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Developing effective latent curing agent for rapid curing of epoxy resins at low temperatures remains challenging. This study reports a latent curing agent, ortho‐cresol phenolic epoxy resin‐bisphenol A (EOCN‐BPA), prepared through the addition reaction of o‐methyl phenolic epoxy resin with BPA. When blended with dicyandiamide (DICY) in a 1:3 molar ratio, EOCN‐BPA/DICY is used to cure a linear epoxy phenolic novolac (EPN) resin (epoxy equivalent: 550 g eq−1, softening point: approximately 82°C), at an onset curing temperature of 90°C, which is considerably lower than the onset curing temperature of DICY with EPN (160°C). However, EOCN‐BPA does not react with EPN without a catalyst. Therefore, this latent curing system is successfully applied in powder coatings, rapid curing at 120°C within 3 min without an additional catalyst, outperforming the EPN/EOCN‐BPA system using cocatalyst 2‐methylimidazole. Consequently, DICY catalyzes the curing reaction between the phenol hydroxyl group and epoxy resin and participates in it. The prepared powder coating exhibits excellent storage stability, maintaining its properties for over 3 months at room temperature. These findings demonstrate the excellent latent properties of EOCN‐BPA/DICY, highlighting its potential as a highly effective latent curing agent. [ABSTRACT FROM AUTHOR]

To address the limitation of poor conductivity in composite bipolar plates (CBPs), a three‐dimensional (3D) conductive skeleton structure of graphite flakes (GF) is constructed using the sacrificial template method. This method prepares 3D polybenzoxazine/graphite flakes composite bipolar plates (3D‐PBA/GF CBPs) with high conductivity through vacuum impregnation of benzoxazine resin (BA). In this paper, the effect of the presence of a conductive network structure on the key properties of CBPs is analyzed, and the performance of GF randomly dispersed CBPs obtained through traditional solution dispersion is also compared. Thanks to the efficient conductive path within its 3D conductive skeleton structure, the 3D‐PBA/GF CBP achieves excellent conductivity meeting US Department of Energy (DOE) targets (in‐plane conductivity greater than 100 S/cm, area‐specific resistance less than 10 mΩ cm2) at a low filler content (50 wt%). In addition, CBPs with 3D conductive skeleton structures also exhibit qualified service performances to meet the requirements of proton exchange membrane fuel cells (PEMFCs). Compared with GF randomly dispersed CBPs, 3D‐PBA/GF CBPs exhibited higher power density in a single cell. This study demonstrates that constructing PBA/GF CBPs with a 3D conductive skeleton to achieve an accumulation distribution of conductive fillers is an efficient method for enhancing the conductivity of CBPs. [ABSTRACT FROM AUTHOR]

This research conducts a comprehensive cradle‐to‐gate life cycle assessment, comparing four distinct epoxy composites with each other and with the pure matrix. The composites investigated include epoxy resin reinforced with 25% and 50% untreated Luffa cylindrica fiber mats and 25% and 50% chemically treated Luffa cylindrica mats. The study defines the functional unit concerning the load at the fracture point and explores a real‐world scenario related to a potential industrial installation in southeastern Europe. The assessment utilizes 22 ReCiPe 2016 endpoint indicators to quantify impacts on human health, ecosystems, and resource availability. The findings indicate that the 50% chemically treated Luffa cylindrica‐reinforced epoxy has the least environmental impact, closely followed by the 50% untreated Luffa cylindrica. All four composites exhibit lower impacts than the pure epoxy resin. Notably, the 50% Luffa‐reinforced composites stand out as significantly environmentally favorable due to the substitution of fossil‐derived resin with natural fibers. This study underscores the potential of Luffa cylindrica as a promising and eco‐friendly reinforcement for epoxy composites. [ABSTRACT FROM AUTHOR]

Recent studies have hypothesized that the reinforcing effects of boehmite nanoparticles (BNPs) in polymer nanocomposites (PNCs) are partly related to the particles themselves and partly to the water released from the BNP during curing. In this work, PNCs made from dried BNP (dBNP) with concentrations up to 15 wt% are investigated to differentiate particle and water related effects. The observed trend of the storage modulus in dynamic mechanical thermal analysis measurements was found to be independent of the drying procedure. Stiffness maps from intermodulation atomic force microscopy showed that dBNP leads to a stiffening of the interphase surrounding the particles compared with the unaffected epoxy matrix, while a softer interphase was reported for PNCs with as received BNP. A slight decrease in the glass transition temperature was observed by broadband dielectric spectroscopy related to a lowered crosslink density due to the particles. A significantly higher decrease was reported for PNCs with BNP, attributed to water influencing the curing process. In conclusion, the stiffening of PNC with BNP is related to the particles themselves, while the release of water causes the formation of a soft interphase in the vicinity of the particles and a significant decrease in crosslink density. [ABSTRACT FROM AUTHOR]

Quercetin (Q), one of the most abundant molecules in nature, remains relatively unexplored in the realm of bio-based thermosets. In line with the pursuit of sustainability, we report the successful synthesis of a novel bio-based phthalonitrile (PN) monomer (Q-Ph) using Q. The synthesis involved a nitro displacement reaction with 4-nitrophthalonitrile (4-NPN). Confirmation of the monomer's structure utilized hydrogen and carbon nuclear magnetic resonances (1H and 13C NMR), Fourier transform infrared spectra (FTIR), and elemental analysis. Curing characteristics were examined by differential scanning calorimetry (DSC), and polymerization was analyzed using FTIR. The resulting monomers showed a wide processing window and low melt viscosity via rheological analysis. Thermal and thermomechanical properties were assessed using dynamic mechanical analyzer (DMA) and thermogravimetric analysis (TGA), revealing lower curing and polymerization temperatures compared to petroleum-based counterparts. The synthesized resin achieved a high Tg exceeding 400°C, a char yield of 79% at 1000°C, and T5% and T10% values of 564 and 660°C, respectively. The Q-Ph polymer demonstrated superior performance, with evidence of an autocatalytic curing mechanism. These results highlight quercetin as a promising petrochemical replacement for the preparation of self-curable PN thermosets, especially for high-performance applications. [ABSTRACT FROM AUTHOR]

Inspired by the significant catalytic charring effect of metal–organic frameworks (MOFs), Cu‐MOF decorated ammonium polyphosphate (APP@Cu‐MOF) was prepared by coupling agents to improve the fire safety of epoxy resin (EP). After adding 9 wt% APP@Cu‐MOF, the fire performance of EP is significantly improved with limiting oxide index (LOI) value of 29.4 and UL‐94 V‐0 rating. The peak heat release rate (PHRR), total smoke production (TSP), CO production, and CO2 production of EP composite samples decreased by 34.6%, 54.7%, 24.6% and 30.0%, respectively. It is proposed that the synergistic effect among Cu‐MOF and APP promoted the char formation of EP. The dense carbon layers formed a barrier that prevented the transfer of heat and inhibited the release of toxic gases, thus acting as a flame retardant. This work provides a new strategy to develop a high‐efficient MOF‐decorated flame retardant with smoke inhibition, toxicity reduction, and catalytic carbonization effect. [ABSTRACT FROM AUTHOR]

The renewable and biosynthetic molecule, vanillin, were used in the preparation of new phthalonitrile (PN) and ethynylbenzene (EB) bifunctional resins without pre‐modification of the vanillin structure. This PN resin was characterized by differential scanning calorimetry, thermogravimetric analysis, nuclear magnetic resonance spectroscopy, rheometry, and single crystal x‐ray diffraction. The monomers exhibited excellent rheometric viscosities below 250 Cp at processing temperatures and a good pot life. After complete curing, the PN polymers exhibited thermal stability above 500°C, a glass transition temperature (Tg) above the final postcure temperature of 380°C, and exceptional retention of structural integrity over a large temperature range. These results suggest that vanillin derived EBPN based resins are excellent candidates for use in a variety of applications where high temperature and mechanical stability is critical. [ABSTRACT FROM AUTHOR]

A series of triphenol‐diamine‐type hyperbranched benzoxazines are synthesized by using polyformaldehyde, 1,1,1‐tri(4‐hydroxyphenyl) ethane, and primary amines such as p‐phenylenediamine, 4,4′‐diaminodiphenylmethane, polyetheramine, and bifuranocyclic diamine via Mannich condensation. Then, copolymers with bifunctional benzoxazine (BA‐a) are prepared to obtain superior properties. The polymerization behavior of the copolymers examined using a differential scanning calorimeter and a Fourier transform infrared indicates that the introduction of hyperbranched benzoxazines facilitates the benzoxazine curing reaction, decreasing the onset and peak temperatures of the curing process. Thermogravimetric analysis results suggest the cured hyperbranched benzoxazine demonstrates good thermal stability and can improve the heat resistance of benzoxazine. In addition, dynamic mechanical analysis suggests the glass transition temperature of the copolymers with BA‐a was increased after copolymerization, thus making all the copolymers obtain higher service temperatures. The test results from the universal testing machine and the fracture morphologies of copolymers indicate the hyperbranched benzoxazines with branched structures cause dendritic folds to appear on the surface of copolymers upon polymerization, preventing rapid cracking and spreading of the thermoset resin by dissipating more impact energy through this irregular dendritic appearance, thus obtaining strength and toughness superior to that of BA‐a resins. [ABSTRACT FROM AUTHOR]

Epoxy resin foams are lightweight materials commonly utilized as core materials in shipbuilding and aerospace applications. Mechanical properties and yielding behavior were the basis of the application of epoxy resin foams. In order to reveal the yield behavior and mechanical properties of epoxy resin foams. The compression and tension behavior of epoxy resin foams were investigated. The compression modulus and the tensile modulus increased with the strain rates and foams' density. Epoxy resin foams exhibited excellent toughness and the maximum elongation at break could reach 17.2%. The mechanical properties (εtotal < 5%) of epoxy resin foams were successfully predicted through combining phenomenological strain rate‐dependent constitutive model for epoxy resin and cell structures. The yield point was represented through the elastic strain fraction. The compressive elastic strain fraction (C∅e,εinelastic=0.2%) was 0.908, and the tensile elastic strain fraction (L∅e,εinelastic=0.2%) was 0.884. [ABSTRACT FROM AUTHOR]

Allyl ether naphthol resin (ANPF) was synthesized by introducing 1,5‐dihydroxynaphthalene and 2,7‐dihydroxynaphthalene into phenolic resin and was copolymerized with 4,4′‐bismaleimidodiphenylmethane resin (BDM) to obtain allyl ether naphthol‐modified bismaleimide resins (15‐ANPF‐BDM and 27‐ANPF‐BDM). The resulting thermal stability and glass transition temperature (Tg) were explored by thermogravimetric and dynamic mechanical analyses. The char yield of 15‐ANPF‐BDM at a temperature of 800°C was 46.0%. Additionally, the Tg of 15‐ANPF‐BDM was measured as 311°C, which is an increase of 44°C compared to that of c. The mechanical properties of the ANPF‐BDM/quartz fiber (Qf) composites were also investigated. The results reveal that ANPF‐BDM/Qf composites exhibit similar mechanical strength to APF‐BDM/Qf composites at room temperature. In addition, the mechanical properties of the ANPF‐BDM/ Qf composites demonstrated significant improvement in mechanical properties retained significantly improved at 200°C, with a 68% flexural strength retention and a 96% interlaminar shear retention of 15‐ANPF‐BDM/Qf composites. Thus, ANPF‐BDM/Qf composites exhibit outstanding mechanical properties at 200°C. [ABSTRACT FROM AUTHOR]

Softening and subsequent deformation are significant challenges in additive manufacturing of thermal-curable thermosets. This study proposes an approach to address these issues, involving the preparation of thermosetting composite powders with distinct curing temperatures, the utilization of cold spray additive manufacturing (CSAM) for sample fabrication, and the implementation of stepwise curing for each component. To validate the feasibility of this approach, two single-component thermosetting powders P1 and P2 and their composite powder C were subjected to CSAM and stepwise curing. From the sample morphology observation and deposition/curing mechanism investigation based on thermomechanical analysis and differential scanning calorimetry, it is found that severe plastic deformation occurs during the CSAM process, accompanied by heat generation, leading to local melting to promote a good bond at the contact surface of the particles and form small pores. During the progressive curing, the samples printed using C demonstrate superior deformation resistance compared with those using P1 and P2, and the curing time is reduced from 16.7 h to 1.5 h, due to the sequential curing reactions of P1 and P2 components in composite C, allowing the uncured P2 and cured P1 to alternately remain solid for providing structural support and minimizing deformation. [ABSTRACT FROM AUTHOR]

AbstractNanodiamond has been categorized among remarkable zero dimensional nanocarbon. This carbon nanoparticle has been applied as important nanofiller in the polymeric matrices. This state-of-the-art review article portrays fundamentals, physical properties, and prospects of nanodiamond filled thermosetting matrices. Among thermosets, most research efforts have been reported on the nanodiamond filled epoxy and polyurethane matrices. Consequently, the epoxy/nanodiamond and polyurethane/nanodiamond nanocomposites have been designed. The nanodiamond nanoparticle addition in polymers caused microstructural variations and enhancements in mechanical, thermal, wear, adhesion, and related advanced features. The property improvement was observed due to the nanofiller dispersion, matrix-nanofiller interactions, and interface formation. Type of thermosetting polymer, curing agent, nanodiamond content, nanodiamond functionalities, and processing method define the final nanocomposite architecture, morphology, and ensuing characteristics. Consequently, the high-tech epoxy/nanodiamond nanocomposites and polyurethane/nanodiamond nanocomposites exposed capability toward technological relevance like coatings, microwave absorption, and biomedical. As few thermosetting matrices have been used with the nanodiamond nanofillers so far, more comprehensive future efforts are needed to disclose the actual potential of thermosetting polymer/nanodiamond nanocomposites. [ABSTRACT FROM AUTHOR]

Phthalonitrile thermosets are known for their excellent mechanical, physico-chemical, and fire-retardant properties, making them attractive for aerospace and mechanical engineering applications. When producing and applying phthalonitrile-based structural parts, it is essential to consider aspects such as processability and the long-term stability of the material's properties at high temperatures. In our previous studies, we demonstrated that resins containing phosphate-bridged bisphthalonitrile monomers are easily processable due to their low melting temperature and wide processing window. In this study, we investigated the impact of bis(3-(3,4-dicyanophenoxy)phenyl)phenyl phosphate (PPhPN) monomer content on physico-chemical and mechanical properties, thermal stability, and thermal oxidative stability. This research highlights the importance of conducting long-term thermal oxidative aging studies in addition to thermogravimetric analysis to properly assess the stability of thermosets. The findings indicate that adding less than 15% of PPhPN results in the formation of a crystalline phase, which impairs the resin's processability. Conversely, a high PPhPN content reduces the material's thermal oxidative stability. Therefore, based on mechanical and physico-chemical tests after thermal oxidative aging, it can be concluded that a 10–15% concentration of the phosphate-containing monomer enables easy processability of the phthalonitrile resin and provides excellent long-term thermal oxidative stability at temperatures up to 300 °C, while maintaining a flexural strength exceeding 120 MPa and an elasticity modulus of 4.3 GPa. [ABSTRACT FROM AUTHOR]

Three ethanolic solutions containing different imidazolium ionic liquids (IL), namely 1‐butyl‐3‐methylimidazolium chloride, 1‐carboxymethyl‐3‐methylimidazolium chloride or 1,3‐dicarboxymethylimidazolium chloride), were used for the surface modification of aramid pulp (AP) (5 wt.% of IL in relation to AP mass) to improve its interfacial interaction with triethylene tetramine‐cured epoxy resin. Composites were prepared by casting with 0.4 phr of AP. Scanning electron microscopy, mechanical tests, isothermal dynamic mechanical analysis (at 1, 10 and 100 Hz), and conventional non‐isothermal analysis were performed. The IL‐modified AP (AP‐IL) presented greater defibrillation and strengthened interaction with the polymeric matrix, minimizing fiber pullout in the mechanical tests. The AP distribution in the epoxy matrix was assessed, and morphological changes were partly responsible for the improvement in the mechanical and dynamical mechanical response of the AP‐IL/epoxy composites. The AP/epoxy composite compatibilized with IL 1‐butyl‐3‐methylimidazolium chloride presented the lowest activation energy and, in turn, the strongest interaction with the epoxy matrix. Normalized DMA curves provided more detailed information on the differences between neat epoxy and the studied composites. [ABSTRACT FROM AUTHOR]

This article extensively explores moisture resistance treatments for natural fiber-reinforced composites (NFRCs), aiming to mitigate the hindrance posed by their high moisture absorption and limited applications. The study delves into five distinct fiber treatments, emphasizing their roles in improving fiber separation, wettability, homogeneity, and crucial fiber/matrix adhesion by removing surface impurities. Chemical treatments applied are instrumental in inducing hydrophobic behavior in treated fibers, validated by Fourier-transform infrared spectroscopy (FTIR) analysis and an observed increase in water contact angle. Scanning electron microscopy (SEM) analysis underscores the treated NFRCs' superior mechanical properties, showcasing extensive fiber breakage and enhanced energy-dissipating mechanisms. The article employs a 2D finite element (FE) model to visually represent the impact of moisture resistance treatments on NFRCs using the thermal-moisture analogy. Treated samples initially exhibit faster moisture absorption than untreated epoxy, creating a moisture gradient. However, over time, treated NFRCs demonstrate reduced moisture absorption compared to neat epoxy, with the hydrophobic interphase actively attracting and subsequently retarding moisture progression. This comprehensive study identifies effective moisture resistance treatments for NFRCs. It explains their mechanisms, helping to understand how these treatments improve the performance of natural fiber-reinforced composites in practical applications. [ABSTRACT FROM AUTHOR]

This study aims to explore new flame-retardant composites based on a phosphorus-functionalized cellulose derivative and epoxy/benzoxazine thermosetting resins in order to broaden the use of natural fibers in advanced applications. The study involved the phosphorylation of microcrystalline cellulose followed by its characterization through employing various analytical methods to corroborate the accomplishment of its functionalization. The curing behavior of composites based on the polybenzoxazine/epoxy copolymer reinforced with (1 and 5 wt.%) modified microcrystalline cellulose was hereafter considered. The thermal behavior of these composites was correspondingly investigated using thermogravimetric analysis, where improved thermal stability and the limiting oxygen index were stressed. Flame retardancy tests using the vertical burning test UL 94 and heat of combustion analysis utilizing an oxygen bomb calorimeter were also carried out to deeply examine the possible flame retardancy ability of the considered composites. [ABSTRACT FROM AUTHOR]

In this study, two cardanol based epoxidized resins, NC514 with less than two epoxies per molecule and side chain epoxidized cardanol glycidyl ether (SCECGE) with approximately 2.45 epoxies (1.0 phenolic+1.45 aliphatic epoxies) per molecule were methacrylated. The methacrylated versions of cardanol based NC514 (NC514VE) and SCECGE (SCECGEVE) epoxy resins were used as cross‐linker units in vinyl ester formulations with methacrylated lauric acid (MFA) and styrene (ST) as bio‐based and synthetic based reactive diluents respectively, at various concentrations (10–40 wt%). The curing reactions of the resins were studied via FTIR and the extent of polymerization was determined for different cross‐linker units in the presence of ST and MFA. Our mechanical and thermomechanical characterizations showed that VER formulations prepared with cardanol based SCECGEVE cross‐linker unit have significantly improved properties than the samples prepared with commercially available counterpart NC514VE using either reactive diluent. These properties of SCECGEVE were also comparable with to that of methacrylated petroleum‐based diglycidyl ether of bisphenol A vinyl ester (DGEBAVE) formulations unlike NC514VE formulations due to more effective side chain functionalization and cross‐linking. [ABSTRACT FROM AUTHOR]

The flammability of unsaturated polyester resins (UPRs) limits their applications. Herein, a reactive P‐ and N‐containing flame retardant (DPET) having triazole and piperazine rings is reported. The 9,10‐Dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide (DOPO) was used to introduce P atoms, and eugenol was used to import reactive double bonds to DPET. Different ratios of DPET were mixed with a commercial UPR and the thermal, mechanical, optical, and flame retardancy properties were measured. The addition of 15% of DPET into neat UPR led to a decrease in the water contact angle from 70° ± 2 to 61° ± 2. The gel content values of the UPRs were found to change between 97.5% and 89%. The optical properties of the UPR were adversely affected by the incorporation of DPET. The modulus of the DPET‐containing UPRs increased with increasing amount of DPET and 15% of DPET‐containing UPR displayed a modulus value of 1784 ± 86 MPa. When 15% DPET was added to neat UPR, char yields were increased (from 5.6% to 16.6%). Limiting oxygen index (LOI) values increased with increasing amounts of DPET and reached up to 23.4%. Micro cone calorimeter (MCC) test results showed up to a 20.5% reduction in the peak heat release rate (PHRR) of the UPR when 15% DPET was added. [ABSTRACT FROM AUTHOR]

Thermoset materials, known for their stable topology structure, have garnered significant interest in recent years for their applications in coatings, foam, adhesives, and other fields. In general, the low chemical crosslinking density of thermoset materials means poor mechanical properties. In this study, we adjusted the topological structure of thermoset elastomers through formula design and controlled their hard segment content at the same level. The mechanical tensile test results show that as the chemical crosslinking density of the elastomer decreases, the fracture tensile strength shows a trend of first increasing and then decreasing. Although the content of amino ester groups in the elastomer is the same, low field nuclear magnetic resonance and Fourier transform infrared analysis show that as the density of the chemical cross‐linking network decreases, more physical cross‐linking points are formed between the elastomer network chains. Furthermore, the polyurethane hard segment formed an amorphous microphase separation structure in the elastic matrix. This study proves that constructing a moderate physical hydrogen bonding association structure between the network chains in polyurethane cross‐linked thermoset elastomers is another important way to prepare thermoset elastomers with excellent mechanical properties. [ABSTRACT FROM AUTHOR]

Carbon fibers (CFs) are experiencing a growing demand owing to their low specific weight, exceptional mechanical properties, superior temperature, and corrosion resistance, however, their sustainability and energy consumption during manufacturing is still a challenge. Therefore, reclamation of waste CFs and their reformatting has gained significant attention. Herein, we synthesized a chemically degradable vitrimer matrix by curing bisphenol‐A diglycidyl ether (BADGE) with 2‐aminophenyl disulfide (2‐AFD) and further utilized the matrix for the development of CF reinforced composites (CFRCs) through vacuum‐assisted resin infusion molding (VARIM) process. The obtained vitrimeric system and its composites show excellent mechanical, self‐adhering, shape‐memory, and reprocessing properties. Meanwhile, the developed CFRP vitrimer composites can be rapidly dissolved in thiol solvent (1‐octanethiol), resulting in the efficient recycling of CFs. X‐ray diffraction, scanning electron microscopy, and Raman spectroscopy validate that the chemical structure of the recycled fibers closely resembles the structure of the original CFs. The recycled CFs were further used to prepare second generation composite materials with excellent thermal, dynamic, and mechanical properties for nonstructural applications (e.g., sports, automotive, etc.). Thus, with an effective CF recycling method, this study can assist in preparing reliable, long‐term functional, recyclable, and high‐performance composites. [ABSTRACT FROM AUTHOR]

The effects of grafting level of polyethylene glycol (PEG) grafted styrene ethylene propylene styrene (SEPS) on the intrinsic brittleness of epoxy thermosets were studied. The SEPS‐g‐PEG block copolymer (BCP) was synthesized by grafting various grafting degree of PEG (i.e., 10%, 20%, 30%, and 40%) on polystyrene (PS) blocks of SEPS following Williamson ether synthesis method. A total of 10 wt% of the BCP modifiers were dispersed in epoxy thermosets. PEG side chains were miscible in the epoxy which formed a uniform BCP dispersion within the epoxy thermoset matrix. As the degree of PEG grafting was increased, the BCP phase was absorbed in the epoxy matrix. This absorption occurred because the increase in PEG grafting provided more miscible PEG chains to bind the BCP and epoxy nanostructures together. The differential scanning calorimeter and dynamic mechanical thermal analysis analyses indicated that BCP toughened epoxy exhibited an improved glass transition temperature (Tg). At a 40% PEG grafting degree in the BCP, the critical stress intensity factor (KIC) and critical strain energy release rate (GIC) increased up to 80% and 180%, respectively. This trend suggested that the energy associated with fractures could be absorbed through the deformation of the softer phases when a load was applied to them. [ABSTRACT FROM AUTHOR]

A multifunctional photoinitiator is presented, offering precise control over light‐induced polymerization initiation at 450 nm and material degradation at 365 nm. This is accomplished by covalently linking photoactive bis(acyl)phosphane oxide and photocleavable o‐nitrobenzyl ether moieties onto the surface of γ‐cyclodextrin. Upon degradation, the resulting linear polymers can be easily re‐dissolved in their corresponding monomer and re‐cured, exhibiting superior mechanical properties compared to the pristine material. Moreover, this photoinitiator enables the successful 3D printing of intricate and precise structures, representing a promising general strategy for developing recyclable photoresins for 3D printing applications. [ABSTRACT FROM AUTHOR]

A novel epoxy resin, DPHP, was synthesized from diphenolic acid, which contains biobased levulinic acid, with triethylphosphite, to improve the flame retardancy of bisphenol‐A diglycidyl ether (BADGE) epoxy. Curing experiments were conducted using isophorone diamine as a curing agent for BADGE and DPHP mixtures. Variations in cure kinetics, mechanical properties, and flame retardancy were evaluated across different DPHP contents. The introduction of phosphorus functional groups into DPHP affected the polarization of epoxide CO bonds, resulting in reduced apparent activation energy for epoxy curing reactions. However, the higher epoxy equivalent weight of DPHP compared with that of BADGE led to a decrease in the tensile strength and the glass transition temperature of the cured material with increasing DPHP content. A significant increase in char yield for combustion of the epoxy blend was observed, ranging from 8.3% at 0 wt% DPHP to 20.1% at 50 wt% DPHP. Additionally, cone calorimeter measurements showed significant reductions in heat release rate and total heat release, leading to a decrease in fire spread from 1.07 MJm−2 s−1 at 0 wt% DPHP to 0.43 MJm−2 s−1 at 50 wt% DPHP. These results show that the flame retardancy of the cured material improved significantly as the DPHP content increased. [ABSTRACT FROM AUTHOR]

Toughening thermo‐setting resins with both high impact strength and tensile strength is a challenging issue. In this study, a novel cross‐linked polyurethane nano spheres for toughening epoxy resin were prepared by self‐emulsification method with hexamethylene diisocyanate trimer (HDI trimer) and diethylene triamine (DETA) as the crosslinkers. The structure, morphology and particle size of cross‐linked polyurethane nano spheres were investigated by infrared spectroscopy, laser particle size analyzer and scanning electron microscopy. Results showed that the prepared cross‐linked polyurethane nano spheres showed spherical shape and had the size in the range from 40 to 258 nm. The application of cross‐linked polyurethane nano spheres in toughing epoxy resin was investigated. The results showed that cross‐linked polyurethane nano spheres can be uniformly dispersed in epoxy resin and no obvious aggregation phenomenon was observed. And the tensile strength and impact strength of epoxy resin can be increased simultaneously when the cross‐linked polyurethane nano spheres were used in toughening epoxy resin. With the increase of the amount of polyurethane nano spheres in epoxy resin, both the tensile strength and impact strength of epoxy resin had the trend of first increase and then decrease. The amount of HDI trimer in the microspheres had a great impact on their toughening effect on epoxy resin. When the cross‐linked polyurethane nano spheres contained HDI trimer content of 12 wt% and the amount of the nano spheres in epoxy resin was 8 wt%, the impact strength of the epoxy resin can reach as high as 23 kJ/m2, which was 4.33 times that of pristine epoxy resin. And the tensile strength of toughened epoxy resin was 50.7 MPa, which was at same level of that of pristine epoxy resin. The results of this study indicate that the cross‐linked polyurethane nano spheres have a great potential in toughening thermo setting resins, such as epoxy resin. [ABSTRACT FROM AUTHOR]

In order to improve the performance of desulphurized rubber modified asphalt, especially the high‐temperature performance, epoxy resin was selected to modify the modified asphalt with three curing agent and accelerator components. The conventional properties, rheological properties, curing effect, process energy, and modification mechanism of epoxy resin—desulfurized rubber modified asphalt were analyzed. The experimental results show that the addition of epoxy resin to asphalt can all improve the high‐temperature performance of modified asphalt. The promoter component (PC) further improves the high‐temperature performance and reduces the viscosity. Among them, diaminodiphenyl sulfone and methylhexahydrophthalic anhydride in a 1:1 mass combination with epoxy resin modified asphalt not only had better high‐temperature performance, but also had excellent low‐temperature performance and ideal curing process. From the results, it can be seen that 5% epoxy resin with mixed curing agent with 3% PC had the best overall performance. [ABSTRACT FROM AUTHOR]

Aiming at the problem of phase separation between thermoplastic toughener and epoxy after curing, which leads to the reduction of mechanical properties, in this paper we improve the compatibility of the two phases by introducing reactive groups into the molecular chain of thermoplastic resins, thus improving the impact strength of the epoxy system. Phenolphthalein polyether sulfone (C‐PESC) with designable and controllable carboxyl group content was prepared via SN2 nucleophilic substitution copolymerization. Further C‐PESC was evaluated for epoxy toughening, and the effects of carboxyl group content of C‐PESC on mechanical properties and thermal stability of the resin system were investigated. The results show that C‐PESC resin has good compatibility with E51 epoxy resin. Carboxyl group accelerates the dissolution rate of thermoplastic resins in epoxy and also participates in the curing reaction with epoxy to enhance the interfacial bonding ability between the toughening component and the matrix resin. The reactive toughener C‐PESC can not only improve the impact properties of E51 epoxy, but also maintain the high Tg and thermal properties of the resin system. Among them, the addition of 5 PHR of C‐PESC3 increased the impact strength of the modified resin by 45%, with uniform fracture surface and tough fracture shape. [ABSTRACT FROM AUTHOR]

Aligned with the prevailing sustainability paradigm, the imperative adoption of bio‐based substitutes for constituents within petroleum‐derived epoxy resin becomes evident. Blending bio‐based and petroleum‐based epoxy resins and curing agents, establishes a synergistic compromise addressing both sustainability imperatives and the mechanical efficacy of thermosets. The conventional approach to discovering optimal compositions for multi‐component mixtures under specific boundary conditions includes empirical trial and error and is seen as a protracted and inefficient endeavor. Conversely, leveraging machine learning might afford a streamlined and confident resolution to this challenge. This investigation elucidates the requisite strategies for maximizing the efficiency of material property optimization through the application of Bayesian optimization and active learning. Illustratively, the study demonstrates the proficient optimization of the glass transition temperature within a four‐component epoxy resin system. This optimization is conducted across varying ranges of bio‐content and cost considerations. The study underscores the utility of machine learning in achieving this task with notable efficiency. The efficacy of least squares, kernel ridge regression, Gaussian process regression, and artificial neural networks, is meticulously evaluated through comprehensive seven‐fold cross‐validation and validated against experimental data. [ABSTRACT FROM AUTHOR]

An overview of bionanocomposites of polybenzoxazine, which is a highly promising material, is presented in this review paper along with an update on the current developments in this material. With an enormous range of applications, polybenzoxazines are emerging as a latest set of phenolic resins. Its favorable features make it an excellent replacement for many current polymers due to its simplicity in structure design, synthetic process, and polymerization reactions. Problematic aspects of petro‐based raw materials are their nonrenewable nature, toxicity, and rising expense. Hence, the advent of sustainable benzoxazines is promising since it enables the synthesis of monomers without the need for solvents and the processing of these monomers to create extremely thermally stable thermoset resins. This is particularly true when the monomer is derived from naturally occurring, agro‐waste cardanol. A platform for additional structural alterations to expand the uses of cardanol benzoxazine in adhesives, composites, and energy storage devices is provided by its intrinsic properties. There are numerous articles are available for biobased polybenzoxazine, and hence, the focus of the present review is dedicated to (1) nanomaterails loaded bio‐based polybenzoxazines, and (2) bio‐derived nanomaterials loaded polybenzoxazines. [ABSTRACT FROM AUTHOR]

This review article gathers the most recent recycling technologies for thermoset and thermoplastic polymers. Results about existing experimental procedures and their effectiveness are presented. For thermoset polymers, the review focuses mainly on fibre-reinforced polymer composites, with an emphasis on epoxy-based systems and carbon/glass fibres as reinforcement, due to the environmental concerns of their end-of-life management. Thermal processes (fluidised bed, pyrolysis) and chemical processes (different types of solvolysis) are discussed. The most recent combined processes (microwave, steam, and ultrasonic assisted techniques) and extraordinary recycling attempts (electrochemical, biological, and with ionic liquids) are analysed. Mechanical recycling that leads to the downgrading of materials is excluded. Insights are also given for the upcycling methodologies that have been implemented until now for the reuse of fibres. As for thermoplastic polymers, the most state-of-the-art recycling approach for the most common polymer matrices is presented, together with the appropriate additivation for matrix upcycling. Mechanical, chemical, and enzymatic recycling processes are described, among others. The use of fibre-reinforced thermoplastic composites is quite new, and thus, the most recent achievements are presented. With all of the above information, this extensive review can serve as a guide for educational purposes, targeting students and technicians in polymers recycling. [ABSTRACT FROM AUTHOR]

In this study, carbon fiber/epoxy composites (CFRP) were fabricated by vacuum‐assisted resin infusion molding (VARIM) with polyphenylene ether (PPE) as a toughening agent. The PPE contained hydroxyl end groups that facilitated chemical bonding with epoxy during curing. PPE was incorporated into the epoxy matrix by dissolution, and spreading in the interlaminar regions. The presence of PPE as a toughener exhibited significant improvement in the Mode‐I fracture toughness of the composites. The CFRP samples, which were toughened with 5 wt.% and 10 wt.% PPE, showed about 191% to 380% enhancement, respectively, in the critical energy release rate (GIC) compared to the unmodified sample. Dynamic mechanical analysis (DMA) showed about a 6°C increase in the glass transition temperature of the toughened composites, which is an interesting aspect of this work. These results indicate the potential of using PPE as a toughening agent in CFRP composites. [ABSTRACT FROM AUTHOR]

Recently, considerable effort has been made to study cellulose/epoxy composites. However, there is a gap when it comes to understanding the post‐conditioning anomalous effect of moisture uptake on their mechanical and dynamic‐mechanical properties, and on their creep behavior. In this work, up to 10.0 wt% microcrystalline cellulose (MCC) was incorporated into epoxy resin by simple mixing and sonication. Epoxy/MCC composites were fabricated by casting in rubber silicone molds, and rectangular and dog‐bone test specimens were produced. The moisture uptake, dynamic mechanical, chemical, tensile, and creep behavior were evaluated. The incorporation of MCC increased the water diffusion coefficient. The changes in storage modulus and glass transition temperature, combined with Fourier‐transform infrared spectroscopy analysis, evidenced that water sorption in epoxies causes both plasticization and additional resin crosslinking, although the latter is prevented by the addition of MCC. The creep strain of the composites increased by 60% after conditioning, indicating that plasticization induced by water sorption plays an important role in the long‐term properties of the composites. [ABSTRACT FROM AUTHOR]

Vinyl methyl oxazolidinone (VMOX®) is studied as a new reactive diluent (RD) for highly polar unsaturated polyesters (UPs). Molecules with special structure properties are extensively investigated as components for unsaturated polyester resins (UPRs) and thermosets, particularly for high‐temperature applications. Special diols with a cyclic structure like isosorbide and tricyclodecanedimethanol or special diols with side groups like 2‐methyl‐2‐propyl‐1,3‐propanediol and 2‐ethyl‐2‐butyl‐1,3‐propanediol can provide interesting properties. Bio‐based diols such as isosorbide and 1,3‐butanediol improve the sustainability profile. However, UPs based on such special diols have a higher polarity, limiting their solubility in styrene. This demands a RD, which provides adequate solubility and is suitable for high‐temperature applications. Therefore, our study compares the solubility of highly polar UPs based on special diols in styrene and VMOX®. UPs with different formulations, polarities, and Hansen parameters were synthesized and characterized. The solubility sphere of styrene was determined experimentally with the synthesized UPs. The influence of the special diols on the thermoset properties was investigated in dynamic mechanical analysis measurements. In conclusion, VMOX® as a RD enables full utilization of special diols properties due to the wide solubility window. Moreover, a new class of high‐temperature styrene‐free UP resin was developed. [ABSTRACT FROM AUTHOR]

The increased importance of nanostructured lignin exhibits a plethora of multifunctional groups, making it a highly adaptable material basis with significant potential for use in the rapidly expanding composite sector. Initially, lignin nanoparticles (NPs) were incorporated into epoxy networks via an in situ polymerization process where isophorone diamine functioned as a hardener to produce lignin/epoxy resin nanocomposites (lignin@TN). These lignin@TN exhibit promising characteristics, enhancing UV‐blocking efficiency (35.69% at 404 nm with 3.72 wt% lignin) in transparent nanocomposite films while simultaneously improving mechanical properties compared with neat epoxy resin. Adding lignin nanoparticles to epoxy nanocomposites boost up tensile strength by an impressive 24% compared with the pristine epoxy but it affected the glass transition temperature (Tg). After all, this study has opened new possibilities for utilizing renewable, sustainable, and economic lignin feedstocks as a potential ingredient for reinforcing with thermoset polymers like epoxy. [ABSTRACT FROM AUTHOR]

Knowledge of the evolution in the mechanical properties of a curing polymer matrix is of great importance in composite parts or structure fabrication. Conventional rheometry, based on small amplitude oscillatory shear, is limited by long interrogation times. In rapidly evolving materials, time sweeps can provide a meaningful measurement albeit at a single frequency. To overcome this constraint, we utilize a combined frequency- and amplitude-modulated chirped strain waveform in conjunction with a homemade sliding plate piezo-operated rheometer (PZR) and a dual-head commercial rotational rheometer (Anton Paar MCR 702) to probe the linear viscoelasticity of these time-evolving materials. The direct controllability of the PZR, resulting from the absence of any kind of firmware and the microsecond actuator-sensor response renders this device ideal for exploring the advantages of this technique. The high frequency capability allows us to extend the upper limits of the accessible linear viscoelastic spectrum and, most importantly, to shorten the length of the interrogating strain signal (OWCh-PZR) to subsecond scales, while retaining a high time-bandwidth product. This short duration ensures that the mutation number (NMu) is kept sufficiently low, even in fast-curing resins. The method is validated via calibration tests in both instruments, and the corresponding limitations are discussed. As a proof of concept, the technique is applied to a curing vinylester resin. The linear viscoelastic (LVE) spectrum is assessed every 20 s to monitor the rapid evolution in the time and frequency dependence of the complex modulus. Comparison of the chirp implementation, based on parameters such as duration of the experiment, sampling frequency, and frequency range, in a commercial rotational rheometer with the PZR provides further information on the applicability of this technique and its limitations. Finally, FTIR spectroscopy is utilized to gain insights into the evolution of the chemical network, and the gap dependence of the evolving material properties in these heterogeneous systems is also investigated. [ABSTRACT FROM AUTHOR]

Knowledge of the evolution in the mechanical properties of a curing polymer matrix is of great importance in composite parts or structure fabrication. Conventional rheometry, based on small amplitude oscillatory shear, is limited by long interrogation times. In rapidly evolving materials, time sweeps can provide a meaningful measurement albeit at a single frequency. To overcome this constraint, we utilize a combined frequency- and amplitude-modulated chirped strain waveform in conjunction with a homemade sliding plate piezo-operated rheometer (PZR) and a dual-head commercial rotational rheometer (Anton Paar MCR 702) to probe the linear viscoelasticity of these time-evolving materials. The direct controllability of the PZR, resulting from the absence of any kind of firmware and the microsecond actuator-sensor response renders this device ideal for exploring the advantages of this technique. The high frequency capability allows us to extend the upper limits of the accessible linear viscoelastic spectrum and, most importantly, to shorten the length of the interrogating strain signal (OWCh-PZR) to subsecond scales, while retaining a high time-bandwidth product. This short duration ensures that the mutation number (NMu) is kept sufficiently low, even in fast-curing resins. The method is validated via calibration tests in both instruments, and the corresponding limitations are discussed. As a proof of concept, the technique is applied to a curing vinylester resin. The linear viscoelastic (LVE) spectrum is assessed every 20 s to monitor the rapid evolution in the time and frequency dependence of the complex modulus. Comparison of the chirp implementation, based on parameters such as duration of the experiment, sampling frequency, and frequency range, in a commercial rotational rheometer with the PZR provides further information on the applicability of this technique and its limitations. Finally, FTIR spectroscopy is utilized to gain insights into the evolution of the chemical network, and the gap dependence of the evolving material properties in these heterogeneous systems is also investigated. [ABSTRACT FROM AUTHOR]

In this paper, the abrasion resistance of a carbon fiber composite based on epoxy nanocomposite matrix filled with layered-silicate clay nanoparticles was evaluated. In the first step of the work, the clay-epoxy nanocomposite was first studied to assess the dispersion and the performance, and then to select the best content for the fiber composite production. The nanocomposite mixture was prepared by finely dispersing clay nanoparticles into the epoxy monomer through mechanical stirring, then the hardener was added. After this step, the fiber reinforced composite was produced by vacuum infusion, and then the properties were evaluated. The abrasion resistance has been assessed using different approaches. A test was specifically designed to simulate the impact of abrasive powders which could potentially be found in the atmosphere and crash into aircraft or air vehicles (such as for instance volcanic ashes). The results showed that the presence of nanoclay reduces the weight loss of the sample with the impacted surface, which can be clearly correlated to a damage reduction. Highlights • Sandblasting tool made to mimic impact of abrasive powder on composite surface • Presence of nanoclay does not significantly affect the vacuum infusion process • Layered-silicate nanoparticles lead to improve composites abrasion resistance. [ABSTRACT FROM AUTHOR]

Photocurable acrylates and vinyl esters are among the most commonly used resins in cured‐in‐place‐pipe (CIPP) rehabilitation technology, as they impart excellent thermomechanical properties in composite pipes. In the quest for achieving a higher energy efficiency of the photo‐curing process in CIPP, the frontal polymerization technique is a viable alternative that requires a lower irradiation dosage coupled with exceptionally high curing speeds and depths. Herein, for the first time, we report the application of frontal polymerization in the rehabilitation of underground pipes using a newly developed frontally curable epoxy‐based resin (Trelleborg Self‐Curing*). The neat resin is characterized for degree of cure, glass transition temperature, and mechanical properties via FTIR, DMA, and tensile tests, respectively. In a comprehensive way, the properties are benchmarked against commercially available acrylate (Trelleborg Light Cure*) and vinyl ester (Trelleborg Rapid Cure*) resins to evaluate their applicability for CIPP. The results show a higher glass transition temperature and final monomer conversion for the frontally cured resin, which cures significantly faster than the reference resins under the same irradiation conditions. In proof‐of‐concept trials, the newly developed resin successfully cures polymeric liners in a PVC host pipe with 100% water tightness and without losing its structural integrity. Results from ring stiffness tests for cured composite pipes additionally show that liners cured with Trelleborg Self‐Curing* resin pass the minimum required Young's modulus for non‐pressure drainage pipes as per ASTM F1216. Thus, frontally curable epoxy‐based resins are a promising and competitive alternative to acrylates and vinyl esters in CIPP. [ABSTRACT FROM AUTHOR]

The tensile behavior of a flexible epoxy resin reinforced with knitted reinforcements from various fiber materials was comprehensively studied in the wale and course direction. By measuring dry yarns, temperature‐treated yarns, dry knitted fabrics and flexible composites, the effect of the fiber material and the knitted fabric on the tensile properties was analyzed. The interlock knit structure strongly affected the deformation behavior of the flexible composites which differed significantly from the dry knitted fabrics. The deformation behavior of the flexible composites was monitored using digital image correlation which revealed the formation of cracks and high local strain differences in the course direction for all fiber materials. This was linked to fiber‐matrix debonding by scanning electron microscope observations. In the wale direction, the deformation of the knitted structure under tensile load led to plastic deformation of the matrix material. Overall, with yarns from recycled thermoplastic fibers, a higher maximum stress and strain at break was achieved compared to bio‐based fibers. However, irreversible damage occurred for all fiber materials at similar strain values. Highlights: Tensile tests on yarns, knitted fabrics and flexible composites.Investigation of the effect of fiber material on mechanical properties.High local strain differences in composites due to knitted structure.Fiber‐matrix debonding in course direction.Plastic deformation of the matrix material in the wale direction. [ABSTRACT FROM AUTHOR]

We designed three‐dimensional (3D) structures through a combination of glass fiber cloth and in situ formation of nano polyphenylene oxide (PPE) fibers during the fabrication process of thermosetting cyanate ester/bismaleimide composites and developed a self‐stitching technique based on PPE fiber and interpenetrating polymer networks (IPNs) for aiding the crack self‐healing. The building of 3D structure effectively improves the interface interaction between fiber and matrix and suppresses the crack propagation process in composite, leading to significant enhancement in the mechanical properties. When PPE content is 20%, the interlaminar shear strength, flexural strength, impact strength, and tensile strength of the resulting composite are 98%, 74%, 95%, and 101% higher than those of the composite without PPE. The resulting composites possess excellent thermomechanical and lower dielectric properties. Because IPNs within composites can create interspaces and easily deform above glass‐transition temperature, PPE components may penetrate through the interspaces under thermal expansion force, and the contraction stresses of polymers generate strong locking effects in composite after cooling to room temperature, then the crack surfaces of composites can be stitched by PPE fibers, significantly recovering the mechanical properties. The healing efficiency of the composite with 30% PPE after impact and then heating at approximately 280°C can reach 96%. Highlights: 3D structures were constructed during the fabrication process of glass‐fiber‐reinforced thermosetting cyanate ester/bismaleimide composite.A self‐stitching technique was developed for aiding the crack self‐healing of composite.3D structures significantly improved the interface interaction between fiber and matrix in laminated composite.The mechanical properties of the resulting composite could be significantly improved by 3D structures.The healing efficiency of the healed composite could reach 96%. [ABSTRACT FROM AUTHOR]

Softening and subsequent deformation are significant challenges in additive manufacturing of thermal-curable thermosets. This study proposes an approach to address these issues, involving the preparation of thermosetting composite powders with distinct curing temperatures, the utilization of cold spray additive manufacturing (CSAM) for sample fabrication, and the implementation of stepwise curing for each component. To validate the feasibility of this approach, two single-component thermosetting powders P1 and P2 and their composite powder C were subjected to CSAM and stepwise curing. From the sample morphology observation and deposition/curing mechanism investigation based on thermomechanical analysis and differential scanning calorimetry, it is found that severe plastic deformation occurs during the CSAM process, accompanied by heat generation, leading to local melting to promote a good bond at the contact surface of the particles and form small pores. During the progressive curing, the samples printed using C demonstrate superior deformation resistance compared with those using P1 and P2, and the curing time is reduced from 16.7 h to 1.5 h, due to the sequential curing reactions of P1 and P2 components in composite C, allowing the uncured P2 and cured P1 to alternately remain solid for providing structural support and minimizing deformation.

Phthalonitrile thermosets are known for their excellent mechanical, physico-chemical, and fire-retardant properties, making them attractive for aerospace and mechanical engineering applications. When producing and applying phthalonitrile-based structural parts, it is essential to consider aspects such as processability and the long-term stability of the material’s properties at high temperatures. In our previous studies, we demonstrated that resins containing phosphate-bridged bisphthalonitrile monomers are easily processable due to their low melting temperature and wide processing window. In this study, we investigated the impact of bis(3-(3,4-dicyanophenoxy)phenyl)phenyl phosphate (PPhPN) monomer content on physico-chemical and mechanical properties, thermal stability, and thermal oxidative stability. This research highlights the importance of conducting long-term thermal oxidative aging studies in addition to thermogravimetric analysis to properly assess the stability of thermosets. The findings indicate that adding less than 15% of PPhPN results in the formation of a crystalline phase, which impairs the resin’s processability. Conversely, a high PPhPN content reduces the material’s thermal oxidative stability. Therefore, based on mechanical and physico-chemical tests after thermal oxidative aging, it can be concluded that a 10–15% concentration of the phosphate-containing monomer enables easy processability of the phthalonitrile resin and provides excellent long-term thermal oxidative stability at temperatures up to 300 °C, while maintaining a flexural strength exceeding 120 MPa and an elasticity modulus of 4.3 GPa.

It is of great significance to design epoxy coatings with superior antibacterial properties and high adhesive properties, as well as excellent processing, superior durability, and high transparency. However, it is still a challenge because of the common complex design and synthesis. Herein, the bio-based monomer protocatechuic acid (PCA) was used as raw material, the catechol structure with high bonding and antibacterial properties was introduced into the flexible alkane segment of ethylene glycol diglycidyl ether (EGDE) through an efficient, and green method, and it was cured with isophorone diamine (IPDA) to prepare corresponding thermosets. The cured resins exhibited excellent all-around qualities, particularly in bonding and antibacterial. When 30% PCA was added to pure epoxy resin, the adhesion between substrate and coating increased from 4.40 MPa to 13.60 MPa and the antibacterial rate of coating against E. coli and S. aureus could approach 100%. All of this is due to the fact that the catechol structure present in PCA has the ability to interact with various substrates and alter the permeability of bacterial cell membranes. The architecture of this method offers a fresh approach to dealing with the issues of challenging raw material selection and complex synthesis techniques. [ABSTRACT FROM AUTHOR]

Improvements in the performance of electronic devices necessitate the development of polymer materials with heat dissipation properties. Liquid crystalline (LC) epoxies have attracted attention because of the orientation of their polymer network chains and their resultant high thermal conductivity. In this study, a diglycidyl ether of 1-methyl-3-(4-phenylcyclohex-1-enyl)benzene was successfully synthesized as an LC epoxy and the LC temperature range was evaluated via differential scanning calorimeter (DSC). The synthesized LC epoxy was cured with m-phenylenediamine (m-PDA) as an amine-type curing agent and 1-(2-cyanoethyl)-2-undecylimidazole (CEUI) as a latent curing catalyst, respectively. The LC phase structure and domain size of the resultant epoxy thermosets were analyzed through X-ray diffraction (XRD) and polarized optical microscopy (POM). High thermal conductivity was observed in the m-PDA system (0.31 W/(m·K)) compared to the CEUI system (0.27 W/(m·K)). On the other hand, in composites loaded with 55 vol% Al2O3 particles as a thermal conductive filler, the CEUI composites showed a higher thermal conductivity value of 2.47 W/(m·K) than the m-PDA composites (1.70 W/(m·K)). This difference was attributed to the LC orientation of the epoxy matrix, induced by the hydroxyl groups on the alumina surface and the latent curing reaction. [ABSTRACT FROM AUTHOR]

The non-toxic and biodegradable nature of chitosan makes it a valuable resource offering promising opportunities in the development of bio-based materials with enhanced mechanical and thermal properties. In this work, the combination of epoxidized linseed oil, oxalic or citric acids, and chitosan (CHI) as a curing accelerator presents an attractive strategy to create bio-based and sustainable thermosetting materials. This article aims to provide a comprehensive exploration of the systems reactivities, characteristics, and performance evaluation of the designed bio-thermosets. Both the nature of the two carboxylic acids and the presence of chitosan are shown to have a big impact on the thermomechanical properties of the developed networks. While oxalic acid favours the formation of elastic networks, with low Tg values (increasing with CHI content between 0.7 and 8.5 °C) and relatively low Young's modulus (~2.5 MPa), citric acid promotes the formation of very dense networks with lower mass of the segments between the crosslinks, having 20 times higher Tg values (from 36 to 45 °C) and ~161 times higher Young's modulus (from 94 MPa up to 404 MPa in these systems). The CHI has a strong impact on the curing reaction and on the overall properties, by increasing the materials' performance. [ABSTRACT FROM AUTHOR]