Contents

Cover

Title page

Copyright page

Preface

Chapter 1: Introduction

1.1 Introduction

Chapter 2: Green Resins from Plant Sources and Strengthening Mechanisms

2.1 Introduction
2.2 Green Resins from Agro-Resources
2.3 Green Resins from Microbial Fermentation
2.4 Green Resins Using Monomers from Agricultural Resources
2.5 Strengthening of Green Resins using Nano-Fillers
2.6 Conclusions
References

Chapter 3: High Strength Cellulosic Fibers from Liquid Crystalline Solutions

3.1 Introduction
3.2 Fibers from Liquid Crystalline Solutions of Cellulose Derivatives
3.3 Fibers from Liquid Crystalline Solution of Nonderivatized Cellulose
3.4 Regenerated-Cellulose/CNT Composite Fibers with Ionic Liquids
3.5 Future Prospects
Summary
References

Chapter 4: Cellulose Nanofibers: Electrospinning and Nanocellulose Self-Assemblies

4.1 Introduction
4.2 Electrospinning of Cellulose Solutions
4.3 Cellulose Nanofibers via Electrospinning and Hydrolysis of Cellulose Acetate
4.4 Bicomponent Hybrid and Porous Cellulose Nanofibers
4.5 Wholly Polysaccharide Cellulose/Chitin/Chitosan Hybrid Nanofibers
4.6 Surface-Active Cellulose Nanofibers
4.7 Nanocelluloses
4.8 Nanocelluloses from Agricultural By-Products
4.9 Source Effects – CNCs from Grape Skin, Tomato Peel, Rice Straw, Cotton Linter
4.10 Process Effect – Nanocelluloses from Single Source (Corn Cob, Rice Straw)
4.11 Ultra-Fine Cellulose Fibers from Electrospinning and Self-Assembled Nanocellulose
4.12 Further Notes on Nanocellulose Applications and Nanocomposites
Acknowledgement
References

Chapter 5: Advanced Green Composites with High Strength and Toughness

5.1 Introduction
5.2 ‘Greener’ Composites
5.3 Fully ‘Green’ Composites
5.4 ‘Advanced Green Composites’
5.5 Conclusions
References

Chapter 6: All-Cellulose (Cellulose–Cellulose) Green Composites

6.1 Introduction
6.2 Preparation of ACCs
6.3 Structures and Properties of ACCs
6.4 Future Prospects
6.5 Summary
6.6 Acknowledgements
References

Chapter 7: Self-Healing Green Polymers and Composites

7.1 Introduction
7.2 Types of Self-Healing Approaches Used in Thermoset Polymers
7.3 Self-Healing Polymers from Green Sources
7.4 Summary and Prospects
Acknowledgements
References

Chapter 8: Transparent Green Composites

8.1 Introduction
8.2 Cellulose Nanofiber-Based Composites and Papers
8.3 Chitin-Based Transparent Composites
8.4 Electronic Devices Based on CNF Films and Composites
8.5 Future Prospects
8.6 Summary
References

Chapter 9: Toughened Green Composites: Improving Impact Properties

9.1 Introduction
9.2 Significance of Fiber Length in Toughened Fibrous Composites
9.3 Impact Properties of Green Composites
9.4 Role of Large Elongation at Break in Regenerated Cellulose Fibers
9.5 Toughened Cellulose Fibers and Green Composites
9.6 Conclusions
Appendix
References

Chapter 10: Cellulose Reinforced Green Foams

10.1 Introduction
10.2 Bio-Based Foams
10.3 Surface Engineering of Cellulose Fibres Used in Foams
10.4 Prospects
10.5 Summary
Acknowledgements
References

Chapter 11: Fire Retardants from Renewable Resources

11.1 Introduction
11.2 Fire Retardant Additives Based on Phosphorus and Nitrogen from Renewable Resources
11.3 Natural Phenolic Compounds as Flame Retardant Additives
11.4 Other FR Materials from Renewable Sources
11.5 Prospects
11.6 Summary
11.7 Acknowledgements
References

Chapter 12: Green Composites with Excellent Barrier Properties

12.1 Introduction
12.2 Biodegradable Polymers: Classifications and Challenges
12.3 Summary
Acknowledgements
References

Chapter 13: Nanocellulose-Based Composites in Biomedical Applications

13.1 Introduction
13.2 Nanocellulose Sources and Properties
13.3 Biomedical Applications of Nanocellulose-Based Composites
13.4 Summary
13.5 Prospects
Acknowledgments
References

Index

End User License Agreement

List of Illustrations

Chapter 2

Figure 2.1 Various categories of green resins.
Figure 2.2 Protein primary structure, amino acid residues and peptide bonds [11].
Figure 2.3 Levels of protein structure organization [12].
Figure 2.4 Chemical structures of amylose and amylopectin.
Figure 2.5 Chemical structures of PH3B, PHV, and PHBV.
Figure 2.7 Chemical structures of (a) L-lactic acid, (b) D-lactic acid ad (c) Polylactic acid (PLA).
Figure 2.6 Chemical formula of pullulan.
Figure 2.8 Typical polymerization processes for Polylactic acid (PLA) [115].
Figure 2.9 The general structure of clay-based nano-fillers [127].
Figure 2.10 Schematic illustration of two different types of thermodynamically achievable clay-reinforced nanocomposites [128].
Figure 2.11 (a) Basic structure of cellulose and (b) structure of a strand of cellulose.

Chapter 3

Figure 3.1 Illustration of a cellulose derivative: (acetoxypropyl) cellulose composed of anhydroglucose units with ether and ester substituents.¹
Figure 3.2 Raw pulp cellulose structure by WAXD pattern.²
Figure 3.3 Regenerated cellulose structure by WAXD pattern.³

Chapter 4

Figure 4.1 Cellulose: (a) cellubiose repeating unit; cellulose Iβ unit cell (b) top view along C axis; (c) along A axis [1] (Reprinted with permission from Industrial & Engineering Chemistry Research. Copyright 2015 American Chemical Society).
Figure 4.2 Electrospun CA (DS=2.45, 30 kDa, 20 w%) in 2:1 acetone/DMAc: (a) top and planar view, (b) cross-sectional view.
Figure 4.3 Electrospun cellulose acetate (CA, DS=2.45, 30 kDa) from 2:1 acetone/DMAc: (a) 20% CA collected on paper; (b) 20% CA collected on water; (c) 15 % CA collected on water, showing fiber packing as affected by collecting materials (a & b) and fiber size as affected by solution concentrations (b & c) [11] (Reprinted with permission from Journal of Polymer Science Part B: Polymer Physics. Copyright © 2002 Wiley Periodicals, Inc.).
Figure 4.4 Cellulose nanocrystals (CNCs) by sulfuric acid hydrolysis (64–65% H₂SO₄, 45 °C, 60 min): (a) AMF of CNCs from cotton linter; (b) protonation and scission of cellulose chains in amorphous domains; (c) esterification of surface hydroxyl to sulfate [20] (Reprinted with permission from Carbohydr. Polym. Copyright © 2010 Elsevier Ltd).
Figure 4.5 Electrospun cellulose nanofibers (inset) and cotton fibers (background).
Figure 4.6 Cellulose nanofibers from: (a) electrospinning of CA and alkaline hydrolysis; (b) self-assembling from freezing (–196 °C) and lyophilization (–50 °C) of CNFs from coupled TEMPO mediated oxidation and blending of rice straw cellulose.

Chapter 6

Figure 6.1 Chemical structure of cellulose (n: degree of polymerization).
Figure 6.2 Hierarchical structure of wood cellulose and characteristics of cellulose microfibrils. This figure is based on a figure in Ref. [10] and is produced with permission from Royal Society of Chemistry (© RSC, 2013).
Figure 6.3 (a) One-phase preparation of all-cellulose composites (ACCs). (b) Scanning electron micrographs of cross-sections of ACCs with different immersion times. Reproduction of this figure, modified from Ref. [60], with permission from Elsevier (© Elsevier, 2008).
Figure 6.4 Two-phase preparation of all-cellulose composites. Reproduction of this figure, modified from Ref. [63], with permission from Elsevier (© Elsevier, 2014).
Figure 6.5 Optically transparent all-cellulose composite film. Reproduction of this figure, modified from Ref. [62], with permission from American Chemical Society (© ACS, 2011).
Figure 6.6 Lengthwise sectional transmission electron micrograph images of (a) randomly and (b) uniaxially reinforced all-cellulose composites with 10% filler. Arrow indicates drawing direction. Reproduction of this figure, modified from Ref. [65], with permission from Springer (© Springer, 2016).
Figure 6.7 Mechanical properties of all-cellulose composites [27,60-65,67-70,73-77,79,80]: (a) modulus, (b) strength, and (c) strain at break versus filler content, and (d) modulus versus strength.
Figure 6.8 Fungicide-treated laminates are referred to as ACC-f, while the untreated laminates are referred to as ACC-u. Photographs of all-cellulose composites (30 × 30 mm²) and rayon-poly(lactic acid) composite (20 × 22 mm²) before and after soil burial testing at ambient temperature (T1) and elevated temperature (T2). Reproduction of this figure, modified from Ref. [97], with permission from Elsevier (© Elsevier, 2014).

Chapter 7

Figure 7.1 Schematic of the damage modes in polymer composites [3].
Figure 7.2 Three types of commonly used self-healing approaches: (a) capsule-based, (b) vascular, and (c) intrinsic methods [3].
Figure 7.3 Chemical self-healing reaction of DCPD and Grubbs’ catalyst resulting in cross-linking network in the resin [5].
Figure 7.4 DCPD-loaded silica microcapsules produced using sol-gel encapsulation [83, 84].
Figure 7.5 Microcrack healing in epoxy composite containing GMA-loaded microcapsules. Hydroxyl and ternary amine groups can cross-link on the fracture surfaces: (a) distribution of the released GMA in the damaged region and (b) hydrogen bonds formed between the microcrack surfaces [45].
Figure 7.6 Optical microscopy images of healing of a typical scratch in epoxy paint films containing linseed oil-loaded UF microcapsules for 90 s [51].
Figure 7.7 Healed epoxy film containing Tung oil-loaded UF microcapsules: (a) artificial scratches before healing, (b) healed scratches after 72 h, (c) SEM image of a scratch before healing, and (d) SEM image of a scratch after 72 h healing [96].
Figure 7.8 Self-healing of resins prompted by sunlight: (a) after healing, and (b) before healing of the microcrack under fluorescence microscopy [22].
Figure 7.9 Typical load–displacement curves of virgin and healed epoxy resins with (a) 5 wt% DCDP-loaded microcapsules containing 5 wt% Grubbs’ catalyst and (b) 2.5 wt% Grubbs’ catalyst [53].
Figure 7.10 SEM image of fracture surface of self-healing epoxy composite reinforced with woven glass fabrics [103].
Figure 7.11 The dual microcapsules system contained both epoxy and polyamine microcapsules in the epoxy resin [61].
Figure 7.12 Self-healing epoxy vinyl ester coating after 24 h healing at RT: (a) optical microscopy image of scratches before healing, (b) optical microscopy image of scratches after healing, (c) SEM image of a scratch before healing, and (d) SEM image of a scratch after 24 h healing [66].
Figure 7.13 Typical load–displacement curves of self-healing composite contains 5 wt% epoxy-loaded microcapsules and 2.5 wt% the mixture of pentaerythritol tetrakis(3-mercaptopropionate) and tertiary amine-loaded microcapsules as the hardener resulted in 103.3% healing efficiency after 24 h at 20 °C [30].
Figure 7.14 Scheme of multi-layer single capsules containing healing agent and catalysts [72].
Figure 7.15 Life cycle of a self-healing pristine woven composite laminate with dual channels (the red channel is filled with epoxy and the blue channel is TETA as the hardener) in the dual vascular network [110].
Figure 7.16 Vascular self-healing is organized according to the connectivity of the vascular network. One-dimensional (1-D) networks are obtained from hollow channels/fibers filled with healing agent(s), Two- and three-dimensional (2-D and 3-D) vascular healing networks require more sophisticated manufacturing to ensure connectivity [3].
Figure 7.17 The range of the healing efficiency, damage volume, and rate depending on the three types of self-healing approaches [3].
Figure 7.18 Self-healing test methods: (a) a SEM image of microcrack plane morphology for a Mode I tapered double-cantilever beam (TDCB) self-healing epoxy specimen containing DCPD capsules and Grubbs’ catalyst [18], (b) optical images of Mode I crack growth in a double cleavage drilled compression (DCDC) intrinsic self-healing specimen based on the Diels-Alder–retro-Diels-Alder reversible bonding. Stable crack growth (left) is healed (right) after 10 h at 85 °C and 0.35 MPa clamping pressure and after 3 h at 95 °C with no clamping pressure [126], and (c) optical images of mixed-mode cutting (left) and healing (right) of an intrinsic self-healing polymer based on molecular diffusion and entanglement of dangling chains in a weak polyurethane gel. A polymer sample is stretched over a cylinder for viewing crack damage and healed morphology [125], and (d) optical image (top) and scanning electron micrograph (bottom) of a Mode III trouser tear self-healing polydimethylsiloxane (PDMS) specimen [104].
Figure 7.19 SEM images of microcrack morphology for Mode I fatigue test of a TDCB self-healing epoxy specimen containing DCPD-loaded microcapsules and dispersed Grubbs’ catalyst [132].
Figure 7.20 In situ Raman microscopy observation: (a) the typical Raman spectra collected from the center of the fracture surface of a self-healing specimen with 15 wt% GMA-loaded microcapsules, and (b) time dependence of the characteristic Raman peak area ratio, showing the consumption of GMA during polymerization as a function of time [46].
Figure 7.21 Electrochemical impedance spectroscopy (EIS) of self-healing coating [52].
Figure 7.22 Various approaches used to synthesize self-healing gels using physical and chemical reactions [144].
Figure 7.23 Chitosan–Fe₃O₄ self-healing magnetic hydrogel [146].
Figure 7.24 pH-responsiveness of self-healing hydrogel from catechol derivatized poly(ethylene glycol), covalent gel reactions at alkaline pH 9 and dissociation into a viscous liquid at neutral and acidic pH 3 [147].
Figure 7.25 Self-healing reaction and bridging zone of soy protein isolate-loaded poly(d,l-lactide-co-glycolide) (SPI-PLGA) microcapsules in SPI resin: (a) the cross-linking reaction between SPI and glutaraldehyde, (b) fracture surface of SPI resin containing SPI-PLGA microcapsules, and (c) bridging zone healed from released SPI from microcapsules between two fracture surfaces in SPI resin [157].
Figure 7.26 Optical microscopy images of bullet entrance and exit zone after self-healing of ethylene/methacrylic acid copolymer resin [161].
Figure 7.27 The self-healing behavior of blends of cis-1,4-polyisoprene and epoxidized natural rubber with dicumyl peroxide as a cross-linking agent [162].

Chapter 8

Figure 8.1 Stability of the optical transmittance of BC nanofiber composites compared to the variations in refractive index of matrix resins (three types shown) due to temperature change. [3]
Figure 8.2 Organic light emitting diode deposited on a cellulose nanofiber-reinforced composite film. [12]
Figure 8.3 Crab carapaces before chemical treatment (a), after chemical treatment (removal of proteins, minerals and pigments) (b), and after chemical treatment and resin impregnation (c). [44]
Figure 8.4 SPreparation of the CNF hybrid film. (a) A schematic image of an electrospinning epoxy backbone and spraying CNF fillers simultaneously. Schematics and scanning electron microscopy (SEM) images (top and cross-sectional views) of (b) the electrospun three-dimensional (3D) epoxy nanoweb structure, (c) the CNF–epoxy hybrid before hot pressing and (d) the CNF–epoxy hybrid after hot pressing. White scale bars are 10 µm, and black scale bars are 20 µm. [59].

Chapter 9

Figure 9.1 Influence of fiber length on normalized glass fiber-reinforced composites (Data plots in Figure 16 [4] are converted into numerals by Simple Digitizer, and plotted again in this graph)
Figure 9.2 A schematic of fracture energy as a function of fiber length in a fiber-reinforced composite under impact force.
Figure 9.3 Unnotched Charpy impact of • kneaded flax/PP/MAPP and ϒ kneaded flax/PP, ♦ extruded flax/PP/MAPP and extruded flax/PP compounds, compared with ■ hackled flax/PP/MAPP NMTs, versus fiber weight fraction. The fitted lines are: — kneaded and — extruded flax/PP/MAPP. The PP value is for Retiflex PP used for the NMTs, the PP used for the compounded materials did not break during the test. Error bars falling within the markers are not shown [28].
Figure 9.4 Impact strength of abaca-reinforced composites with and without MAPP coupling agent [31].
Figure 9.5 Notched impact strength as a function of fiber length in flax/PP composites [8].
Figure 9.6 Pull-out of an oblique fiber from a matrix (l: embedded length, S: sliding length) [45].
Figure 9.7 Stress-strain curves for Cordenka EHM (CA), Cordenka 1840 (CB), Enka viscose (CC), and Lyocell (CD) regenerated fibers [47].
Figure 9.8 Schematic of (a) modified series model, (b) possible physical structure of a semicrystalline cellulose fiber [47].
Figure 9.9 Chemical structure of untreated ramie fiber microfibrils [50, 52].
Figure 9.10 Schematics of cellulose microfibril structure before and after mercerization (a) without load application and (b) with load application [50].
Figure 9.11 Impact damage morphology on the reverse side of green composites reinforced by (a) UT yarns, (b) AT0 yarns and (c) AT0 fabric [53].

Chapter 10

Figure 10.1 Image of a polyurethane foam [4].
Figure 10.2 Starch-based foams prepared by (a) extrusion, (b) hot mould baking, (c and d) microwave heating, (e) freeze-drying, and (f) solvent exchange. [28]
Figure 10.3 Fibres morphological changes upon modification via lss route using chloride salts. The reference fibres (a) show clearly visible S1 layer. Spruce fibre’s surface topology changes greatly at submicron level after modification with high number of LDH (100 mM) (b). Arrows are pointing towards the fibre axis. [93]
Figure 10.4 TEM images of reference bleached thermomechanical pulp fibres (a) and hybridized fibres (b, c). LDH particles appear to have nucleated mainly on fibre surface and lumen as well as to fine structures. [93]
Figure 10.5 Mass release rate of CO₂ (a, b) and CO (c, d) (black lines) during the oxidative pyrolysis compared against heat release rate (blue line) in fibre foam reference (a, c) and LDH-fibre foam(B,D), and, data from mass fraction extent (e) and combustion efficiency (f) are presented. Time to ignition (tIG) and time to flame out (tFO) are marked with red vertical lines. [93]
Figure 10.6 SEM images from the large residues of reference fibre foam (a) and LDH-fibre foam (b) after oxidative pyrolysis in cone calorimeter. [93]

Chapter 11

Figure 11.1 Chemical structure of DNA segments and the role of its constituents in imparting FR characteristics [38, 39].
Figure 11.2 Picture of DNA powder (a), DNA residue at 180 °C (b), SEM magnification of the DNA residue at 180 (c) and 230 °C (d) [40].
Figure 11.3 HRR-time curves of untreated (Control, C) and protein-treated cotton, PET, and PET-cotton fabrics measured by cone calorimetry [9].
Figure 11.4 Chemical structures of (a) phytic acid and (b) chitosan [47].
Figure 11.5 Images of uncoated cotton fabrics (control) and cotton fabrics coated with chitosan-phytic acid complex deposited at varying pH level after the vertical flame/burning tests [16].
Figure 11.6 Chemical structures of (a) alginate and (b) starch [62, 63].
Figure 11.7 Three main types of monolignols identified as building blocks in lignin: (1) para-coumaryl alcohol, (2) coniferyl alcohol and (3) sinapyl alcohol.
Figure 11.8 Digital photos of composites of (a) PBS, (b) PBS with 2.5 wt% of lignin, (c) PBS with 2.5 wt% of lignin modified with P-N-Zn additives, and (d) PBS with 10 wt% of lignin modified with P-N-Zn after cone calorimeter measurements [92].
Figure 11.9 Combustion processes of PU and PU-LPMC₁₅ at oxygen concentration of 19.2 and 26.7 vol%, respectively [93].
Figure 11.10 Chemical structure of: (1) condensed tannin and (2) hydrolysable tannin (tannic acid).
Figure 11.11 Postulated reaction scheme for thermal and thermo-oxidative degradation of tannic acid [96].
Figure 11.12 FTIR spectra of evolved gas from thermal decomposition of tannic acid under nitrogen [96].
Figure 11.13 Highly intumescent char from tannic acid powders after applying flame for 20 seconds.
Figure 11.14 Vertical flame test samples of a. neat PA 6,6 fabric and b. tannic acid-coated (modified) PA 6,6 fabric (after washing).
Figure 11.15 Results of burning tests of polydopamine coated PU foam and uncoated PU foam (control) [122].
Figure 11.16 Comparison of burning behavior between control and BPS-treated jute fabrics at different time intervals [126].

Chapter 12

Figure 12.1 Biodegradable polymers with various source of origin derived from different renewable resources.
Figure 12.2 Schematic of surface cross-linking of the substrate induced by hyperthermal hydrogen collision (HHC) technique.
Figure 12.3 Different routes for production of PLA and its stereocomplexation for potential applications in various sectors.
Figure 12.4 Effect of different varieties of nanocelluloses on the barrier properties of films.
Figure 12.5 Potential applications of chitosan and its derivatives in various sectors.
Figure 12.6 Different routes for surface modification of chitosan.
Figure 12.7 Fabrication of PLA/OLLA-g-CH bionanocomposite films.
Figure 12.8 (a) Structural fragments of gum arabic having various components i.e. arabinopyranose (A_p) [135]; rhamnose (R); arabinose (A); galactose (G); 4-O-methyglucuronic acid (U_m) and glucuronic acid (U), chemical structural of (b) guar gum [137]and (c) xanthan gum [138].
Figure 12.9 Synthesis of (a) gum arabic-graft-polyaniline copolymer by radical polymerization and microwave-accelerated oxidative radical polymerization and (b) LA-g-GA by polycondensation reaction [56].
Figure 12.10 (a) Taxonomix classification of silk spinning organisms showing common varieties of cocoons available; (b) Mulberry silk (bombyx mori); structural arrangement of silk fiber of bombyx mori; (c) Eri silk (samia ricini); (d) Muga silk (antherea assama) [150].
Figure 12.11 Hierachical arrangement of silk (a) raw silk fiber, (b) dimesnions of silk fiber, (c) incompletely degummed silk fiber, (d) completely degummed silk fiber, (e) opical micrograph of degummed silk, (f) microfibrils emerging out of silk fibers upon size reduction, (g) nanofibrils emerging out of silk fibers upon size reduction [153, 157].

Chapter 13

Figure 13.1 Sources and isolation processes of nanocellulose varieties.

List of Illustrations

Chapter 2

Table 2.1 Properties of various edible protein sheets*.
Table 2.2 Properties of various non-edible protein sheets*.
Table 2.3 Properties of various agricultural starch-based resin sheets*.
Table 2.4 Properties of various PHA resins [94–97].
Table 2.5 Properties of PLA resin [116].
Table 2.6 Mechanical properties of green resins reinforced with various inorganic nano-fillers.
Table 2.7 Mechanical properties of green resins reinforced with various organic nano-fillers.

Chapter 4

Table 4.1 CNCs from sulfuric acid hydrolysis (64-65% H₂SO₄, 45 °C) of cellulose of different origins.
Table 4.2 Nanocelluloses from rice straw derived by different processes and their self-assembled fibers.

Chapter 6

Table 6.1 Summary of all-cellulose composite preparation methods.

Chapter 7

Table 7.1 Encapsulation systems used for self-healing materials, the healing agents and shell material, a catalyst, healing conditions, and healing efficiency in single or double capsule-based system.

Chapter 9

Table 9.1 Mechanical properties of green composites with poor interfacial bond.
Table 9.2 Relation between tensile and impact properties in green composites.
Table 9.3 Comparison of selected mechanical characteristics of glass fiber reinforced PP (GF-PP, Piolen G30CA60) and Cordenka-PP composite with 30 wt% fibers (PPRayCo30) [42].
Table 9.4 Impact properties of laminated composites reinforced with mercerized ramie yarns [53],
Table 9.5 Mechanical properties of green composites reinforced with natural fibers undergone various chemical treatments.

Chapter 10

Table 10.1 Starch-based foams reinforced with various fibres.
Table 10.2 Vegetable oil-derived foams reinforced with various fibres.
Table 10.3 PLA-derived foams reinforced with various fibres.

Chapter 11

Table 11.1 Bio-derived materials and their roles in imparting FR characteristics.
Table 11.2 Summary of reports on bio-based FR molecules.
Table 11.3 Summary of FR coatings on fabrics through sequential electrostatic adsorption (LBL technique).
Table 11.4 Summary of results from vertical flame tests of neat PA 6,6 fabric and PA 6,6 fabric coated with modified tannic acid [108].
Table 11.5 Flammability tests of different materials coated with BPS [125–127].

Chapter 12

Table 12.1 Mechanical and gas barrier properties of various biopolymers and biodegradable polymers along with its comparison with petroleum derived polymers.

Chapter 13

Table 13.1 Mechanical properties of nanocellulose, nanocellulose-based composites and tissues.
Table 13.2 Biomedical applications of nanocellulose-based composites.

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Library of Congress Cataloging-in-Publication Data

ISBN 978-1-119-32326-6

Preface

Polymer composites are made of two distinct components: matrix or resin (continuous phase) and filler or reinforcement (discontinuous phase) and have properties that cannot be achieved by a single component alone. Conventionally, advanced composites have been defined as those that have excellent tensile properties. Three factors contribute to their high tensile properties: (1) high strength fibers such as carbon, aramid, or glass used as reinforcement, (2) good resins such as epoxies, and (3) excellent bonding between the fiber and the resin. Specific tensile properties of advanced composites are significantly higher than most metals because of their low density. As a result, advanced composites have replaced metals in many applications from aerospace to sports gears and from automobiles to wind turbines. It is being envisioned that future civil structures such as bridges and buildings will use advanced composites in place of steel, which will require significantly larger volumes. As we know, every material has a life span, and advanced composites are no exception. Unfortunately, we have not found an environmentally friendly way to dispose these composites at the end of their useful life nor have we found any sustainable raw material source to make them. Composites, at present, use unsustainable petroleum as the raw material to synthesize fibers and resins and end up in landfills at the end of their life, making that land useless for any other use for several decades or even centuries. Fortunately, this is slowly beginning to change with the advent of green polymers that are derived from fully sustainable plant based sources. Green composites are also being fabricated using these polymers with plant based fibers as reinforcement. At the end of their life, they can be easily composted, rather than being dumped into landfills. Thus, they can not only save the petroleum but also the land used for landfills.

Significant research is going on around the world to develop green composites that use both fibers and resins that are derived from plants. However, composites using common fibers such as jute, kenaf, sisal, ramie, hemp, banana, and many others have only moderate tensile properties, comparable to wood and wood-based products such as particle board and medium density fiber (MDF) boards. They are not suitable for structural applications where much higher strength and stiffness are required. Their durability, fire performance, and other functionalities are also not par with conventional composites. As a result, their applications have been very limited.

In the last decade or so, however, many new developments in the area of green composites have come about that are changing the landscape drastically. For example, high strength cellulose fibers have been developed using liquid crystalline cellulose solutions and air-gap wet spinning technique used for spinning Kevlar^® fibers. Being 100% cellulose, they are fully degradable. Although this technology is still not mature, fibers with strength in the range of 1.5–1.7 GPa have been obtained. Furthermore, researchers have found ways to improve their properties further to around 2.0 GPa using chemical and heat treatments under tension. There is great promise that once the technology matures, these fibers could have tensile properties close to Kevlar^®. Advanced green composites with high strength and stiffness have already been fabricated using these fibers and soy protein and maize starch based resins that would be suitable for structural applications.

Other than high strength and stiffness, composites are also being developed with a wide range of functional properties for a variety of applications. This has changed the conventional definition of Advanced Composites based on mechanical properties and now includes all composites that have special functional properties such as high transparency, fire resistance, ultra-light weight, autonomously repairing, and resin-less composites. Researchers have been able to obtain many of these properties in green composites as well, making them Advanced Green Composites.

This book provides the current state of advanced green composites that have been developed or are at the research stage of being developed with a variety of functional properties. Chapter 1 presents a broad introduction to green composites and their development to date. In Chapter 2, Rahman and Netravali discuss green resins that have been derived from plant-based sources and seem to be promising to fabricate structural composites. The chapter also discusses some of the most promising bio-based and inorganic nano-fillers that are considered as potential candidates for enhancing the properties of these green resins. Improving resin tensile properties should automatically reflect on composite properties made using them. The third chapter by Huang and Chen discusses the development of high strength cellulosic fibers, the primary load-bearing component in current green composites. Viscose rayon process used for spinning cellulose fibers is more than a century old and is incapable of producing high strength cellulose fibers. This chapter provides an overview of high strength cellulosic fibers that can be obtained from liquid crystalline solutions of cellulose derivatives and nonderivatized cellulose as well as new methods to reinforce the liquid crystalline solutions of cellulose. It is to be noted that all high strength advanced green composites, until today, have been made using liquid crystalline cellulose (LCC) fibers. In the fourth chapter, Hsieh highlights top-down and bottom-up approaches to generate ultra-fine cellulose fibers of nano-scale dimensions, micro- and meso-porous and sheath-core hybrid structures as well as surface-functionalized fibrous materials. Micro- and nano-fibrillated cellulose (MFC/NFC) and other forms of nanocelluloses have high strength as well as aspect ratio and can be efficiently extracted from a variety of waste products such as apple, carrot, and orange pulps that remain after extracting juice, grape, and tomato skins, various straws, etc. They have been used as reinforcement in resins among many other applications. Chapter 5 discusses up to date efforts in developing high strength composites that use LCC fibers and are termed as advanced green composites. There are other opportunities for obtaining high strength composites as well. For example, researchers are trying to develop high strength fibers from spider-silk like protein. Once such fibers are commercially produced, they can be used to make green composites. Bacterial nanocellulose is another fiber with high strength. If these fibers can be oriented, they would be excellent as reinforcement as well. Chapter 6, by Fujisawa and colleagues, summarizes the latest in a new class of composites that do not require resin at all. These composites are made using only one component, cellulose, which acts as the reinforcing fibers as well as the resin that bonds the fibers. These all cellulose composites (ACC) are considered a green alternative to glass- and carbon-fiber-reinforced polymer composites. The authors also provide a future perspective on ACC development for applications in various fields, including optical devices, food, and medicine. Chapter 7 presents composites that have the ability to autonomously self-heal the damages such as microcracks, punctures, cuts, and scratches that result from the constant stress and strain they are subjected to during use. The damages continue to accumulate, ultimately failing the composites. Self-healing is designed to heal the damages as they occur and, hence, can increase the service life of the composites significantly. The chapter discusses different ways developed by researchers to achieve self-healing in conventional composites and how some methods have been extended to self-heal green resins and green composites. Self-healing green resins and composites, with increased service life, should be more acceptable in mainstream applications in the future. In Chapter 8, Nakagaito and colleagues discuss optically transparent composites that have been developed of late for use in place of glass as substrates in electronic devices. Flexible electronics represents a common technology employed in gadgets that are ever-present in our daily lives. Among them, electronic displays are about to become flexible and foldable in the near future. Nanofibers that are invisible to our eyes can not only strengthen amorphous polymers but retain their transparency and also reduce their coefficient of thermal expansion, a critical requirement for electronic displays. Making transparent green composites is an active area of research at present and this chapter presents a thorough review of the current efforts. One of the deficiencies of the thermoset green resins such as plant-based proteins and starches as well as poly(lactic acid) is their brittle nature. That also translates into brittle composites. This is the topic of Chapter 9 in which Goda discusses ways of toughening composites with an emphasis on their impact properties. Chemical treatments of natural cellulosic fibers can make them stronger or tougher. Another key strategy to obtaining higher toughness is to control fiber/resin interfacial shear strength.

Chapter 10 by Obradovic and colleagues introduces the science, technologies, and applications of ultralight porous green composites in the form of biofoams. The chapter presents a thorough review of the biofoam compositions, process methods, properties as well as their performance and applications. In Chapter 11, Xia and colleagues discuss fire retardants developed from renewable resources. Most fibers and composites used in construction, transportation, electronics, and protective textile applications must have fire retardant functionality. Commercially available halogenated flame retardants tend to be toxic and persist in the environment for a long time. The authors, based on the current state of research, conclude that exploring the use of renewable materials as feedstock for FR alternatives is quite promising. In addition to sustainability aspects, the research has unlocked exciting new possibilities in fundamental understanding of fire retardants and their mechanisms of action. Chapter 12 by Gupta et al. discusses the recent technological advancements and innovations in the development of novel biodegradable polymers and nanofillers derived from renewable feedstock with a strategy to convert “waste into wealth” with special focus on green composite films for stringent food packaging that require excellent barrier properties. Finally, in Chapter 13, Osorio and colleagues discuss nanocellulose-based composites in biomedical applications. Although cotton has been used in gauzes for treatment of wounds since ancient times, nanocellulose-based composites have become of great interest in biomedical applications, given their inherent biocompatibility. Nanocellulose from microorganism assembly is similar to that of collagen, the major component of extracellular matrices, and its applications are diverse, ranging from scaffolds for tissue engineering, implants for cell regeneration or biosensors. Although the chapter discusses some relevant biomedical applications of nanocellulose based composites, authors predict that in medium to long term, nanocellulose-based composites will play an important role for developing in vitro tissues and organs, accelerating healing processes and improving life quality of mankind without impacting the environment.

The book covering a broad range of green technologies should be of interest to researchers in academia, in government research labs, and R&D personnel in a host of industries (e.g., aerospace, automotive, biomedical, composites, fibers, medical, microelectronics, packaging, plastics, textiles, and others) who are interested in designing with green fibers, polymers, and composites or advancing the sustainable materials technology. Industries such as aerospace and automotive that are increasingly turning to composites for lightweighting each component but use conventional composites should be able to find greener alternatives in their applications. Anyone working in sustainable plastics/polymers and composites industries should find this book of great interest and very useful as well.

It is my great pleasure to thank all those who made this book possible. First and foremost, I would like to profusely thank the outstanding authors who spent enormous amount of their valuable time in writing the chapters. Sharing their deep knowledge in the field and cutting edge research they are involved in, with the interested community, is greatly appreciated. This book would have been impossible to complete without their hard work, sustained interest, great enthusiasm, and cooperation. Thanks are also due to Martin Scrivener (Scrivener Publishing) for his unwavering support, interest, and encouragement, as well as patience in getting this book completed.

Anil N. Netravali
Cornell University
Ithaca, NY
ann2@cornell.edu
August 2018