Bio-Based Epoxy Polymers, Blends, and Composites E-Book

• Herausgeber: Wiley-VCH GmbH
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 657

Veröffentlichungsjahr: 2021

Beschreibung

State-of-the-art overview on bioepoxy polymers as well as their blends and composites -- covering all aspects from fundamentals to applications!

Bioepoxy polymers is an emerging area and have attracted more and more attention due to their biodegradability and good thermo-mechanical performance. In recent years, research progress has been made in synthesis, processing, characterization, and applications of bioepoxy blends and composites. Bioepoxy polymers are very promising candidates to replace the traditional thermosetting nonbiodegradable polymers.

Bio-Based Epoxy Polymers, Blends and Composites summaries recent research progress on bioepoxy polymers as well as their blends and composites. It covers aspects from synthesis, processing, various characterization techniques to broad spectrum of applications. It provides a correlation of physical properties with macro, micro and nanostructures of the materials. Moreover, research trends, future directions, and opportunities are also discussed.

• Attracts attention: Bioepoxy polymers are environmentally friendly and considered as a promising candidate to replace the traditional thermosetting nonbiodegradable polymers

• Highly application-oriented: Bioepoxy polymers can be used in a broad range of applications such as polymer foams, construction, aerospace, automobiles, self-healing systems   

• One-stop reference: Covers all aspects of bioepoxy polymer, their blends and composites, such as synthesis, properties, processing, characterization and applications

• Broad audience: Attracts attention from both academia and industry

Leseprobe

Table of Contents

Cover

Title Page

Copyright

Dedication

Preface

About the Authors

1 Synthesis of Bio‐Based Epoxy Resins

1.1 Introduction

1.2 Plant Oil Bio‐Based Epoxy Resins

1.3 Substitutes for Bisphenol A Replacement

1.4 Bio‐Based Epoxy Curing Agents

References

2 Natural/Synthetic Fiber‐Reinforced Bioepoxy Composites

2.1 Introduction

2.2 Synthetic and Natural Fibers

2.3 Bioepoxy

2.4 Fiber‐Reinforced Bioepoxy Composites

2.5 Future Perspectives

2.6 Conclusions

Acknowledgments

References

3 Polymer Blends Based on Bioepoxy Polymers

3.1 Introduction

3.2 Plant Oils

3.3 Preparation of Bioepoxy Polymer Blends with Epoxy Resins

3.4 Application of Bioepoxy Polymer Blends

3.5 Conclusion

References

4 Cure Kinetics of Bio‐epoxy Polymers, Their Blends, and Composites

4.1 Introduction

4.2 Fundamentals of Curing Reaction Kinetics

4.3 Curing of Bio‐thermosets

4.4 Curing Kinetics of Bio‐epoxies and Blends

4.5 Case Study: Non‐isothermal Kinetics of Plant Oil–Epoxy–Clay Composite

4.6 Conclusion and Future Prospective

References

5 Rheology of Bioepoxy Polymers, Their Blends, and Composites

5.1 Introduction

5.2 Rheology of Bioepoxy‐Based Polymers

5.3 Rheology of Bioepoxy‐Based Composites

5.4 Rheology of Bioepoxy‐Based Blends

5.5 Conclusions and Future Scope

References

6 Dynamical Mechanical Thermal Analysis of Bioepoxy Polymers, Their Blends, and Composites

6.1 Focus

6.2 Bioepoxies and Reinforcers

6.3 Dynamic Mechanical Analysis and Polymer Dynamics

6.4 Applications

6.5 Conclusion

References

7 Mechanical Properties of Bioepoxy Polymers, Their Blends, and Composites

7.1 Introduction

7.2 Mechanical Properties of Bioepoxy Polymers

7.3 Blends of Bioepoxy Resin

7.4 Bioepoxy‐Based Composites

7.5 Conclusion

7.6 Future Perspectives and Recommendations

Acknowledgment

References

8 Bio‐epoxy Polymer, Blends and Composites Derived Utilitarian Electrical, Magnetic and Optical Properties

8.1 Introduction

8.2 Significance of Bioepoxy‐Based Materials

8.3 Bioepoxy‐Derived Utilitarian Electrical, Magnetic, and Optical Properties

8.4 Conclusion

References

9 Spectroscopy and Other Miscellaneous Techniques for the Characterization of Bio‐epoxy Polymers, Their Blends, and Composites

9.1 Introduction

9.2 Various Methods for Epoxy Polymer Characterization

9.3 Various Bio‐Based Epoxy Polymers, Theirs Uses, and Methods of Characterization in Review

References

10 Flame Retardancy of Bioepoxy Polymers, Their Blends, and Composites

10.1 Introduction

10.2 Methods for Analyzing Flame‐Retardant Properties

10.3 Halogen‐Free Flame‐Retardant Market

10.4 Bioepoxy Polymers with Flame‐Retardant Properties

10.5 Use of Fillers for Improving Flame‐Retardant Properties of Bioepoxy Polymers

10.6 Conclusion

Acknowledgment

References

11 Water Sorption and Solvent Sorption of Bio‐epoxy Polymers, Their Blends, and Composites

11.1 Introduction

11.2 Bio‐epoxy Resins

11.3 Conclusion

References

12 Biobased Epoxy: Applications in Mendable and Reprocessable Thermosets, Pressure‐Sensitive Adhesives and Thermosetting Foams

12.1 Introduction

12.2 Mendable and Reprocessable Biobased Epoxy Polymers

12.3 Pressure‐Sensitive Adhesives (PSAs) From Biobased Epoxy Building Blocks

12.4 Biobased Epoxy Foams

References

Index

End User License Agreement

List of Tables

Chapter 1

Table 1.1 The content of various fatty acids in selected vegetable oils.

Table 1.2 Proportions of interunit linkages in softwood and hardwood 50.

Table 1.3 Thermal analysis data for epoxy resin blends containing DGEBA and c...

Table 1.4 Thermal decomposition of BPA‐based epoxy resin and the DGEBA/lignin...

Table 1.5 Thermal and mechanical properties of PTCP, neat epoxy, and EP/PTCP ...

Table 1.6 TGA,

T

g

, and

T

d

values of epoxy resin samples cured with different c...

Table 1.7 Properties of epoxy resin networks cured with bio‐based curing agen...

Chapter 2

Table 2.1 Some commercial aramid fibers [9].

Table 2.2 Typical melting temperature ranges of PE [17-19].

Table 2.3 Composition ranges (%) and applications for commercial glass fibers...

Table 2.4 Compiled properties and chemical compositions of natural fibers [56...

Table 2.5 Mechanical and physical properties of two types of silk fibers [79,...

Table 2.6 Mechanical and physical properties of basalt fiber [92].

Table 2.7 Price of several fibers [95].

Table 2.8 Mechanical properties of epoxidized natural oil.

Table 2.9 Comparison of the bio‐based DGEI with the petroleum‐based DGEBA wit...

Table 2.10 Comparison of Epidian 5 DGEBA and isosorbide‐based epoxy with four...

Table 2.11 Tensile and fracture properties of furan‐based epoxy compared with...

Table 2.12 Flexural strength of polyphenolic epoxy compared with DGEBA [115].

Table 2.13 Comparison of mechanical propertie of polyphenolic epoxy and DGEBA...

Table 2.14 Impact properties of ENR‐modified DGEBA [118].

Table 2.15 Thermal properties of epoxidized lignin and DEGBA [121].

Table 2.16 Tensile properties of vanillin‐derived epoxy [122].

Table 2.17 Flexural properties of DGEDVCP [123].

Table 2.18 Flexural and impact properties of rosin‐based resin [125–128].

Table 2.19 Tensile properties of bioepoxy with different ratios of FPR and EG...

Table 2.20 Mechanical properties of glass fiber‐reinforced CSE‐modified epoxy...

Table 2.21 Tensile properties of carbon and glass fiber‐reinforced bioepoxy [...

Table 2.22 Mechanical properties of flax fiber‐reinforced flaxseed oil based ...

Table 2.23 Comparison of hemp, ramie, and flax for cardanol‐modified epoxy [1...

Chapter 3

Table 3.1 The fatty acid distribution of numerous common plant oils [34].

Chapter 4

Table 4.1 List of cross‐linkers used to cure bio‐thermosets.

Table 4.2 Literature summary on curing kinetics of bio‐epoxy and blends.

Table 4.3 The kinetic parameters of the curing systems by non‐isothermal meth...

Chapter 5

Table 5.1 Gel time data for the reactive systems DGEBA/IPD, DGEDAS

n

/IPD, and ...

Table 5.2 Epoxy resins produced from rosin.

Table 5.3 Gel time data of the hybrid resins at various temperatures (mean da...

Chapter 7

Table 7.1 Mechanical properties of bioepoxy polymers.

Table 7.2 Tensile and flexural properties of bioepoxy blend systems.

Table 7.3 Tensile strength and modulus properties of bioepoxy‐based composite...

Table 7.4 Mechanical properties of bioepoxy‐based nanocomposites.

Table 7.5 The improvements attained on the properties of bioepoxy‐based nanoc...

Chapter 8

Table 8.1 Electrical and electronic properties, method of epoxy casting techn...

Table 8.2 Electrical systems, method of epoxy casting technique, and methodol...

Chapter 9

Table 9.1 Typical bands in the IR spectra.

Table 9.2 Sample of electronegativity effects and chemical shift.

Chapter 10

Table 10.1 The oxygen index of representative plastics.

Table 10.2 UL‐94 rating.

Table 10.3 CFT factors with variation of polymer molecular structures.

Chapter 12

Table 12.1 Detailed data from microcombustion calorimetry of the PSA.

List of Illustrations

Chapter 1

Figure 1.1 Schematic structure of triglycerides.

Figure 1.2 The reaction of triglyceride epoxidation with organic peracids.

Figure 1.3 Chemical structure of cationic photoinitiators.

Figure 1.4 The synthesis of high‐molecular‐weight epoxy resins based on modi...

Figure 1.5 Cross‐linking reactions of epoxy fusion process products.

Figure 1.6 Chemical structure of the cycloaliphatic resin (3,4‐epoxycyclohex...

Figure 1.7 Triarylsulfonium salts applied as the cationic photoinitiators.

Figure 1.8 Structure of vernolic acid methyl ester and product of its reacti...

Figure 1.9 Structure of norbornyl epoxidized linseed oil.

Figure 1.10 Structure of epoxidized cyclohexene‐derivatized linseed oil.

Figure 1.11 Simplified structure of softwood lignin (including three monolig...

Figure 1.12 Summary of the main strategies for lignin conversion [49, 55].

Figure 1.13 Cured epoxy resins from lignin hydrogenolysis products.

Figure 1.14 Synthesis of lignin‐based epoxy and epoxy asphalt.

Figure 1.15 Schematic routes of lignin modification and crosslinking: (a) ep...

Figure 1.16 Route of the synthesis epoxy monomers from selectively hydrodeox...

Figure 1.17 Lignin modification and cross‐linking: (a) ozone oxidation of Kr...

Figure 1.18 Chemical structures of (

a

) vanillin and its naturally occurring ...

Figure 1.19 Synthesis of vanillin from guaiacol.

Figure 1.20 Synthesis of vanillin from guaiacol using glyoxylic acid.

Figure 1.21 Synthesis of vanillin from eugenol.

Figure 1.22 Schematic illustration of possible synthesis pathways (a) and (b...

Figure 1.23 Synthesis of 2‐methoxyhydroquinone and its epoxy derivatives ‐ s...

Figure 1.24 The

O

‐alkylation of vanillin derivatives (a), followed by the ep...

Figure 1.25 Esterification of vanillic acid, followed by the

O‐

alkylat...

Figure 1.26 Synthesis of glycidyl derivatives (b) based on the product of va...

Figure 1.27 Synthesis of hydrovanilloin and the epoxy resin based on this va...

Figure 1.28 Synthesis of 2,5‐bis(4‐hydroxy‐3‐methoxybenzylidene)cyclopentano...

Figure 1.29 Synthesis of the vanillin coupling product (a) and the flame‐ret...

Figure 1.30 The coupling of vanillin with pentaerythritol and synthesis of t...

Figure 1.31 Schematic illustration of components of CNSL.

Figure 1.32 Synthesis of NC‐514.

Figure 1.33 Reactive sides of cardanol.

Figure 1.34 Chemical transformation of cardanol.

Figure 1.35 Synthesis of carboxyl functional cardanol and structures of the ...

Figure 1.36 Chemical structure of cardanol NC‐514.

Figure 1.37 Epoxy reactants: epoxidized isosorbide and polyglycidyl ether of...

Figure 1.38 Chemical structure of DOPO.

Figure 1.39 Synthesis of PTCP.

Figure 1.40 Chemical structures of isosorbide.

Figure 1.41 Schematic reaction pathway for the production of bio‐based isoso...

Figure 1.42 Possible reaction pathways for the synthesis of the diepoxide de...

Figure 1.43 Structure of isosorbide‐based epoxy resins.

Figure 1.44 Synthetic route of diallyl isosorbide and isosorbide diglycidyl ...

Figure 1.45 Synthesis of isosorbide diglycidyl ether using 4‐allyoxybenzoly ...

Figure 1.46 Formation of plant terpenes.

Figure 1.47 Outline of the biosynthetic pathway leading to the major monoter...

Figure 1.48 Isomerization and oxidation processes for converting pinenes int...

Figure 1.49 Mechanism of the cationic polymerization of β‐pinene.

Figure 1.50 Chemical structures of TME, TME‐based emulsifier, and aliphatic ...

Figure 1.51 Preparation of T‐PABA and T‐PABA dispersion.

Figure 1.52 Synthesis of epoxy resins starting from naphthol and limonene.

Figure 1.53 Synthetic route to a rosin‐based siloxane epoxy monomer (AESE)....

Figure 1.54 Synthesis of C

21

cycloaliphatic dicarboxylic acids and reactive ...

Figure 1.55 Scheme of soybean oil functionalization with thioglycolic acid....

Figure 1.56 Synthesis of a polyamine cross‐linking agent via thiol‐ene react...

Figure 1.57 Synthesis of carboxylic acid from lignin.

Figure 1.58 The curing of epoxy resin using aminated lignin as a curing agen...

Figure 1.59 Preparation of partially depolymerized lignin (PDL) and lignin p...

Figure 1.60 Scheme of preparation cross‐linked epoxy resin.

Figure 1.61 Scheme of epoxy resin by cross‐linking LSGLYPA with a mixture of...

Figure 1.62 Synthesis of dihydroxyaminopropane of 2‐methoxyhydroquinone (a) ...

Figure 1.63 Synthesis of the cardanol‐based novolacs.

Figure 1.64 Synthesis of the isosorbide‐based cross‐linking agent.

Figure 1.65 Synthesis of the isosorbide‐based cross‐linking agent via cyanoe...

Figure 1.66 Synthesis of bio‐based epoxy curing agent derived from myrcene a...

Chapter 2

Figure 2.1 The classification of fibers [5].

Figure 2.2 Chemical structure of (a)

meta

‐aramid and (b)

para

‐aramid fibers....

Figure 2.3 (a) Structure of LDPE and (b) HDPE [16].

Figure 2.4 Carbon fabric [35].

Figure 2.5 The global annual required quantity for carbon composites by appl...

Figure 2.6 Glass fabric [40].

Figure 2.7 GFRP production in Europe by application industry in 2018 [36].

Figure 2.8 Structure of natural fibers [50].

Figure 2.9 World natural fiber production: 110 million tons in 2018 [57].

Figure 2.10 Flax fabric [2].

Figure 2.11 The three main hybrid configurations: (a) intrayarn or fiber‐by‐...

Figure 2.12 Representative chemical structures of soybean oil [100].

Figure 2.13 Chemical structure of

D

‐isosorbide and the synthesis process of ...

Figure 2.14 Chemical structure of epoxidized natural rubber [117].

Chapter 3

Figure 3.1 PO‐based bioepoxy resin blend with DGEBA epoxy resin.

Figure 3.2 Schematic representation of vegetable plant oils used for various...

Figure 3.3 The life cycle of plant oil (PO)‐based polymer materials.

Figure 3.4 Structure of fatty acid in plant oil‐based triglycerides.

Figure 3.5 Structure of triglyceride.

Figure 3.6 Representation of castor oil production [60].

Figure 3.7 Schematic representations of epoxy/ECO bioepoxy blend systems.

Figure 3.8 The representation of PKA‐cured epoxy/ECO blend cross‐linked netw...

Figure 3.9 The representation of PKA‐cured epoxy/EMR blend cross‐linked netw...

Figure 3.10 K

IC

, G

IC

, and notched impact strength of pure epoxy, bioepoxy, a...

Figure 3.11 Morphology analysis of fracture surface of (a) pure epoxy, (b) b...

Figure 3.12 Synthetic route of bioepoxy resin from soybean oil.

Figure 3.13 Fracture toughness and impact strength of epoxy and its bioepoxy...

Figure 3.14 Mechanical properties of bioepoxy blends [70].

Figure 3.15 Schematic representation of the cross‐linked network of EPMO/m‐X...

Figure 3.16 Applications of bioepoxy polymer in different fields.

Chapter 4

Figure 4.1 Curing reaction of epoxides with amine [33].

Figure 4.2 Curing reaction of epoxides with anhydride [51].

Figure 4.3 Curing reaction of epoxides with carboxylic acid [52].

Figure 4.4 DSC curing thermogram of (a) epoxy, (b) epoxy/ESO blend, and (c) ...

Figure 4.5 Activation energy vs. degree of conversion plot of epoxy systems....

Figure 4.6 ln(

A

(

f

(

α

)) vs. ln(1−

α

) plot of virgin epoxy, epoxy/ESO,...

Figure 4.7 Linear plot of Value II vs. ln(

α

−

α

2

) of epoxy, epoxy/ES...

Figure 4.8 Linear plot of Value I vs. ln((1−

α

)/

α

) for virgin epoxy...

Chapter 5

Figure 5.1 Rheological analysis of the isothermal curing of the polyamine gr...

Figure 5.2 Rheological behaviors of polypols with different ratios between C...

Figure 5.3 Rheological behaviors of polyols with different reactions.

Figure 5.4 Comparing the diglycidyl ether of bisphenol A to diglycidyl adipa...

Figure 5.5 Viscoelastic properties of the ECO‐based resin with an equimolar ...

Figure 5.6 Isosorbide concentration effect on viscosity.

Figure 5.7 Effect of SCNER content on the viscosity of DGEBA at 25...

Figure 5.8 (a) Isochronal plots of complex modulus at 0.1 Hz for the epoxidi...

Figure 5.9 Effect of shear rate on the melt viscosity of various ENRs in 60/...

Figure 5.10 Results of (a, b) storage modulus and (c, d) loss factor of ENR‐...

Figure 5.11 Viscous flow curves at 25 °C for epoxidized lignin...

Figure 5.12 Evolution of the storage and loss moduli with frequency for epox...

Figure 5.13 Variation of viscosity vs. time for acrylic acid (AA)/diabietyl ...

Figure 5.14 Curing curves at different temperatures.

Figure 5.15 Curing profile of eco‐friendly green epoxy resin at isothermal c...

Figure 5.16 Comparison of storage moduli (

G

′), loss moduli (

G

″), and complex...

Figure 5.17 (a) Representative storage (

G

′) and loss (

G

″) modulus curves for...

Figure 5.18

G

*/sin vs. temperature at 10 rad/s. At 60 °C...

Figure 5.19 Vacuum infusion. Results of (a) a temperature ramp and (b) isoth...

Figure 5.20 Frequency dependence of (a) dynamic storage modulus,

G

′ and (b) ...

Figure 5.21 (a) Shear stress vs. shear rate plot, and (b) and (c) viscosity ...

Chapter 6

Figure 6.1 Type of fillers utilized to reinforce bioepoxies.

Figure 6.2 Distribution of materials utilized to reinforce bioepoxies.

Figure 6.3 Distribution of natural fibers utilized to reinforce bioepoxies....

Figure 6.4 Dynamic temperature ramp of a semi-crystalline, high performance ...

Figure 6.5 Dynamic temperature ramp of neat PVC, an amorphous polymer. Dualc...

Figure 6.6 Dynamic temperature ramp of PVC reinforced with 4 wt% bentonite....

Figure 6.7 Dynamic temperature ramp of crosslinked PCL‐POSS. Film tensile mo...

Figure 6.8 Dynamic temperature ramp of thermotropic

liquid crystalline polym

...

Figure 6.9 Dynamic frequency sweeps of an acrylic coating holding isothermal...

Figure 6.10 Master curve of an acrylic coating using TTS and the data of Fig...

Figure 6.11 WLF shift factors

a

T

as a function of temperature

T

of an acryli...

Figure 6.12 Master curve of a coating using TTS,

T

ref

...

Chapter 7

Figure 7.1 SEM micrographs of (a) pure synthetic epoxy, and blends of (b) ep...

Figure 7.2 The (a) impact strength and (b) fracture toughness (

G

IC

) properti...

Figure 7.3 Scanning electron microscopy (SEM) micrographs of bamboo/bioepoxy...

Chapter 8

Figure 8.1

Poly(DPDPM) line width

(▪) and

free spin population

(

♦

Figure 8.2 Poly(DPDPM) electron spin resonance (ESR) spectra vs. heating tim...

Figure 8.3 Temperature dependence (140–440 K) of spin–lattice interaction ti...

Figure 8.4 Concentration dependence of susceptibility

χ

3

of poly(1,6‐he...

Chapter 9

Figure 9.1 The schematic of NMR analysis processor.

Figure 9.2 Sample of NMR plot as a result of analysis.

Chapter 10

Figure 10.1 LOI test method.

Figure 10.2 UL‐94 method.

Figure 10.3 Cone calorimeter configuration.

Figure 10.4 Heat flux‐dependent HRR and THR for glass fiber‐reinforced PA 66...

Figure 10.5 Sample thickness‐dependent HRR for PMMA [48].

Figure 10.6 HRR curves for different types of samples. (a) Thin samples, (b)...

Figure 10.7 Effect of distance between a sample surface and the cone heater ...

Figure 10.8 MCC configuration.

Figure 10.9 Eugenol‐derived epoxy monomers.

Figure 10.10 Vanillin‐derived epoxy monomers.

Figure 10.11 Furan‐derived epoxy monomers.

Figure 10.12 Conceptual diagram of (a) single‐walled carbon nanotube (SWCNT)...

Figure 10.13 Structure of 2 : 1 layered silicate such as montmorillonite cla...

Figure 10.14 Carbon nanotubes coated with phosphorus–nitrogen flame retardan...

Figure 10.15 Postulated mechanism of flame‐retardant additives. al. [61, 62]...

Figure 10.16 Heat release rate of reference and flame‐retarded GFTE composit...

Figure 10.17 Chemical structure of the epoxy resin components and applied fl...

Chapter 11

Figure 11.1 Structure of gallic acid.

Figure 11.2 Water uptake of polymeric composites at an absorbed dose of (a) ...

Figure 11.3 Structure of eugenol.

Chapter 12

Figure 12.1 Schematic representation of the most common extrinsic self‐heali...

Figure 12.2 Difference between extrinsic and intrinsic healing polymeric net...

Figure 12.3 (A) Coating surface after immersion for 500 hours in 3.5% NaCl s...

Figure 12.4 Rearrangement of cross‐links through reversible covalent bonds (...

Figure 12.5 (a–c) Scratch healing process on a DGEBA‐FA‐BMI cross‐linked pol...

Figure 12.6 (A): (a) Neat ENR and (b) ENR‐CMCS self‐healing qualitative test...

Figure 12.7 (a) Stress–strain curves for modified lap‐shear tests of control...

Figure 12.8 Rows 1–3: Reparation of a crack in lignin‐PEG epoxy thermosets w...

Figure 12.9 (A) Pictures depicting a crack mending in an isosorbide‐based ep...

Figure 12.10 Schematic representation of the phases of bonding under light p...

Figure 12.11 Peel and loop tack strength with cohesion/adhesion balance.

Figure 12.12 Synthesis pathway of ESO/OLA copolymers [78].

Figure 12.13 Rheological behavior of ESO‐SA samples (epoxy : COOH 1 : 1)....

Figure 12.14 Structure of syntactic foam. Entrapped voids are marked as “A.”...

Figure 12.15 Structure of diepoxy cardanol.

Figure 12.16 SEM image syntactic foams with different ESO content: (a) 0% (2...

Figure 12.17 (a) Storage modulus and (b) tan δ curves of syn...

Figure 12.18 SEM micrographs of the pure and reinforced epoxy foams with dif...

Figure 12.19 Epoxy–foam adhesives between automotive panels (a) before and (...

Figure 12.20 Horizontal plane SEM micrographs of foams with different foamin...

Figure 12.21 Photo (a), light microscopy ((b) magnification: 50...

Figure 12.22 Foams based on EAO and ELO and SEM pictures.

Figure 12.23 Epoxy foams based on epoxidized cardanol.

Guide

Cover Page

Table of Contents

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Bio-Based Epoxy Polymers, Blends, and Composites

Synthesis, Properties, Characterization, and Applications

Edited by

Jyotishkumar Parameswaranpillai

Sanjay Mavinkere Rangappa

Suchart Siengchin

Seno Jose

Editors

Dr. Jyotishkumar Parameswaranpillai

King Mongkut's University of Technology North Bangkok

Center of Innovation in Design and Engineering for Manufacturing

1518 Pracharaj 1

Wongsawang Road, Bangsue

10800 Bangkok

Thailand

Dr. Sanjay Mavinkere Rangappa

King Mongkut's University of Technology North Bangkok

Department of Mechanical and Process Engineering

1518 Pracharaj 1

Wongsawang Road, Bangsue

10800 Bangkok

Thailand

Prof. Dr.-Ing.habil. Suchart Siengchin

King Mongkut's University of Technology North Bangkok

Department of Mechanical and Process Engineering

1518 Pracharaj 1

Wongsawang Road, Bangsue

10800 Bangkok

Thailand

Dr. Seno Jose

Government College Kottayam

Department of Chemistry

Nattakom P O

Kottayam

686013 Kerala

India

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Dedication

Editors are honored to dedicate this book to their family members and friends. Editors would like to thank King Mongkut's University of Technology North Bangkok (KMUTNB), Thailand for the support through Grant No. KMUTNB-BasicR-64-16.

Preface

Epoxy polymers are thermosetting polymers widely used in construction and building, automobile, aerospace, and marine industries. However, traditional epoxy systems are nonbiodegradable and cannot be recycled. The plastic waste is generating at an alarming rate and only 9% is recycled, and the remaining 91% is either landfilled or dumped in the natural environment. Moreover, plastic waste accumulation in the seawater, especially in the Pacific Ocean, is increasing at an alarming rate. Therefore, researchers and scientists are concentrating to develop biodegradable polymers. One of the inventions in this area is the production of bioepoxy resins from different plant sources. A surge in the production of bioepoxy resins was observed in the past decade. The polymer manufacturers (Sicomin, Gougeon Brothers, Wessex Resins, Bitrez, etc.) are now producing bioepoxy resins. Generally, bioepoxy resins are brittle, which limits their application in advanced composite industries. Studies have shown that the incorporation of fillers/fibers can significantly enhance the thermomechanical, electrical, and other physical properties of the bioepoxy composites. The high acceptance level of bioepoxy resins in automobile, aerospace, construction, and marine industries all across the world is expected to increase the production of bioepoxy resins in the coming years.

The research in the field of bioepoxy resins and their blends and composites are flourishing. This leads to an upsurge in the number of publications. However, no books have been published in the area of bioepoxy resins. Therefore, we believe that it is important to edit a book on “Bio‐Based Epoxy Polymers, Blends, and Composites: Synthesis, Properties, Characterization, and Applications.” We hope that the present book will benefit scientists, engineers, academic staff, and students working in the area of bio‐based epoxy polymers, blends, and composites.

This book consists of 12 chapters that describe “Bio‐Based Epoxy Polymers, Blends, and Composites: Synthesis, Properties, Characterization, and Applications.” The chapter “Synthesis of Bioepoxy Resins” summarizes the synthesis of fully bio‐based epoxy resins, their properties, and potential uses. The chapter “Natural/Synthetic Fiber‐Reinforced Bioepoxy Composites” focuses on the different bioepoxy resins and natural/synthetic fiber‐reinforced bioepoxy composites, their mechanical properties, and applications. The chapter “Polymer Blends Based on Bioepoxy Polymers” reviews the preparation of bio‐based epoxy blends for various applications. The chapter “Cure Kinetics of Bioepoxy Polymers, Their Blends, and Composites” emphasizes the importance of kinetics studies of the bioepoxy/hardener reaction. The chapter “Rheology of Bioepoxy Polymers, Their Blends, and Composites” discusses the role of rheological studies on the processing of the bioepoxy composites. The chapter “Dynamical Mechanical Thermal Analysis of Bioepoxy Polymers, Their Blends, and Composites” describes the viscoelastic properties of bioepoxy blends and composites. The chapter “Mechanical Properties of Bioepoxy Polymers, Their Blends, and Composites” discusses the factors influencing the mechanical aspects of bioepoxy composites. The chapter “Bioepoxy Polymer, Blends, and Composites Derived Utilitarian Electrical, Magnetic, and Optical Properties” reviews the electrical, electronic, magnetic, and optical properties of bioepoxy systems. The chapter “Spectroscopy and Other Miscellanies Techniques for the Characterization of Bioepoxy Polymers, Their Blends, and Composites” gives an overview of the characterization of bioepoxy systems using various techniques such as Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. The chapter “Flame Retardancy of Bioepoxy Polymers, Their Blends, and Composites” highlights the recent developments in flame‐retardant bio‐based epoxy resins. The chapter “Water Sorption and Solvent Sorption of Bioepoxy Polymers, Their Blends, and Composites” focuses on the water absorption properties of bioepoxy systems. The chapter “Bio‐Based Epoxy: Applications in Mendable and Reprocessable Thermosets, Thermosetting Foams, and Pressure‐Sensitive Adhesives” give an overview of the recent developments in self‐healing bioepoxy systems and bio‐based epoxy foams.

The editors are thankful to the contributors of all chapters and the Wiley editorial and publishing team for their kind support. The editors are also thankful to Ms. Junjiraporn Thongprasit (Baifern) for her involvement at the initial screening process of chapters.

20 August 2019

Dr. Jyotishkumar Parameswaranpillai (Thailand)

Dr. Sanjay Mavinkere Rangappa (Thailand)

Prof. Dr.-Ing. habil. Suchart Siengchin (Thailand)

Dr. Seno Jose (India)

About the Authors

Dr. Jyotishkumar Parameswaranpillai is currently working as a research professor at the Center of Innovation in Design and Engineering for Manufacturing, King Mongkut's University of Technology North Bangkok. He received his Ph.D. in Polymer Science and Technology (Chemistry) from Mahatma Gandhi University. He has research experience in various international laboratories such as Leibniz Institute of Polymer Research Dresden (IPF), Germany, Catholic University of Leuven, Belgium, and University of Potsdam, Germany. He has published more than 100 papers in high‐quality international peer‐reviewed journals on polymer nanocomposites, polymer blends and alloys, and biopolymers and has edited five books. He received numerous awards and recognitions including the prestigious Kerala State Award for the Best Young Scientist 2016, INSPIRE Faculty Award 2011, Best Researcher Award 2019 from King Mongkut's University of Technology North Bangkok.

https://scholar.google.co.in/citations?user=MWeOvlQAAAAJ&hl=en

Dr. Sanjay Mavinkere Rangappa, received his B.E degree (Mechanical Engineering) from Visvesvaraya Technological University, Belagavi, India, in the year 2010, M. Tech degree (Computational Analysis in Mechanical Sciences) from VTU Extension Centre, GEC, Hassan, in the year 2013, Ph.D (Faculty of Mechanical Engineering Science) from Visvesvaraya Technological University, Belagavi, India, in the year 2017, and Postdoctorate from King Mongkut's University of Technology North Bangkok, Thailand, in the year 2019. He is a Life Member of Indian Society for Technical Education (ISTE) and Associate Member of Institute of Engineers (India). He has reviewed more than 50 international journals and international conferences (for Elsevier, Springer, Sage, Taylor & Francis, and Wiley). In addition, he has published more than 85 articles in high‐quality international peer‐reviewed journals, more than 20 book chapters, 1 book, and 15 books as an editor and also presented research papers at national/international conferences. His current research areas include natural fiber composites, polymer composites, and advanced material technology. He is a recipient of DAAD Academic exchange‐PPP Programme (Project‐related Personnel Exchange) between Thailand and Germany to the Institute of Composite Materials, University of Kaiserslautern, Germany. He has received a Top Peer Reviewer 2019 Award, Global Peer Review Awards, Powdered by Publons, Web of Science Group.

https://scholar.google.com/citations?user=al91CasAAAAJ&hl=en

Prof. Dr.‐Ing. habil. Suchart Siengchin is the president of King Mongkut's University of Technology North Bangkok (KMUTNB), Thailand. He received his Dipl.‐Ing. in Mechanical Engineering from the University of Applied Sciences Giessen/Friedberg, Hessen, Germany, in 1999, M.Sc. in Polymer Technology from the University of Applied Sciences Aalen, Baden‐Wuerttemberg, Germany, in 2002, M.Sc. in Material Science at the Erlangen‐Nürnberg University, Bayern, Germany, in 2004, Doctor of Philosophy in Engineering (Dr.‐Ing.) from the Institute for Composite Materials, University of Kaiserslautern, Rheinland‐Pfalz, Germany, in 2008, and Postdoctoral Research from Kaiserslautern University and School of Materials Engineering, Purdue University, USA. In 2016, he received the habilitation at the Chemnitz University in Sachen, Germany. He worked as a lecturer for Production and Material Engineering Department at The Sirindhorn International Thai‐German Graduate School of Engineering (TGGS), KMUTNB. He has been a full professor at KMUTNB and became the president of KMUTNB. He won the Outstanding Researcher Award in 2010, 2012, and 2013 at KMUTNB. His research interests are in polymer processing and composite material. He is the editor‐in‐chief of KMUTNB International Journal of Applied Science and Technology and the author of more than 150 peer‐reviewed journal articles. He has participated with presentations in more than 39 international and national conferences with respect to materials science and engineering topics.

https://scholar.google.com/citations?user=BNZEC7cAAAAJ&hl=en

Dr. Seno Jose, a native of Kerala, India, is an assistant professor of Chemistry at Government College Kottayam. He did his masters in Chemistry in Mahatma Gandhi University. He has availed DST/DAAD fellowship and worked as a visiting researcher at the Institute for Composite Materials Ltd., Germany. He received his Ph.D. in Chemistry from Mahatma Gandhi University in 2007. He has coauthored over 40 peer‐reviewed publications. His research interests include polymer blends, polymer nanocomposites, and shape memory polymeric materials.

https://scholar.google.com/citations?user=uoJt2ckAAAAJ&hl=en

1Synthesis of Bio‐Based Epoxy Resins

Piotr Czuband Anna Sienkiewicz

Cracow University of Technology, Department of Chemistry and Technology of Polymers, ul. Warszawska 24, 31‐155 Cracow, Poland

1.1 Introduction

The term “epoxy resin” is understood to mean compounds containing at least one active epoxy group in their structure and which are capable of forming a cross‐linked three‐dimensional structure in the curing process involving these groups. Naturally, epoxy rings are found only in vernonia oil. However, epoxy functionality can be easily introduced into the compound structure, even by the oxidation of unsaturated bonds to oxirane rings. This is a typical method of obtaining cycloaliphatic resins, applied on a large scale in electronics to encapsulate electronic systems. The second method is the use of epichlorohydrin, which is commonly applied to prepare epoxy compounds via the reaction with polyalcohols or polyphenols. Epichlorohydrin together with bisphenols (mainly bisphenol A or F, and S) are the main raw materials used in industrial methods for the synthesis of epoxy resins most often produced and used on a large scale. All these compounds are of petrochemical origin. There are three main reasons for the search of new raw materials of natural origin for the synthesis of epoxy resins. The first is the need to replace petrochemical raw materials. The volatility of oil and gas prices and their strong connections with the changing political situation in various regions of the world, as well as the inevitable prospect of imminent exhaustion of their sources, and ecological considerations are the main reasons for the search of alternative sources of raw materials. Moreover, potential toxicological and endocrine disrupting properties of bisphenol A are discussed and emphasized, especially in recent years. The second reason is the need to solve the problem of annually increasing amount of postconsumer plastic waste. Epoxy resins belong to the category of polymeric materials practically not biodegradable. The application of bio‐based raw materials can enable and facilitate their decomposition under the influence of biological factors. Epoxy resins are widely used as coating materials in products intended for contact with food or even storage of food (e.g. can‐coating or paints for securing ship hold walls). Therefore, the third reason is the need to limit the penetration of harmful substances such as bisphenol A into food from the coating material, preferably by eliminating them already at the stage of synthesis.

While searching for new bio‐based resources for the synthesis of epoxy resins, particularly bisphenol substitutes, the crucial issue must be remembered. One of the most important challenges is to provide new bio‐based resins with comparable performance properties to the currently manufactured and applied petrochemical‐based commercial products, i.e. primarily high mechanical strength, thermal stability, and chemical resistance. The mentioned properties are characteristic of the resins based on bisphenol A (or other bisphenols), thanks to which these materials are produced on a large scale for many applications. Therefore, this chapter presents the most promising raw materials whose structure can provide the desired final properties of the epoxy system after cross‐linking. At the same time, they must be raw materials easily available in large quantities from renewable sources, nontoxic and cheap to obtain and in preparation.

1.2 Plant Oil Bio‐Based Epoxy Resins

Vegetable oils, as a material of natural origin and from renewable sources, are the subject of numerous studies aimed at their application for the synthesis or modification of various polymers [1]. Soybean, castor, linseed, rapeseed, sunflower, cotton, peanut, and palm oils are primarily used on a larger scale depending on the type of oil produced in a given region [2]. From the chemical point of view, plant‐based oils are a mixture of esters derived from glycerol and free fatty acids, mainly unsaturated acids (primarily oleic, linoleic, linolenic, ricinoleic, and erucic acids) and in a small amount of saturated acids (stearic and palmitic acids) (Figure 1.1), depending on the type of oil.

When choosing vegetable oil for use in the synthesis of polymers, first of all, its structure should be taken into account: the presence of unsaturated bonds and possibly other functional groups (e.g. hydroxyl in castor oil or epoxy in vernonia oil), the amount of unsaturated bonds present in the molecule (referred as the oil functionality), and chain length alkyl derived from fatty acids (Table 1.1).

Figure 1.1 Schematic structure of triglycerides.

Table 1.1 The content of various fatty acids in selected vegetable oils.

Fatty acid

Vegetable oil, content of individual acids (wt%)

Soybean

Rapeseed

Linseed

Sunflower

Castor

Palm

Palmitic

12    

4    

5    

6    

1.5    

39    

Stearic

4    

2    

4    

4    

0.5    

5    

Oleic

24    

56    

22    

42    

5        

45    

Linoleic

53    

26    

17    

47    

4        

9    

Linolenic

7    

10    

52    

1    

0.5    

—    

Castor

—    

—    

—    

—    

87.5    

—    

Other

—    

2    

—    

—    

—        

2    

Functionality

4.6

 3.8

 6.6

 4.6

  2.8    

 1.8

The functionality of oils (understood as the content of unsaturated bonds) primarily determines the cross‐linking density of oil‐based chemosetting polymers or polymers obtained by free radical polymerization as well as oil‐modified polymeric materials. In turn, the final polymer properties such as mechanical strength, thermal stability, and chemical resistance strongly depend on the cross‐linking density. The elasticity of the polymers with the addition of vegetable oil or based on them depends on the length of the alkyl chains in the oil molecule derived from fatty acids.

Vegetable oils can be easily and efficiently converted into epoxy derivatives by oxidizing unsaturated bonds present in fatty acid residues. Several methods of double bond oxidation in triglyceride molecules are known and commonly used [3]: the method based on the Prilezhaev reaction, the radical oxidation, the Wacker‐type oxidation, dihydroxylation of oils and fats, and enzyme–catalyst oxidation. The Prilezhaev reaction is the most often used method for natural oil epoxidation, commonly applied in the industry. In this method, the process of epoxidation of natural fatty acids and triglycerols is carried out in the system consisting of hydrogen peroxide, an aliphatic carboxylic acid, and an acidic catalyst. The organic peracid formed in situ by the reaction of acid with hydrogen peroxide is the real oxidizing agent in this method (Figure 1.2).

Carboxylic acids with one to seven carbon atoms are the most commonly used (in practice, mainly acetic acid). Inorganic or organic acids and their salts, as well as acidic esters, can be used as catalysts; however, sulfuric and phosphoric acid are the most often used in industrial practice. A promising method is oxidation in the presence of enzymes [4], heteropolyacids [5], and even ion exchange resins [6] as catalysts. The most commonly used oxidizing agent is hydrogen peroxide in the form of solution with a concentration of 35–90% (usually 50%). Epoxidation of plant oils in ionic liquids, as well as in supercritical carbon dioxide, is also described [7].

The earliest epoxidized esters of higher fatty acids have found wide applications as both plasticizers and stabilizers for thermoplastics, mostly poly(vinyl chloride), poly(vinylidene chloride), their copolymers, and poly(vinyl acetate) and chlorinated rubber [8, 9]. Epoxidized fatty acids containing oleic acid are used as a valuable intermediate in the production of lubricants and textile oils [10, 11]. It seems that epoxidized vegetable oils could also be used as hydraulic liquids [12]. However, primarily, they can also act as reactive diluents of bisphenol‐based epoxy resins [13], which are usually highly viscous. They have oxirane groups, although less reactive because of their central location in triglyceride chains (compared to terminal glycidyl groups), but also capable of reacting with polyamines or carboxylic anhydrides. By building into the structure of the cured resin in the process of co‐cross‐linking with it, they affect its final properties – improving flexibility and impact strength. In this way, embedded triglycerides not only facilitate the processing of resins with high intrinsic viscosity but also allow limiting their typical disadvantages (high brittleness, low impact strength, and flexibility) resulting from the rigid structure they owe because of the structure of bisphenols [14].

Figure 1.2 The reaction of triglyceride epoxidation with organic peracids.

However, the first, logically implied possibility of use of epoxidized vegetable oils is their application as stand‐alone materials: the networks cross‐linked with bifunctional compounds such as dicarboxylic acids or aliphatic and aromatic diamines, which are typically used as hardeners for the epoxy resins. Because of the content of more than one epoxy group in the molecule, epoxidized triglycerides may, according to the generally accepted definition, be treated as epoxy resins. However, curing of, e.g. epoxidized soybean oil [15] or vernonia oil (natural epoxidized oil mainly obtained from plant Vernonia galamensis), dicarboxylic acids [16] resulted in obtaining only soft elastomers. Materials with higher mechanical strength are synthesized by reacting epoxidized oils first with polyhydric alcohols (e.g. resorcinol) and phenols or bisphenols and then cross‐linking the obtained modified oil with partially reacted epoxidized rings [17]. Finally, curing by photopolymerization or polymerization with latent initiators allows to obtain from modified vegetable oils, without the addition of the bisphenol‐based or cycloaliphatic resins, coating materials with satisfactory mechanical properties. It was found [18] that the properties of hardened vegetable oils also depend on the type of used thermal latent initiator. The properties of epoxidized castor oil cross‐linked with N‐benzylpyrazine (BPH) and N‐benzylquinoxaline (BQH) were studied (Figure 1.3).

It was found that materials characterized by a higher glass transition temperature, a higher value of the coefficient of thermal expansion, and greater thermal stability are obtained using BPH as a photoinitiator. Nevertheless, the composition cross‐linked with BQH is characterized by better mechanical properties. Most likely, the better final properties result from the higher cross‐linking density of cured with BPH composition. Anhydrides of various carboxylic acids are used to cure epoxidized linseed oil [19], and cross‐linking reactions are catalyzed by various tertiary amines and imidazoles. The materials obtained with phthalic anhydride and methylendomethylenetetrahydrophthalic anhydride hardeners exhibit a lower cross‐linking density than those obtained with cis‐1,2,3,6‐tetrahydrophthalic anhydride. It was found that a greater degree of oil–anhydride conversion and thus higher cross‐linking density and greater rigidity of the cured material are obtained using imidazoles. The best properties are achieved for the composition cured with cis‐1,2,3,6‐tetrahydrophthalic anhydride as the hardener and 2‐methylimidazole as the catalyst.

Figure 1.3 Chemical structure of cationic photoinitiators.

High‐molecular‐weight epoxies are a special group of very important epoxy resins commonly used as coating materials, especially for powder, can and coil coatings mainly in automotive industry. Theoretically, they can be obtained in the traditional way in the Taffy process with epichlorohydrin and bisphenol. However, even the use of a slight excess of epichlorohydrin does not provide high‐molecular‐weight solid resins. Therefore, industrially, they are synthesized from low or moderate molecular weight epoxy resins and bisphenol A by the epoxy fusion process. It is the method of polyaddition carried out in bulk, in the molten state of reagents, and without the use of solvents. In this way, it is possible to obtain resins with a softening temperature of 100–150 °C, characterized by an epoxy value of 0.020–0.150 mol/100 g, and an average molecular weight of 1.5–10 thousands of Daltons. The application of epoxidized vegetable oils in place of low/medium molar mass resins, as well as hydroxylated oils in place of bisphenols, in the epoxy fusion process with bisphenol A (BPA) or BPA‐based epoxy resin was proposed [20, 21]. Hydroxylated oils are obtained from epoxidized oils in the reaction of opening of oxirane rings using diols and the most often glycols. Depending on the type of starting oil, catalyst used, and reaction time, the products of the epoxy fusion process using modified oils (Figure 1.4) contain a large amount of hydroxyl groups (hydroxyl value 120–160 mg KOH/g), some free epoxy groups (epoxy value 0.050–0.150 mol/100 g), and are characterized by weight‐average molecular weight even above 30 000 g/mol.

Therefore, for the cross‐linking of these products, diisocyanates or blocked diisocyanates can be applied (Figure 1.5).

Figure 1.4 The synthesis of high‐molecular‐weight epoxy resins based on modified vegetable oil: (a) epoxidized or (b) hydroxylated soybean oil.

Figure 1.5 Cross‐linking reactions of epoxy fusion process products.

The resins cross‐linked with polyisocyanates are characterized by differential mechanical properties, which depend on the type of used isocyanate, and are higher than the one of the low‐molecular‐weight bisphenol A‐based resin crosslinked with methyl‐tetrahydrophthalic anhydride, however lower while cured with isophoronediamine [22]. Moreover, the presence of epoxy groups in the polyaddition products can be used to obtain two‐layer materials [23], in which one layer is cured with polyamine epoxy resin and the other is a polyaddition product cross‐linked with diisocyanate. The reaction of the amine hardener with the free epoxy groups that are present within the polyaddition product ensures a very good interlayer bonding.

Because of the usually unsatisfactory properties of the oils cured with amines or acid anhydrides, epoxidized vegetable oils began to be used as one of the components of epoxy compositions [24]. The compositions consisting of epoxidized esters of higher fatty acids obtained by the transesterification of various vegetable oils and natural or hydrocarbon resin acids can be used as an ingredient in, among others, epoxy adhesives with reduced crystallization tendency [25]. Compositions of modified vegetable oils with epoxy resins based on various bisphenols can generally be prepared via two methods. One of them is the homogenization of the components of the composition and their simultaneous co‐cross‐linking. In this way, compositions of bisphenol F diglycidyl ether with epoxidized linseed oil are prepared [26] and cured with methyltetrahydrophthalic anhydride in the presence of 1‐methylimidazole or polyoxypropylenetriamine [27]. It turned out that with an increase in the content of epoxidized linseed oil in the anhydride‐cured compositions, the storage modulus, glass transition temperature, and heat resistance under load decrease, while the impact strength measured by the Izod method does not change, but above 70 wt% of oil content increases the cross‐linking density. In contrast, compositions cured with the use of amine are characterized by an almost fivefold increase in impact strength at the oil content of 30% by weight. Other discussed cured parameters change in the same way as in the case of anhydride cross‐linked materials. In turn, comparison [28] of the properties of the composition with epoxidized linseed oil and soybean oil shows significant differences between the materials based on both oils. It was found that, due to the greater compatibility of linseed oil with the epoxy resin and better oil solubility in the resin (resulting from greater polarity and functionality and lower molecular weight), linseed oil does not tend to form a separate phase. However, the two‐phase structure, observed in the case of epoxidized soybean oil, is responsible for improving the impact strength and fracture toughness of the epoxy resin composition. A decrease in cross‐linking density is also observed in the compositions of 4,4′‐tetraglycidyldiamino‐diphenylmethane with epoxidized soybean oil cured with diaminodiphenylmethane [29]. Also in this case, besides the improvement in impact strength, as the effect of reducing the cross‐linking density, a decrease in the heat resistance and the glass transition temperature is observed. Using the example of a bisphenol‐based epoxy resin compositions with different contents of epoxidized castor [30] or soybean oil [31], cured with thermal latent initiator BPH, it was proven that the final properties of cross‐linked materials are determined not only by the polarity, functionality, or structure of the used oil but also by its content, ensuring the optimal amount of flexible fragments embedded in the rigid epoxy resin structure, and the most favorable phase composition of the material.

Bisphenol‐based epoxy resin compositions with modified vegetable oils might also be prepared in the two‐step method. The first stage is the initial cross‐linking of oil so that free functional groups capable of co‐cross‐linking with the epoxy resin remain in it. In this way, a prepolymer or, as it is called in some publications, a rubber is obtained from the modified oil. Only then, the prepared prepolymer is mixed in appropriate proportions with epoxy resin, and finally, the composition is cured. The cross‐linked composition is characterized by a two‐phase structure, analogous to that of epoxy resins modified with liquid acrylonitrile butadiene copolymers with reactive carboxyl or amine end groups and acrylic elastomers. The two‐phase structure of the composition determines their postcuring properties. Using the two‐step method, composition of diethylene epoxy resin with epoxidized soybean oil was prepared [32]. Initially, both the oil and then the composition with the epoxy resin were cross‐linked with 2,4,6‐tri(N,N‐dimethylaminomethyl)phenol. The soybean prepolymer, cross‐linked for 12–84 hours, is a highly viscous liquid that mixes well with the epoxy resin [33]. The formation of the two‐phase structure of the cured composition was confirmed by DSC and DMA analyses. The adhesive joint prepared with the use of the tested composition shows a significant improvement in the impact strength and the strength. It has been found that the properties of the composition depend on both the content of soybean prepolymer and the time of its pre‐cross‐linking. The best results are obtained using the addition of 20 wt% of prepolimer pre‐cross‐linked for 60 hours. Compositions characterized by greater cross‐linking density and mechanical strength than the networks with epoxidized soybean oil were obtained using methyl and allyl esters, synthesized by the transesterification of soybean oil [34]. The esters were epoxidated and then precured with p‐aminocyclohexylmethane, which showed the highest reactivity to soybean oil derivatives among the tested polyamines. The curing conditions were selected in such a way that cross‐linking of both esters and epoxidized oil, which was chosen for the comparison purposes, terminates at the gelation stage. The bisphenol‐based epoxy resin compositions, with the content of prepolymers of 10–30 wt%, were cured using various polyamines, and their mechanical properties were compared with those of the samples of analogous composition but obtained via the one‐step method. Generally, the mixed compositions with various soybean oil derivatives obtained by the two‐stage method are characterized by the best strength parameters, definitely better than the networks synthesized only with epoxidized oil. In particular, the addition of epoxidized allyl ester increases the glass transition temperature and provides greater rigidity and mechanical strength of the composition.

Additionally [35], the process of cross‐linking of the above‐described materials with acid anhydride (the commercial product called Lindride LS 56V produced by Lindau Chemicals, USA) was studied. Based on the results of DSC and viscometric measurements, models describing the course of curing reactions have been developed, which might be applied in the industrial processing of the described compositions. The DMTA analysis showed [36] that the conservative modulus of elasticity and glass transition temperature increase with an increase in the content of epoxidized allyl ester in the case of anhydride cross‐linking while decrease for polyamine‐cured materials. Moreover, the value of the loss factor decreases in the case of anhydride cross‐linking, but it is definitely higher for polyamine‐cured compositions. That kind of formation of dynamic mechanical properties results from a greater degree of cross‐linking of anhydride‐cured compositions. The epoxidized palm oil was prepolymerized in a reaction with isophorone diamine [37]. The resulting palm oil derivatives were used as modifiers of a bisphenol A‐based low molecular weight epoxy resin. The prepared compositions and the pure unmodified epoxy resin were cured with isophorone diamine. It was found that the palm oil derivatives led to a decrease in the mechanical strength of the resin, but on the other hand, they contributed to an increase in relative elongation at break and significant improvement (even twice) in impact strength of the cross‐linked products. A two‐phase structure of the compositions studied, responsible for the increase of their impact strength, was observed.

Figure 1.6 Chemical structure of the cycloaliphatic resin (3,4‐epoxycyclohexylmethyl‐3′,4′‐epoxycyclohexane carboxylate).

One of the most important areas of application of epoxidized vegetable oils are compositions with epoxy resins, capable of cross‐linking with UV or visible light. Photoinitiated polymerization is a commonly used industrial method of cross‐linking of coating materials. Throughout this method, the cured coating is obtained in a short time and above all at the room temperature. Modified natural oils are a very interesting alternative to acrylic monomers, commonly used to obtain photosetting coatings, and starting from the first reports [38] are the subject of the research performed by scientific teams around the world. Compositions consisting of vernonia oil or epoxidized soybean oil and cycloaliphatic epoxy resin were tested [39] (Figure 1.6).

The compositions were cross‐linked by photopolymerization using a cationic UV initiator, which was a mixture of triarylsulfonium salts of hexafluoroantimone with a trifunctional primary triol based on ε‐caprolactone. Coatings with the addition of epoxidized vegetable oils are characterized by excellent adhesion to the surface, high impact strength, UV stability, corrosion resistance, and long‐lasting shine. It was also found that pencil hardness and tensile strength of coating films decrease with increasing oil content. Similarly, the glycidyl castor oil derivative [40], added in an amount of up to 60 wt% to the same cycloaliphatic resin and cross‐linked with it using triarylsulfonium salts as cationic initiators (Figure 1.7), leads to a significant improvement of epoxy coating properties: increasing its elasticity and gloss as well as reducing water absorption.

Flexible coatings characterized by high tensile strength and hardness are obtained by adding epoxidized palm oil to cycloaliphatic resin (Figure 1.6) [41]. Additionally, in the described research, the possibility of photopolymerization of prepared compositions with UV light in the presence of various initiators, radical, cationic, and hybrid ones, was tested. Because of the low solubility of triarylsulfonium salts in oil, divinyl ethers of various structures were also added to the composition, which, as it was found in the course of the study, did not affect the mechanical properties of cured coatings. The photocuring process of highly branched resins obtained from modified vernonia oil was also investigated [42]. For the reason that the final properties of cross‐linked compositions with modified vegetable oils depend not only on the amount of oil but also on their structure, the authors decided to study the photopolymerization of epoxy resin with a strictly defined composition and structure. For this purpose, obtained in the oil transesterification reaction of Euphorbia lagascae, methyl vernolate was reacted with trimethylol propane to give the compounds depicted in Figure 1.8.

Figure 1.7 Triarylsulfonium salts applied as the cationic photoinitiators.

Figure 1.8 Structure of vernolic acid methyl ester and product of its reaction with trimethylol propane.

The obtained derivatives, including the hyperbranched polyether, were used to prepare compositions with different contents of individual components, with methyl vernolate acting as a reactive diluent. The compositions were polymerized with a cationic photoinitiator (octyloxydiphenyliodine hexafluoroantimonate). The application of methyl vernolate reduces the viscosity of the polyether as well as significantly decreases the glass transition temperature. An interesting example of the synthesis of epoxy resin based on vegetable oil, hardened later by the photopolymerization, is the attachment of bicyclo[2.2.1]heptane to linseed oil [43]. The derivative, which is shown in Figure 1.9, was obtained by the Diels–Alder reaction of cyclopentadiene with linseed oil, carried out at the temperature of 240 °C and a pressure of 1.4 MPa.

Compositions consisting of a epoxidized derivative, the addition of various divinyl ethers of epoxidized linseed oil, and cycloaliphatic epoxy resin (Figure 1.6) have been cured using the already mentioned triarylsulfonium salts. Divinyl monomers fulfilled the role of reactive diluents and compatibilizers primarily of oil and photoinitiator. It is also known that the presence of this type of monomers accelerates photocuring of cycloaliphatic epoxy resins. It has been observed that the cross‐linking of the cycloaliphatic linseed oil derivative proceeds at a lower rate than the cycloaliphatic epoxy resin, but with a higher rate than epoxidized oil. The addition of divinyl monomers accelerates the speed of curing and increases the elasticity of the cured materials. A similar relationship was also observed during kinetic studies of the cationic photopolymerization reaction of a cycloaliphatic linseed oil derivative [44]. It was found that the photo‐cross‐linking rate is controlled by the diffusion of active macromolecules, which depends on the viscosity of the environment. The different reactivity of the cycloaliphatic and epoxidized oil derivative in the main chains results from the differences in the diffusion of the molecules of both compounds and depends on the presence of divinyl monomers in the reaction environment. The improvement of the final properties of the described compositions was obtained by adding up to 20 wt% of tetraethyl orthosilane (TEOS) [45]. The organic–inorganic hybrid materials obtained in this way, containing the optimum amount of TEOS oligomers, amounting to about 10 wt%, were characterized by the highest value of the elastic modulus, the highest glass transition temperature, and the highest cross‐linking density. Although the incorporation of TEOS oligomers in the structure of a cured cycloaliphatic linseed oil derivative simultaneously reduces the relative elongation at break and fracture toughness, it should be remembered that the biggest disadvantages of modified vegetable oils as materials susceptible to photocuring are low glass transition temperature and low speed of cross‐linking. Another example of a cycloaliphatic linseed oil derivative, also intended for photocuring, is the product of a Diels–Alder reaction of linseed oil with 1,3‐butadiene [46] (Figure 1.10).

Figure 1.9 Structure of norbornyl epoxidized linseed oil.

Figure 1.10 Structure of epoxidized cyclohexene‐derivatized linseed oil.

Compositions based on modified vegetable oils, hardened by photopolymerization, are mainly intended for coating materials. However, it has been shown that it is also possible to use epoxidized soybean and linseed oils together with cycloaliphatic epoxy resin as binders for glass fiber‐reinforced composites and cross‐linked with visible or UV light [47].

1.3 Substitutes for Bisphenol A Replacement

1.3.1 Lignin‐Based Phenols

Lignin (Figure 1.11) is the relatively large‐volume renewable aromatic feedstock. Next to heteropolysaccharides, it is one of the most abundant biopolymer on Earth, which is found in most global plants [48, 49]. It is deposited in the cell walls and the middle lamella.

Lignin, whose concentration systematically decreases from the outer layer to the inner layer of the cell wall, is generally responsible for reinforcing the plant structure. It is described as a water sealant in the stems, playing an important role in controlling water transport throughout the cell wall. Additionally, lignin of outer layers acts as a binding agent, holding the adjoining cells together, whereas the lignin within the cell walls gives rigidity by the chemical bonding with hemicellulose and cellulose microfibrils [50]. Moreover, it protects plants against decay and biological attacks [51].

Figure 1.11 Simplified structure of softwood lignin (including three monolignols, the building blocks of lignin) [48, 49].