Bio-based Thermosets Research Articles

High biomass content in epoxy vitrimers: a study on bio-based and reprocessable thermosets

High biomass content in epoxy vitrimers: a study on bio-based and reprocessable thermosets

Biobased recyclable epoxy composites reinforced with carbon nanotubes for electromagnetic interference shielding and Joule heating

AbstractCurrent epoxy thermosets are facing various challenges such as resource scarcity, environmental concern, and limited functionalities. Here, we present a novel solvent free approach to fabricate multifunctional carbon nanotubes (CNTs) reinforced biobased and recyclable epoxy thermoset composites through precuring in an internal mixer followed by curing in an oven. The epoxy matrix, a covalent adaptable network (CAN) based on dynamic imine bonds, was synthesized from entirely biobased feedstocks, including glycerol triglycidyl ether, vanillin, and 1,10‐diaminodecane. The shear force during precuring facilitated dispersion of CNTs in CAN matrix, allowing for high CNTs loading (up to 20 wt%). The well‐dispersed CNTs not only reinforced mechanical properties of CAN but also introduced new functionalities like electrical conductivity, electromagnetic interference (EMI) shielding capacity, and Joule heating performance. The composite with 20% CNTs exhibited a tensile strength and Young's modulus of 78.1 MPa and 3.07 GPa, respectively, marking a 34.2% and 63.6% improvement over pristine CAN. It also demonstrated a high electrical conductivity of 35.3 S/m, resulting in a remarkable EMI shielding effectiveness (22.8 dB) and excellent Joule heating performance (reaching 131.7°C at 27 V input). Furthermore, these composites are thermally and chemically recyclable due to dynamic imine bonds, promoting sustainability and circular economy.

Tough bio-based thermosets with dual curing capability via epoxy and allylic functionality

Acrylic monomer from high oleic soybean oil (HO-SBM) was combined with vanillin-derived aromatic counterpart, 2-glycidoxy-5-vinylanisole (GVA), in chain copolymerization to design tough biobased thermosets with a dual-curing capability. Under specified conditions, a polymer network can be formed by selective cross-linking of epoxy groups of GVA or HO-SBM allylic groups as well as dual-curing via epoxy-amine and autoxidation mechanisms simultaneously. Glass transition temperature of the synthesized copolymers increases with the GVA content, although the values fall in a rather narrow range (−10 °C to 7 °C).Thermosets cured via epoxy-amine and dual-curing have a significantly denser network when compared to autooxidation. Such an increase in cross-link density led to improved chemical (solvent) resistance and hardness of thermoset coatings. At the same time, a higher GVA fraction in the chain (from 37 to 44 wt%) noticeably increases Young's modulus of thermosets (up to 235 MPa). A substantial modulus increase at the rubbery plateau was observed for epoxy-amine and dual-curing thermosets with 44 wt% of GVA.

Synthesis, degradation Behavior, and recyclability property of novel bio-based Polyimine thermosets

Given the challenges in recycling, degradation, flammability and environmental protection of most petroleum-based thermosets, it is of great significance to develop degradable, recyclable, and flame-retardant thermosets from renewable feedstocks for material safety and promote sustainable development. Herein, novel Polyimine thermosets (PIts) were prepared from renewable vanillin and their degradation behavior and recyclability properties were systematically investigated. The prepared PIts exhibited excellent thermal properties (Tg: 91–158 °C and T5% above 250 °C), degradability and high monomer recovery rates (above 80 %). Meanwhile, the PIts demonstrated outstanding flame retardancy with a UL-94 V-0 rating achieved by forming noncombustible gas, phosphorus-containing species and nitrogen-containing hexatomic rings. Additionally, these PIts displayed high malleability with Ea ranging from 77.0-118.8 kJ.mol−1 and could be recycled via hot pressing without altering their chemical structure and original mechanical properties. This work presents a new strategy for fabricating bio-based advanced thermosets from renewable resources.

Exploring anti-corrosion properties and rheological behaviour of tannic acid and epoxidized soybean oil-based fully bio-based epoxy thermoset resins

This research explores the physicochemical attributes of a fully bio-epoxy thermoset aimed at serving as an anti-corrosion coating for safeguarding carbon steel structures in marine environments. Throughout this investigation, various epoxy thermosets formulations, based on epoxidized soybean oil (ESO) and tannic acid (TA), were synthesized by adjusting the initial ratios of epoxide:hydroxyl groups (epoxy:OH). These formulations were subsequently applied onto carbon steel substrates and subjected to thermal curing at moderate temperatures (170 °C) to evaluate their anti-corrosion effectiveness using electrochemical impedance spectroscopy (EIS). The examination of the total impedance values derived from EIS Bode diagrams (>106 Ω) revealed a notable anti-corrosion efficacy that endured over several months of immersion in 3.5 wt% NaCl solutions. In addition to electrochemical assessment, a rheological analysis was conducted to determine the optimal curing temperature for each formulation and to track the evolution of their mechanical properties throughout the curing process. Furthermore, the progression of corrosion at the coating-metal interphase was quantified using samples featuring artificially created notches to facilitate rapid water penetration, reaching the protected surface. Moreover, cross-cut and pull-off adhesion tests were conducted on coatings cured with various epoxide:hydroxyl ratios, yielding exceptional results on carbon steel substrates. Overall, a great potential for anti-corrosion protection has been demonstrated on the developed fully bio-based coatings with tuneable mechanical properties, regarding the initial component ratio, to reach the specific requirements for specific applications.

Recycling of Commercially Available Biobased Thermoset Polyurethane Using Covalent Adaptable Network Mechanisms.

Until recently, recycling thermoset polyurethanes (PUs) was limited to degrading methods. The development of covalent adaptable networks (CANs), to which PUs can be assigned, has opened novel possibilities for actual recycling. Most efforts in this area have been directed toward inventing new materials that can benefit from CAN theory; presently, little or nothing has been applied to industrially producible materials. In this study, both an industrially available polyol (Sovermol780®) and isocyanate (Tolonate X FLO 100®) with percentages of bioderived components were employed, resulting in a potentially scalable and industrially producible material. The resultant network could be reworked up to three times, maintaining the crosslinked structure without significantly changing the thermal properties. Improvements in mechanical parameters were observed when comparing the pristine material to the material exposed to three rework processes, with gains of roughly 50% in elongation at break and 20% in tensile strength despite a 25% decrease in Young's modulus and crosslink density. Thus, it was demonstrated that theory may be profitably applied even to materials that are not designed including additional bonds but instead rely just on the dynamic urethane bond that is naturally present in the network.

Recyclable bio-based epoxy resin thermoset polymer from wood for circular economy

Due to their extraordinary durability and thermal stability, Epoxy Resin Thermosets (ERTs) are essential in various industries. However, their poor recyclability leads to unacceptable environmental pollution. In this study, Wu et al. successfully synthesized a completely bio-based ERT using lignocellulose-derived building blocks which exhibit outstanding thermal and mechanical properties. Remarkably, these bio-materials degrade via methanolysis without the need of any catalyst, presenting a smart and cost-effective recycling strategy. Furthermore, this approach could be employed for fabricating reusable composites comprising glass fiber and plant fiber, thereby expanding its applications in sustainable transportation, coatings, paints or biomedical devices.

A dual cross-linking strategy enables fully bio-based epoxy thermosets with superior low dielectric properties and mechanical properties

Bio-based epoxy resins with superior low dielectric properties and mechanical properties is of great significance for sustainable development and environmental protection. Herein, a bio-based active ester curing agent with large free volume was synthesized through a substitution reaction between magnolol and cinnamoyl chloride following by curing epoxidized linseed oil for fully bio-based epoxy thermosets. The curing kinetics of the curing behavior and the curing condition was systematic studied and optimized. The relationship between chemical structure and properties (thermo-mechanical, mechanical, dielectric, and etc.) of the resulting fully bio-based epoxy thermosets was discussed in-depth. The results showed that free radical polymerization and epoxy ring-opening reactions simultaneously occurred in the curing reaction led to a dual cross-linked structure of the resulting fully bio-based epoxy thermosets. The unique structures and the introduction of the rigid benzene groups rendered the tensile strength and the thermal stability of the resulting fully bio-based epoxy thermosets high up to 33.63 MPa and 332.40 °C, respectively. The absence of the secondary hydroxyl groups and the presence of the low polar fatty acid chains in the backbone of the epoxy resins resulted in the dielectric constant and dielectric loss low to 3.19 and 0.012, which was much lower than those of the polymer previously reported. This study provides a simple and facile strategy for the design of environmentally friendly fully bio-based epoxy resins for microelectronics and electronic packaging application.

Techno-economic assessment and carbon pricing analysis for economic feasibility of epoxidized sucrose soyate: A biobased thermoset resin

The substantial environmental issues associated with plastic production have prompted researchers to accelerate the development of environmentally friendly biobased alternatives to reduce reliance on petroleum-based resources and mitigate emissions. Epoxidized Sucrose Soyate (ESS), a high-performance biobased epoxy resin obtained from soybean oil and sucrose, has shown promising potential in polymers and coatings applications. The success of ESS performance necessitates further investigations into its industrial-scale production and viability as an environmentally sustainable alternative to conventional petroleum-based resins. This study consists of a comprehensive techno-economic analysis (TEA) and cradle-to-gate life cycle assessment (LCA) to evaluate the technical, economic, and environmental feasibility of industrial-scale ESS production. The minimum selling price (MSP) of ESS at various production scales was estimated which offers insights into cost optimization. The MSP for 0.1, 1.0, and 10 ton/h processing capacity of sucrose soyate was calculated to be $9.57, $6.74, and $6.62 per kg of ESS, respectively. Relative to a comparable petroleum-based epoxy resin with similar functionality, such as bisphenol A diglycidyl ether (with a price range of $1.8 to $5.2 per kg), larger scales of ESS production have the potential to compete economically. The LCA results demonstrated the superior environmental performance of ESS, especially in the global warming potential category, indicating its potential as a compelling sustainable choice for replacing petroleum-based resins. This combined TEA and LCA study demonstrated the economic viability and environmental benefits of ESS, highlighting its promise as a sustainable alternative for industrial applications.

Toward the Manufacturing of a Non-Toxic High-Performance Biobased Epoxy-Hemp Fibre Composite.

This study describes the production of a new biobased epoxy thermoset and its use with long hemp fibres to produce high-performance composites that are totally biobased. The synthesis of BioIgenox, an epoxy resin derived from a lignin biorefinery, and its curing process have been optimised to decrease their environmental impact. The main objective of this study is to characterise the rheology and kinetics of the epoxy system with a view to optimising the composite manufacturing process. Thus, the epoxy resin/hardener system was chosen considering the constraints imposed by the implementation of composites reinforced with plant fibres. The viscosity of the chosen mixture shows the compatibility of the formulation with the traditional implementation processes of the composites. In addition, unlike BPA-a precursor of diglycidyl ether of bisphenol A (DGEBA) epoxy resin-BioIgenox and its precursor do not have endocrine disrupting activities. The neat polymer and its unidirectional hemp fibre composite are characterised using three-point bending tests. Results measured for the fully biobased epoxy polymer show a bending modulus, a bending strength, a maximum strain at failure and a Tg of, respectively, 3.1 GPa, 55 MPa, 1.82% and 120 °C. These values are slightly weaker than those of the DGEBA-based epoxy material. It was also observed that the incorporation of fibres into the fully biobased epoxy system induces a decrease in the damping peak and a shift towards higher temperatures. These results point out the effective stress transfers between the hemp fibres and the fully biobased epoxy system. The high mechanical properties and softening temperature measured in this work with a fully biobased epoxy system make this type of composite a very promising sustainable material for transport and lightweight engineering applications.

Programming degradation and closed-loop recycling of ultra-stable bio-based thermosetting polyurethane relied on double-locked covalent adaptable networks

Castor oil (CO) derived thermoset polyurethanes are usually limited by their poor mechanical properties and the difficulty in removing or recycling because of the aliphatic or alicyclic backbone and their permanent cross-linking structures. Although covalent adaptable networks (CANs) based on dynamic bonds have been proposed, it is still highly desired to fabricate polymer CANs with high performance, stimulus resistance, stepwise degradation and closed-loop recycling from renewable CO for sustainable development. In this study, CO-based poly(urethane urea) (PU) thermosets relied on double-locked covalent adaptable networks (DLCANs) were proposed to achieve programmable degradation and closed-loop recycling. From a CO-derived isocyanate monomers and two dynamic curing agents of aminophenyl disulfide (AFDS) and aminophenyl diimine (AFDI), bio-based thermosets of PU DLCANs were prepared. The bio-based PU DLCANs were ultra-stable and still kept cross-linked upon disadvantageous chemical stimuli instead of dissociating like the conventional CANs. Moreover, the bio-based PU DLCANs became degradable only by applying programmed stimuli, when the two types of dynamic cross-links in parallel connection were both broken step by step. Meanwhile, the broken cross-links could be reformed when dynamic bonds regenerated upon heating, leading to the closed-loop recycling of the bio-based PU DLCANs. Besides, being applied as coatings, the bio-based PU DLCANs exhibited UV shielding, self-healing properties and long-term stability as well as programming removable properties. The bio-based thermosets relied on DLCANs have the potential to guarantee the reliability of polymeric CANs and maintain the closed-loop recycling by applying programmable stimuli, which is quite meaningful and practical for life-time environmental-friendly coatings.

Quercetin allylation and thiol–ene click photopolymerization to produce biobased polymer thermosets with robust thermomechanical properties

AbstractThe development of biobased and functionalized monomers along with eco‐friendly photopolymerization processes represent promising methods for the development of renewable and more environmentally friendly thermosets. Thiol–ene ‘click’ photopolymerization is particularly advantageous in this regard; however, the materials derived from this method often exhibit low glass transition temperatures (Tg) and unsuitable thermomechanical properties for applications at room temperature. Herein, we report the synthesis of biobased allyl derivatives from quercetin, a renewable flavonoid compound widely available in fruits, vegetables and plants. We demonstrated the isolation of tetra‐ and penta‐allylated quercetin (Q1 and Q2, respectively) and their subsequent photoactivated thiol–ene polymerization. By introducing a biobased thiol curing agent (PTTMP) derived from glycerol and mercaptopropionic acid, we produced fully biobased crosslinked thermosets with high content of aromatic moieties provided by the framework of the monomers. Real‐time infrared spectroscopy showed the effective thiol–ene photopolymerization of Q1 and Q2 and PTTMP with conversions of 60% and 75%, respectively, after 15 min of UV irradiation. Due to the modulated crosslinking degree from the allyl group functionalization in the monomers, the biobased crosslinked networks showed storage moduli from 420 to 739 MPa, thermal stability from 220 to 257 °C and Tg values ranging from 75 to 90 °C. This work outlines straightforward strategies for creating biobased thermosets that overcome the limited thermomechanical properties of thiol–ene networks and offer potential antimicrobial and antioxidant properties. © 2024 Society of Chemical Industry.

Optimizing biobased thermoset resins by incorporating cinnamon derivative into acrylated epoxidized soybean oil

The study successfully developed thermoset materials utilizing acrylate epoxidized soybean oil (AESO) and allyl cinnamate (ACIN) with tert-butyl peroxybenzoate (TBPB) as the initiator. Isothermal curing at temperatures between 110 °C to 140 °C of the developed formulations, showed that higher temperatures accelerated the conversion process. The higher curing temperature increased the degree of conversion, leading to obtain the best flexural strength for samples cured at 130 °C. However, samples cured at 120 °C exhibited better impact properties due to a lower degree of conversion, which allows for a more mobile reticular network. In addition, morphological observations confirmed these mechanical property trends. Dynamic thermal characterization revealed changes in glass transition temperature and exothermic reactions due to unreacted products appeared for materials cured at low temperature. Increasing curing temperature allowed to enhance thermal stability by increasing molecular weight. Finally, thermomechanical analysis confirmed stiffness and glass transition temperature increases observed during flexural tests and thermal characterization.

DLP 3D Printing of Levoglucosenone-Based Monomers: Exploiting Thiol-ene Chemistry for Bio-Based Polymeric Resins.

Additive manufacturing (AM) is a well-established technique that allows for the development of complex geometries and structures with multiple applications. While considered a more environmentally-friendly method than traditional manufacturing, a significant challenge lies in the availability and ease of synthesis of bio-based alternative resins. In our endeavor to valorize biomass, this work proposes the synthesis of new α,ω-dienes derived from cellulose-derived levoglucosenone (LGO). These dienes are not only straightforward to synthesize but also offer a tunable synthesis approach. Specifically, LGO is first converted into diol precursor, which is subsequently esterified using various carboxylic acids (in this case, 3-butenoic, and 4-pentenoic acids) through a straightforward chemical pathway. The resulting monomers were then employed in UV-activated thiol-ene chemistry for digital light process (DLP). A comprehensive study of the UV-curing process was carried out by Design of Experiment (DoE) to evaluate the influence of light intensity and photoinitiator to find the optimal curing conditions. Subsequently, a thorough thermo-mechanical characterization highlighted the influence of the chemical structure on material properties. 3D printing was performed, enabling the fabrication of complex and self-stain structures with remarkable accuracy and precision. Lastly, a chemical degradation study revealed the potential for end-of-use recycling of the bio-based thermosets.

Fabrication of fully bio-based malleable thermoset derived from cellulose, furfural and plant oil for advanced capacitive sensor

Fabrication of sustainable bio-based malleable thermosets (BMTs) with excellent mechanical properties and reprocessing ability for applications in electronic devices has attracted more and more attention but remains significant challenges. Herein, the BMTs with excellent mechanical robustness and reprocessing ability were fabricated via integrating with radical polymerization and Schiff-base chemistry, and employed as the flexible substrate to prepare the capacitive sensor. To prepare the BMTs, an elastic bio-copolymer derived from plant oil and 5-hydroxymethylfurfural was first synthesized, and then used to fabricate the dynamic crosslinked BMTs through Schiff-base chemistry with the amino-modified cellulose and polyether amine. The synergistic effect of rigid cellulose backbone and the construction of dynamic covalent crosslinking network not only achieved high tensile strength (8.61 MPa) and toughness (3.77 MJ/m3) but also endowed the BMTs with excellent reprocessing ability with high mechanical toughness recovery efficiency of 104.8 %. More importantly, the BMTs were used as substrates to fabricate the capacitive sensor through the CO2-laser irradiation technique. The resultant capacitive sensor displayed excellent and sensitive humidity sensing performance, which allowed it to be successfully applied in human health monitoring. This work paved a promising way for the preparation of mechanical robustness malleable bio-thermosets for electronic devices.

Synthesis of bio-based polyimine networks with flame-retardancy, acid-degradablility, and reprocessability

Conventional thermosetting materials lack of reprocessability, acid-degradability, and fire-safety, which limit the further popularization and application of materials. In this study, a hexasubstituted cyclotriphosphazene (HVP) was synthesized from abundant renewable vanillin, and then combined with two bio-based amines (castor oil polyamine and furan-derived diamine) to establish polyimine networks through a condensation reaction between amino groups and aldehyde groups. Five bio-based polyimine thermoset networks (FA-0, FA-25, FA-50, FA-75, and FA-100) were prepared with an ammonia-formaldehyde ratio of 1:1, and varying the ratio of the two bio-based amines allowed for regulating the final mechanical properties (from tough plastic-like to hard plastic-like) and flame resistance of the materials. Among the five experimental samples, FA-100 exhibited the best physical properties stress and Tg of 28.47 MPa and 63.8 °C, respectively. FA-100 networks also showed the best flame retardant properties (LOI, 28.8 vol/%). Furthermore, due to the dynamic imine bonds in the polymer network, the material could be recycled under hot pressing conditions (120 °C and 15 MPa). Meanwhile, the monomer HVP could be recovered under mild acidic circumstances. These thermosetting polyimine networks provide a new avenue for the development of multifunctional bio-based polymer materials for practical applications.

Bio-based epoxy and unsaturated polyester resins: Research and market overview

The presented study provides an overview of the current research achievements and the emerging market of bio-based thermosetting polymers. Environmental attributes related to bio-based polymers trigger a steadily growing interest in this novel and promising field. Due to their importance among thermosets in terms of composite applications and quantity, this review focusses on epoxy and unsaturated polyester resins. Current studies are mainly concerned with alternative renewable raw materials to substitute fossil content and their synthesis to improve their end-properties. A common target is the increase of bio-based content within the cured resin. In spite of today’s efforts in research, the recent market review reveals only few commercially available bio-based thermosetting resin systems. However, they are commonly suited for a broad variety of processing methods and applications with bio-contents up to 75%.

Bio-Based Thermosetting Resins: From Molecular Engineering to Intrinsically Multifunctional Customization.

Recent years have witnessed a growing interest in bio-based thermosetting resins in terms of environmental concerns and the desire for sustainable industrial practices. Beyond sustainability, utilizing the structural diversity of renewable feedstock to craft bio-based thermosets with customized functionalities is very worthy of expectation. There exist many bio-based compounds with inherently unique chemical structures and functions, some of which are even difficult to synthesize artificially. Over the past decade, great efforts are devoted to discovering/designing functional properties of bio-based thermosets, and notable progress have been made in antibacterial, antifouling, flame retardancy, serving as carbon precursors, and stimuli responsiveness, among others, largely expanding their application potential and future prospects. In this review, recent advances in the field of functional bio-based thermosets are presented, with a particular focus on molecular structures and design strategies for discovering functional properties. Examples are highlighted wherein functionalities are facilitated by the inherent structures of bio-based feedstock. Perspectives on issues regarding further advances in this field are proposed at the end.

Fast-curing bio-based thermoset foams produced via the Michael 1,4-addition using fatty acid-based acetoacetate and acrylate

This study introduces an approach for creating bio-based polymer foams exploiting the Michael reaction that could be utilized as thermal insulation. The thermoset foams were developed using a second-generation bio-based feedstock – tall oil. Tall oil is a by-product of wood pulping in paper manufacturing and mainly comprises unsaturated fatty acids like oleic and linoleic acid. The study explores the use of tall oil-based acetoacetates (Michael donor) combined with various acrylates (Michael acceptor), petrochemical-based (bisphenol-A ethoxylate diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate), and bio-based (epoxidized soybean oil acrylate, epoxidized tall oil free fatty acids-based acrylate), to develop polymer foams that meet today's sustainability requirements. The developed polymer foams underwent extensive characterization. Matrix curing parameters were assessed by measuring changes in dielectric polarization during curing. Foaming parameters, including start and rise times, were precisely measured. The chemical composition of the foams was analysed using Fourier-transform infrared spectroscopy. Their thermal, thermo-mechanical, and mechanical properties were evaluated through thermal gravimetric analysis, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and compression tests. Additionally, the content of closed-cell and the coefficient of thermal conductivity were determined, further characterizing the foams as potential thermal insulation materials. Foams from bio-based donors with petrochemical-based acceptors exhibited a range of enhanced properties. They not only achieved high glass transition temperatures (up to 85 °C by DSC and up to 108 °C by DMA) but also displayed a spectrum of mechanical strengths (compression strength ranging from moderate to as high as ∼ 0.40 MPa) and good thermal isolation properties (thermal conductivity coefficient ∼ 31mW/(m·K)). Bio-based foams, derived from renewable resources, were characterized by properties fitting for flexible foam applications, such as low glass transition temperatures (down to −9.7 °C by DSC and down to 9.8 °C by DMA), reduced compression strength (approximately 0.011 MPa), and increased thermal conductivity (up to 46.7mW/(m·K)), indicating their potential utility in applications where flexibility is a key requirement.

Biobased Thermoset Substrate for Flexible and Sustainable Organic Photovoltaics

AbstractToward a sustainable development of the flexible electronics industry, the design and facile preparation of sustainable flexible substrates with satisfactory mechanical properties and transparency is still a challenge. Herein, taking structural advantages of biobased eugenol and vanillin, a polymerizable aromatic carbonate monomer with α,ω‐diene functionality (2E), and a robust aromatic acetal monomer with α,ω‐tetraene functionality (4E), are designed and prepared. Then, they are cross‐linked with pentaerythritol tetrakis(2‐mercaptoacetate) (4SH) via thiol‐ene click reaction to generate a series of ternary poly(thioether carbonate acetal) thermosets. It is found that the introduction of 4E allows the production of thiol‐ene thermosets with higher crosslink density, which can balance their mechanical, optical, and surface properties. In addition, the thermoset shows good resistance against various natural environmental conditions and can be decomposed into recyclable small molecules under harsher conditions (3 m NaOH, 80 °C). As a result, the optimal thermoset is well‐suited for the fabrication of flexible organic solar cells (OSCs), yielding a power conversion efficiency of 15.41%, which is superior to polyethylene terephthalate‐based OSC. The results provided significant insights for the design and preparation of sustainable polymer substrates for OSCs, even flexible electronics.