like lactic acid bacteria (LAB), L. mesenteroides (L. mesenteroides). The enzymes involved are dextransucrase and glucansucrase which catalyzes slow transfer of D-glucopyranosyl from sucrose to dextran. Dextran production was found to be high around 7.23 g/L when L. mesenteroides was cultured in a medium containing whey and sucrose [1]. The best operational conditions are 30 °C for 24 h [27]. It becomes a functional hydrocolloid because of its flexible structure due to the free rotation of glycosidic bond which facilitates its biodegradability, biocompatibility and solubility in water [6].

6.4.5 PHA PHA is produced intracellularly and is energy as well as a carbon storage source. Pseudomonas sp. strain P was analyzed through 16s rRNA level which was confirmed to be a potential producer of PHA from low cost carbon sources like rice bran, dates and soy maces. The synthesis of PHA proceeds with the condensation of a carboxyl group of the hydroxyalkanoic acid with another hydroxyl group forming an ester bond. These are normally found as granules formed by the actions of polymerase and depolymerase

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enzymes or even when they are administered to stress conditions like limited nitrogen, sulfur, phosphorus, magnesium, oxygen, etc. [6, 28].

6.4.6 PHB A. latus were used to utilize the waste materials in the production of PHB [29], which was subjected to nutritional stress in bacteria [15] producing intracellular granules. Fermentation is done in fed-batch reactors rather than in batch reactors with appropriate amendment of carbon and nitrogen sources. The produced PHB depends upon the concentration of the medium provided. Bioplastic is composed of linear chains of hydroxybutyric acid and hydroxylvaleric acid which gives them the features as being optically active, high crystallinity, piezoelectric features. These are commercially produced by R. eutropha which uses propionic acid and glucose as the substrates [30].

6.4.7 Biosurfactant EPS’s are produced due to an environmental stimulus and is used as a biosurfactant (BS) and are produced by bacterial genera like Arthrobacter, Acinetobacter, Pseudomonas, Bacillus, Enterobacter and Rhodococcus. These can be potentially produced from sources like lipids, sugars, alkanes, and other cheap raw-materials products [1, 31]. BS can produce microemulsions by reducing interfacial and surface tension. Pre-treatments of sludge like heat, alkaline, and acid treatment with addition of inoculums [31] can also be a parameter to improve EPS production at a higher rate. P.mendonica can produce alginate and PHA simultaneously, while EPS and PHB were produced by A. chroococcum provided with the media of fructose, glucose and sucrose amended with ammonium sulfate. This resulted with high production of EPS and PHB by using the sources glucose and sucrose respectively. But the coupled production of PHA and BS can lead to the decreased production of PHA; this states that the optimal requirements for both are different [1].

6.4.8 Gellan It is a poly-functional gelling agent having a complex biosynthetic pathway. These are produced by bacterial strains of Sphingomonas paucimobilis [1, 32] and Sphingomonas azotofigens, where S. paucimobilis synthesize sugar precursors like UDP-glucuronate, UDP-glucose, and dTDP-rhamnose by addition of sugar precursors to an active lipid carrier through glycosyltransferases, followed by gellan polymerization and then exporting. Waste glycerol is the main feed used for industrial production. Laboratorial works estimated with the culture medium which consist of lactose as the main carbon source and peptone and yeast extract is used as the main nitrogen source which produces

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a gellan concentration of 16 g/L, while S. azotofigens are cultivated in CW or molasses medium. The comparative production in CW and molasses showed a higher gellan production but of lower content of glucuronate, higher rhamnose and glycerate content [1].

6.4.9 Hyaluronate production Consists of a linear polymer of repeating units of disaccharides of N-acetyl-D-glucosamine and D-glucuronic acid which are commercially produced by bacteria such as Pasteurella multocida and Streptococcus zooepidemicus. Genetically modified animal tissues or microbial strains are used for production through fermentation [1, 11, 16]. Hyaluronan synthase (Has A) catalyzes the reaction for the HA which involves the precursors such as UDP-N-acetyl-glucosamine and UDP-D glucuronate. S. zooepidemicus and S. thermophilus are cultured in the CW containing media or whey protein amended media, but the production of concentration of HA differs significantly.

6.4.10 Cellulose production The bacterial cellulose (BC) is a homopolysaccharide consisting with polymers of D-glucose formed from the precursors of UDP-D-glucose through membrane embedded glycosyl transferase. The bacterial strains like Kamagataeibacter xylinus, G. xylinus, and Komagataeibacter rhaeticus are commercially used strains, where, K. xylinus was cultured in ethanol while the rest two were cultured in CW hydrolysate medium resulted in the production of higher BC yield. The nutrient sources like, beet molasses, coconut water, whey, used beer yeast, disposed (rotten) fruits and so on, have been exploited as the best nutrient source for BC production as well as simultaneously reduced the production costs [1, 33]. A drastic development in biopolymer industries has set a trend to replace commercially used chemical polymers in various industries, such as synthetic polymer polytheylene used in packaging industries replaced by a biopolymer, polyethylene glycol, synthetic heart stents (metal mesh or silicones) replaced by the poly alkanoates (PAH), polypropylene used in food industry are replaced by PHB, polyacylamides used in cosmetic industry are replaced by alginate biopolymer, and polysulfones used in agricultures are replaced by chitosan biopolymer.

6.5 Factors affecting the production of microbial biopolymers With the production of various numbers of biopolymers, these have attained wide range of application due to its biodegradability, biocompatibility, but have shortcomings as they cannot meet requirements such as reliability and purity which are

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important for pharmaceutical applications [1, 6, 7]. These often prohibit commercial use due to expensive fermentation methods and high production costs [6, 15]. Like for example, PHA’s have high crystalline nature, which can restrict their applications as it causes stiffness, poor thermo chemical properties, low glass transition temperature (at a particular temperature range, a physical transition occurs from a hard state of a glass to a soft rubbery state), stickiness and high hydrophobicity. While in a few other polysaccharides, they possess poor mechanical stability and reduced solubility, lacking elastomeric properties or even a high molecular mass are major constraints in their utility. The pharmaceutical and biotechnological applications of biopolymers are restrained by “Generally recognized as safe” (GRAS) standards stipulated by United States Food and Drug Administration of the production strain, for example, polymer products from Gramnegative bacteria are not regarded as GRAS because of the host-derived impurities like endotoxins which can reduce the product quality. The requirements of GRAS are through established standard assays, biopolymers from microbial cell factories (especially bacteria) should meet the purity criteria and be safe to be used as a medical device which ensure long-term use and should be through quality checks on its side effects and the main factors which have an influence on the production can be the producing strains, medium composition, effect of carbon source, effect of agitation and apparatus, the effect of downstream processing (DSP), and the aging of the materials. 1. Producing strains: There are only a few specific strains which can be used commercially for the production of biopolymers, where the type of bacterial strain determines the physical, chemical and final molecular weight of the biopolymer [15]. Depending upon the molecular weight, thermal and mechanical properties can differ. Crystallinity of a polymer is considered as the key characteristic to detect the change in the changes in the produced polymer. 2. Effect of medium composition: For the successful bacterial fermentation, a nutrient medium with the best composition is required for the better yield [24, 25]. Through the studies it was concluded that biopolymers produced by solid-state fermentation (SSF) was providing a higher yield when compared to the submerged fermentation (SmF) even though biopolymers produced were identical to those produced through SSF, but the degree of crystallinity (DOC) and molar mass differs [15]. Lower DOC is exhibited in SSF which leads to the polymerization of the molar mass at a slower rate. 3. Effect of downstream processing (DSP): When compared to the polymer production from petrochemicals, the cost of production of biopolymers is very expensive, especially the cost of carbon sources at the peak values. The commercially used carbon sources include glucose, sucrose, ethanol and methanol, where these all yield high amounts but require high production cost. Utilization of industrial and agricultural waste material as the carbon source led to the production of lower yield of biopolymers. The carbon source provided can have an impact upon the structure and other characteristics which are important [6, 7, 15, 25, 33, 34]. Recent comparison studies on the production of biopolymers from rice bran and glucose-rich carbon

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sources have estimated higher yield of biopolymers with high heat resistance and low melting temperature with rice bran as the carbon source [27]. The type of carbon source used can alter the preferred characteristics of the biopolymers in its thermal crystallinity properties. The biosynthesis of biopolymers through autotrophic growth, where CO2 is provided as the carbon source and H2 is the energy, resulted in producing higher yield of biopolymer with better characteristics of melting temperature, glass transition, degree crystallinity, and low thermal degradation [1, 15, 25]. The bacterial cells with accumulated biopolymers are subjected to centrifugation for the recovery of harvested cells followed by extraction process using solvents which is considered as the important step as these biopolymers possess medical applications. But these extractions lead to high manufacturing cost due to the use of large quantities of solvents [25]. The quality of the extracted biopolymer depends highly on the solvent which is used for the extraction, as it can also alter its characteristics and properties. The temperature administered during the extraction process can have a deleterious effect on its properties and induces polymer degradation resulting in a decrease in molecular weight when the temperature exceeds the boiling point [15]. Hence the polydispersity index which includes solvent, temperature, molecular weight can determine whether the final product can be used for the specific applications. 4. Effect of agitation and apparatus: The produced material quality relies on the agitation and apparatus used for fermentation. When compared to the batch fermentation process, orbital shakers help in extracting the final quality of the polymer as these are well controlled and monitored. 5. Aging of the materials: The phenomenon like secondary crystallization and physical aging leads to its amorphous and crystalline properties causing the weakening of the material. The decrease in crystallinity in the material can affect its perfunctory properties, resistance, young’s modulus, and elasticity [15, 27], i.e. this expresses the capability of a material to resist changes without forming a crack.

6.6 Recent approaches in separation and purification of microbial biopolymers The general separation and purification of biopolymers involve centrifugation, solventbased extraction and other purification processes for the better quality [35], Figure 6.2, displays the general method of separation and purification. Chemical, mechanical and thermal methods deactivate the cells. But chemical and enzymatic methods alter the properties of the material. Thus, the cells are deactivated through heat treatment, and the process is named “Pasteurization” which can also result in improved recovery of the material from the cells and reduced viscosity of the broth [25, 34, 35]. Thus, application

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Figure 6.2: Mass production of biopolymer (scale-up and scale-down process).

of the heat is necessary prior to the centrifugation or filtration. Through centrifugation, the materials precipitates and the most common agents used for precipitation are isopropyl, alcohol, ethanol or acetone are all water-miscible non-solvents or can also use calcium, aluminum or quaternary ammonium salts as the polyvalent cations which can form complexes with the poly-anionic biopolymer like xanthan, dextran, etc. [25, 33, 34]. Alcohols are added with the solvent-based extraction method to remove the scums like precipitated byproducts and used microbial cells are simultaneously washed out. For industrial applications, precipitation with isopropyl alcohol (IPA) is favored but due to cost for alcohol, this becomes a decisive parameter. Hence sodium chloride and electrolytes addition can significantly reduce the IPA required [35]. For further purification, the concentration of the medium is allowed to pass through filters, where permeate were purified out from the impurities. When compared to ultrafiltration and pressure electro filtration (PEF), cross-flow filtration (CFF) is better by high transmembrane flux and cost operations. CFF filters the liquid having a high concentration of filterable matter. Although, PEF can increase filtrate flux and reduce the shear forces which can lead to the deprivation of biopolymer. In PEF, since cations are originating from medium salts these can mask the material with negative charge and reduce the spinning velocity, hence desalination process is necessary before PEF and this adds up to the peak cost of productions.

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6.7 Environmental applications of microbial biopolymers Even though biopolymers produced can contribute to the pathogenic characteristics, but have also attracted one or the other industry due to their biocompatibility and biodegradability which can also help in enhancing the functions of other bioactive molecules by altering their physical and chemical properties. The applications are wide and vast; a few of them are listed in Table 6.4.

6.8 Global market value of microbial biopolymers In 2021, the global bioplastics and biopolymer market made worth 10.51 billion in USD, with estimates about the worth of 28.94 billion in achievements by 2028, along with a compound annual growth rate (CAGR) of 21.90%. It is estimated that by 2030, the global market value of microbial biopolymer production will be around $35.25 billion. The industries that prosperously exploiting microbial biopolymers are pharma, food, baking, dairy, beverage, feed (paper and pulp), leather and textile, cosmetics industries, organic synthesis and fertilizers industry, detergent manufacturing industries and for treatment of waste water. The global market values of a few microbial polymers are used in the industries are given below (Table 6.5). These studies show that the towering application of biopolymers in various industries can efface the use of synthetic polymers completely and restore environment. The methodologies should be again revised to make it within the cost, hence to develop ways to eradicate the malnutrition faced.

6.9 Bottlenecks and future perspectives of microbial biopolymers The approaches developed help in producing biopolymers making bacteria an ideal host by utilizing biosynthetic pathways and key enzymes which can be used as commodity products or a high value in the medical industry [7]. Its capability to replace petroleum-based products stresses for conducting deep knowledge research in the field of production of biopolymers [24]. The overall production cost depends upon the yield of the polymer, amount of carbon sources, downstream processing. The separation process is challenging when the particular polymer is used for medical applications, but with constant research these limitations can be neglected later on [7, 24]. Volume of culture, type of bioreactor, and downstream equipment determines the capital cost to be invested followed by product specific separation process. The biological means of

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Table .: Environmental applications and other applications of biopolymers. Biopolymer

Application

Biomedical industry Bacterial cellulose

Alginates

Xanthan gum

Hyaluronic acid

PHB

Used in devices targeting the drug delivery–swelling controlled by entrapment. Scaffolds in regenerative medicines – Due to the biocompatibility nature, these materials have properties to design and fabricate in tissue engineering. Dressing of wounds – The high water holding capacity provides BC with a unique property of wound healing [, , ]. Wound dressing – the mixture of calcium alginate and sodium help in healing of the wound and achieving haemostasis. Moist, pain and odor by absorbing protease are being controlled. Also the strategies like gel-electrospun mats, hydrogels and sponges provide gelling characteristics that strongly adhere to the wound exudates leading to homeostasis. In drug delivery system – function as carrier and encapsulation of drugs. Pseudo plastic and shear thinning nature these are extensively used in the production of cosmetics and toothpastes. In the pharmaceutical industry these prevent the removal of insoluble particles (degumming) [, , ]. Used as the substitute for vitreous humor in eye surgery. Application in gel preparations as drug delivery in eyes. Prolonged delivery of quintessential amount for profile smoothening by making corneal shields from HA. Other uses include: epithelial regeneration, wound healing, attains alveolar patency by providing viscosity in pulmonary diseases, treatment method for Sjogren’s syndrome, medical filler that can regenerate cutaneous lines and wrinkles, added in intra-articular injections. Visco-supplementation with HA derivatives help in reducing pain and improves mobility. Detachment of bacteria on dental implants, catheters, intraocular lenses. Augment soft tissues in cosmetic surgeries as [, , ]. In tissue engineering – maintain the growth as well as organization. Modulate the growth of cells like osteoblasts, fibroblasts, umblical endothelial veins, smooth muscles, and chondrocytes from cartilage. Can be synthesized through as microbial storage granule. In reconstructive surgeries – used to make vascular grafts, heart valves and pericardial patches are developed. Controlled drug delivery system – with its biocompatible property, developed sutures, pins, swabs and also have aligned application in wound healing, bones and replacement and drug delivery.

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Table .: (continued) Biopolymer

Application Peripheral implants and substitutes –replace pericarditis and are a substitute for blood vessels. The piezoelectric property enables it to act as a dental and cardiovascular implant. Disease treatments – with PHB diseases like narcolepsy, addition to alcohol, schizophrenia, atypical psychosis, chronic brain syndrome, Parkinson’s disease, radiation exposure and cancer, and other neural disorders [, , , ].

Application in nanotech-nology and nanoscience Metal nanoparticles

Act as a substituent for different toxic reagents developed through green chemistry strategy. Magnetic alginate beads and chitosan nano- Used for the removal of organic dyes [, , ]. composite sponge Food industry PLA and PHA Lysozyme Amylase combined to plasticizers

Used for packaging food as it can provide transparency and high water resistant. Microencapsulation of solids, liquids, and gasses inside small capsules. Edible films are used to give aroma or flavor. Widely used antimicrobial enzyme in food packages. Manufacture strident films for packaging food materials.

In food packaging industries PHA and PLA

Helps in improving the shelf life [, , , ].

Mechanical applications Xanthan and dextran

Xanthan and Gellan gum

In combination with clay these biopolymers are used to decrease soil permeability hence providing resistance against erosion. Xanthan helps in strengthening the soil. While gellan is an excellent additive for improvement and stabilization of soil [, , ].

Microbial enhanced oil recovery (MEOR) Biosurfactants Dextran

Help in improving the enhanced recovery of oil. The injection approach helped in attaining sensitive optimization and analysis which resulted in higher recovery of oil compared to that of the basic process [, , , , ].

Wastewater treatment . Alginate, alginic acid, cellulose, chitosan, carboxy methyl cellulose, and chitin

Detoxification of heavy metals polluted wastewater by biosorption [].

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Table .: Global market value of biopolymers. Biopolymer

Global market price by

Uses

Cellulose

USD . billion by  USD . million by  USD . billion by  USD . billion by  USD . billion by  USD . million by 

In electronics as diaphragms of acoustic transducers, in medicine as in tissue engineering, tissue replacement []. In food as gelling agents, while in medicine as drug delivery [].

Alginate Chitin/chitosan Hyaluronan Pullulan Gelling agents (Gellan gum, Curdlan)

Galactopol Fucopol

USD . million by  Not certain

In agricultural pesticides, in medicine as for drug delivery system []. In cosmetics, as viscosupplementation for tissue repair []. In cosmetics, binder and stabilizer in food []. Gellan – As gelling and stabilizing agents, as well as in baked and meat products []. Curdlan – thickener, stabilizer, and moisturizer in food industry []. Galactopol – oil recovery and coatings []. Fucopol – for food and feed and also in pharmaceutical applications [].

biopolymer production process reduces capital cost, operational cost; waste disposal cost, and notably less toxic metals pollutants compared to chemical means of polymers production. The price of synthetic polymers primarily depends upon the price of crude oil while biopolymer depends upon the availability and price of the feedstock [7]. Virulence factors are contributed by the polymers, where most of the biosynthesis process of polymers have been altered for specific production required polymers but do pose one or the other limitation by cost, safety profiles. Hence it is important to develop strategies which can yield better polymers in cost effective as well as by overcoming the limitations exhibited. For antimicrobial activity the pathway of the virulence factor is targeted to inhibit the synthesis. Hence biopolymer industries have a prospective future which is determined by the environmental and economic aspects of natural way of producing biological products [24].

6.10 Conclusions Biopolymers as excellent products have achieved its importance in one other aspect, which also shows that it is much better than the conventional plastics. But even though, limitations of the strategies, equipment and cost have restricted exploration of the

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17. Lee HM, Vo P, Na D. Advancement of metabolic engineering assisted by synthetic biology. Catalysts 2018;8: 619. 18. Mitra R, Xu T, Xiang H, Han J. Current developments on polyhydroxyalkanoates synthesis by using halophiles as a promising cell factory. Microb Cell Factories 2020;19:86. 19. Espinoza M, de Los Angeles S, Ascazuri M, Achaga J, Viduzzi G, Tognana SA. Biopolymers to mitigate the environmental impact. Inglomayor Mag, 11th. ed. Major University; 2019, 17:275–86. 20. Arriaga AMH, Campano C, Rivero-Buceta V, Prieto MA. When microbial biotechnology meets material engineering. Microb Biotechnol 2022;15:149–63. 21. Castro IP, Ramsay BA, Rehm BHA. Pathway, genetic and process engineering of microbes for biopolymer synthesis. Front Bioeng Biotechnol 2020;8:618383. 22. Reddy MSB, Ponnamma D, Choudhary R, Sadasivuni KK. A comparative review of natural and synthetic biopolymer composite scaffolds. Polymers 2021;13:1105. 23. Siracusa V. Microbial degradation of synthetic biopolymers waste. Polymers 2019;1. https://doi.org/10. 3390/polym11061066. 24. Ibrahim MS, Sani N, Adamu M, Abubakar MK. Biodegradable polymers for sustainable environmental and economic development. MOJ Biorg Org Chem 2018;2:192–4. 25. Palaniraj A, Jayaraman V. Production, recovery and applications of xanthan gum by Xanthomonas campestris. J Food Eng 2011;106:1–12. 26. Cheng KC, Demirci A, Catchmark JM. Pullulan: biosynthesis, production, and applications. Appl Microbiol Biotechnol 2011;92:29–44. 27. Sarwat F, Ul Qader SA, Aman A, Ahmed N. Production & characterization of a unique dextran from an indigenous Leuconostoc mesenteroides CMG713. Int J Biol Sci 2008;4:379–86. 28. Waheed M, Mubeen B, Sarwar M, Hafeez MM, Ali Q. Biosynthesis of poly (hydroxyalkanoates). Biol Clin Sci Res J 2021;2021. https://doi.org/10.54112/bcsrj.v2021i1.71. 29. Serafim LS, Lemos PC, Albuquerque MGE, Reis MAM. Strategies for PHA production by mixed cultures and renewable waste materials. Appl Microbiol Biotechnol 2008;81:615–28. 30. Getachew A, Woldesenbet F. Production of biodegradable plastic by polyhydroxybutyrate (PHB) accumulating bacteria using low cost agricultural waste material. BMC Res Notes 2016;9:509. 31. Nouha K, Kumar RS, Balasubramanian S, Tyagi RD. Critical review of EPS production, synthesis and composition for sludge flocculation. J Environ Sci 2018;66:225–45. 32. Raghunandan K, Kumar A, Kumar S, Permaul K, Singh S. Production of gellan gum, an exopolysaccharide, from biodiesel-derived waste glycerol by Sphingomonas spp. 3 Biotech 2018;8. https://doi.org/10.1007/ s13205-018-1096-3. 33. Zhong C. Industrial-scale production and applications of bacterial cellulose. Front Bioeng Biotechnol 2020; 8:1–19. 34. Singh R, Gaur R, Tiwari S, Gaur MK. Production of pullulan by a thermotolerant Aureobasidium pullulans strain in non-stirred fed batch fermentation process. Braz J Microbiol 2012;43:1042–50. 35. Joshi A, Verma KK, Rajput VD, Minkina T, Arora J. Recent advances in metabolic engineering of microorganisms for advancing lignocellulose-derived biofuels. Bioengineered 2022;13:8135–63. 36. Chang I, Jeon M, Cho GC. Application of microbial biopolymers as an alternative construction binder for earth buildings in underdeveloped countries. Int J Polym Sci 2015;2015:1–9. 37. Wu N, Wei H, Zhang L. Efficient removal of heavy metal ions with biopolymer template synthesized Mesoporous titania beads of hundreds of micrometers size. Environ Sci Technol 2012;46:419–25. 38. Anderson LA, Islam MA, Prather KLJ. Synthetic biology strategies for improving microbial synthesis of “green” biopolymers. J Biol Chem 2018;293:5053–61.

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Krishnan Harshan, A. Prashanth Rajan, Danie Kingsley, Rahul Amin Sheikh, Jemima Aashmi and Anand Prem Rajan*

7 Plant-based biopolymers for wastewater pollutants mitigation Abstract: Pollution is one of the most pressing issues of modern times. Effluent in the world is escalating due to the exponential growth in the industrial and agricultural sectors. The effluents contain heavy metals, pesticides, and inorganic substances ultimately leading to the deterioration of the ecosystem. Even though there are numerous wastewater treatment methods like adsorption, membrane separation, ion exchange, and physical, mechanical, and chemical treatments. They are expensive and have the risk of second-hand pollution. Biopolymers are alternate and superior to synthetic polymers due to their environmentally friendly approach and high efficiency in treating wastewater. The most prominent plant-based biopolymers for the treatment of pollutants are cellulose, starch, carrageenan, alginate, xylan, inulin, pectin, and tragacanth. These have their advantages and disadvantages in bioremediation. The mechanism of pollution removal has adsorption, flocculation, bridge formation, and electrostatic patches. They are biodegradable as they are natural in origin. They have proved to remove toxic pollutants like chitosan, pullulan, polyhydroxy alkonates and butyrates, dextran, starch and cellulose, polyvinyl alcohol and polycaprolactone, gelatin, collagen and wheat gluten, alginate, heparin, and pectin to name a few. Biopolymers are also sourced from diverse sources like agricultural wastes and well-known sources like plants, animals, and microbes. Biopolymer and its composites are utilized as coagulants and flocculants. They are cellulose graft polyacrylamide, anionic sodium carboxymethylcellulose, guar gum graft polyacrylamide, pectin polyacrylamide, starch, and tannin. Nanotechnology has led to the development of elite nanohybrid bio-adsorbents to actively remove pollutants. These nano adsorbents have been targeting pollutants like azo dyes, bovine serum albumin, cationic dyes, parabens, and methylene blue among others. Biopolymer composites are also widely used for diverse applications primarily due to their enhanced mechanical and thermal properties. Biopolymers from natural and synthetic sources can be modified and used as per the requirement.

*Corresponding author: Anand Prem Rajan, School of BioSciences and Technology, Vellore Institute of Technology, Vellore, India, E-mail: [email protected]. https://orcid.org/0000-0001-5659-0386 Krishnan Harshan, Danie Kingsley, Rahul Amin Sheikh and Jemima Aashmi, School of BioSciences and Technology, Vellore Institute of Technology, Vellore, India, E-mail: [email protected] (K. Harshan). https:// orcid.org/0000-0001-8240-7880 (K. Harshan). https://orcid.org/0000-0001-7838-5017 (D. Kingsley). https:// orcid.org/0009-0007-1106-0809 (R.A. Sheikh). https://orcid.org/0009-0000-8646-7493 (J. Aashmi) A. Prashanth Rajan, Department of Biotechnology, Karunya Institute of Technology & Sciences, Coimbatore, India. https://orcid.org/0000-0001-9075-3724 As per De Gruyter’s policy this article has previously been published in the journal Physical Sciences Reviews. Please cite as: K. Harshan, A. Prashanth Rajan, D. Kingsley, R. A. Sheikh, J. Aashmi and A. Prem Rajan “Plant-based biopolymers for wastewater pollutants mitigation” Physical Sciences Reviews [Online] 2023. DOI: 10.1515/psr-2022-0220 | https://doi.org/10.1515/9783110987188-007

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Keywords: mechanisms of pollutant removal by biopolymers; plant-based biopolymers; Pollution; wastewaters.

7.1 Introduction Pollution is driving the world economy to find sustainable solutions that will be effective and sustainable. Diverse treatment methods, including coagulation/flocculation, reverse osmosis, electrochemical, adsorption, ion exchange, membrane filtration, biological degradation, and sonochemical methods, have been used to remove pollutants from the environment [1, 2]. However, these techniques have their problems, including limited removal efficiency, a high-power need, expensive tools and chemicals, high maintenance costs, complicated procedures, and secondary pollution sources [3]. Even though there are numerous ways to mitigate pollutants, biological methods are preferred over synthetic ones. This is because of the less amount of pollution caused to the surrounding environment. Plant-based biopolymers proved to be the best alternative to environmental pollution that has occurred in recent years. The term “polymer” has been often used over the past few decades in a variety of industries due to its tremendous properties in a variety of applications. Due to their laborious degradation processes, polymers and their composites made from chemical monomer sources have proven to be potentially hazardous to the environment. Biopolymers, which can be successfully extracted from natural sources, are organic alternatives to synthetic polymers. They are primarily offered as covalently bonded monomeric units as well as polymeric components. These eco-friendly biopolymers and their composites can be divided into groups based on many sources, preparation techniques, and prospective applications for which they may be used [30]. According to Enitan et al. [31] Ficus religiosa, Mangifera indica, and Azadirachta indica fared well with the air pollution tolerance index (APTI) being directly proportional to the anticipated performance index (API). This research helps us to appreciate the usefulness of indigenous plants in the control of pollution. This is attributed to the presence of specific phyto compounds present in plants that exhibit the desired characteristics. Similarly, plant-based biopolymers are effective in reducing pollutants to a form that is nontoxic while being biodegradable too (Figures 7.1–7.3).

7.1.1 Need for plant-based biopolymers and their importance Synthetic plastics, which are derived from petroleum, are the polymers that are used most frequently all over the world for packaging and storage. Among these, polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polystyrene, polycarbonate, and polymethyl methacrylate are the most frequently utilized materials. The long-term effects of synthetic polymers include problems due to nondegradable raw

7.2 Plant-based biopolymers for the treatment of pollutants

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materials and a large amount of energy for their production. Its disposal after usage is also a global threat and universal menace. They pose a severe threat to biodiversity and all sorts of species as a result of their degradation, which also amplifies the greenhouse effect and the impacts of accumulation in ecosystems. UV light and oxidative degradation are both harmful to polyethylene, polypropylene, and polymethyl methacrylate. On the other side, polyvinyl chloride can lose hydrogen chloride at high temperatures, which causes it to discolor and become brittle [32]. Hence it can be replaced with a natural biopolymer like a pectin-based biopolymer produced by adding glycerol as a plasticizer and calcium chloride as a cross-linker making it an alternative to conventional food package materials [33]. Numerous polymers are produced by living things as a large component of their morphological, cellular, and dry matter. To support the important metabolic and cellular functions of organisms, these biopolymers are crucial to their life cycles. In many different areas where sustainable and biodegradable solutions are required, biopolymers have attracted a lot of interest [34]. Plants have been producing a variety of polymers as an important part of their living system which has its advantages in different aspects. These polymers play a significant role in supporting their cellular, morphonology, and other metabolic activities. Biopolymers are produced by different components of plant tissue ranging from their cell wall, and organelles to the cytoplasm for various enzymatic processes. These biopolymers can be extracted from plants and used for various applications in diverse fields [7]. These biopolymers can be used in various aspects of replacing synthetic polymers to deal with the increase in pollution.

7.2 Plant-based biopolymers for the treatment of pollutants Starch, cellulose, and pectin are examples of natural polymers that are produced by a variety of living things. Due to their biodegradability and compatibility with the extracellular matrix (ECM), natural polymers are frequently employed in bioremediation apart from usage in regenerative therapy for burn and wound dressings [35]. Chitin, or poly-(1–4)-N-acetyl-d-glucosamine, is a polysaccharide biopolymer that is typically produced by a variety of living organisms [36]. The exoskeleton of arthropods, fungi, and yeast cell walls are all examples of natural sources of chitin. Chitosan, a cationic polysaccharide generated from chitin, is a linear, semi-crystalline polymer made up of (14)-2-acetamido-2-deoxy-D-glucan (N-acetyl d-glucosamine) and (14)-2-amino2-deoxy-d-glucan (d-glucosamine) sub-units. The free amino groups left behind after the partial removal of the chitin acetyl groups provide it a cationic property making it suitable for the removal of anionic and charged pollutants [37, 38].

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7 Plant-based biopolymers for wastewater pollutants

Starch Inulin

Cellulose

Biopolymers

Pec n

Carregeenan

Alginate

Tragacanth Xylan

Figure 7.1: Different types of biopolymers used for the mitigation of pollutants.

Figure 7.2: The step-by-step process of flocculation in the wastewater in presence of biopolymers.

Figure 7.3: Shows the overall schematic diagram of the production of biopolymers and mitigation of pollutants using them.

7.2 Plant-based biopolymers for the treatment of pollutants

151

Major industrially useful plant-based biopolymers obtained from various plant parts which are also used in pollution treatment are mainly cellulose, hemicellulose, pectin, and lignin [7].

7.2.1 Cellulose Cellulose is a natural biopolymer that is biodegradable, biocompatible with all materials, and recyclable. Cellulose in combination with nanocomposite increases its specific surface area and porosity. Cellulose is used for the fabrication process of various nanoparticles which increases the stability of the material. Cellulose when amalgamated with carbon nanomaterials changes the structural and morphological properties of the nanoparticles such as the adsorption of pollutants, specific surface area, mechanical strength, and porosity. Using cellulosic materials, the degradation efficiency is increased by increasing the ability to accept and transfer electrons which in terms boosts the migration charge carriers [4]. Cellulose fibers are obtained from wood and manual purification of flax, cotton, hemp, and jute [39]. Cellulose has remarkable adsorption process characteristics. It is more affordable and valuable because it is more common and can be obtained from agricultural waste. It is more effective than starch-based biopolymers in adsorption credited to its hydrophilic nature making it soluble in neutral water. The abundance of –OH hydroxyl groups aid in the combination of various chemical moieties that adsorb various contaminants from aqueous effluents [40]. Biopolymers like cellulose are obtained from diverse sources. Faria et al. [41], produced bacterial cellulose biopolymer from the bacteria Komagataeibacter saccharivorans where the maximum yield was obtained with the optimal conditions of 2% glucose, pH of 3.25 and 7 days of cultivation yielded a maximized time-efficient concentration of roughly 2.95 g L−1, as a bio-adsorbent matrix for removing dyes, proteins, and heavy metals. Bacterial cellulose (BC) has proven successful in many fields [42–44]. Additionally, it has been demonstrated that this biopolymer is most suitable as an ecofriendly ultrafiltration membrane [45, 46] with a removal efficiency of 98.3% and 99.3% for stabilized and unstabilized oil emulsions, respectively. Hassan et al. [45] proved that Bacterial cellulose (BC) serves as an excellent ultrafiltration membrane to remove oil emulsions from water. Additionally, BC membranes were effectively used by Isik et al. [46] to filter aqueous dyes from the textile sector, resulting in a 90.9% clearance rate. Guleria et al. [47] have mentioned that cellulose can be used to remove pollutants from wastewater in such a way that; Cellulosic biopolymer obtained from Hibiscus esculentus was graft copolymerized with acrylamide and acrylic acid monomer mixture using hydrogen peroxide and ascorbic acid. This forms a cellulose-g-poly- (acrylamide-coacrylic acid) polymer, which can be used for the adsorption of inorganic metal ions such as copper, zinc, cadmium, and lead.

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7.2.2 Carrageenan Carrageenan is obtained from plants of the Rhodophyceae family found in aquatic flora. Carrageenan has been known as no dietary good but has many other uses for its outstanding chemical properties [7]. Carrageenan composite hydrogel was used for the removal of methylene blue from water [9]. Pethsangave et al. [10] prepared a graphenecarrageenan sponge absorbent for the absorption of oils from water and other organic solvents. Carrageenan is hybridized with other composites to remove pollutants like (a) silica nanoparticles (b) nano clay/nanomembrane. 7.2.2.1 Carrageenan-based hybrids with silica nanoparticles A well-known nanomaterial with a high surface-to-volume ratio and surface reactivity is nano-silica. Due to its smaller size (100 nm) and superior physicochemical characteristics compared to its bulk form, it is known as the nanoform of SiO2 or silica nanoparticles (SiNPs) [48]. Magnetic iron oxide nanoparticles covered with -carrageenan/silica organic/ inorganic hybrid shells were used as novel adsorbents to remove methylene blue from wastewater [49]. Bio-adsorbents made of silica and carrageenan have been developed to remove toxic heavy metal ions (Cd2+ and Pb2+) generated by various industries. The bio adsorbent was found to include 1.10 g/cm3 density, 2.10% moisture, 81.70% ash level, and 21.80% iodine adsorption [50]. 7.2.2.2 Carrageenan-based hybrids with nano clay/nanomembrane Nano clays, silicate clay minerals, are created through the chemical weathering of other silicates [51]. There are several uses for nano clays in a variety of fields, including those related to agriculture, animal feed, water purification, medicine, and the food industry. Super hydrophilic membranes made from bioinspired materials with high hydrophilic performance is used to effectively remove soluble and insoluble organic contaminants from water. Although controlling the hydrogel thickness and membrane pore size is challenging, materials made by hydrogel-forming species with low-adhesive superoleophobicity can provide superior anti-fouling. To create bio-inspired underwater superoleophobic membranes, Prasannan et al. [52] investigated the production of hydrolyzed polyacrylonitrile (h-PAN) membranes by the combination of nano clay laponite and K-carrageenan. Modified membranes that serve as effective adsorbents for underwater superoleophobic processes make it simple to remove organic contaminants.

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7.2.3 Starch Among all the natural polymers, starch is one of the most abundant biopolymers and is readily available. Starch is used in natural form as well as in modified form to increase its pollution removal properties. Starch in combination with other biopolymers is used for the synthesis of nanomaterials which increases physical, chemical, and mechanical properties. Biodegradable starch-based nanoparticles are used in various fields like packaging, agriculture, biomedical, as well as bioremediation. In agriculture practice, biodegradable films are preferred over traditional synthetic films which easily degrade over desired time and enhance nutrients and fertility of the soil on degradation. These biofilms help in soil humidity, temperature, vapor permeability, etc. providing a good root environment for the growth of plants. On the other hand, the packaging sector generates a considerable degree of pollutants. To deal with this issue, starch-based biopolymers are synthesized into nanofilms which provide a wide range of industrially desirable properties like strength, plasticity, transparency, translucent appearance, and stability which gives texture making them suitable for all packaging needs. Starch-based nanocomposites help in the remediation of heavy metals by absorbing and adsorbing the metals or reducing them to fewer toxic pollutants [53]. Moreover, Sb2S3-CeO2/chitosan-starch has been used as a catalyst heterojunction catalyst for the photo-degradation of toxic herbicide compounds [54]. A readily available, highly biodegradable, affordable, and renewable biopolymer is starch. However, some research has revealed that compared to petroleum-based plastic, the mechanical and water barrier qualities of starch biopolymers are somewhat worse. To solve this problem, nanofillers like nanocellulose are now being used. Nanocellulose has received a lot of attention because of its favorable mechanical and physical characteristics. Since the technique can address environmental challenges, nanocellulose has also piqued the interest of researchers in recent years [55]. Starch is a biodegradable, renewable, and nontoxic polymer, which can be obtained from plants in the cytoplasm of the plant cells [56]. Some of the starch-rich sources are cassava, rice, corn, etc., Starch obtained from rice and corn is processed with glycerol, citric acid, and gelatin to form a bioplastic material and can be used as an alternative to low density polyethylene (LDPE) and high density polyethylene (HDPE) plastic carry bags [57]. Sganzerla et al. [58] reported a new alternative for food packaging materials. They have formed a biodegradable, antimicrobial, and antioxidant food packaging material with 2% pinhao starch (obtained from Brazilian pine seeds), 3% citric pectin, 2% glycerol (plasticizer), and 2–3% of feijoa peel flour (obtained from feijoa fruit). This packaging film was tested on apples and it was found that this food packaging material maintained the

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quality of the apples during storage. Similarly, yam-starch based films with eugenol, cowpea-starch based films with a maqui berry extract, Pea starch/polylactic acid-based bilayer films, rye starch films containing rosehip extract, cassava-starch based films with zinc nanoparticles, corn starch and gelatin films with N-lauroyl-l-arginine ethyl ester monohydrochloride, and acetylated cassava thermoplastic starch and green tea blends with linear low-density polythene films are also there as alternate food packaging materials [59].

7.2.4 Alginate Alginates are obtained from the cell wall of brown algae, kelps which are anionic in nature. Alginate exhibits a high surface functional group of hydroxyl and carboxyl which can bind to cationic and metallic ions by exchanging ions with pollutants. Composites of alginates are synthesized for organic and inorganic contaminants which are absorbent in nature and help in the absorption of pollutants. This absorption process involves the exchange of ions by electrostatic interactions. Alginates are used for the absorption of heavy metals, antibiotics, and dyes. Apart from these applications, alginates are used for the remediation of various other pollutants as well [60].

7.2.5 Xylan Xylan is hemicellulosic, mainly found in the cell wall of plants with hardwood. Elgueta et al. [61] studied the selective removal of metals from a solution containing a multicomponent solution of cadmium, copper, and lead each of 100 mg L−1 concentrations. Their study involved the hydrogels synthesized from xylan with some modifications which were able to retain cadmium and lead and copper ions separately and also from an aqueous solution. Xylan is also used for the removal of dyes and other pollutants from water bodies [12].

7.2.6 Inulin Inulin is a biodegradable, renewable, water-soluble, carbohydrate polymer. Inulin was extracted from Allium sativum. Inulin is the second most stored carbohydrate next to starch. Inulin- TiO2 bio-nano composite prepared by solvent casting method can be used in the removal of methylene blue dye from the water [62]. Fe3O4−inulin nano bio adsorbent used in treating methyl orange and crystal violet dyes in wastewater [63].

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7.2.7 Pectin Pectin is a natural complex polysaccharide present in the cell walls of plants. Most commonly pectin was extracted from sugar beet root, apple pomade, and citrus fruits. It has many uses such as a colloidal stabilizer, gelling and thickening agent. It contains α-(1,4)-linked D-polygalactronic acid residues. Pectin can also be used as a biopolymer to remove pollutants [56]. Pectin-cross linked-guar gum/superparamagnetic ion oxide (Pc-cl-GG-SPION) nanocomposite hydrogel can be used as an efficient biopolymer for the removal of organic pollutants like o-chlorophenol and m-cresol from the contaminated water [64]. Pectin biofilms, prepared by adding choline chloride and glycerine (ChCl/Gly – 1:2) as plasticizers can be used as an alternative for food packaging plastics [65]. Pectin-g(Sodium acrylate-co-N-isopropyl acrylamide) (PC-g-(SA-co-NIPA)) hydrogel can be used to adsorb the dyes and metallic contaminants from aqueous medium [66].

7.2.8 Tragacanth Gum tragacanth is a biopolymer extracted from the plant Astragalus gummifer. It is a heterogenous hydrophilic carbohydrate natural biopolymer. It can withstand heat, aging, and acidity. The tragacanth acid present in tragacanth makes it insoluble in water but forms a stiff gel when it interacts with water. It has a major role in the pharmaceutical and food industries because of its physical, chemical, and biological properties [56]. Dyes are one of the major pollutants released into water from textile industries, these dyes do not allow sunlight to penetrate the water and thus creating a major problem in the aquatic system. Tragacanth gum can be used to sort out this problem. TiO2 gum tragacanth hydrogel (TGTH) is a polymer formed by the combination of TiO2 and Tragacanth gum and is more effective in treating wastewater. Almost 87% of dyes were cleared by using a very low quantity (0.15 g/L) of TGTH [67]. The polymer of TiO2-loaded 2-hydroxyethyl methacrylate cross-linked gum tragacanth (GumT-cl-HEMA-TiO2) is also having a dye removal efficiency of 99.3% [68]. Tragacanth can form biofilms and hence it can be used in food packaging apart from being used for bioremediation thus it will reduce the usage of plastics in food packaging consequently reducing soil pollution. The polymer of alginate–aloe vera–tragacanth films can be used as an alternative to plastic bags. The composition of alginate–aloe vera–tragacanth biofilm is 3% sodium alginate, 10% aloe vera, 50% sorbitol (plasticizer), and 12% tragacanth which is reported to be highly effective biopolymer formation [69] (Tables 7.1 and 7.2).

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Table .: Shows the applications of various plant – based biopolymers and their sources. Sl. no.

Type of biopolymer

Source

Applications



Cellulose

Plant tissue bacteria (Acetobacter xylinum) Wood and bamboo

Water treatment, degradation of antibiotics, textile dyes, chromium reduction Absorption of oils and organic pollutants up to – times their weight Removal of methylene blue dye Remove metals such as lead, mercury

[]

Removal of organic dyes and heavy metals Removal of methylene blue from water, recovery of oil and organic solvents from water Removal of dyes, metal ions, oils Heavy metal ions, dye removal

[] [, ]

Color removal, COD reduction, wastewater remediation for pollutant adsorption like Cu, Cd, Pb, and Cr

[–]



Pectin



Carrageenan



Xylan



Alginate

Sugarcane bagasse Plant cell walls, citrus peels, apple pomace Plant-based Cell wall matrix of red seaweeds Red seaweed Almond shell, rice husk, corn cobs. Brown seaweed

References

[] [] []

[] []

Table .: Performance efficiency of various plant-based biopolymers on pollutant removal. Sl. no.

Source

Nature

Pollutants

Pollutant removal efficiency



Rice straw

Cellulose

%

[]



Citrus peel

Cellulose

– mg/g

[]



Bamboo powder Cellulose

.%, .%

[]

 

Pineapple peel Sugarcane bagasse Sweet potato Pectin-rich fiber Sugar beet Phyllospadix iwatensis Pectin gel Chondrus crispus

Cellulose Cellulose

Methylene blue, Congo red Crystal violet, methylene blue Methylene blue, malachite green Methylene blue Methylene blue

% .%

[] []

Pectin Pectin Pectin Pectin

Pb+ Pb+ Hg+ Cd+, Pb+

[] [] [] []

Pectin Carrageenan with chitosan Carrageenan with chitosan Carrageenan with alginate Carrageenan with poly (acrylonitrile-coacrylamide)

Methylene blue Eriochrome black-T

. mg/g  mg/g . mg/g . mg/g .–. mg/g . mg/g  mg/g

Cd+

.–. μmol/g

[]

Heavy metals and methylene blue Brilliant green dye

–

[]

 mg/g

[]

     

References

[] []

7.3 Mechanism of pollution removal using Biopolymers

157

7.3 Mechanism of pollution removal using Biopolymers The removal of pollutants using Biopolymers can be performed by following the mechanisms listed below. (i) Adsorption. (ii) Flocculation. (iii) Bridge formation. (iv) Electrostatic patches.

7.3.1 Adsorption Adsorption is a surface phenomenon, where the adsorbates are bounded or attached to the adsorbents. There are two types of adsorptions such as (1) chemisorption (or) electrostatic sorption and (2) physisorption. The first one involves the covalent bond or ionic bond, respectively, and the second one involves the weak Van der Waals forces. An equilibrium is formed between the solution and the adsorbent [70].

7.3.2 Flocculation Flocculation is one of the most widely used methods for the treatment of wastewater. The charges are neutralized and the small molecules are aggregated to form a large mass that absorbs all the other small and organic contaminants present in the solution and is further filtered or sedimented to remove the flocculants from the solution [70].

7.3.3 Bridge formation Long polymeric chains in the biopolymer are capable of extending from one particle to another, essential for effective bridging. Bridge formation occurs when there are vacant sites on the particle’s surface. Usually, extra polymers are required to achieve this and the major advantage of this mechanism is larger amounts of flocculates can be formed than any other methods [70].

7.3.4 Electrostatic patches When a highly positive (cation) charged polymer comes in contact with a negatively charged particle in water cannot be neutralized and as a result, cationic patches will be formed. A larger number of cationic patch units and particle attachment takes place [70].

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7.4 Plant-based biopolymers for the mitigation of xenobiotic compounds Gelatin, cellulose, lignin, chitin, chitosan, gum arabic, alginate, and gellan gum are a few biopolymers that have been used for the control of xenobiotic compounds. Prominently these biopolymers are involved in the preparation of magnetic biocomposites which are used for the control and effective removal of xenobiotic compounds. Recently the nanoparticles of these biopolymers have proved effective in handling toxic metals [71]. Some of the documented mechanisms of action include chemical adsorption when it is acidic in nature and physical adsorption under alkaline conditions. Chitosan is indicated in the adsorption of the following metals viz, Au3+, Cu2+, Ni2+, Hg2+, Co2+, Fe3+, Cd2+, Cr2+, Mo2+, and Pb2+. Gellan gum is effective for the adsorption of Mn2+, Cr2+, and Pb2+. Chitin and Gum Arabic are utilized for the removal of Cu2+. Alginate is indicated in the adsorption of AsO42+, Cu2+, and Co2+ electrostatic force of attraction. Similarly, plant and plant-based products are also indicated in the removal of toxic metals including spent grain, barley straw, sawdust, the bark of trees, and spent coffee grounds [72].

7.5 Advantages and disadvantages of biopolymers 7.5.1 Advantages of biopolymers Many developed countries have restricted the usage of plastics and are encouraging biopolymer-based biodegradable plastics [73]. Polysaccharides like starch, chitosan, and cellulose are widely used for food packaging applications because of their characteristic long chains of monosaccharides linked by glycosidic bonds making them available for microbial degradation. They are cheaper than synthetic alternatives and can be easily produced using naturally available raw materials which have no toxicity and are thereby readily degradable [74]. Cellulose being biodegradable and hydrophilic is also gaining attention globally for packaging [75]. Biopolymers made from chitosan have low oxygen permeability along with high mechanical stability, and waterproof properties hence making them extremely useful for the bioremediation filtration membrane, and various uses in the food industry [76].

7.5.2 Disadvantages of biopolymers Biopolymers like starch alone cannot be used for the synthesis of strong biopolymers due to their low mechanical strength making them brittle with time and difficult to degrade due to high hydrophobic properties. Thereby natural biopolymers are used

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along with plasticizers, nanoparticles, and other polymers which have proven to enhance their mechanical and physical strength [77, 78]. Unlike starch-based biopolymers, cellulosic packaging materials are not suitable to be used as packaging material but are made of durable resin material for the bioremediation of charged anionic and cationic pollutants [79].

7.6 Conclusions Biopolymers are novel solutions for the bioremediation of toxicants, pollutants, heavy metals, and pesticides. The pollutants are either cationic or anionic in nature which bind with the charged polymers. They do not produce problems like sludge formation and waste disposal problems as they have very short shelf-life making them an environmentfriendly green technology alternative to the existing technologies. Many biopolymers like pullulan, polyhydroxyalkanoates and butyrates, dextran, polyvinyl alcohol and polycaprolactone, gelatin, collagen, wheat gluten, alginate, heparin, and pectin must be explored for their pollutant removal efficiency in the environment.

7.7 Summary This study focused on plant-based biopolymers which can mitigate pollutants. This opens up avenues for further research about green eco-friendly technologies based on biopolymers for ever-increasing environmental pollution problems. Biopolymers are bio-degradable since their origin is from natural products such as plants, animals, microbes, agricultural wastes, etc. Biopolymers like chitosan, pullulan, polyhydroxyalkanoates and butyrates, dextran, starch and cellulose, polyvinyl alcohol and polycaprolactone, gelatin, collagen, wheat gluten, alginate, heparin, and pectin to name a few which have a natural origin, have replaced traditional chemical counterparts in the mitigation of toxic pollutants. Biopolymers are also sourced from diverse sources like agricultural wastes and wellknown sources like plants, animals, and microbes. Biopolymer and its composites are utilized as coagulants and flocculants. Biopolymer composites are also widely used for diverse applications primarily due to their enhanced mechanical and thermal properties. Biopolymers from natural and synthetic sources can be modified and used as per the requirement. Presently cellulose, starch, carrageenan, alginate, xylan, inulin, pectin, and tragacanth are used for pollution mitigation. There are numerous other biopolymers that are to be studied in the environment for their feasibility to be used in wastewater treatment.

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Vipendra Kumar Singh, Priya Gunasekaran, Medha Kumari, Dolly Krishnan and Vinoth Kumar Ramachandran*

8 Animal sourced biopolymer for mitigating xenobiotics and hazardous materials Abstract: Over the past several decades, xenobiotic chemicals have badly affected the environment including human health, ecosystem and environment. Animal-sourced biopolymers have been employed for the removal of heavy metals and organic dyes from the contaminated soil and waste waters. Animal-sourced biopolymers are biocompatible, cost-effective, eco-friendly, and sustainable in nature which make them a favorable choice for the mitigation of xenobiotic and hazardous compounds. Chitin/chitosan, collagen, gelatin, keratin, and silk fibroin-based biopolymers are the most commonly used biopolymers. This chapter reviews the current challenge faced in applying these animal-based biopolymers in eliminating/neutralizing various recalcitrant chemicals and dyes from the environment. This chapter ends with the discussion on the recent advancements and future development in the employability of these biopolymers in such environmental applications. Keywords: biopolymer; chitosan; collagen; environmental pollutants; heavy metal ions; recalcitrant dye.

8.1 Introduction During urbanization and the industrial revolution, the overall environment’s poisoning by a hazardous mixture of xenobiotics has become a considerable environmental hazard globally [1, 2]. Xenobiotic chemicals like phenolic compounds, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), cosmetic products, azodyes, halogenated chemicals, pharmaceuticals’ active chemicals, nitroaromatic chemicals,

*Corresponding author: Vinoth Kumar Ramachandran, Department of Biotechnology, College of Science and Humanities, SRM Institute of Science and Technology, Ramapuram, Chennai, Tamil Nadu, India, E-mail: [email protected] Vipendra Kumar Singh, School of Biosciences and Bioengineering, Indian Institute of Technology Mandi, VPO Kamand, Mandi, Himachal Pradesh, India Priya Gunasekaran, Department of Biotechnology, College of Science and Humanities, SRM Institute of Science and Technology, Ramapuram, Chennai, Tamil Nadu, India Medha Kumari, Brainology Research Fellow, Neuroscience and Microplastic Lab, Brainology Scientific Academy of Jharkhand, Ranchi, Jharkhand, India Dolly Krishnan, Secretary cum Founder Director, Research Wing, Brainology Scientific Academy of Jharkhand, Ranchi, Jharkhand, India As per De Gruyter’s policy this article has previously been published in the journal Physical Sciences Reviews. Please cite as: V. K. Singh, P. Gunasekaran, M. Kumari, D. Krishnan, V. K. Ramachandran “Animal sourced biopolymer for mitigating xenobiotics and hazardous materials” Physical Sciences Reviews [Online] 2023. DOI: 10.1515/psr-2022-0221 | https://doi.org/10.1515/9783110987188008

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chlorinated chemicals, and triazines severely affect the environment due to their persistent and non-biodegradable nature in the ecosystems [3–5]. Once hazardous and nonbiodegradable chemicals enter the environment, they eventually penetrate the food chain, producing detrimental effects at each trophic level, negatively affecting animal and human health. In the early 1960s, the discovery of dichloro-diphenyl-trichloro-ethane (DDT) and parallelly the detection of residues of methyl mercury in fish (and wildlife) pivoted the spotlight on ‘bioaccumulation of hazardous chemicals’ [6–9]. These xenobiotic chemicals have mutagenic, carcinogenic, teratogenic, and toxic impacts on lower to higher animals and human beings. Hence, the bioremediation of toxic nonbiodegradable chemicals from the environment is the need of the hour. These xenobiotic substances have been remediated by various physical and chemical methods like filtration, adsorption, electrolysis, coagulation, etc. Unfortunately, the techniques used are expensive, lack space, involves complex methods, have tight regulatory procedures urged on decontamination by many countries, calls for issues related to waste disposal, public unhappiness, and harmful by-products converted into more toxic than the native compounds [1, 10, 11]. The humans are estimated to be exposed to approximately 1–3 million xenobiotic substances in their lifespan [43]. Most of these chemicals enter the human body via drinking water, air, diet, changes in lifestyle, and drug administration. They undergo a wide range of detoxification processes that exhibit them in a less toxic form, more polar, and immediately excretable. Detoxifying the xenobiotic substances in the lower animals in the food chain may also affect human health. Partial detoxification in lower organisms in the food chain may influence the lengthening of human exposure to xenobiotic chemicals, such as hepatotoxic microcystins, a type of cyanotoxins from algal blooms as well as mycotoxins ingested by species of agriculture [44, 45]. However, the wellestablished principles of remediation of xenobiotic substances were outlined long ago. It was also identified that xenobiotic substance’s metabolisms could alter the drugs’ pharmacological characteristics or even initiate inactive chemicals into active forms [46, 47]. Biopolymers are obtained from a living species, a macromolecule synthesized from plants or animals [48–50]. Various isolated biopolymers have different functions, such as information storage and transfer, and few allow integrity in the form of hard shells [51]. Primarily, biopolymers are extracted from ‘biomasses,’ most from viscous or gels in water [52]. Biopolymers obtained from marine or animal sources have been extensively utilized in food sectors or other product development or commercial applications for many decades [53, 54]. These biopolymers are low-cost, biodegradable, and highly compatible, making them chemically and biologically deserving of use in many fields [50, 55]. Over the last two to three decades, animal-sourced biopolymers have been used for the bioremediation of xenobiotic and hazardous chemicals. Animal-sourced biopolymers have evolved as an environmentally-friendly, effective method with its potential application in bio-medical and food industries, tissue engineering, drug delivery etc. [50, 56, 57]. However, the utility of animal-based biopolymer in mitigating

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xenobiotic and hazardous materials is demonstrated in recent times. In this chapter, we outlined various types of animal-sourced biopolymers and its compatibility in remediating various xenobiotic chemicals and mitigation of hazardous chemicals.

8.2 Xenobiotics and its effect on environment Xenobiotics originated from the Greek word, xenos (foreign) and bios (life), denoting “foreign things in living form”. Xenobiotics are chemical substances of synthetic origin, alien to biological systems which generally includes environmental pollutants, pharmaceutical residues, improperly disposed medical wastes, petroleum effluents, pesticides, plastics, paints, pesticides, chemical from paper industries, car industries, additives, cosmetic products etc., which often gets accumulated into numerous life forms, having no metabolic function [58–60] (Figure 8.1). By various anthropogenic actions these substances are getting mixed into water, air and soil, responsible for causing pollution. It can be taken up by plants or eaten up by fishes, eventually paving its way to the food chain ultimately affecting humans, continuing the vicious cycle [61–63]. Currently, xenobiotic chemicals are a severe issue worldwide caused by man-made activities like industrial development and urbanization. The vast amount of hazardous chemicals directly released into the environment adversely affects the ecosystem. Xenobiotic and hazardous substances such as heavy metals, pesticides, oil spills in the ocean, fertilizers, and polycyclic aromatic hydrocarbons are extensively found in water bodies such as river ponds and lakes in ocean, soil, and sediments [3, 64].

Figure 8.1: Types and sources of xenobiotic compounds.

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Xenobiotic compounds such as dioxins, DDTs, nitroaromatics, PCBs, and PAHs are widely regarded as the primary menace to the soil ecosystems and have adverse influence on various metabolic processes of marine ecosystems [3, 65, 66]. The fuel combustion, industrial activities, military movement, and use of pesticides and fertilizers are the source of these detrimental xenobiotic compounds [67]. The urban industrial production, transportation, building construction, and housing resulted in surface and groundwater contamination in urban areas. For example, a numerous aquatic species is continuously exposed to xenobiotics throughout the year [60, 68]. The heavy metals such as arsenic, cadmium, lead, and mercury affect the physiological and morphological characteristics of plants in multiple ways. For example, changes in the photosynthetic pigments, protein, cysteine contents, leaf area, and the foliar surface of plants can be contributed by the particulate matter generated from the automobile sector [69–71]. Accumulation of various xenobiotics into our environment may instigate several health issues in humans such as organism mortality, genetic disorders, suppression of the immune system, metabolic diseases, allergic diseases, etc., and degradation of the environment [72–77].

8.3 Animal source-based biopolymers Biopolymers are generally organic molecules produced by living organisms that are made up of repeating units of monomers. It may either be repeated units of two or more than two different types of monomers or may be branched or heterogeneous in nature [78]. Animal-based biopolymers are beneficial due to their toughness, reusability, and flexibility [50, 79]. These biopolymers can be amalgamated with numerous natural and artificial substances to synthesize polymeric admixtures [80]. These animal-based polymeric compounds play crucial role in numerous sectors, including chemical, cosmetic, dairy, drug and pharmaceutical industries [81]. Recently, these animal-derived biopolymers have been most used in medical equipment, food additives, confectionary, and textile industry, as well as biosensing applications [50]. Due to their minimal toxicity, low immunogenic and high pharmacological properties, these biopolymers can also be used in the field of tissue engineering, wound covers, drug delivery systems, and tissue implants [51, 82]. There are distinct forms of biopolymers that are derived from animal sources [83, 84] (Figure 8.2). The advantages of naturally occurring polymers over synthetic polymers are as follows–biodegradable, biocompatible, biorenewable, cost-effective, economical, easy availability, ecofriendly, non-pollutant, wider application, safe, and non-toxic with no side effect. Despite the advantages of animal sourced biopolymers over synthetic polymers, there are few drawbacks in using it for commercial purposes. They are as follows–batch to batch variation during synthesis, chance of heavy metal contamination, chance of microbial contamination, low stability, slower production process and structurally more complex.

8.4 Animal sourced biopolymers for the mitigation of xenobiotic and hazardous chemicals

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Figure 8.2: Types of animal sourced biopolymers used for mitigating hazardous xenobiotic compounds.

8.4 Animal sourced biopolymers for the mitigation of xenobiotic and hazardous chemicals Several polymers such as collagen, chitosan, gelatin, keratin, and silk fibroin from various animal sources have been successfully employed in remediating hazardous xenobiotic chemicals (Table 8.1). The role of widely used animal-based biopolymers in mitigating xenobiotic chemicals and hazardous materials is listed below-

8.4.1 Collagen Collagen is most commonly occurring protein present in the animal body, fibrous in nature, and especially found in the connective tissue and flesh of mammals and, is used as a biopolymer for various clinical and industrial purposes [85]. The biological properties of collagen like biodegradability, biocompatibility, and low antigenicity have built collagen an excellent candidate for many applications. Mature collagen was observed as an excellent absorbent that is greatly crosslinked and is insoluble in water, can be mixed with other biopolymer or metals to enhance recovery and efficacy [86]. Mining and metallurgical industry, as well as nuclear industry releases a significant amount of toxic

170

Table .: Animal sourced polymers used for the mitigation of xenobiotic chemicals and hazardous materials. Animal sourced polymer Source

Mitigation of xenobiotic/hazardous chemicals

References



Collagen

Adsorption of malachite green and methylene blue dyes Adsorption of crystal violet dye from the industrial effluents Removal of mordant brown and direct red dyes, and metal ions from the waste waters Removal of hazardous chemicals, recalcitrant, and heavy metals from the industrial effluents and waste waters Adsorption of heavy metal ions Adsorption of heavy metals Removal of copper ions in the wastewater Mitigation of inorganic non-metallic pollutants and organic dyes Adsorption of heavy metal ions Adsorption of arsenic from water Mitigation of crystal violet from the aqueous medium Adsorption of heavy metal ions Adsorption of heavy metals and recalcitrant dyes Removal of iron from the contaminated waste water Adsorption of cationic heavy metals from the waste water Sequestering of hazardous dyes from the waste water Removal of the heavy metals from the contaminated soil Removal of heavy metals (Fe, Cu, Al, Ti, and Zn) from waste water and or nuclear fuel reprocessing flows

[] [] []

Mammalian cells, insects



Chitosan

Shells of shellfish, shrimp, crab, and crustacean waste materials

 

Polysaccharide Keratin

Sea creatures Feathers, hair, nails, wool, horn and hooves, stratum corneum, and scales



Silk fibroin

Silkworm, spider

 

Wool Gelatin



Chitin

Sheep Fish, goat, cattle hides, bones, fish, and pig skins Spiders, lichens or many insects, crabs, and crayfish

[–] [] [–] [, ] [, ] [–] [] [] [–] [] [] [] [–] [, ] [, ]

8 Xenobiotics elimination using animal-based biopolymers

S. No.

8.4 Animal sourced biopolymers for the mitigation of xenobiotic and hazardous chemicals

171

metal pollutants such as uranium (U), copper (Cu), and lead (Pb). The inappropriate throw down of metal waste, concentrated stockpiles, and leaking contamination produces a serious health effect to public through inhalation, ingestion of food and water, and dermal contact [87–94]. A magnetic N-doped carbon aerogel prepared from the sodium carboxymethyl cellulose/collagen composite has showed excellent adsorption capacity for malachite green and methylene blue dyes [12]. Similarly, a magnetic collagen nanocomposite from the fish scales was synthesized by mixing of iron nanoparticles with the collagen. These collagen biopolymer from fish and magnetic collagen nanocomposite have the ability to adsorb the crystal violet dye from the industrial effluents, and thus reducing the polluted water cytotoxicity [13]. A bio-based hydrogel prepared from collagen and guar gum was used for the removal of textile dyes such as mordant brown and direct red, and metal (copper and zinc) ions from the waste waters [14]. Also, several collagenic waste-based biocomposites/hydrogels have been employed for the efficient adsorption and costeffective removal of water pollutants such as hazardous chemicals (p-nitrophenol), recalcitrant dyes (safranine and brilliant cresyl blue) and heavy metals (Pb2+ and Hg2+) from the industrial effluents and waste waters [15–17]. Li et al. (2022) fused a collagen matrix to design a polyphenol-functionalized collagen based artificial liver (PAL) for the removal of heavy metals [18]. PAL shows excellent adsorption potentials for ions of Pb2+, Cu2+, and UO22+. PAL also demonstrates an excellent binding affinity for these ions even in the presence of a complicated environment of serum containing biologically relevant ions such as Mg2+ and Ca2+. The combination of polyphenol/collagen-based fully bio-derived hemoperfusion adsorbent for heavy metal with excellent efficacy and biosafety [18].

8.4.2 Chitosan Chitosan is an animal sourced biopolymer acquired by deacetylation of chitin obtained from waste of marine. It is widely used in various fields such as food additives and drug delivery chitosan is widely used in many fields due to its biocompatibility, biodegradable nature, and economically feasible properties [95]. Chitosan based adsorbents are used removing for inorganic non-metallic and xenobiotic organic pollutants, and these biopolymers are used for heavy metal adsorption [19, 96]. Copper is a heavy metal known for polluting water globally, which is largely from products of industries like fertilizer, pesticides, metal processing and electronics and so on [97–99]. Recently, chitosan stacking mats and sulfoethyl derivative of chitosan are used for the adsorption of heavy metals such as Cd(II), Cu(II), Hg(II), and Pb(II) in the environment [19–21]. The stack membranes of chitosan by the electrospinning have significantly enhanced the specific surface area and enhance the adsorption of copper ions. Stacking membranes of chitosan containing three layers attained adsorption equilibrium quickly, and had a highest absorbance of 276.2 mg/g. The absorbance rate was greater to almost all of the reported

172

8 Xenobiotics elimination using animal-based biopolymers

chitosan absorbents. Stacking structure of chitosan membranes showed multilayer adsorption nature and provided excellent efficacy. In future, stack membranes of chitosan may progress as a reliable method for the outline of environmental-friendly animal-sourced biopolymers for the removal of copper ions in wastewater [21, 22]. In addition to heavy metal adsorption, chitosan-based biopolymers and crosslinked chitosan/bentonite composite are used for the mitigation of various inorganic nonmetallic pollutants and organic dyes such as anionic azo dye, reactive blue 19, acid red 1 and reactive red 2 etc. [19, 23, 24, 96].

8.4.3 Gelatin Gelatin is a water-soluble proteinaceous substance which is prepared by the incomplete hydrolysis of collagen obtained from the bones of animals, skin, and white fibrous tissue. The main commercial sources of gelatin are cow bones, hides, pig skins, and fish. Because of its surface-dynamic properties, it has been widely used as emulsifying, foaming, and wetting agent in food, medical and pharmaceutical industries [79]. It is also used as an efficient adsorbent to remove heavy metals and other organic pollutants from the contaminated water. Gelatin-based composite beads have been successfully used for the sequestering of hazardous dyes such as Congo red, rhodamine, methylene blue, and Direct Red 80, from the waste water [36–38]. Recently, the removal of pollutants from the textile industrial wastes using gelatin/κ-carrageenan crosslinked polyacrylic acid hydrogel has been demonstrated [39]. Similarly, silver nanoparticles embedded in gelatin biopolymer have been employed in the reductive degradation of pollutants [40]. Similarly, polyethylenimine-grafted gelatin sponge and gelatin composite hydrogels have been used to remove the heavy metals such as Pb (II), Cr (VI), and Cd (II) ions from the contaminated soil [41, 42].

8.4.4 Keratin Keratin is a cysteine-rich filament protein, and the major source of keratin sources are appendages, skin, fingernails, hairs of the head, cloven hoof, scute, a layer of skin feathers, and wool. A modified keratin can serve as a potential biosorbent for removing toxic pollutants from water resources on account of exceptionally important role of exposed functional groups. Khosa and Ullah (2014) have developed a cost-effective method for the removal of toxic forms of arsenic from waters by using chemically modified chicken feathers [28]. Keratin nanoparticles were employed for the mitigation of crystal violet from the aqueous medium [29]. Arsenic is a commonly occurring environmental pollutant and is present in the groundwater, air, and soil [100]. The long-term utilization of arsenic affected water holds a potential carcinogenic property. The keratin/ graphene oxide-based biosorbents from chicken feather has exhibited successful removal of metal oxyanions such as arsenic (As), selenium (Se), chromium (Cr) and

8.5 Summary and future prospects

173

cations including nickel (Ni), cobalt (Co), lead (Pb), cadmium (Cd), and zinc (Zn) [30]. In addition, keratin/polyacrylic acid-based hydrogel and keratin/PET composite nanofiber membrane have been successfully demonstrated in improving the performance of adsorption towards Pb(II) and Cr(VI), respectively [31, 32].

8.4.5 Silk fibroin and wool Silk is one of the important animal-sourced biopolymers obtained by silkworms, and is used for various domestic and industrial applications. Silk fibroin has been reported to adsorb and abolish various toxic heavy metal ions (chromium, copper, cadmium, lead, thorium, and uranium ions) and dyes (acid yellow 11, naphthol orange, direct orange S, and methylene blue) from the contaminated water reservoirs [33]. Further, Pilley et al. (2022) has prepared silk fibroin for the removal of iron from the contaminated wastewater [34]. It has been reported that oxidized wool fibers possess excellent adsorbent potentials for cationic heavy metals such as Pb2+, Cd2+, and Cu2+ from the waste water [35].

8.4.6 Other sources The animal biopolymers derived from hen eggshell membrane and broiler chicken feathers have been employed successfully in the removal of the oxyanions Se (IV), Se (VI), As (III), and As (V) from the aqueous solutions [101]. Interestingly, a chemical modification of biopolymer carboxyl groups has dramatically enhanced the adsorption capacity of As (V) [101]. Similarly, biopolymers generated from the hen eggshell membrane and silk proteins were used for selective recovery of uranium and thorium ions from the dilute aqueous solutions [102]. A chick and duck feather-sourced bioploymers have been used for efficient adsorption of lead ions [103]. Furthermore, polysaccharide-based hydrogels from animal origin have been effectively used for removal and recovery of heavy metals from the industrial waste water [25–27].

8.5 Summary and future prospects Xenobiotics are challenging to mitigate due to their complex structures and magnification/bioaccumulation in living organisms. Various studies showed that partial degradation of xenobiotic chemicals is more deleterious components than the parental chemicals. Further, these recalcitrant dyes and chemicals can pollute soil and water, and have been associated with severe human and animal health issues. In the recent past, various methods (such as advanced oxidation processes, phytoremediation, adsorption, constructed wetlands, biotransformation, bioremediation, and membrane processes) are employed for the bioremediation of xenobiotic and hazardous chemicals. However, these

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8 Xenobiotics elimination using animal-based biopolymers

methods have some limited. Recently, biopolymers have emerged as a possible and effective solution to tackle such limitations. Recent researches have demonstrated that its unique characteristics such as biocompatibility and eco-sustainability, offer greater benefits and expand their potential use in tackling these environmental hurdles. With advanced research and development in biotechnology and public awareness, the applications of biopolymers have spread to various industries/sectors i.e., from consumer goods to high-tech applications. In particular, animal-based biopolymers have wider applications in the industries such as food, cosmetic, tissue engineering, drug delivery, and pharmaceutical sectors. To date, many technologies have been introduced for the mitigation of xenobiotic and hazardous chemicals from the environment such as physicochemical methods like precipitation ion exchange, membrane separation and biological methods by the use of different microorganisms. These technologies are promising, but they are expensive. In the past, carbon materials such as carbon nanotubes activated carbon graphene and carbon foam, nanosized metal oxides, and low-cost adsorbents are all well documented in the literature for the removal of xenobiotic chemicals and hazardous materials. But these technologies have some restrictions. However, acquiring cost effective and high adsorption capacity technologies for the removal of xenobiotic chemicals and hazardous chemicals is a challenging task. Due to excellent stability, minimal toxicity, biodegradable nature as well as renewable potential, animal sourced biopolymers have been employed for the effective mitigation of xenobiotic and hazardous chemicals in recent times (Figure 8.3). Though animal sourced biopolymers have been providing multiple opportunities in mitigating xenobiotic and hazardous chemicals, there are still a few areas that require

Figure 8.3: Mitigation of xenobiotics and hazardous materials using animal-based biopolymers.

References

175

further investigation. They are-At present, the technologies employing animal-based biopolymers in mitigation of xenobiotics are confined to laboratory level. Hence, more research should be carried out for its large-scale application. Further, its application is limited to the adsorption of a single type of heavy metal ions. To broaden the spectrum of animal-based biopolymer application in the removal of recalcitrant dyes from the industrial effluents, advanced research is the need of hour to have its wider applications. The research should also focus on the production of more structurally complex material to increase the adsorption efficiency of metal ions and dyes.

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94. Wang Z, Hu H, Huang L, Lin F, Liu S, Wu T, et al. Graphene aerogel capsulated precipitants for high efficiency and rapid elimination of uranium from water. Chem Eng 2020;15:125272. 95. Pal P, Pal A, Nakashima K, Yadav BK. Applications of chitosan in environmental remediation: a review. Chemosphere 2021;266:128934. 96. Fatullayeva S, Tagiyev D, Zeynalov N, Mammadova S, Aliyeva E. Recent advances of chitosan-based polymers in biomedical applications and environmental protection. J Polym Res 2022;29:259. 97. Fu F, Wang Q. Removal of heavy metal ions from wastewaters: a review. J Environ Manag 2011;92:407–18. 98. Asiabi H, Yamini Y, Shamsayei M, Molaei K, Shamsipur M. Functionalized layered double hydroxide with nitrogen and sulfur co-decorated carbondots for highly selective and efficient removal of soft Hg2+ and Ag+ ions. J Hazard Mater 2018;357:217–25. 99. Shi T, Jia S, Chen Y, Wen Y, Du C, Guo H, et al. Adsorption of Pb(II), Cr(III), Cu(II), Cd(II) and Ni(II) onto a vanadium mine tailing from aqueous solution. J Hazard Mater 2009;169:838–46. 100. Frumkin H, Thun MJ. Arsenic. CA Cancer J Clin 2001;51:254–62. 101. Ishikawa SI, Sekine S, Miura N, Suyama K, Arihara K, Itoh M. Removal of selenium and arsenic by animal biopolymers. Biol Trace Elem Res 2004:102:113–27. 102. Ishikawa SI, Suyama K, Arihara k, Itoh M. Selective recovery of uranium and thorium ions from dilute aqueous solutions by animal biopolymers. Biol Trace Elem Res 2002;86:227–36. 103. Kumari AR, Babu UK, Sobha K. Optimization of lead adsorption using animal biopolymers by factorial design. IJSID 2011;1:303–19.

Vardhana Janakiraman, Srinivasarao Sowmya and Mani Thenmozhi*

9 Biopolymer based membrane technology for environmental applications Abstract: The visible deterioration of environmental health, as witnessed for a few decades now, has been the subject of debate and research for a long time. In the desperation to remove the pollutants from the available natural resources, countless physical, chemical, and biological methods have been introduced. However, they hold a few drawbacks and tend to alter the nature of the resources. To avoid intentional alteration, physical and biological methods are put-together to develop biopolymer-based membranes that would help the crisis and sort out the preferences. The technique includes trapping industrial carbon dioxide and other gases, drinking water treatment, wastewater treatment, desalination, reclamation, and reuse. Membrane technology is still a hot topic for new openings. Biocompatibility, biodegradability, and cost-effectivity of biopolymers are the greatest assets for developing technology. The efficacy of biopolymer-based membranes is covered in this chapter and their techniques in helping the environment. Keywords: biocompatible; biopolymer; environmental risk; membrane techniques; pollution; remedy.

9.1 Introduction Biopolymers are long chain molecules which has naturally degradable monomeric units. They are produced from living things like plants and bacteria. They are either extracted from natural resources or synthesized from natural resources. They are formed with in the cells during the growth cycle in the process of metabolism. Since they are naturally engineered molecules, they are huge moieties with uniform molecular mass. They are biocompatible, biodegradable, renewable, and cost-effective materials that are being used in almost every field [1]. Recently, biopolymer-based membranes have come to light as prospective replacements for these synthetic polymers, giving rise to new and potent membrane fabrication technologies that aim for more ecologically friendly

*Corresponding author: Mani Thenmozhi, Department of Biotechnology, Vels Institute of Science, Technology and Advanced Studies (VISTAS), Pallavaram, Chennai 637001, Tamil Nadu, India, E-mail: [email protected]. https://orcid.org/0000-0002-7957-6648 Vardhana Janakiraman, Department of Biotechnology, Vels Institute of Science, Technology and Advanced Studies (VISTAS), Pallavaram, Chennai 637001, Tamil Nadu, India. https://orcid.org/0000-0002-8192-0735 Srinivasarao Sowmya, Department of Chemistry, Vels Institute of Science, Technology and Advanced Studies (VISTAS), Pallavaram, Chennai 637001, Tamil Nadu, India. https://orcid.org/0000-0002-4790-0247 As per De Gruyter’s policy this article has previously been published in the journal Physical Sciences Reviews. Please cite as: V. Janakiraman, S. Sowmya and M. Thenmozhi “Biopolymer based membrane technology for environmental applications” Physical Sciences Reviews [Online] 2023. DOI: 10.1515/psr-2022-0222 | https://doi.org/10.1515/9783110987188-009

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manufacturing techniques. Additionally, the superior performance of biopolymers in PV separations over conventional polymers has increased the use of these materials in separation processes. The mounting population and industries had polluted the natural resources to the extreme that there is an urgent requirement for technology to remove the pollutants without causing secondary pollution. Membrane technology is one among those that assist the environment in cleaning up efficiently. In the past couple of decades, membrane processes had acquired widespread use in a variety of industries, including, seawater desalination, water, and air purification, wastewater treatment, purification of chemical and biological products, pharmaceuticals, biotechnology, and many others. A semipermeable material is used in making the membranes. Upon applying a potential gradient, the selective thin layer cut the undesired materials off the polluted resources based on the affinity of the membrane and the pollutant, and the size of the pore and the material. The driving forces could be concentration gradient, electrical difference, temperature, or pressure. The filtration rate and the membrane separation properties demonstrate the efficiency of the driving force of the membrane [2]. Even before the introduction of the membrane processes, conventional filters were in use. However, those filters had several limitations such as causing secondary pollution to the environment was expensive and ineffectual. Improper disposal of the used membranes or the absorbents causes secondary pollution. Especially, the membranes made out of petrochemical (fossil) based polymers pose a high risk to the environment. Green environment-based initiatives and their principles raise awareness of the importance of environmental protection for future generations. Apart from the Green environment view, the consumers are fond of nontoxic or low toxic meters in the products along with low environmental impact. The membrane made out of high and easily degradable biopolymers, overcome the limitations quite effortlessly. However, the success of these products will be determined by the performance of the biopolymer membranes – if not highly effective as the other membranes, rather at the least similar to them. The vital part of the membrane process is the membrane itself. Hence the energy-efficient and sustainable membrane can be developed from materials that possess suitable physicochemical and thermo-mechanical characteristics. The process and production of a membrane with the biopolymer is simple. The usage is efficient since it is cheap and readily available. The flexibility of operations, high removal capacity, minor energy requirement, and modularity are the eye-opening advantages of biopolymers in the membrane process [3]. Since the effective separation and less hazardousness to the environment are conclusively proved by the membrane technology, the processes are looked upon over the conventional separation process such as coagulation, adsorption, photocatalysis, filtration, and ozonation. Though the proven technology has the upper hand in all aspects, it still is not devoid of disadvantages. An extensive collection of synthetic and nonbiodegradable polymers are used as raw materials in the manufacturing of the membrane.

9.2 Membrane production methods

183

These synthetic membranes possess an unfavorable hydrophobic property which results in membrane fouling. Membrane fouling is nothing but a process by which the particles that are to be filtered away get adhered to the membrane pores and block them. This unfavorable condition is a major setback in the membrane process as the membrane fouling requires further physical or chemical treatment to remove the blockage and reuse the membrane. Hence the maintenance cost will also be included in the process which is not feasible for commercial purposes [4]. To overcome the fouling, the synthetic polymers are replaced by biopolymers which are hydrophilic. Absorption and filtration can be easily done with this membrane made of biopolymers. However, the biopolymers are found to be fragile and delicate, and their tensile strength and elasticity are compromised without much effort. Under these terms, the biopolymers cannot be operated in a highly stressed condition. While, biopolymers are insoluble in common solvents, limiting their use in a variety of membrane processes [5].

9.2 Membrane production methods Different types of membranes for environmental application along with their methods of preparation with environmental application given in Table 9.1

9.2.1 Selective membrane surface morphology There are different types of membranes that can be prepared from biopolymers (Figure 9.1), each with their unique method of preparation, properties, and potential applications in the environment. One type of membrane is the film, which can be prepared using the solvent casting method. The thickness of the film can be controlled based on the intended application. These types of membranes have potential applications in water treatment and reverse osmosis. Another type of membrane is the porous membrane, which can be prepared using the breath figure or phase inversion method. The breath figure method produces a porous honeycomb structure with low pore density, while the phase inversion method produces a porous honeycomb structure with uniform pore size and density that can be controlled. Porous membranes have potential applications in water treatment and the adsorption of gases, such as in sensors and heavy metal removal. Nano-porous membranes can be prepared using the electrospinning method, which produces a nano-porous structure. These types of membranes have potential applications in the adsorption of gases and air filtration. Overall, biopolymerbased membranes have significant potential for environmental applications, including water treatment, gas adsorption, heavy metal removal, and air filtration. The method of preparation and properties of these membranes can be tailored to suit specific applications, making them a promising area of research for environmental scientists and engineers.

184

Table .: Types of membranes (Biopolymer) and their environmental applications. Method of preparation

Properties of the membrane

Environmental applications

Cellulose acetate

Phase inversion Solution casting, freezedrying, electrospinning

Alginate

Ionic gelation, electrospinning

Gelatin

Crosslinking, selfassembly

Water filtration for removal of organic and inorganic pollutants Removal of heavy metals and dyes from wastewater, biodegradable packaging materials Controlled release of fertilizers and pesticides, immobilization of microorganisms for environmental remediation Food packaging, wastewater treatment, and environmental sensors

[]

Chitosan

Biocompatible, hydrophilic, high mechanical strength, and high permeability Biodegradable, biocompatible, antimicrobial, high adsorption capacity, and low cytotoxicity Biocompatible, non-immunogenic, and low cytotoxicity

Silk fibroin

Electrospinning, solution casting

[]

Collagen

Self-assembly, electrospinning

Keratin

Electrospinning, solution casting Solvent casting, electrospinning Solvent casting, extrusion

Removal of heavy metals and dyes from wastewater, biosensors for environmental monitoring Tissue engineering for environmental restoration and waste management, biosensors for environmental monitoring Oil spill cleanup, biosensors for environmental monitoring Production of bioplastics and biocomposites, adsorption of pollutants from wastewater Production of biodegradable packaging materials, adsorption of pollutants from wastewater Production of biodegradable packaging materials, removal of heavy metals from wastewater

Lignin Starch Pectin

Ionic gelation, electrospinning

Biodegradable, biocompatible, adjustable mechanical properties, and celladhesive properties Biodegradable, biocompatible, tunable mechanical properties, and high tensile strength Biodegradable, biocompatible, adjustable mechanical properties, and celladhesive properties Biodegradable, biocompatible, and high mechanical strength Biodegradable, abundant, and low-cost Biodegradable, renewable, and low-cost Biodegradable, biocompatible, and lowcost

Reference

[]

[]

[]

[]

[] [] [] []

9 Environmental applications of biopolymer based membranes

Type of biopolymeric membrane

Table .: (continued) Type of biopolymeric membrane

Method of preparation

Properties of the membrane

Environmental applications

Polyhydroxyalkanoates (PHA) Polysaccharide-based hydrogels Chondroitin sulfate

Microbial fermentation

Biodegradable, biocompatible, and renewable Biodegradable, biocompatible, and high water content Biodegradable, biocompatible, and low immunogenicity

Production of biodegradable packaging materials, bioplastics, and biocomposites Controlled release of fertilizers and pesticides, soil stabilization, and wound healing in plants Production of biodegradable implants for marine life, wound healing in marine animals

Self-assembly, crosslinking Crosslinking, electrospinning

Reference [] [] []

9.2 Membrane production methods

185

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9 Environmental applications of biopolymer based membranes

Figure 9.1: Surface morphology of membrane.

Polymeric membranes are thin semipermeable films that are gaining interest among many researchers due to their extensive properties. Polymeric membranes can be prepared by various methods. Among them, solvent casting method, breath figure method, phase inversion method, and electrospinning method are the prominent methods. The solvent casting method is a simple and easy method for polymer membrane preparation. In the solvent casting method, the polymeric solution is cast on the support and dried to get the polymeric membrane. It can be air-dried, oven dried, or freeze-dried depending on the solvent used. The polymeric membrane of desired thickness can be obtained by controlling the area of the support material and the viscosity of the polymeric solution. The membranes prepared by this method are mainly used as adsorbents in environmental applications. The membranes produced by the breath figure method and phase inversion methods are highly porous. In the breath figure method, the polymer solution is cast on the support material and placed inside the vacuum desiccator with water at the bottom. The casted support material is placed above some distance from the water and a vacuum is maintained inside the desiccator. Due to the difference in the vapor pressure between the water and the solvent of the polymeric solution porous membrane is obtained. This type of film can be formed only when the solvent used for the preparation of polymeric solution is immiscible with water. Phase inversion also produces porous film but, in this case, the solvent used for the preparation of polymeric solution is miscible with water. The electrospinning technique produces nanoporous membranes. In this

9.3 Biopolymeric membranes

187

technique, the polymeric solution is converted into a polymeric nanofibrous membrane by the application of high voltage. The porous membranes can be customized according to their applications. The pore size and pore volume can be controlled by controlling the parameters. Among the porous membranes, nanoporous membranes are highly effective for environmental applications due to their nanoporous size and large surface area. The porous membranes can be used for many environmental applications like air filtration, adsorption of gases, water purification, desalination, heavy metal removal, etc [18].

9.3 Biopolymeric membranes 9.3.1 Membrane derived by bacterial fermentation The preparation of tissue regeneration structures for biological cellular metabolism and endorsement for controlled drug administration using polylactic acid (PLA) is common in the fields of health and medicine [19], but it has only recently been taken into consideration as a substance for membrane surface in relation with applications for water treatment. Tanaka et al. [20] created PLA MF membranes using PLA-1,4-dioxane-water solutions using thermally induced phase separation (TIPS). They were successful in creating membranes with pores that ranged in size from 0.6 to 4.4 m. Tanaka et al. [21] investigated the impact of manufacturing using TIPS on the functionality of MF membranes in future work. They specifically evaluated the membranes’ effectiveness in separating bacteria cells from protein molecules. These membranes offer a viable substitute to conventional membranes made of synthetic polymers typically used to treat water since they are constructed from recyclable components and a compostable polymer. Poly ethylene glycol (PEG) was used as a pore-forming by Chitrattha and Phaechamud [22] to create a porous PLA membrane. The same research evaluated how non-solvents (glycerine, ethanol, and isopropanol) affected membrane development and PLA matrix film pore formation [23]. If solvents that can partly solubilize the polymer were active, dense films were created. While combining PEF and PLA were combined in the molding solution, pores were visible in the structures. Additionally popular in tissue engineering, PLA serves a variety of functions in the development of medication delivery systems [24]. This is because PLA biodegrades into lactic acid, a transitional metabolite in Kerb’s cycle, because of its biocompatibility and absorbability. Recently, unique blended membranes were created using poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and PLA [25]. In comparison to pure PHBV membranes, the membranes created by combining these two polymers demonstrated greater strength and ductility. The natural degradation process could be sped up at the same time, which in certain uses might be too lengthy for membranes constructed only from PHBV. By employing nonsolvent induced separation using PLA combined with phosphate buffer saline, polybutylene adipate terephthalate, or

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9 Environmental applications of biopolymer based membranes

poly (3-hydroxybutyrate-co-3-hydorxyvalerate) with N-methyl-2-pyrrolidone (NMP) as a solvent and liquid as a non-solvent, Keawsupsak et al. [26] created biodegradable substrates to treat water. Polyether sulfone (PES), cellulose acetate (CA), and poly butylene succinate (PBS) have recently been combined to create blended membranes [27]. These two amorphous polymers were combined with PBS to create membranes that had stronger mechanical resistance and less crystallinity than PBS by itself. The system of PES-PBS demonstrated more capable characteristics when compared to CA-PBS systems at equivalent blend ratios, particularly in terms of enhanced tensile strength and decreased membrane crystallinity, in particular. PBS-PES-PEG combination was used to create new membranes for wastewater treatment.

9.3.2 Membranes based on biopolymers derived from vegetable sources In reverse osmosis (RO) and ultrafiltration (UF) procedures as well as to limit the number of microorganisms in raw water, CA membranes, which are made by acetylating the naturally occurring abundant polymer cellulose, have been employed widely on an industrial scale [27]. Newer materials like perfluoro polymer membranes are starting to replace CA membranes, but only because of their slight selectivity for CO2. Alginate is typically used in conjunction with CS to create multilayer membranes for water treatment applications where electrostatic interactions between both the Alginate’s carboxyl group poly-anions and nucleophilic amines’ poly-cations of CS chains “glue” the membrane coatings together [28]. The development of concoction alginate-CS membranes for the adsorption of herbicide was researched by Agostini De Moraes et al. [29]. In specific, the mixed polymeric bio membranes demonstrated the ability to simultaneously grasp the negatively charged herbicides in CS layer and adsorb the positively charged chemicals on the layer of alginate. In both their non-stretched and stretched forms, polyisoprene rubber membranes have been created and researched by Dobre et al. [30]. They investigated and researched the effects of the membranes on the diffusion of hydrogen, oxygen, nitrogen, methane, and carbon dioxide gases. According to the results collected, the degree of stretching in the membrane had an impact on the gas permeability. According to Liu et al. [31], antibacterial membranes can be made by combining degraded starch and chitosan as polymers and glycerine as a plasticizer. The development of the target bacteria was completely suppressed on the membrane surface, and the antibacterial activity of the produced membranes, demonstrated by E. coli, suggested the possible use of the starch and chitosan membranes in the therapeutic and food sectors. In order to create bio composite films, Weerawan et al. [32] worked on CMC and montmorillonite (MMT) as strengthening fillers in a starch medium. The ability of amylum to withstand water was increased by mixing nanoclay and CMC.

9.3 Biopolymeric membranes

189

9.3.3 Membranes based on biopolymers derived from animal sources As the first two abundant biopolymers in nature, cellulose and chitosan offer numerous opportunities for use in high-end applications such as water purification. Together are effective stain and heavy metal adsorbents. Chemicals such as glutaraldehyde, glyoxal, formaldehyde, and epichlorohydrin are employed to stabilize and enhance the performance of biopolymer adsorbents [33]. Biopolymers are used to remove contaminants such as nitrates, phosphates, fluorides, perchlorates, hydrocarbons, and pesticides, in addition to dyes and heavy metals. Various methods used for the functionalization of cellulose and chitosan biopolymers, the current state of study, and the metabolism involved in heavy metal and dye adsorption using nanocellulose and nano chitosan have been carefully reviewed [34]. The remediation of trace levels of metal ions like Cd(II) and Pb present in natural and treated water could be accomplished using functionalized nanofiber mats of cellulose and chitosan packed in miniature columns. The amounts of trace metals in the experimental water samples were undetectable because they were below detection thresholds. After percolating through the functionalized biosorbents in cartridges, the metal ions’ detectability was increased. These components could contribute to raising the standard of householders’ drinking water [35]. Using bovine collagen fibers and fibrils as their source of collagen, Maser et al. [36] created cross-linked hydrophilic membranes for PV. The pervaporate capacities of these membranes for the dehydration of ethanol, isopropanol, ethylene glycol, and acetone were evaluated. One of the key characteristics of these membranes was their capacity to maintain high flux even at low temperatures. Protein membranes are susceptible to high temperatures, extremely low pH, and microorganisms. The biopolymer that is most frequently employed for medicinal membrane use is collagen. In 1987, collagen membranes were first made available as superabsorbent materials. Due to collagen’s exceptional biocompatibility properties, various applications utilizing collagen membranes for guided tissue regeneration have been developed since then. According to Gimenes’s method [37] of blending sericin and PVA into a membrane using dimethylolurea (DMU) as a cross-linking binder. When compared to ethanol, the produced membranes showed a strong preference for water during PV operation [38]. Polylactic acid, polyethylene glycol, polyhydroxy alkonates, polybutylene succinate, cellulose, alginate, chitosan, starch, collagen, polyisoprene, and sericin based biopolymers are prepared using different solvents, however particular solvents only suitable for biopolymer membrane preparation for environmental application. Table 9.2 describes biopolymer preparation solvents and membrane formation.

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9 Environmental applications of biopolymer based membranes

Table .: Different biopolymer preparation solvents and types of membrane formation. Biopolymer

Solvent

Type of membrane

Polylactic acid

Acetone-dichloromethane

[]

Polyethylene glycol Polyhydroxy alkonates Polybutylene succinate Cellulose Alginate Chitosan Starch Collagen

Chloroform Formic acid

Porous membranes with uniform diameter of nanofibers Thin fibers with high porosity Nanofibers with uniform pore size Nanoporous membranes Porous membrane Crosslinked fibrous membrane Porous membrane Crosslinked fibrous membrane Crosslinked fibrous membrane

[] [] [] [] []

Porous membrane Porous membrane

[] []

Polyisoprene Sericin

Chloroform and dichloromethane LiCl with dimethyl acetamide Water  % acetic acid Dimethyl sulfoxide Ethanol with phosphate buffered saline Chloroform and dimethyl formamide Trifluoro acetic acid

Reference

[] [] []

9.4 Environmental applications of biopolymeric membranes Biopolymers are used for a wide range of environmental applications including the removal of heavy metals, fluoride, dye, herbicides, pesticides, radionuclide, and desalination, dairy wastewater purification, coagulation, and flocculation (Figure 9.2).

9.4.1 Heavy metal removal Biopolymer membranes have been widely studied for their potential use in heavy metal removal from water due to their high selectivity, biocompatibility, and biodegradability. These membranes can be designed with specific functional groups that enable them to selectively bind heavy metal ions, making them an attractive alternative to conventional synthetic membranes. Various biopolymers such as chitosan, alginate, cellulose, and their derivatives have been used in the development of biopolymer membranes for heavy metal removal, with promising results reported in several studies. Table 9.3 provides information on the heavy metal removal efficiency of different biopolymers. According to studies, cross-linked and modified chitosan adsorbents have a higher capacity than pure chitosan [50]. GO increased the firmness of CS and its effectiveness at adsorbing hefty metals (nickel, copper, arsenic, cadmium, and lead) [51]. Following the general procedure, they made the beads and changed them using polyvinyl alcohol (PVA) to

9.4 Environmental applications of biopolymeric membranes

191

Figure 9.2: Biopolymer in different environmental application.

remove the ions of zinc, copper, and chromium from the water. Modified chitosan was examined for its ability to remove chromium ions, it was discovered that modified beads exhibited a higher level of adsorption than unmodified chitosan. Even at low doses, Cr (VI) is the most poisonous type of chromium and is challenging to remove. This research concluded that pH 3 is optimal to remove Cr(VI) from chitosan beads, whereas pH 5 is best for removing Cr(III) as much as possible. The ability of chitosan powder to remove Zn and Ni was studied by Jaafarzadeh et al. [65] who also demonstrated how different parameters affect the ability of chitosan to coagulate. While increasing the pH of the solution, it determined that Zinc and Nickel removal rose from 10.1 to 3.4 %, 81.8 %, and 51.08 %, respectively. High pH levels cause increased adsorption and interparticle adhesion, as well as amino group deprotonations. Additionally, as the settling time is extended, zinc and nickel settle as additional floccule

192

9 Environmental applications of biopolymer based membranes

Table .: Different types of biopolymers in heavy metal removal. Biopolymer

Heavy metal(s)

Membrane type

Reference

Chitosan Cellulose Alginate Starch Silk fibroin Keratin Polyvinyl alcohol (PVA) Pectin Sodium alginate Gelatin Collagen Polydopamine Carrageenan

Pb, Cd, Cu, Ni, Zn, Cr(VI) Pb, Cd, Cr(VI) Cu, Cd, Pb, Zn Pb, Cd, Cr(VI) Hg, Cd, Pb Cu, Pb, Zn Pb, Cd Hg, Cd, Pb Cr(VI), Cd, Pb Pb, Cd, Cu Cr(VI), Pb, Cd Pb, Cd, Cr(VI) Cd, Pb, Cu

Ultrafiltration Nanofiltration Ultrafiltration Reverse osmosis Nanofiltration Ultrafiltration Nanofiltration Ultrafiltration Nanofiltration Ultrafiltration Nanofiltration Nanofiltration Ultrafiltration

[, ] [] [] [] [] [] [] [] [] [] [] [] []

in the presence of chitosan. Cu (II) ion adsorption was the subject of an investigation by Karthikeyan et al. [66]. To create beads that can endure the fluctuating pH circumstances encountered throughout the studies, chitosan and chitosan that had been chemically modified were created in the aforementioned work. Cu (II) was removed from wastewater using the produced composites. Chitosan membrane was created by Prakash [46] by mixing nylon 6 with the following uses the cross-linking compound glutaraldehyde in the ratios (1:1, 1:2, and 2:1). In order to characterize membranes, top-notch equipment such as Fourier transformed infrared spectroscopy (FTIR), X-ray diffractometer (XRD), thermogravimetric analysis (TGA), differential scanning colorimetry (DSC), and scanning electron microscopy was used. Cadmium and copper ions were removed using prepared adsorbents. The research found that at the concentration of 0.5 g/L of adsorbate, pH 5 was best for the produced adsorbent’s maximal cadmium removal effectiveness. This research concluded that the contact time also affected the adsorption process. In order to eliminate Pb (II) ions from aqueous solutions with various pH values, Jin and Bai [67] developed chitosan/PVA hydrogel beads. The largest lead removal, according to the authors, occurred at pH 14 4.0 and is pH-dependent when utilizing chitosan/PVA hydrogel beads. Removal capability declined as pH increased, and it was discovered to be minimal at a pH of around 6.4. Ngah and Fatinathan [68] conducted comparative research on the elimination of Pb(II) from single and binary metal systems utilizing chitosan, chitosan-GLA, and chitosan-alginate beads. The effects of numerous limitations, including the beginning pH, the dosage of the adsorbent, and the initial concentration of Pb (II), were also assessed. Chitosan, chitosan-GLA, and chitosan-alginate beads have respective adsorption capacities of 34.98, 14.24, and 60.27 mg/g. The exclusion was also tested in a binary system, which revealed modest adsorption between Pb (II) and Cu(II), reducing the volume for lead ions to bind to molecules. Lalhmunsiama et al. [38] mixed

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chitosan and 3-aminopropyltriethoxysilane with acetic acid and ethanol in an inert atmosphere to create the cross material. The pH 3.0–7.0, equilibrium in 120 min, and early As (V) absorption of 1.12–19.75 mg/L are ideal conditions for the investigation. The percentage of As (V) removal, according to the author, was 99.99 % for the beginning absorption (1.12 mg/L), but it reduced as the concentration rose and reached 62.10 % for As(V) 1/4 19.75 mg/L. For a concentration of 1.12–19.75 mg/L of As (V), the As(V) adsorbed onto the ChiAPTES (chitosan modified with (3-aminopropyl) triethoxysilane) rose from 0.559 to 6.13 mg/g. When utilized in the packed column under dynamic conditions with an initial As (V) concentration of 10.0 mg/L and a high percentage removal, ChiAPTES also had the maximum adsorption capacity of 2.576 mg/g. According to Rangel-Mendez et al. chitosan may be useful in fluoride removal adsorption techniques. At pH 5.0 and an initial fluoride content of 15 mg/L, the composite was found to have an effective fluoride adsorption capacity of 0.29 mg/g. The composite’s capacity was halved compared to pure chitin’s capacity [69]. In the case of radioactive metal removal, the biopolymeric membrane can be designed to selectively remove certain radioactive metals from contaminated water. For example, the membrane can be designed to selectively remove uranium or plutonium ions. The process of using a biopolymeric membrane to remove radioactive metals typically involves passing contaminated water through the membrane. The selective properties of the membrane will cause the radioactive metal ions to be trapped in the membrane, while allowing other types of ions to pass through. The trapped radioactive metal ions can then be removed from the membrane and safely disposed of. Traditional chemical methods for removing radioactive metals from the environment are problematic because they are not biodegradable, posing a risk to the environment. However, biological systems can also be unreliable, and high pollutant dosages may have adverse effects. To address this issue, researchers have developed a method that uses a combination of attapulgite and chitosan to flocculate and recover Cr(II), Pb(II), and Cu(II) ions over a wide pH range (3–7), achieving an 85 % chromium recovery and reduction with attapulgite alone and a 96 % recovery and reduction when combined with chitosan. Moreover, volcanic ash has been used to treat uranium Pb(II) and iron, resulting in greater than 90 % removal and extraction [70]. There are several types of biopolymeric membranes that have been studied for their ability to remove radioactive metals from contaminated water. Chitosan-polyvinyl alcohol (PVA) membranes: Chitosan-PVA biopolymeric membranes have been shown to have good selectivity for removing uranium and thorium ions from contaminated water. These membranes have been tested under a range of conditions and have been found to be effective in removing these radioactive metals. Polyethylene glycol (PEG)-polysulfone (PS) membranes: PEG-PS biopolymeric membranes have been developed for the removal of plutonium from contaminated water. These membranes have been found to have good selectivity for plutonium ions and have shown promising results in laboratory studies. Polyacrylonitrile (PAN)-polyvinyl chloride (PVC) membranes: PAN-PVC biopolymeric membranes have been developed for the removal of uranium and thorium ions from

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contaminated water. These membranes have been found to have good selectivity for these ions and have shown good removal efficiency in laboratory studies.

9.4.2 Dye removal Biopolymeric membranes have been extensively studied for their potential application in dye removal from wastewater. Some of the commonly used biopolymeric membranes for dye removal include chitosan, cellulose, and alginate. Chitosan, a biopolymer derived from chitin, has been reported to be effective in removing different types of dyes, including acid dyes, basic dyes, and reactive dyes. The mechanism of dye removal involves electrostatic interaction between the positively charged chitosan and the negatively charged dye molecules, as well as hydrogen bonding and covalent bonding. Cellulose, the most abundant biopolymer on earth, is also a promising candidate for dye removal due to its high surface area and porosity. Modification of cellulose with functional groups, such as carboxyl, amino, and hydroxyl, can enhance its adsorption capacity for dyes. Alginate, a biopolymer extracted from brown seaweed, has also been studied for its ability to remove dyes from wastewater. The negatively charged alginate can absorb cationic dyes through electrostatic attraction, while anionic dyes can be absorbed through hydrogen bonding and covalent bonding [71]. Synthetic colors usually withstand biodegradation, it is unsettling that they continue to exist in the environment. The preferred technique for dye removal is generally recognized as adsorption. Biopolymers have been extensively studied as potential economical and safe-for-the-environment adsorbents for dye removal. Chitosan-based adsorbents can also be used to remove basic colors. Basic blue 41 and basic red 18 are eliminated using the functionalized biopolymer adsorbent chitosan-ethyl acrylate (Ch-g-Ea). After the adsorbent was changed, dye removal increased noticeably, which could be attributable to the addition of many carboxyl groups to the chitosan backbone [72]. Rigueto et al. [73] confirmed that the composite made from gelatine recovered from fur wastes tanned with chromium (III) had an adsorption capacity for diclofenac sodium that was comparable to the compound made from type B marketable gelatine. Gelatine composites containing CoFe2O4 and multiwalled carbon nanotubes, for example, demonstrated increased efficacy in the acid red dye adsorption in the first 10 min, with limited progress thereafter due to the adsorbent elements actuality nearly exhausted and having no area to capture further contaminant molecules. The majority of the dye adsorption by gelatine composites takes place on a homogenous surface, where the ions form a monolayer on the adsorbent’s exterior and the intermolecular interactions between the adsorbent and adsorbate gradually weaken over time. The creation of adsorbent materials is crucial for the elimination of hazardous metals from wastewater. In adsorption studies with a multicomponent solution, Perumal et al. [74] created gelatine and chitosan hydrogel particles that were embedded in graphene oxide. This led to the elimination of more than 75 % of metals like lead (II), cadmium (II), mercury (II), and chromium (III).

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9.4.3 Herbicides and pesticides removal 2,4-Dichlorophenoxyacetate (2,4-D), an organochlorine chemical that has been sold commercially since 1945, is one of the first herbicides. It has low toxicity for humans; save for some acid and salt forms that can irritate the eyes. Two biopolymers, chitin and chitosan, could be employed to absorb this substance. The hydroxyl group governed the structure of chitin as well as the stereochemistry of chemical reactions and kinetics. Functional groups dramatically changed the absorption spectra when they were present. Tests on the 2,4-D recovery compound renewed interest in it as a biosorbent [75]. The efficiency of the chitosan nanocomposite beads as an adsorbent has been proven in a number of trials, and they may be studied as a potential biocompatible, economical, and environmentally acceptable technique for pesticide removal. A number of chitosan composites made with different metal oxide nanoparticles have been used to remove pesticides with success. Silver oxide nanoparticles (CS-AgONPs) and zinc oxide nanoparticles (CS-ZnONPs) were synthesized to remove permethrin from chitosan. At a starting concentration of 0.1 mg/L, CS-AgONPs nanoparticles were able to remove 99 % of the pesticide from permethrin. Using CS-ZnONP composites, 99 % of the permethrin was removed from a 25 mL adsorbate solution with a permethrin concentration of 0.1 mg/L [76]. The biobased polymers and biodegradable polymers can be categorized under the umbrella term “biopolymer.” Biobased polymers may not always be biodegradable, whereas the latter are materials that can be completely degraded by aerobic or anaerobic processes. One must keep in mind that not all biodegradable polymers are also biobased. The majority of biopolymers, however, come from natural sources and can be extracted manually or manufactured by specific types of organisms. Both chitin and chitosan were used by Rissouli et al. [77] to remove the herbicide linuron, but chitosan displayed significantly higher adsorption capacity than chitin did. At a pH of 5.75, adsorption capacity was highest in both cases. Abdeen and Mohammad [78] used chitosan prepared from shrimp shells to remove ethoprophos from aqueous solutions, achieving good results for physical adsorption of the compound. Chitosan has also demonstrated good isoproterenol removal activity. Agostini de Moraes et al. [29] looked into the efficacy of pure and multilayer alginate and chitosan membranes in the elimination of diquat, difenzoquat, and clomazone. It was shown that the polymeric material and the herbicide adsorb due to electrostatic interactions. The negatively charged alginate membranes were able to remove the positively charged diquat and difenzoquat, while the pristine chitosan membrane was unable to do so. Even more so, neither the negatively charged alginate nor the positively charged chitosan were able to remove the neutral compound clomazone. Arvand et al. [79] investigated how different adsorbent types affected oxadiazon removal. These adsorbents were tested: chitin, chitosan, bentonite, and activated carbon. It was found that chitosan and activated carbon, with their respective maximum activities at pH 6 and 2, were the most effective at removing the pesticide. Glyphosate was also removed

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using chitosan membranes, one of which also contained alginate. Sodium alginate salt, the most common and commercially available alginate, is made by treating brown algae with NaOH. A linear copolymer of mannuronic (M) and guluronic (G) acids, alginate is a water-soluble anionic polysaccharide with three distinct types of repeating units (blocks): all G residues, all M residues, or alternating M and G residues. There are over 200 distinct alginate structures possible due to variations in M and G content and block length across various alginate sources.

9.4.4 Water filtration New techniques for water treatment have been developed by researchers. Green water treatment strategies, which allow for water recycling, are also being pursued. Because of the incredible properties of biopolymers, it is ideal and appealing to use natural polymers in membrane synthesis, fabrication, and production to create completely biodegradable membrane materials. Pure biopolymers have been used to make membranes for water treatment. These biopolymers/membranes have the potential to be used as adsorbents. For example, cellulose biopolymers and derivatives are being transformed into ultrafiltration, nanofiltration, and osmotic membranes for water filtration. These membranes are particularly useful for removing contaminants such as dyes, microorganisms, heavy metals and salts, pharmaceuticals, pesticides, and oil/grease. To enhance the characteristics and performance properties of biopolymers, however, additional research is required. Biopolymers, such as cellulose, are primarily insoluble in common solvents, which presents a problem for their use in membrane production. Nonetheless, N-methylmorpholine-N-oxide can dissolve cellulose. Moreover, cellulose can be dissolved in dual-solvent systems, such as dimethylacetamide (DMAc)/lithium chloride (LiCl), hydrazine/thiocyanate, N-methylmorpholine-N-oxide (NMMO)/water, and ammonium fluorides/dimethyl sulfoxide. Fortunately, cellulose is compatible with other biopolymers, allowing scientists to create novel bio-based mixture materials. In contrast to functionalized/modified biopolymers, pristine biopolymers have a limited adsorption capacity. Thus, biopolymer modification remains optimal for enhanced adsorption– desorption capacities, increased compatibility with other biopolymers, and solubility in diverse solvents [80].

9.4.5 Water treatment Mechanical instability is the main disadvantage and limitation of biopolymers in water treatment applications. Because of the high pressures used in water filtration, biopolymers’ poor mechanical properties limit their application in water filtration. As a result, the biopolymeric membranes are susceptible to rupture. These characteristics, however, can be improved through modification processes. As a result, the modifications not only improve the mechanical stability of the membranes, but also their antifouling,

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self-cleaning, and water permeability. As a result, more research has been conducted to better understand the effect of combining various types of synthetic or natural polymers with biopolymers in order to achieve maximum separation performance, such as higher flux, swelling capacity, permeation, and selectivity [81]. The two techniques most frequently used in desalinization operations are vacuum distillation and membrane technology, which boil water at lower temperatures and lower pressure than typical (reverse osmosis). When crosslinked with the appropriate chemical, such as hemicellulose (diethylene triamine penta-acetic acid (DTPA) and polyamide-6), chitosan can also be used to absorb salts and heavy metals from water in addition to these techniques. The salt absorption capacity and weight loss in sterile water were evaluated using produced composites at the ideal values for elements including concentration, reaction time, and temperature. In the aforementioned research, the highest salt uptake was 0.30 g/g of prepared biosorbent [82]. Deacetylated chitosan (MW 20 kDa) powder treatment of dairy effluent is another application. Nutrients, lipids, oil, and fatty debris discharged by the dairy and food industries are the reason of the high COD, BOD, and turbidity of WW. To optimise the settings, experimental studies were carried out by varying a number of variables, such as contact time, stirring speed, pH, and adsorbent dosage. Results indicated that when mixed for 50 min at 50 rpm while maintaining a pH of 5, 150 mg/L of chitosan reduced COD by 79 %, turbidity by 93 %, and total suspended solids (TSS) by 73 % [83]. Chitosan is used in wastewater treatment plants as a flocculant and coagulant in addition to as an adsorbent. Common coagulants in wastewater treatment facilities include ferric chloride, ferrous chloride, poly aluminum chloride, hydrated aluminum sulfate, and cationic polymer (WWTP). Using chitosan powder and flakes, several types of wastewaters can be successfully flocculated and coagulated (for protein recovery). The chitosan-based flocculants’ charge neutralization, charge patching, bridging, and particle sweeping flocculation processes. High biochemical oxygen demand (BOD) and chemical oxygen demand (COD) suspended particles, oil, and grease, heavy metals, and other organic debris can all be treated with chitosan as a coagulant [82]. Carboxymethyl cellulose (CMC), cellulose nanofibrils (CNF), and bacterial cellulose (BC) membranes are all products of Males et al.’s work, in which they introduced new functionalities to cellulose. Azol and anthraquinone dyes were therefore effectively removed from wastewater by using these modified membranes. The anthraquinone dye was completely blocked by the CMC and CNF membranes. However, the modified biopolymeric membranes’ removal efficiencies were poor when tested with azo dyes. Because of their high adsorption capacity, biopolymers can aid in the clean-up of these contaminants [84].

9.4.6 Green hydrogen The membrane is a significant cost and performance driver in electrolysers and fuel cells, accounting for a significant portion of total system costs and defining the system’s

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efficiency, power density, and lifetime. Although the primary function of the membrane is to conduct ions while protecting the system from electrical short circuiting, OEMs are also concerned with many other key performance indicators such as gas crossover, water management, dimensional stability, and chemical and mechanical robustness. A polymer backbone and negatively charged ion exchange groups are typically found in polymer electrolyte membranes (PEM). To improve stability and reduce gas crossover, additional additives and reinforcements may be added. Perfluoro sulfonic acid (PFSA), a costly perfluorinated ionomer produced through the copolymerization of tetrafluoroethylene and perfluoro sulfonyl vinyl ether, is the most widely used membrane class for both electrolysis and fuel cells. The high complexity of the production route, as well as the toxicity of intermediates, limits the potential for cost reduction and slow production capacity expansion. In fact, only a few manufacturers worldwide handle the highly explosive precursors needed for PFSA synthesis. Several strategies for lowering the cost of traditional PFSA-membranes have been developed [85]. In addition to the water and wastewater treatment methods that have been covered so far in the review, biopolymers are also used in a wide range of other environmentally conscious applications. One such field is hydrogen generation, and the use of lignocellulosic polymers as substrates for biohydrogen production is a pertinent area of research given their abundant availability, renewable nature, and non-polluting properties. But because cellulosic polymers are not taken into account in this review, advancements and opportunities in this field are not covered. Alginate is the most obvious example of a biopolymer-based catalyst, but there are notable cases of other ones that are helpful in the process. A reusable catalyst for hydrogen generation from the hydrolysis of NaBH4 is cobalt grown in situ on macroscale alginate hydrogels. Alginate hydrogels have a promising future in the hydrolysis of borohydrides to produce hydrogen due to their low cost and environmental friendliness as well as their superior catalytic activity. In order to create samples of TiO2 and Au-TiO2 with high photocatalytic activity for the production of hydrogen from mixtures of water and methanol, alginate could also be used. In comparison to an equivalent sample made using the traditional deposition-precipitation method, the Au-TiO2 sample made using the biopolymer templating method was about eight times more active in hydrogen generation using a solar simulator [86].

9.4.7 Enhancing soil characteristics Soil strength is improved when the concentration of biopolymers is raised. The friction angle of the treated soil decreases over time, but the direct shear test showed that XG, GG, and BG tend to increase the cohesion of the silty sand. Also, it’s important to realize that a linear relationship between mechanical properties and biopolymer concentration is not always the case. That is to say, there is an optimum biopolymer concentration for each type of biopolymer-improved soil. This means that high

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biopolymer content in the soil does not necessarily equate to a strong soil. Biopolymer type, soil composition, and moisture levels can all affect what concentration of biopolymer is best [87]. In comparison to other biological soil treatment methods, biopolymer-based soil treatment (BPST) offers benefits in terms of speed and quantity/quality control. In particular, ensuring sufficient CaCO3 precipitation for soil strengthening through endo-cultivating microbial induced calcite precipitation (MICP) requires a great deal of time and resources (e.g., nutrients, aeration, and cultivation environment control), with the exact quantity of CaCO3 being highly variable and case-dependent. However, the foundation of BPST is based on the utilization of biopolymers cultivated in an exo-cultivation facility, where both quantity and quality can be strictly regulated. Additionally, uniform biopolymer-treated soil (BPTS) mixtures are created when biopolymers are mixed directly with soil, and these mixtures immediately strengthen due to the formation of an electrostatic biopolymer-soil matrix [88]. When combined with the negative charges on clay particles, xanthan gum forms a rigid plastic-like matrix. The soil type, moisture level, xanthan gum concentration, and mixing technique all play a role in xanthan gum’s reinforcing effects. Soil’s sheer strength can be increased by using guar gum and xanthan gum to improve the soil’s mechanical properties [89]. Large areas of land are losing their soil quality and becoming decertified as a result of global warming. Soil erosion can be mitigated by treating it with biopolymers, even at low concentrations, because they increase interparticle cohesion. These biopolymer treatments may be used to enhance current desertification prevention efforts. These measures are extraordinarily beneficial in arid and semiarid regions. Encapsulating agrochemical formulations in biopolymers could stabilize them and improve their efficacy as a biopolymer application in the agricultural sector. By removing the water from an oil-in-water emulsion stabilized with n-octenyl succinic starches as surfactants, Lavandin (Lavandula hybrida) essential oil was encapsulated in n-octenyl succinic-modified starches. For the encapsulation, the high-pressure precipitation technique of drying particles from a gas-saturated solution was utilized. By carefully selecting the operating conditions, oil losses resulting from its dissolution in supercritical CO2 or emulsion destabilization were minimized [90].

9.4.8 Construction sector The technology of biopolymer-based building materials is then presented to help the reader comprehend the functionality and benefits of biopolymers, followed by a discussion of the principal applications of biopolymers in various segments of the construction industry. Due to space constraints, only biopolymers with significant volumes of use are discussed here. Despite the increased use of biopolymers, their volume is frequently very limited.

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Soil must be fortified prior to its use as a building material, for which cement is widely employed despite its contribution to greenhouse gas emissions. Several researchers have examined the feasibility of substituting biopolymers for cement. The manner in which biopolymers interact with soil and strengthen it has been thoroughly analysed. The increased compressive strength of β-1,3/1,6-glucan-treated Korean residual soil wangtooth was accompanied by greater economic competitiveness and a lower environmental impact than cement. The optimal curing temperature of the polymer soil mixture was 60 °C. Thermal gelation polymers are also quite applicable for soil reinforcement in both land and water constructions. Clayey and sandy soils were fortified with gellant gum and agar gum, which are capable of hydrogen bonding. Due to its interaction with soil fine particles, which resulted in the formation of solid soilbiopolymer matrices, gellant gum was preferred for use in soils with significant fine content [91]. Exploring additional applications for biopolymers in the construction industry, they could be used as natural sealants for concrete cracks. In one study, Pseudomonas aeruginosa strains 8821 and PAO1 capable of producing extracellular polymeric substances were genetically modified by incorporating the gene sequences of Sporosarcina pasteurii to confer calcium carbonate precipitation ability and improve their performance as bio sealants [92]. These engineered strains offer promising prospects for the development of bio sealants that could be used in the future to protect the environment. Additionally, biopolymers reduce water-induced degradation and enhance the mechanical properties of earthen structures. Lignosulfonate use in construction has already reached its peak and will likely continue to decline, primarily due to the scarcity of sulfite liquor and changes in technology. New synthetic superplasticizers based on polycondensation or polycarboxylate chemistry have made inroads in the concrete and gypsum industries. The process of replacement will continue. Polymer muds derived from cellulose, starch, or synthetic polymers have gradually replaced dispersed lignite-lignosulfonate muds in oil well drilling. New drilling fluid systems based on biodegradable oils, such as palm oil esters or -olefins, are now available and continue to eat into the market share of lignosulfate and lignite. Consequently, a downward trend is likely for these products [93]. Starch and especially cellulose derivatives appear to maintain a strong position in the construction market, and volumes are anticipated to increase as more sophisticated building products that require these additives are created. This growth is also attributable to the spread of advanced technology such as machine plastering to countries that previously employed more conventional building methods. This shift from a laborintensive to an industrial approach to construction utilizing prefabricated building materials presents an opportunity for suppliers with derivation technology. Regarding technology, the industry will likely continue to chemically modify or blend its products with other chemicals to tailor them to specific applications. This is typical of a mature business, and significant innovations can be anticipated by employing new gums such as guar gum and by applying highly sophisticated starch and cellulose derivation knowledge to these new raw materials.

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9.4.9 Merits and demerits of biopolymeric membranes 9.4.9.1 Merits Biopolymeric membranes have several merits that make them a highly desirable material for various applications. One of their most significant advantages is biodegradability, as they are made of natural polymers that are biodegradable, making them environmentally friendly. Additionally, these membranes have low toxicity as natural polymers are nontoxic, ensuring they are safe for use in various applications. Another significant benefit of biopolymeric membranes is their high selectivity, which can be engineered for specific pollutants, making them effective for the removal of contaminants from wastewater and other environmental sources. Furthermore, biopolymeric membranes are relatively low-cost compared to traditional membrane materials such as ceramics and metals, making them cost-effective for large-scale applications. Natural polymers used to make biopolymeric membranes are renewable and can be obtained from sustainable sources, reducing their environmental impact. Biocompatibility is another benefit of these membranes, making them suitable for use in medical applications. Moreover, biopolymeric membranes can be designed with specific properties such as pore size and surface charge, making them versatile for a range of applications. Biopolymeric membranes require lower energy consumption for water treatment and other applications compared to traditional methods, making them energy-efficient. They can also reduce the waste generated during manufacturing compared to traditional materials, helping to reduce the environmental impact of production processes. Finally, biopolymeric membranes can be produced on a large scale using simple and cost-effective methods, making them an attractive option for a variety of applications. 9.4.9.2 Demerits Despite their many benefits, biopolymeric membranes also have some demerits that should be taken into consideration. One significant limitation is their lower mechanical strength compared to traditional membrane materials, which may limit their use in certain applications. Additionally, biopolymeric membranes may have poor stability in some environments such as high or low pH, which can affect their performance and longevity. Biopolymeric membranes may also have a limited temperature range and limited chemical resistance, which can restrict their use in high-temperature applications or applications involving certain chemicals. Furthermore, natural polymers used to make biopolymeric membranes may vary in composition and properties, which can affect the consistency and reproducibility of the membrane properties. Biopolymeric membranes can also be difficult to sterilize, limiting their use in medical applications. Some biopolymeric membranes may be challenging to recycle or reuse, leading to waste generation. Moreover, biopolymeric membranes may be more

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susceptible to biofouling, reducing their effectiveness and lifespan. Furthermore, some biopolymeric membranes may have limited chemical and physical stability, making them unsuitable for certain applications. Finally, some natural polymers used to make biopolymeric membranes may have limited availability or require specialized sourcing, which can affect their cost and availability.

9.5 Conclusion The increasing pollution at all levels begs for a long-term change in the system as a whole. Desperation in removing the already set pollutants paves the way to settling more pollutants as the removing materials are made up of nondegradable or partially degradable materials. This biopolymer membrane technology also has potential in other environmental applications, such as air filtration, soil remediation, and environmental sensing. For example, biopolymer membranes can be used to filter pollutants from the air, reducing the number of harmful particles in the atmosphere. In soil remediation, biopolymer membranes can be used to remove contaminants from soil, making it safer and more productive for agriculture. In environmental sensing, biopolymer membranes can be used to detect and quantify pollutants in the environment, helping to identify and address environmental issues. Overall, biopolymer membrane technology has the potential to be a game-changer in environmental applications. It provides a sustainable, eco-friendly, and effective solution for a wide range of environmental problems. As research and development in this field continue to advance, we can expect to see more innovative applications of biopolymer membrane technology in the future. Overall, the future of biopolymer-based membrane technology for environmental applications looks promising. Continued research and development in this field are likely to lead to new and innovative applications that can help address some of the world’s most pressing environmental challenges.

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29. Agostini de Moraes M, Cocenza DS, Da Cruz Vasconcellos F, Fraceto LF, Beppu MM. Chitosan and alginate biopolymer membranes for remediation of contaminated water with herbicides. J Environ Manag 2013;131: 227. 30. Dobre T, Parvulescu OC, Sanchez-Marcano J, Stoica A, Stroescu M, Iavorschi G. Characterization of gas permeation through stretched polyisoprene membranes. Sep Purif Technol 2011;82:202–9. 31. Liu F, Qin B, He L, Song R. Novel starch/chitosan blending membrane: antibacterial, permeable and mechanical properties. Carbohydr Polym 2009;78:146–50. 32. Nicharee W, Chalitangkoon J, Monvisade P. Self-healing hydrogels based on sodium carboxymethyl cellulose/poly(vinyl alcohol) reinforced with montmorillonite. Biointerface Res Appl Chem 2022;12: 4770–9. 33. Crini G, Badot PM. Application of chitosan, a natural aminopolysaccharide, for dye removal from aqueous solutions by adsorption processes using batch studies: a review of recent literature. Prog Polym Sci 2008; 33:399–447. 34. Olivera S, Muralidhara HB, Venkatesh K, Guna VK, Gopalakrishna K, Kumar KY. Potential applications of cellulose and chitosan nanoparticles/composites in wastewater treatment: a review. Carbohydr Polym 2016;153:600–18. 35. Musyoka SM, Ngila JC, Mamba BB. Remediation studies of trace metals in natural and treated water using surface modified biopolymer nanofibers. Phys Chem Earth, Parts A/B/C 2013;66:45–50. 36. Maser F, Stroher-Glowienka C, Kimmerle K, Gudernatsch W. Collagen film as a new pervaporation membrane. J Membr Sci 1991;61:269–78. 37. Gimenes ML, Liu L, Feng X. Sericin/poly(vinyl alcohol) blend membranes for pervaporation separation of ethanol/water mixtures. J Membr Sci 2007;295:71–9. 38. Lalhmunsiama, Lee SM, Lalchhingpuii, Tiwari D. Functionalized hybrid material precursor to chitosan in the efficient remediation of aqueous solutions contaminated with As(V). J Environ Chem Eng 2016;4: 1537e1544. 39. Huang C, Thomas N. Fabricating porous poly(lactic acid) fibres via electrospinning. Eur Polym J 2018;99: 464–76. 40. Dharneedar R, Xu W, Franklin R, Kanth N, Jambhulkar S, Shukla S, et al. Fabricating fibers of a porouspolystyrene shell and particle-loaded core. Molecules 2019;24:4142. 41. Emaimo AJ, Olkhov AA, Iordanskii AL, Vetcher AA. Polyhydroxyalkanoates composites and blends: improved properties and new applications. J Compos Sci 2022;6:206. 42. Tanaka TT, Kawaguchi M, Hashimoto S, Saitoh T, Kouya H, Taniguchi T, et al. Formation of microporous membranes of poly(1,4-butylene succinate) via nonsolvent and thermally induced phase separation. Desalination Water Treat 2010;17:176–82. 43. He Y, Zhang L, Zhang Y, Chen L, Wu Q, Duan J. Preparation of pectin ultrafiltration membrane and its application in heavy metal removal. Carbohydrate Polym 2015;134:56–62. 44. Yue C, Zhang G. Calcium ion crosslinked sodium alginate coated PVDF membrane for improved smart pH-responsive properties. J Environ Chem Eng 2022;10:108684. 45. Nadia S, Soltanieh M, Mousavi SM, Heydarinasab A. Preparation and characterization of porous chitosan–based membrane with enhanced copper ion adsorption performance. React Funct Polym 2020;154:104681. 46. Temesgen S, Rennert M, Tesfaye T, Nase M. Review on spinning of biopolymer fibers from starch. Polymers 2021;13:1121. 47. Zhao X, Gao J, Hu X, Guo H, Wang F, Qiao Y, et al. Collagen/polyethylene oxide nanofibrous membranes with improved hemostasis and cytocompatibility for wound dressing. Appl Sci 2018;8:1226. 48. Castro-Munoz R, Gonzalez-Valdez J. New trends in biopolymer-based membranes for pervaporation. Molecules 2019;24:3584. 49. Rangi A. The biopolymer sericin: extraction and applications. J Textil Sci Eng 2015;5:188.

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Anil Kumar Moola*, Muhil Raj Prabhakar, Baishali Dey, Balasubramanian Paramasivan, Sita Manojgyna Vangala, Ramya Jakkampudi and Selvam Sathish

10 Biopolymeric composite materials for environmental applications Abstract: The emerging phase of bioeconomy demands that human beings be concerned more with ecofriendly practices in every aspect of life. Thus, the demand for biopolymer/ biopolymer-based composite materials has witnessed a surge in recent decades. Biopolymeric composites at macro, micro, and nano scales have various applications in environmental cleanup. Biopolymers from natural resources have established an important position owing to their easy availability, abundance, and biodegradability. This review reveals the advantages of biopolymer usage in the field of environmental remediation over conventional practices and also the advantages of biopolymer composites over general biopolymeric material. Further, it focuses on the recent rapid development of nanotechnology, which has led to significant advances in the design and synthesis of biopolymer-based nanocomposites, with higher specific surface areas that can be functionalized to strongly adsorb contaminants in comparison with conventional adsorbents. It also presents the biopolymer-based composite materials separated on the basis of scale commonly used for environmental applications such as the removal of dyes, oil–water separation, and air filtration. This review also summarizes the benefits and drawbacks on biopolymer composite usage along with future perspectives to give an idea on the areas for researchers to focus on in the future. Keywords: biodegradability; biopolymers; environmental cleanup; nanocomposites.

Anil Kumar Moola and Balasubramanian Paramasivan contributed equally. *Corresponding author: Anil Kumar Moola, Department of Entomology, College of Agriculture Food and Environment, Agriculture Science Centre North, University of Kentucky, Lexington, KY, USA, E-mail: [email protected]. https://orcid.org/0000-0002-6617-4148 Muhil Raj Prabhakar, Baishali Dey and Balasubramanian Paramasivan, Department of Biotechnology & Medical Engineering, National Institute of Technology Rourkela, Odisha, 769 008, India, E-mail: [email protected] (M.R. Prabhakar), [email protected] (B. Dey), [email protected] (B. Paramasivan) Sita Manojgyna Vangala and Ramya Jakkampudi, Department of Chemistry Services, Excelra Knowledge Solutions, Uppal, Hyderabad, 500039, India, E-mail: [email protected] (S.M. Vangala), [email protected] (R. Jakkampudi) Selvam Sathish, Department of Biotechnology, Bharathidasan University, Tiruchirappalli, Tamil Nadu, 620 024, India, E-mail: [email protected] As per De Gruyter’s policy this article has previously been published in the journal Physical Sciences Reviews. Please cite as: A. K. Moola, M. R. Prabhakar, B. Dey, B. Paramasivan, S. M. Vangala, R. Jakkampudi and S. Sathish “Biopolymeric composite materials for environmental applications” Physical Sciences Reviews [Online] 2023. DOI: 10.1515/psr-2022-0223 | https://doi.org/10.1515/ 9783110987188-010

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10.1 Introduction Plastic, being an omnipresent material with high usage, has become a matter of serious concern as its negative impact is no longer restricted to the land but extended to water bodies, air, and the bodies of living organisms. According to statistics from around the world, 44% of seabird species, 86% of sea turtle species, and 43% of marine mammal species are at risk of consuming microplastic from marine waste [1]. Polymers provide a natural and greener solution to the aforementioned problem. Due to their variety, accessibility, and durability, polymeric materials, which have blossomed on world markets over the past 50 years, are essential to any product [2]. There are two types of polymers, i.e., biological polymers and synthetic polymers, both of which are helpful in making human life much better by providing comforts and facilitation to mankind. These are also responsible for leading a human life to the fullest via medication, nutrition, buildings, highways, transportation, drug delivery, etc. [3]. In this context, biopolymers made of lipopolysaccharides, polysaccharides, proteins, polyhydroxyalkanoates, or glycolipids that are obtained from microbial, plant, and animal sources have received a lot of attention in recent times due to the alarming issues caused by the use of petroleum-derived synthetic polymers and could be utilized for a variety of natural implementations [4]. Heavy metals and chemical dyes are two common contaminants that biopolymer materials are effective at removing. In conjunction with these, chronic contaminants such as nitrates, phosphates, perchlorates, fluorides, hydrocarbons, herbicides, and others have also been addressed. Additionally, biopolymers serve as naturally occurring coagulants and flocculants to cleanse storm water [5], minimizing the dependability on synthetic polyelectrolytes [6]. Natural fibers are widely utilized all over the world in a range of applications, including those in the aerospace and automotive industries, sporting events, the delivery of medical implants and drugs, garments, packaging, infrastructure, and construction, leathers and household equipment, and many housewares [7]. Plastic culture is a method that significantly utilizes plastic products for numerous uses in intensive farming [8]. Engineered biopolymers, including petroleum-based resins, castor oil–based nylons, vegetable oil–based polyesters, and soy oil–based emulsions, are manufactured to custom specifications designed for use in the automotive industry [9]. In the polymer industry, poly (lactic acid) (PLA) has attracted a lot of commercial interest among the natural polymers due to its unique mechanical qualities and biodegradability [10]. Biopolymers are involved in the development of antimicrobial textiles, as mentioned by Shahid and Mohammad [11]. For the environmental remediation of crude oil–polluted sites, biopolymers such as C8 (3-hydroxyoctanoate), C10 (3-hydroxydecanoate), C12 (2-hydroxydodecanoate), C14 (3-hydroxytetradecanoate), and C16 (3-hydroxydecahexanoate) can be widely used. Additionally, polyhydroxyalkanoate plays a vital role in pathogen survival and stress tolerance in hazardous conditions and low food supplies [12]. The presumed shortage of fossil resources is a major commercial driver for biopolymers, especially petroleum. Most conventional polymers currently available are

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made from crude oil [13], which acts as a pollutant for the environment. A major trend in recent years has been the substitution of bioplastics made from fossil fuels with compounds produced from renewable sources that are identical [14]. For example, poly (lactic acid), which is derived via fermentation from renewable sources like starch or sugar, is one of the most successful and popular bioplastics [15]. The low cost and reliable supply of fossil fuels can be achieved by biopolymers. In less than 20 years, petroleumderived plastics have almost completely replaced plant-based materials [16]. In this context, bio-based plastics, polymers, and biocomposites can provide more environmentally friendly substances with a lower impact on the environment. The term “biopolymer composites” refers to biodegradable materials that are augmented with a range of fibers derived from plants and animals and/or natural and/or artificial biopolymers [17]. Further, biopolymers can provide unique qualities like increased rigidity and strength, which when merged with recycled polymers can result in completely bio-based and recyclable systems [18]. Composite materials, which are constituted of a matrix and an active ingredient, are exceptional sorbents because of their remarkable chemical and mechanical stability. The most desirable ingredients for composite sorbents include biopolymers like bentonite and chitosan [19]. Nanotechnologies in the field of industrial water remediation have emerged lately improving the overall efficiency, cost, eco- and environmental-friendliness, as well as providing a greener approach to treating wastewater. Nanoscale particles, platelets, and fibers range between 1 and 100 nm [20]. Nanomaterials offer superior selectivity, sustainability, stability, and adsorption capacities than other substances. Polymer science and nanotechnology are the other areas of interdisciplinary research that will have a direct impact on environmental protection. Environmental protection will be directly impacted through an interdisciplinary approach involving polymer science and nanotechnology. Reddy et al. [21] deliberately explained the benefits of biopolymers, including reduced CO2 emissions, alternative products at a cheaper price, minimizing the toxicity toward the environment, and benefitting to rural economy. Biopolymer composites are more attractive due to their sustainability, low cost, high stiffness, lightweight, higher strength, good thermal properties, eco-friendliness of renewable materials, and health and safety of the manufacturer and consumers [22]. Some of the commonly used biopolymers in composite making are illustrated in Figure 10.1. Since nothing in our world is perfect, biodegradable polymers, which are recommended for older systems, contain a few limitations, including it is not intended to recycle biodegradable plastic along with other types of plastic. Moreover, improper handling results in an inefficient decomposition of the plastic, which can discharge flammable gases and carbon into the atmosphere [21]. Currently, biopolymers are used to minimize the negative environmental impact of “used” plastic products. This study aims to delineate the various biopolymer composites production methods in macro/micro/nano scale along with their applications in environmental clean-up. It also compiles their availability and abundance as well as their tuneable structural,

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Figure 10.1: Structures of commonly used biopolymer. (a) Chitosan, (b) cellulose, (c) alginate, (d) starch, and (e) poly vinyl alcohol.

physicochemical, mechanical, and biological characteristics. The advantages, drawbacks, research gap, and future perspective visualizing the use of biopolymer composites in this field are the other aspects of this review.

10.2 Production strategies and characterization of biopolymers-based composites (macro/micro/ nano level) Due to its low cost and ease of use, the precipitation approach, such as chemical precipitation, has historically been used to remove pollutants. Its inability to remediate environments with high pollution concentrations, however, restricts its economic application. When not renewed, ion exchange systems that produce resins could result in secondary contamination. They are also not cost-effective for treating huge amounts of wastewater. Adsorption, advanced oxidation, membrane separation, and ozonation are a few examples of cutting-edge processes with great efficacy. The ease of use and low cost of operation of adsorption, on the other hand, make it a superior method for eliminating environmental toxins. The development of effective, stable, and affordable adsorbents for application in batch size clean-up methods is receiving increased attention [23]. In this aspect, bio-based and renewable sources have caught the attention of many researchers as they are eco-friendly and sustainable compared to traditional methods, which are no longer economically feasible. Based on their structural moieties, engineering properties like biodegradability, absorptivity, and hydrophilicity/hydrophobicity enable biopolymers to become potential alternatives to their chemical/synthetic/nonrenewable

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counterparts. Bio-based polymers or biopolymers may be derived from animals, plants, or microorganisms and can be composed of repeating monomers forming proteins, polysaccharides, lipopolysaccharides, glycolipids, or polyhydroxyalkanoates [6]. Biopolymers can have a well-defined macro, micro, or nanostructure compared to the random structure of synthetic polymers; they can be broken down into smaller chains or monomeric units by environmental factors, reducing the threat to environmental security [24]. In order to overcome some of the drawbacks of polymeric qualities, such as weak mechanical performance, low resistance, constrained processing capacity, and long-term stability, biopolymer composites were developed. They are produced by adding the right fillers, such as metal, metal oxides, and natural fibers, to biopolymers to strengthen them [25]. There are several ways to create biopolymer composites (as shown in Figure 10.2). Reinforcement materials can be introduced to the growth medium as polymers are formed through the fermentation process, and their polymerization in the form of fibrils occurs extracellularly. These additional components, such as nanomaterials and polymer solutions, can combine with the produced polymers to produce composites. Another production process is the postsynthetic composite synthesis, where the reinforcement elements are treated with prepared biopolymers before being inserted inside of or adhered to the surface of the polymer matrix to create composite structures. Another synthesis technique is polymer blending, which involves combining two polymer solutions in various ratios before casting to create materials like composite films or fibers. Degradability, physical characteristics, mechanical strength, thermal stability, and biocompatibility are just a few of the characteristics of composite materials that can vary greatly. By altering the ratio of the matrix and reinforcing components, these characteristics can be changed [26]. Alginate-based compounds have been proposed for a variety of uses in wastewater remediation for the adsorption of pollutants due to their benign nature, biodegradability, durability, and water permeability. The benefits of stable biohydrogel beads’ network structure, surface moieties, and high surface area have led to their effective use as a

Figure 10.2: Various production strategies for synthesis of biopolymer composites.

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catalytic support material [27]. Alginate-based composites’ synthesis, or the physical and chemical cross-linking techniques used to create them, heavily influences both their properties and possible applications. Alginate-based composites have been created using four popular techniques: ionic cross-linking, electrostatic complexation, emulsification, and self-assembly. Ionic contact, crystallization, hydrophobized polysaccharides, stereo complex formation, protein interaction, and hydrogen bonding all contribute to the physical cross-linking of hydrogels. Contrarily, chemically cross-linked hydrogels are produced using gamma and electron beam polymerization, addition, and condensation polymerization and chain growth polymerization. These synthesis techniques each have advantages and drawbacks of their own. Physically cross-linked sodium alginate hydrogel is easy to make under mild circumstances; however, the gel strength is low [28]. Zhang & Chen [29] proposed that pH-dependent Pb (II) and Cu (II) ion sorbents were cross-linked starch graft copolymers with amine groups. This is because the amine groups on the surface undergo protonation and deprotonation. Guo et al. [30] developed cross-linked porous starch by hydrolyzing maize starch using α-amylase, cross-linking it with epichlorohydrin, and creating a brand-new biopolymer-based sorbent for removing methylene blue (MB) from water. Membranes for hemodialysis, distillation, micro-, nano, and ultrafiltration based on cellulosic nano- and microfibers that are made from cellulose nanomaterial mats embedded in a polymer matrix (cellulose triacetate, poly (ether sulfone)), polypyrrole, poly (acrylonitrile), poly (vinyl alcohol), poly (ethylene oxide), poly (3-hydroxybutyrate), and poly (vinylidene fluoride) [27]. Iota-carrageenan and polyamidoamine dendrimers are physically cross-linked in the presence of varied magnetic nanoparticle (NP) concentrations. Abdellatif et al. [31] created secure, environmentally friendly, and affordable magnetic aerogels (1%, 3%, and 5%). The aerogels’ high removal effectiveness was demonstrated by the evaluation of their adsorption behavior for the metal ions Cr (VI), Cu2+, Co2+, Mn7+, Cd2+, and the fast blue dye Alphanol. Cañizares et al. [32] examined the active entrapment of spirulina maxima in kappa-carrageenan as a tertiary treatment for diluted aeration-stabilized swine manure. The immobilized algae were subjected to several iterations of the effluent cycles. Gopi et al. [33] reported on the efficient treatment of wastewater by multifunctional biohybrid aerogels constructed of cellulose nanofibers (CNFs) and adorned with carbon nanocellulose (CNC). By adjusting the ratio of CNCs used during the freeze-drying process, hybrid bioaerogels were created that were decorated on the CNFs and could be reused at least five times without losing activity or efficiency. Thermal cross-linking between (2,2,6,6-tetramethylpiperidin-1-yl) oxyl (TEMPO)oxidized cellulose nanofibers (TOCNF), branched polyethylenimine (bPEI), and citric acid has produced micro- and nanoporous sponge-like systems with demonstrated sorbent efficiency against various dyes (such as Cibacron Brilliant Yellow, Brilliant Blue R, Orange II, and Naphthol Blue Black) [27]. This work successfully treated cotton waste thermally to create unique carbon microtubes, which were then employed as tannic acid (TA) sorbents. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, zeta potentiometer,

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and N2 adsorption and desorption techniques were used to examine the characteristics of carbon microtubes (CMTs). The temperatures at which CMT and TA were treated to produce the most stable solutions in water were 900 °C, 1300 °C, and 1100 °C, respectively. CMT treated at 1100 °C had the highest TA sorption capacity, which was found to be 596.5 mg/g [34]. Since the Moringa oleifera plant’s seed extracts have coagulation qualities that are excellent for purifying water, they have been utilized extensively for this purpose, especially in impoverished nations. Additionally, because M. oleifera seed husks have an embedded microstructure and a high carbon content, they can be utilized to recover high-quality activated carbon that can be used to cleanse water instead of activated carbon [35]. Zeolites are crystalline, microporous aluminosilicates with ion exchange capabilities that can be used in a variety of catalysis and separation processes for liquid and gaseous mixtures. The diffusion outside of the zeolite crystals can be effectively controlled by incorporating in chitosan membranes, and correctly built composite systems can find a wide range of uses in wastewater treatment. Clinoptillolite microcrystals were disseminated in 3% chitosan in a 1% aqueous acetic acid solution. During the gelling procedure, the chitosan gel was created and the zeolite crystals were enclosed [36]. A bio nanocomposite is a form of hybrid material made up of a combination of an inorganic solid having at least one dimension at the nanometric scale and a natural polymer or biopolymer. Particularly, when compared to conventional microfillers, nanostructures can have higher specific surface areas, surface energies, and densities. This can result in materials with novel and improved properties because of synergistic effects that are superior to those brought on by the simple rule of mixtures [37]. However, the difficulties with NP separation during the process and their subsequent recycling limit their application as aqueous solutions. These NPs are consequently immobilized on a polymer matrix, which can be made of biopolymers such as resins, chitosan, carboxymethyl cellulose, and cellulose acetate. The material’s mechanical, thermal, and biological properties are significantly improved by the integration of nanoparticles inside the polymer matrix. Over the past 20 years, a wide range of bio nanocomposites have been developed by intercalating high molecular mass biopolymers like alginate, cellulose, chitosan, starch, sacran, gelatine, zein, or polylactic acid into clay minerals like palygorskite, smectites, sepiolite, and micas. To date, the removal of heavy metals, pesticides, reactive dyes, and even newly developing contaminants like bisphenol A from aqueous media has all been accomplished using this novel class of biohybrid materials. Additionally, when clays and polymers are combined to create bio nanocomposites, some of the individual drawbacks of each material (particle size, poor specificity, sensitivity to pH, as well as low wettability) are overcome [38]. Based on the intercalation of chitosan in organically or natively occurring vermiculite (with hexadecyltrimethylammonium (HDTMA)), Padilla-Ortega et al. [39] created functional bio nanocomposites (HDTMA) for cadmium uptake. The materials were homogenized using ultrasound, and low-density macroporous foams were created from them. The electrostatic connection between the protonated amino

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groups and the negative charge in the natural vermiculite layers was responsible for the intercalation of chitosan, as per Fourier transform infrared spectroscopy (FTIR) analysis. Salgueiro et al. [40] presented kappa-carrageenan–coated superparamagnetic iron oxide nanoparticles for enhanced removal of MB from aqueous solutions. The generated superparamagnetic composite nanoparticles demonstrated an MB absorption ability dependent on the pH of the solution and included about 12 wt percent carrageenan, making them potential eco-friendly materials for MB removal through magnetic separation. In their study, Saxena et al. [41] evaluated the effects of reinforcement on water transmission while reinforcing acacia fibers, bleached softwood kraft fibers, and nanocrystalline cellulose to xylan/sorbitol films. The results of the experiment showed that the nanocrystalline cellulose composite films have a more closed structure than the control film. The most popular characterization methods for figuring out the interface of biopolymer composites include FTIR spectroscopy, laser Raman spectroscopy, solid state nuclear magnetic resonance (ssNMR) spectroscopy, ion scattering spectroscopy, Auger electron spectroscopy, X-ray photoelectron spectroscopy, wide-angle X-ray scattering (WAXS), and contact angle measurement. Microscopic visualization methods like the atomic force microscope (AFM), polarized optical microscope (POM), SEM, scanning tunneling microscope (STM), and field emission scanning electron microscope (FESEM) are used to examine the particle distribution, reinforcements in the matrix, surface interaction between the fiber and biopolymer, and voids. The necessary magnifications are used to capture the images for simple visualization and analysis. For the purpose of measuring the surface roughness of fibers or biopolymer composites, AFM uses high-resolution nondestructive analysis. The surface depth profile, surface morphology, physiochemical changes, and fiber–matrix interaction are also disclosed by these morphological approaches. The intensity of the band depends on the concentration of nanocellulose, and the FTIR analysis showed a significant interaction at the OH band, showing robust interfacial bonding between nanocellulose and the matrix surface. The effect of natural fiber on the crystallinity of biopolymer composites is researched using X-ray diffraction (XRD) analysis. The XRD data are mostly correlated with the FTIR analysis and the thermal, mechanical, and barrier properties of the composites. It is well known that adding natural fibers to biopolymer composites improves the interfacial bonding and crystallinity of the material, which in turn improves the mechanical properties [42].

10.3 Application of biopolymer-based composites Many biopolymers and biopolymer composites have shown significant potential in tackling contemporary environmental issues and have been successfully used in a variety of areas. Applications for waste water treatment have come into focus as a result of the characteristics of biopolymers and their composites. The cost of the clean-up

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procedure is decreased with the use of economical polymers as an adsorbent. Pollutant adsorption has historically made extensive use of composites. The primary characteristics of biopolymer composites, such as higher durability, processing capabilities, high functionality, and a vast surface area, accelerate the removal of impurities or pollutants from the environment by adsorption [43]. The biopolymer composites utilized for different environmental applications are shown in Figure 10.3.

10.3.1 Biopolymer composite with macro particles An aromatic polymer called lignin has a lot of active functional groups and fascinating electroactive redox characteristics. Using lignin and environmentally friendly methods, harmful colors can be effectively removed from wastewater effluents. Up to 10–25% of lignocellulosic biomass is composed of lignin. By using a solvent evaporation method, lignin-based chitosan composite membranes were created, which were then used to filter water of the MB dye [44]. With a 95% effectiveness, the membrane’s adsorption kinetics mirrored Langmuir’s adsorption kinetics. By repeatedly creating the membrane and assessing its adsorption performance, which remained unaltered from that of the fresh membrane, the reusability of the membrane was also investigated. Wang et al. [45] developed an environmentally acceptable nonsolvent-induced phase separation method for an antibacterial chitosan/polyvinyl alcohol blend system for air filtering. The membrane was made with a concentration of 30 wt% chitosan and a thickness of 300 µm. It had a gradient, interconnected porous structure without a skin layer that was 95.59% effective at filtering air. It was composed of pores of varying sizes, with the biggest pore being 467 nm in diameter and a surface porosity of 21.5%. It was determined that the thickness of the membrane was the most important factor in determining the filtering performance and that the direct interception of NaCl aerosol particles on the surface of the membrane was the most effective mechanism for their removal. Different applications of biopolymer macro composites are listed in Table 10.1.

Figure 10.3: Applications of biopolymer composites in environmental remediation.

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Table .: Different biopolymer macrocomposites and their applications. Biopolymer

Filler

Applications

Chitosan

Gelatin

Polyethylene oxide/ TEMPO-oxidized cellulose Carboxymethyl cellulose Carboxymethyl cellulose Chitosan

Chitosan

Removal of Pb (II), Cd (II), Hg (II), and Cr (III) Removal of Cu (II)

Cellulose nanofibril Poly vinyl alcohol Cellulose Cellulose Cellulose Cellulose nanofibril

Cellulose triacetate Starch

Guar gum and graphene oxide Removal of malachite green Acrylamide and graphene oxide Removal of ionic dyes Alginate Removal of glyphosate herbicide Graphene oxide Removal of broad types of antibiotics Cellulose Removal of ionic dyes from waste water Graphene oxide Removal of methylene blue Graphene oxide/-ethylRemoval of lead, zinc, cobalt, -methylimidazolium acetate and nickel from wastewater Graphene Removal of oil from waste Graphene oxide Removal of doxycycline, chlortetracycline, oxytetracycline, and tetracycline in pharmaceutical wastewater Activated carbon Ultrafiltration membrane for removal of uranium from water Acrylic acid Removal of ionic dyes

References [] [] [] [] [] [] [] [] [] [] []

[] []

Zhu et al. [46] produced a magnetic composite made of polyvinyl alcohol and chitosan using the wet gel technique. This composite has a capacity for adsorption of 14.39 mg/g during 2 h, and it attained 97.5% adsorption efficiency. The inclusion of -NH2 and OH groups in the composite was determined to be the cause of this composite’s increased Co2+ adsorption value. Cu (II), Fe (II), and Cr (VI) can be extracted from hydrogels made of dextran and starch that were produced with the monomers of acrylamide, N-isopropyl acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid and then cross-linked with N, N-methylene bis acrylamide [47]. Ion-exchange groups were included in the synthetic hydrogels, in addition to the hydrogels’ high water absorption capacity. The impact of functionalization upon metal ion uptake has also been investigated. The findings of this research could aid in the advancement of hydrogel-based technologies for extracting and purifying metal ions from water. An ultra-hydrophobic copper nanoparticle–coated cellulose aerogel (Cu/CEA) was created with the aim of separating oil and water. Li et al. [48] found that Cu/CEA has the potential to collect oily pollutants quickly and selectively. Furthermore, it has an excellent oil absorption capacity and good recyclability. The TiO2 nanoparticles were used

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217

to create an aerogel that was generated from gelatin, and glutaraldehyde was used to cross-link the aerogel with bPEI. It has been determined that the hierarchical porous structure of the aerogel and its highly amphiphilic surface are responsible for the exceptional oil/water separation capacity that it possesses in free mixes and emulsions. In addition, aerogel demonstrated a high ability for adsorption of cationic and anionic organic dye. The capacity of composite aerogel to effectively absorb copper ions from aqueous solutions was noteworthy. Most importantly, aerogel can be rejuvenated by the use of methanol, ethylenediamine tetraacetic acid (EDTA), and copper (II), respectively [49].

10.3.2 Biopolymer composite with microparticles Efforts to clean up the environment made extensive use of biopolymer composites based on the substance chitosan. Increasing chitosan’s capacity to absorb inorganic nitrates from wastewater discharge, chitosan is often blended with synthetic hydrophilic polymers such as poly vinyl alcohol (PVA) and polyethylene glycol (PEG). To increase its propensity to interact with nitrates in wastewater, the chitosan-PVA/poly glycolic acid microcomposite is activated at acidic pH, ionizing the amine group on the backbone of chitosan. Rajeswari et al. compared the two microcomposites for their nitrate adsorption effectiveness and found that the chitosan/PEG microcomposite had a higher adsorption capacity (50.68 mg/g) than the PVA/chitosan microcomposite (30 mg/g) [63]. As for the adsorption kinetics, the Freundlich model revealed that the reaction was endothermic and had a high affinity for nitrate. In an alkaline solution, the chitosan microcomposite can be regenerated for further usage. The adsorption of dyes and other colored substances from wastewater has become more common in recent years thanks to the usage of microhydrogels based on alginate. Although alginate by itself is an effective adsorbent for dyes, the use of composite micro hydrospheres comprised of alginate combined with other adsorbents has been shown to be a more effective method of removing dyes from wastewater. Beads made of calcium alginate and activated carbons were combined to make a composite material for the removal of MB from wastewater. When the pH was greater than 6, it was demonstrated that the adsorption of dye followed a pseudo-second order mechanism. In general, the study on thermodynamic parameters during the adsorption process, it was found that the adsorption occurred naturally and generated endothermic activity [64]. In addition, Benhouria et al. [65] synthesized an alginate-based microcomposite hydrosphere that was utilized for the process of removing MB from the wastewater. Simple synthesis is intended for the formation of a composite consisting of activated carbon, bentonite, and alginate. At a temperature of 30 °C, the maximum monolayer adsorption capacity of the hydrosphere for the adsorption of MB was measured at 756.97 mg/g. The application of the pseudo-second-order kinetic model was shown to be appropriate by the adsorption kinetics. The data on the equilibrium adsorption were a

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good fit for the Freundlich isotherm. After undergoing six rounds of regeneration, the composite demonstrated an adsorption absorption capability of greater than 70%. For the elimination of ionic dyes such as methyl orange and MB, a bioadsorbent was created by Sui et al. [66] employing the wet spinning approach. This bioadsorbent was made of calcium alginate and multiwalled carbon nanotube composite fiber. The adsorption efficiency for the elimination of ionic dyes has been improved by a factor of three as a result of the use of multiwalled carbon nanotubes. The composite behaved according to an adsorption isotherm of the second order. Further, they observed that the initial pH value is one of the most crucial elements that affects the dyes’ capacity to be adsorbed onto the composite. Table 10.2 enlists the different biopolymer microcomposites with their application. The leather manufacturing industries make heavy utilization of basic black dye, which is one of the most commonly used dyes in general. Aravindhan et al. [67] conducted research to evaluate the possibility of removing the basic black dye with calcium alginate microhydrogels. At an initial concentration of 300 mg/L, with 4 g/L of alginate dose, at a pH of 4.0, the maximum adsorption capacity of 57.70 mg/g was attained at room temperature. The Langmuir isotherm offers a better fit for explaining the adsorption of the dye by alginate beads, which implies that the binding surface is both homogeneous and monolayer, as was amply demonstrated by adsorption kinetics. The thermodynamic characteristics suggested a spontaneous endothermic adsorption mechanism, while the adsorption kinetics followed a pseudo-second order.

10.3.3 Biopolymer composite with nanoparticles A novel graphene oxide/sodium alginate/polyacrylamide ternary nanocomposite hydrogel with excellent mechanical performance was created by the polymerization of acrylamide and sodium alginate by free radicals in the presence of graphene oxide in an aqueous environment before calcium ions were ionically cross-linked. The hydrogel was fabricated by using graphene oxide as a catalyst. Reinforcing the sodium alginate/ Table .: Different biopolymer microcomposites and their applications. Biopolymer

Filler

Applications

Chitosan Cellulose and welan gum Chitosan/hydroxyapatite

Carboxymethyl cellulose Carbon nanotubes Manganese dioxide

Chitosan

Loofah powder

Chitosan

Bentonite

Removal of ionic dyes Removal of methylene blue Photocatalytic degradation of acid orange  dye Adsorption of surfactant, organic acids, and dyes Heavy metal adsorption

References [] [] [] [] []

10.3 Application of biopolymer-based composites

219

polyacrylamide nanocomposite hydrogel with graphene oxide allows for an increase in the hydrogel’s mechanical properties. Additionally, the nanocomposite hydrogels exhibit excellent elasticity. The robust interfacial interactions that exist between graphene oxide nanosheets and polymer chains are accountable too for this phenomenon. Because graphene oxide was included in the formulation, the composite hydrogels have excellent adsorption capabilities for both cationic and anionic dyes [73]. Zhuang et al. [74] created a brand-new class of porous graphene/alginate double network nanocomposite beads with a porous structure, larger surface area, and greater stability at higher NaCl concentrations. According to the Langmuir model of adsorption, the produced nanocomposite possessed a maximum adsorption capacity of 1.84 g/g even after undergoing 10 adsorption–desorption cycles. This was the case even though the material had been subjected to both conditions. The adsorption of Congo red 4B, acid red GR, and bright yellow K4G was investigated using material generated from cellulose by Jin et al. [75]. A nanocellulose/amphoteric poly-vinylamine nanocomposite microgel was formed in an acidic environment and found to be especially efficient at removing anionic dyes. It was shown that Congo red 4BS, acid red GR, and light-yellow K-4G each had maximal adsorption capacities of 869.1, 1469.7, and 1250.9 mg/g, respectively. In order to purify water using a thin-film composite membrane, silver and platinum nanoparticles were included into nanocellulose-derived composites as additives. These nanoparticles were used for the support layer of the membrane. Samples of nano-pure water, urea, and wastewater were used in the experiment to test the forward osmosis capability of the membrane. The research showed that altered composite membranes made of nanocellulose thin films for wastewater samples exhibited greater water fluxes and solute rejection compared to conventional membranes [76]. Microwave heating was utilized by Mostafa et al. for the synthesis of chitosan/zinc oxide (CS/ZnO) nanocomposite because of the reduced time required for reactions compared to traditional heating [77]. Composites made at 800 W of power for 10 min were discovered to be efficient at removing dye. Due to the presence of zinc cations on the surface, the nanocomposite additionally exhibited improved thermal characteristics and demonstrated better efficiency. According to the findings of the adsorption investigations, the optimal conditions for the removal of MB dye by CS/ZnO nanocomposite and CS were 20 mg/L and 60 mg/L at a pH of 9 for 60 min. The MB dye removal was improved from 81% to 96.7% under these circumstances attributable to the incorporation of ZnO nanoparticle in CS. Activated carbon, chitosan, and polyvinyl alcohol were used by Akter et al. to synthesize CS-AC-PVA beads. At 25 °C and a pH value of 5, the synthesized beads demonstrated a strong affinity for removing Pb (II) from water [78]. In contrast to the usual pH-dependent activity of the sorption mechanism, the CS-AC-PVA beads had about the same affinity at pH 4–6. However, the adsorption capacity in CS-AC-PVA beads rose with increasing concentration, and the kinetics model of Pb (II) shifting onto CS-AC-PVA beads followed pseudo-second-order kinetics, showing that Pb (II) ion was largely adsorbed on the CS-AC-PVA surface via chemical interactions. The thermodynamic

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Table .: Different biopolymer nanocomposites and their applications. Biopolymer

Filler

Applications

Phosphorylated nanocellulose Sodium alginate

Chitosan

Removal of Cd (II) ions from aqueous solution Removal of methylene blue by photocatalysis Removal of methyl violet dye

[]

Removal of Pb (II) and Cu (II) Removal of cationic pesticide – paraquat Removal of a surfactant: cetylpyridinium chloride

[] [] []

Adsorption and removal of neonicotinoid insecticide pollutants from aqueous solution Solid-phase extraction of metal pollutants from surface waters Adsorption of malachite green

[]

Catalytic adsorption of methylene blue (MB) from aqueous solutions

[]

Carboxymethyl cellulose Alginate Alginate Alginate

TiO/bentonite

β-cyclodextrin

Graphitic-carbon nitride and zinc oxide Au/Mica Montmorillonite Maghemite (γ-FeO) nanoparticles coated by citrate ions FeO–graphene oxide

Chitosan

Silver nanoparticles

Gum xanthan

FeO magnetic nanoparticles Titanium dioxide

Cellulose

References

[] []

[] []

analysis pointed to the exothermic character of chemical adsorption as the sorption mechanism. As a result of their high affinity for Pb adsorption in aqueous solutions and relatively straightforward production, CS-AC-PVA beads have emerged as a promising adsorbent for Pb removal in Pb-contaminated water environments. Biopolymer nanocomposites extends its application in various environmental remediation, few are listed in Table 10.3.

10.4 Benefits and limitations on the usage of biopolymers composites in environmental remediation Materials generated from biopolymers are not only environmentally friendly and renewable but they also offer superior performance while leaving a smaller carbon footprint. These polymers are utilized mostly due to the benefits that they offer, which include being chemically inert, lightweight, long-lasting, and flexible in terms of shape and size. Composite materials have the advantage of being able to have a range of qualities designed for them, which can change depending on what the composite will be

10.4 Benefits and limitations on the usage of biopolymers composites

221

used for. This flexibility in design is one of the advantages of composite materials. The programmability of these materials is their primary benefit, which now enables them to be utilized in a variety of contexts. Particularly, biopolymer-based nanocomposites offer advantages, including active functional moieties, dimensional change, and film formation, that make them suitable for usage as catalysts and adsorbent materials. Because they are less expensive, less likely to harm processing machinery, have good mechanical properties like tensile modulus and flexural modulus, improve the surface finish of molded composite parts, are produced from renewable resources, are flexible during processing, biodegrade, and present few health risks, natural fibers are preferable to synthetic ones. It is challenging to use biopolymers in extensive commercial applications due to their inherent limitations, which include their poor processibility, brittleness, hydrophilicity, insufficient gas and moisture barrier, inadequate compatibility, and electrical properties. These barriers need to be diminished with the appropriate changes in order to be used commercially as photocatalyst supports. Low production rates, thermal stability, and physicochemical resistance limit the use of biopolymers as photocatalytic membrane materials. Depending on their concentration, these photocatalysts can occasionally have hazardous consequences. The two main challenges encountered during the manufacture of NPs loaded polymeric membrane are NP aggregation and pore clogging. TiO2 clumping lowers the specific surface area, which leads to poor photocatalytic degradation efficiency. Although electrospinning is a simple method for creating membranes or nanofibers with a large surface area and high porosity, the membrane must be produced at a high voltage or the other hand low deposition rates and a reduced bombardment target area limits the sputtering process [89]. In comparison to activated carbons and zeolites, clay minerals are less effective at removing micropollutants from water due to their limited surface area. Additionally, after adsorption, it is challenging to remove clay particles from the solution, and the adsorption capabilities of the clay minerals are reduced during regeneration for reuse. Low water wettability, sensitivity to particle size, and pH dependence are some cons of polymeric resins, on the other hand. The main disadvantage of dried alginate beads is their weak porosity, which prevents the passage of heavy metals. After adsorption, tannin is challenging to separate since it is a molecule that is water soluble. Thus, one of the promising ways of overcoming these shortcomings is to prepare composites for improving their efficiency. Cross-linkers can also be used to compensate for inherent defects in biopolymers, such as insufficient mechanical stability, poor chemical and thermal resistance, and partial solubility in watery circumstances [90]. Different support materials have different shortcomings, such as (i) metals are expensive, thermally unstable with high mass loss and low reusability; (ii) issues with recovery and reusability exist for carbons; (iii) ceramics have low activity compared to the polymer; (iv) hydrophilicity of cellulose restricts the use of cellulose with hydrophobic pollutants; and (v) restrictions on the protonation of chitosan’s NH2 groups and dissolution in acidic medium, and moreover, polymers have low mass transfer [91]. The

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ability to synthesize and use nano, micro, and macro adsorbents for the removal of toxic metal ions and other toxic contaminants has been limited by the uncontrolled use of chemicals, catalysts, low yield, a series of by-products, and demanding experimental conditions. Environmental protection is a major concern despite the ability of ever-newer chemical strategies to produce precise structures with desirable properties [92].

10.5 Future perspectives In order to develop a sustainable circular economy and gradually decrease the heavy dependence of humans on plastic usage derived from non–eco-friendly sources, considerable efforts and research still have to be put into adapting renewable alternatives such as biopolymers/biopolymer composites and recycling of plastic waste to regenerate the damaged natural system. As most of the research is restricted to laboratory scale, the main constraints in the real time application of biopolymer composites for environmental applications lie in their inability to yield the same results as inside the laboratory and also in their incapacity to mimic real time conditions [93]. For example, at low pollutant concentrations, researchers have been able to specify a precise range of doses/parameters for ideal coagulation and flocculation, for effective wastewater treatment. But, when the volume increases at an industrial scale due to a lack of scale up data, the desired efficiency is not achieved [94]. Thus, further research needs to be carried out using the laboratory scale data for scaling up studies to achieve comparable efficiencies and reduce the risk of commercialization. Moreover, along with scaling up a process, the economical aspect also has to be taken into consideration. Further with the rapid urbanization and industrial advancement, the concentration and chemical nature of the pollutants keep changing, which requisites constant improvement in stability and chemical robustness of biopolymer composites as adsorbents. Newer biopolymer composites need to be developed with cost-effective green methods, with higher efficiency to reduce the dependence on conventional methods and also to remediate the newer pollutants. A better understanding of the mechanism and chemical structure of novel composites, along with the standardization of their synthesis methods, will help in better utilization. As most popular regenerating agents are harmful (e.g., EDTA) and/or harmful to biosorbent polymer backbones (like inorganic acids), researchers are yet to identify safer eluents and better regeneration procedures [95].

10.6 Conclusions Polymeric materials have been thriving in global industries that are widely used in aerospace, sports, medical implant and drug deliveries, textiles, packaging, infrastructure and building, upholstery and furniture, and many household products.

References

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Nondegradable synthetic polymer environmental pollution is a major global challenge that is only getting worse. This review discusses about the biopolymers, which has made an entry to minimize the downside characteristics of polymers on that account they have been a promising alternative for synthetic materials by being solitary solution to our mother planet. Biodegradability, sustainability, eco-friendliness, cost effectiveness, noncorrosive nature, and lightweight characteristics are the attributes of biopolymers along with significant strength of renewable materials by maintaining health and safety of manufacturer and consumers. The removal of heavy metal ions from industrial wastewater has been demonstrated to be a successful application of the bio nanocomposite as an adsorbent. The qualities of these hybrid materials will improve with the continued development of more environmentally friendly biohybrid composites. Additionally, the creation of novel biocomposites with regulated breakdown at the conclusion of their life cycles will reduce the buildup of uncontrolled garbage in landfills.

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Index 2,4-Dichlorophenoxyacetate 195 3-aminopropyltriethoxysilane 193 β-1,3/1,6-glucan 200 accumulation 47 acholetin 22 acid phosphatase 125 acquaintance 57 activated precursor 125 adsorbents 147, 152, 157, 161, 162 adsorption 84, 147, 148, 151, 152, 157, 158, , 161, 163, 171 aerogel 212, 217 agriculture 93 agro-industrial 41 alcaligens 9 alcohol 147, 159, 161 alcoholic 10 alginate 6, 37, 154, 160 alternative 78, 96 analytical 55 analytical instrumentations 68 analytical methods 71 animal sources 166 annual growth rate 139 anthropogenic actions 167 antibacterial 95 antioxidant 4 application 96, 120 aquaculture 79 arabinose 7 aromatic polyesters 93 arsenic 172 atomic force microscopy 64 attachment 157 automotive sector 94 autotrophic growh 137 bacteria 42 bacterial cellulose 41 bacterial fermentation 39 bead 12 beneficial 168 bibliometric 57 bibliometric analysis 31 bibliometrix R-package 57 bioactive 37 bio-admixtures 96

https://doi.org/10.1515/9783110987188-011

bioadsorbent 218 biobased 79 bio-based hydrogel 171 biobased PET 86 biochemical oxygen demand 197 biocompatibility 56, 82, 133, 169, 201 biocompatible 181 biocomposites 1, 103, 209, 223 biocontrol agent 95 biodegradability 4, 201 biodegradable 30, 78, 88, 147–149, 151, 153, 154, 158, 162, 163, 171 biodegradable plastic 78 biodegradation 194 biodeterioration 79 biodiesel 8 bioeconomy 34 bioelectrochemical 43 bioenergy 110 bioengineering 87 biofilm 43, 120 biological 1 biomedical 4, 136, 166 biomedical sector 95 bioplastic 43, 134, 209 biopolymer composites 217 biopolymer film 65 biopolymer networks in biology 56, 62 biopolymer 35, 55, 85, 103, 120, 147–149, 151, 153, 158–161, 166, 181, 208 biopolymer-based membranes 183 biopolymer-based soil treatment 199 bio-polypropylene 79 bioproducts 35 bioreactor 41, 132 biorefinery 30 bioremediation 147, 149, 153, 155, 158, 159, 166 biosynthesis 32, 121 blending 22 boost productivity 94 breath figure method 186 brittle 92 capsule 132 carbon footprint 87 carbon source 41 carrageenan 6, 36, 147, 152, 159–162

230

Index

cassette transporter 124 catalysts 221 cationic 147, 149, 154, 157, 159, 160 cell factories 126 cell growth 46 cellulose 2, 93, 147, 149, 151, 158–163, 221 cellulose acetate 188 cellulose degradation 85 cellulose nanofibers 42 characterization 55 cheap biomass 132 chemical gelation 65 chemical oxygen demand 197 chemical precipitation 210 chemisorption 157 ChiAPTES 193 chitin 44, 149, 158 chitin, chitosan 82 chitosan 4, 135, 147, 149, 153, 158, 159, 161–163, 193 chitosan/PEG microcomposite 217 cleaner 94 clinical applications 95 COBRA and Cameo 128 collagen 3, 68 collagen based artificial liver 171 collagen fibres 189 collision 20 commercialization 82 commercial-scale manufacturing 90 companies 88 composites 19, 42 compostable 187 conceptual 31 condensation 133 construction and electronics 81 construction materials 96 contact angle 68 contaminants 151, 152, 154, 155, 157, 160, 208 contaminated water 172 conventional methods 222 conventional non-biodegradable 80 corn-based polymers 82 cosmetic containers 88 cosmetics 22 cost-effective 201 creep 18 crucial components 71 crystalline 66, 136 crystallinity 81

curdlan 9 cytocompatible biopolymers 82 cytotoxic 4 DDT 166 deactivate cells 137 decomposed 130 deep knowledge 139 degradability properties 80 degradable 130, 181 degradation 148, 149, 151, 153, 158, 160, 162, 163 dendrimers 14 density analyzer 61 destabilization 34 detoxification 166 developed 152, 158 development 90 dextran 9 difenzoquat 195 differential dynamic microscopy 66 difficult to analyze 72 diffraction pattern 67 dimethylacetamide 196 dimethylolurea 189 diverse classes of materials 57 downstream processing 47, 139 downstream recovery 83 drug delivery 168, 222 drugs 97 dyes 147, 151, 154, 155, 160, 162, 163 dynamics and mechanics 65 eco-alloy 88 eco-friendly 130, 148, 151, 159, 202 ecological consequences 93 economic aspects 142 EDTA 222 efficiency 41 eggshell membrane 173 elasticity 18 electromagnetic 37 electron carriers 126 electronic devices 93 electrostatic attraction 194 emissions 90 emulsification 212 emulsions 208 encapsulating 199 encapsulation 64 endoenzymes 85 energy 20

Index

energy density 69 energy flux 126 environmental impact 36 environmental pollution 78 environmental toxins 210 environment-based 182 european bioplastics 87 exopolysaccharide 39, 120 exploration 142 extracellular 9, 124 extracellular proteins 69 extract 56 extraction 34, 35 extruded starches 69 fed-batch reactors 134 feedstock 95, 142 fermentation conditions 83 fiber-based 95 field emission scanning electron microscopy 63 film-forming 133 filtration 138, 183 fingerprint region 67 flash co-pyrolysis 131 flexibility 60 flexible 30, 133 flexural 18 flocculation 147, 148, 157 flowability 96 fluorescence microscopy 69 food industries 92, 166 food packaging sector 93 formation 147, 155, 157, 159 fossil fuels 209 FTIR 67 fucoidan 37 functionalization 44 gaming console cases 93 gelatin 5, 147, 153, 158, 159 gelatin composite hydrogels 172 gelatine composites 194 gelling 123 gelling agent 134 gene expression 92 genes 47, 122 genetic disorders 168 genomic studies 143 global warming 131 glycerol 134 glycoforms 13

glycolysis 46 glycosidic bonds 125 glyphosate 195 granule 133 gratings 14 green food sector 86 guar gum 7 gum 147, 155, 158, 163 harmful 92 hazardous 148, 160 hazardous chemicals 167 health issues 168 heavy metal removal 190 heavy metals 168 helical 12 heteropolysaccharide 39, 132 high dispersity 64 higher temperature 37 higher yield 137 high-resolution 63 hyaluronan 46 hyaluronan synthase 135 hyaluronic acid 5 hydrogel 5, 38, 212 hydrogel’s porosity 63 hydrogen bonds 38 hydrolysis 79 hydrolyzation 87 hydrolyzing glycosidic 85 hydrophilicity 221 hydrophobic BC aerogels 42 hydrophobic pollutants 221 hydrophobicity 136 hydrospheres 217 identification 67 iGEM registry 128 image analyzer 62 immunogenicity 82 improved mechanical 86 improved methods 143 indistinguishable 131 in silico pathway 129 industrial effluents 171 industrialization 78 infrared light 67 innovation 88 inorganic nitrates 217 inorganic non-metallic pollutants 172 instrumental analysis 72

231

232

Index

insulating 12 intermolecular 66 intracellular 47 intracellular assembly 126 inulin 147, 154, 159 invertase 8 investigated properties 70 ionic liquid 35 keratin 3 land filling 94 langmuir’s adsorption 215 levansucrase 132 light scattering measurements 65 lignin 17, 151, 158 lignin-based 92 lignosulfonate 200 linear sweep voltammetry 68 lipid carrier 134 lipopolysaccharides 211 low stability 168 low thermal degradation 137 macro/micro/nano scale 209 macromolecular expression 128 macromolecules 56 manufacturing 30 marine pollution 79 market expansion 86 material features 56 matrix 22 mechanical 14 mechanical damage 130 mechanical stability 136 mechanical strength 47 mechanisms 157, 158 medical industry 139 medicinal applications 88 metabolic engineering 31, 90 metabolic flux analysis 128 metabolic pathway 124 metabolite 83 metals 147, 151, 153, 154, 158, 159, 163 microaerophilic 43 microalgae 33 microbial fermentation 91 microbial Induced Calcite Precipitation 199 microemulsions 134 micro-fauna 85 microfillers 213 microhydrogels 218

microorganisms 39, 78 micropollutants 221 microporous 123 microscopy 57 microwave-mediated extraction 36 mineralization 79, 130 mining and metallurgical industry 169 mode of operation 132 modulus 20 molecular interaction 61 molecular weight 137 monomers 84 monooxygenases 85 montmorillonite 188 mucoadhesive 5 multifunctional qualities 43 mutant 46 nano- and microfibers 212 nano porous membranes 187 nanocellulose 219 nanocomposite 11, 93, 171 nanomaterials 151, 153, 163 nanomedicine 97 nanoparticles 151–154, 158, 159, 161, 163 nanotechnology 209 natural 147–149, 151, 153, 155, 158, 159, 163 natural fibers 211 natural renewable sources 81 natural sources 56 naturally occurring monomers 56 N-methylmorpholine-N-oxide 196 NMR 69 nondestructive analysis 214 non-optical microscope 65 non-pollutant 168 non-renewable 130 non-renewable petroleum sources 79 non-toxic 4, 133, 153 novel 152, 159 nucleoside diphosphate sugars 125 nutraceutical 38 nutrient 136 nutrient source 135 opportunities 88 optical 16 optical microscopy 62 orbital shakers 137 organic dyes 172 organic plastics 92

Index

organic wastes 38 oxo-biodegradable 92 oxyanions 172 packaging 79, 148, 153, 155, 158, 159, 162, 163 paradigm shift 88 pasteurization 137 pathway 44, 122 PCL 80 pectin 7, 147, 149, 151, 153, 155, 159–163 peptide-mass fingerprinting 132 peptidoglycan 46 petroleum products 80 PFSA-membranes 198 pharmacological 1 pharmacological properties 168 phase inversion 186 PHB 39 phosphoenolpyruvate 125 phosphorylation 44 photocatalytic activity 198 physical aging 137 physically 85 physicochemical 39, 152, 160 PLA 80 plant-based 78, 147, 148, 151, 158, 159 plasticization 18 plasticizer 188 plutonium ions 193 polarizability 61 pollutant adsorption 215 pollutants 101, 147–149, 151–155, 157, 159, 160, 162 pollution mitigation 105 pollution 147, 148, 161, 162 poly butylene succinate 188 poly (l-lactic acid) 60 poly vinyl alcohol 217 polyamides 30 polycaprolactone 19 polychlorinated biphenyls 165 polycyclic aromatic hydrocarbons 165 polydispersity index 137 polyether sulfone 188 polyethylene 148 polyhydroxyalkanoate 2, 30, 83 polyhydroxybutyrate 2 polylactic acid 187 polymer 148, 149, 151, 153–155, 157, 161–163 polymer analysis 67

polymer electrolyte membranes 198 polymer matrix 42, 213 polymer structure 83 polymeric resins 221 polymerization 84, 124 polymers 29, 78 polymorph 66 polynucleotide 12 polypropylene 84 polysaccharide 6, 149, 155, 163 polysaccharide-based hydrogels 173 polysaccharides 68, 80 polytetrafluoroethylene 21 polytheylene 135 polyvinyl alcohol 190, 216 potato 160 precipitation 138 preferred characteristic 137 pretreatment 35 probe sensors 64 production 31, 121 proteins 81 proteomics 133 PVA hydrogel beads 192 quality 137 Raman spectroscopy 68 reactive dyes 194 recovery 160 reduce odor 131 regulation 122 reinforced 16 relative properties 60 removal 147–149, 151–155, 157–163 renewable 16 renewable materials 209 reserve carbon source 83 resolution 63 scanning electron microscopy 62 scanning tunneling microscope 214 scopus 57 shape 62 shopping 93 signal transduction 122 silver oxide nanoparticles 195 sludge 159 soil-biopolymer 200 solubility 92, 96 solvent-based extraction 138 solvents 35

233

234

Index

sonication 36 spatial filtering techniques 62 special recycling techniques 83 specific 130 specific enzymes 81 sporopollenin 13 stability 61 starch 2, 147, 149, 151, 153, 154, 158, 159, 162, 163 sterilizing, 95 strains 136 strategies 38 stretchable films 91 structure 61 substrate tethering 123 substrates 92 sugar 155, 161 superabsorbent 94 suppliers 94 surface modifications 63 surface pores 63 sustainable 47 swelling index 70 synthase 125 synthesis 153, 158, 160 synthetic biology 91 synthetic biopolymers 81 technique 57 tensile 17 tensile strength 82 tensile testing 61 textile industry 168 TGA 67 therapeutic 120 thermal 94 thermo-mechanical 182 thermoplastic 19, 130 thermoplastic starch 88 TiO2 nanoparticles 216

tissue engineering 168 tomography 69 topography 65 total suspended solids 197 toxicity 158 traditional membrane 201 tragacanth 147, 155, 159, 163 transcription 122 transition 17 transition temperature 61 translucent 91 transmembrane flux 138 transmission electron microscope 63 transparency 61 tribology 20 trisaccharides 124 ultrafiltration 138, 151, 188 ultra-hydrophobic copper nanoparticle 216 ultrasound 35 uranium 193 utilization 88 utmost purity 143 UV absorbance 69 wastewater 172 wastewater remediation 211 water purification 189 water treatment 183, 196 water-resistant qualities 130 whey protein 135 widely accessible 90 Wzx/Wzy dependent pathway 124 xanthan 10 xenobiotic 158, 165 x-ray scattering 70 XRD pattern 66 xylan 7, 147, 154, 159, 162 zinc oxide nanoparticles 195 ZnO nanoparticle 219