Epoxy Matrix Research Articles

Boron nitride nanosheets synergized with two‐dimensional micron silver sheets to enhance thermal conductivity and insulation of epoxy resin composites

AbstractWith the rapid progress of the advanced electronic device industry, precision electronic instruments are gradually developing towards miniaturization. In this case, epoxy resin gradually attracts people's attention, but its intrinsic thermal conductivity is not high, and the resulting heat dissipation problem limits the further application of epoxy resin in the field of electronic packaging. Therefore, how to enhance the thermal conductivity of epoxy resins has become an urgent problem in the field of electronic packaging. In this work, BNNS was successfully prepared by stripping h‐BN into a flaky two‐dimensional material, which was added to the epoxy resin as a filler to make the composite material. And on the basis of the above, two‐dimensional micron silver flakes (AgMS) with different mass fractions were added to the composites, and the AgMS/BNNS/EP composites were successfully prepared. When BNNS was 25 wt% and AgMS was 1 wt%, its out‐of‐plane thermal conductivity was enhanced from 0.17 W m−1 K−1 of pure epoxy resin to 0.43 W m−1 K−1. When BNNS was 20 wt% and AgMS was 1 wt%, the breakdown strength was enhanced from 105 kV/mm for pure epoxy to 130 kV/mm. This work provides a new strategy for synthesizing high‐thermal‐conductivity epoxy matrix composites.

A Lennard-Jones potential based cohesive zone model and its application in multiscale damage simulation of graphene reinforced nanocomposites

A new mixed-mode cohesive zone model based on Lennard-Jones potential (LJCZM) is proposed to simulate the interface failure between graphene and epoxy matrix. The values of model parameters are obtained from a large number of molecular dynamics simulations, and a UMAT subroutine is programmed and validated to introduce this model into the ABAQUS platform. This process spans from the nanoscale to the microscale, which provides a new routine for the multiscale damage modeling of the graphene reinforced epoxy nanocomposite at microscale. In addition, the continuous damage phase-field model is used to simulate the matrix damage, and the values of model parameters are determined from the molecular dynamic simulations of the bulk epoxy at nanoscale. At last, the effects of parameters such as volume fraction, aspect ratio, orientation, and curvature of graphene nanoplatelets are investigated. The results indicate that the nanocomposite reinforced with high content and large aspect ratio graphene nanoplatelets presents the lower ultimate stress and fracture strain. In addition, the orientation and waviness of the graphene also significantly affect the mechanical properties of the nanocomposites. The nanocomposite reinforced with graphene platelets with greater waviness has higher stiffness and strength but lower toughness. The rationality and effectiveness of the model are verified through comparison with other existing results.

Monolithic Polyepoxide Membranes for Nanofiltration Applications and Sustainable Membrane Manufacture.

The present work details the development of carbon fiber-reinforced epoxy membranes with excellent rejection of small-molecule dyes. It is a proof-of-concept for a more sustainable membrane design incorporating carbon fibers, and their recycling and reuse. 4,4'-methylenebis(cyclohexylamine) (MBCHA) polymerized with either bisphenol-A-diglycidyl ether (BADGE) or tetraphenolethane tetraglycidylether (EPON Resin 1031) in polyethylene glycol (PEG) were used to make monolithic membranes reinforced by nonwoven carbon fibers. Membrane pore sizes were tuned by adjusting the molecular weight of the PEG used in the initial polymerization. Membranes made of BADGE-MBCHA showed rejection of Rose Bengal approaching 100%, while tuning the pore sizes substantially increased the rejection of Methylene Blue from ~65% to nearly 100%. The membrane with the best permselectivity was made of EPON-MBCHA polymerized in PEG 300. It has an average DI flux of 4.48 LMH/bar and an average rejection of 99.6% and 99.8% for Rose Bengal and Methylene Blue dyes, respectively. Degradation in 1.1 M sodium hypochlorite enabled the retrieval of the carbon fiber from the epoxy matrix, suggesting that the monolithic membranes could be recycled to retrieve high-value products rather than downcycled for incineration or used as a lower selectivity membrane. The mechanism for epoxy degradation is hypothesized to be part chemical and part physical due to intense swelling stress leading to erosion that leaves behind undamaged carbon fibers. The retrieved fibers were successfully used to make another membrane exhibiting similar performance to those made with pristine fibers.

Fabrication of Hybrid Epoxy Composites (Joint Compound Adhesive) for Aluminum Substrate Applications and Their Evaluation for Mechanical Properties.

This research endeavor deals with the development of an epoxy hybrid nanocomposite using aliphatic diglycidyl ether of a bisphenol A (DGEBA) epoxy matrix. The formulation used the stoichiometric ratio of the curing agent and incorporated nanopigments such as zirconium and silica, along with other microfillers. We incorporated Zr and SiO2 nanoparticles and various other additives in the epoxy matrix and ensured homogeneous dispersion by using sonication methodology along with silane as a coupling agent. Aluminum molds were utilized to fabricate dumbbell-shaped ASTM standard samples for the testing of mechanical properties. The adhesive properties were evaluated through standard lap shear tests. Fourier transform infrared spectroscopy was utilized to analyze the cross-linking reaction of the epoxy moiety and the polyamidoamine adduct curing agent. Further characterization using field emission scanning electron microscopy, energy-dispersive spectroscopy, and high-resolution transmission electron microscopy confirmed the presence and uniform dispersion of the fillers and nanopigments. The results showed good enhancements in ultimate tensile strength, yield strength, and elastic modulus of 95.3, 162.1, and 425.4%, respectively, compared to formulations using only SiO2. The addition of ZrO2 and SiO2, along with various microfillers, such as talc and aluminum silicate, led to significant improvements in the mechanical properties. This study demonstrates the synergistic efficiency of combining SiO2 and ZrO2 along with microfillers, such as talc and aluminum silicate, in epoxy resin for diverse applications in the construction industry, where mechanical strength and substrate adhesion are crucial.

Facile armour production from cocoon waste by a cold-pressing process

Utilising cocoon waste as reinforcement in composites offers a cost-effective alternative for soft body armour production. Cocoon waste, including damaged or uncoiled cocoons and those with pupae, is recognised as an eco-friendly choice. This study aims to develop and assess the incorporation of varying amounts of cocoon waste as reinforcement in epoxy resin matrix composites through the cold-pressing process. The cocoon waste content in the composite specimens ranged from 0 to 40 wt%. Tensile testing and ballistic impact testing were conducted to evaluate specimen performance. The cocoon waste composite plate exhibited a maximum tensile strength of 62.21 MPa at 30 wt%, slightly surpassing that of woven hemp. These findings indicate the advantageous reinforcement attributes of cocoon waste. However, a limitation was identified: bullets fully penetrated the composite plate. To address this, ultra-high-molecular-weight polyethylene was incorporated into cocoon waste composites, resulting in enhanced tensile strength (107.36 MPa) and complete bullet penetration prevention. These outcomes position the study as a promising avenue for developing body armour plates meeting the stringent level II certification standards set by the National Institute of Justice.

Size Effects in Climatic Aging of Epoxy Basalt Fiber Reinforcement Bar.

The purpose of this study was to obtain information on the influence of the size factor on the climatic aging of circular fiber plastics produced by pultrusion. The kinetics of moisture transfer was obtained in humidification and drying modes at 60 °C in samples of epoxy basalt fiber reinforcement bars: after 28 months of exposure in the extremely cold climate of Yakutsk and 30 months of exposure in the moderately warm climate of Gelendzhik. It was shown that the 2D Langmuir model adequately describes the kinetics. The diffusion coefficients in the reinforcement direction for bars with diameters of 6, 8, 10, 16 and 20 mm turned out to be significantly higher than in the radial direction. To clarify the aging mechanism of the bars and the tensile, compressive and bending strength, the coefficient of linear thermal expansion and the glass transition temperature of the epoxy matrix of the bars with a diameter of 6, 8 and 10 mm after 51 months of exposure in Yakutsk and 54 months of exposure in Gelendzhik were measured. It was shown that after climatic exposure, the deformability of the bars decreased with increasing diameter of the bar; the glass transition temperature increased more significantly in the bar with a smaller diameter. In 6 mm diameter bars, the compressive and bending strength limits decreased by 10-25 % due to the plasticizing effect of moisture. With the same depth of moisture penetration into the volume of the samples, its effect on the strength of thin bars was significant, and for thick bars, it was insignificant. An increase in the glass transition temperature by 6 °C, associated with the additional curing of the polymer matrix, occurred in the surface layer of the epoxy basalt fiber reinforcement bars and was revealed in bars with a smaller diameter.

Multi-objective topology optimization of macro structure and microtubule network structure for self-healing material

Abstract Self-healing materials possess the capability to promptly repair minor damages occurring during service, thereby effectively preventing safety accidents. This paper investigates a multi-objective topology optimization method for the macro structure and microtubule network of self-healing materials around pure epoxy resin materials, aiming to enhance the damage healing capability of the microtubule network while meeting the mechanical performance requirements of the macro structure. By introducing the design variables of macro structure and microtubule network, the corresponding topological description functions are established respectively. And study applies logical operations and post-processing techniques to generate an embedded microtubule network structure description. The objective functions include the flexibility of the macro structure, the along-travel head loss, and the total length of the microtubule network, with material volume serving as a constraint. In order to determine the head loss of the three-dimensional microtubule network structure, a Hardy-Cross method based on flow initialization and loop search is proposed. Multi-objective topology optimization is designed based on moving morphable components algorithm, enumeration method and Pareto principle. Develop iterative termination conditions by assessing the disparity between Pareto solution sets in each generation, thereby ensuring algorithm convergence. The numerical example of the Messerschmitt–Bölkow–Blohm (MBB) beamyields a flexibility of 0.059 without a carrier and 0.0728 with a carrier the macrostructural flexibility without a carrier is 81.0% compared to with a carrier, and the macrostructural profiles and the overall flexibility of the MBB beams with/without a carrier are close to each other. This method serves as a reference for optimizing large-scale self-healing structures.

Polydopamine‐coated iron‐nickel alloy and epoxy composites for electromagnetic interference shielding

AbstractWith the development of electronic devices and wireless communication technology, the quality of human life has improved. However, shielding from electromagnetic interference (EMI) is required due to device malfunctions and harmful effects on human health. Polymer‐based shielding materials getting much attention due to their light weight, flexibility, good processability, and other desirable traits. However, achieving consistent dispersion of conductive fillers and optimizing the balance between electrical, mechanical, and thermal properties remain challenges despite the advantages of polymer‐based materials. Especially, epoxy resins are promising polymer materials for EMI shielding applications due to their excellent mechanical strength, chemical resistance, and excellent adhesive properties. Additionally, epoxy resin exhibits remarkable processability allowing for various fabrication techniques such as casting, molding, and three‐dimensional printing. However, one of the significant drawbacks of epoxy resin is the difficulty in achieving uniform dispersion of conductive fillers within the epoxy matrix. In this study, we propose an iron‐nickel alloy (FeNi) embedded in an epoxy matrix (FeNi/Epoxy) for EMI shielding material. It is manufactured by facile fabrication process due to the advantages of epoxy, which has excellent processability. EMI shielding effectiveness at 12 GHz is enhanced from 9.12 to 17.86 dB by the increase of FeNi concentrations. Furthermore, thermal and mechanical properties were improved by the increase of FeNi concentration. Thermal conductivity for efficient heat dissipation is increased from 0.63 to 1.49 Wm−1 K−1. Moreover, polydopamine (PDA) was employed as a surface coating material for FeNi to overcome the non‐uniform dispersion of FeNi particles in the epoxy matrix. Surface coating by PDA significantly enhanced the dispersion uniformity and strengthened the adhesion between the filler and matrix. Elastic modulus is greatly increased from 83.03 MPa to 1.29 GPa by the surface coating. The enhancement of mechanical properties is derived from the chemical bonds between the filler and matrix.

Preparation and Characterization of Epoxy-Based Composite Materials Reinforced with Graphene Oxide

In this study, modified graphene oxide (GO) with γ-APS silane coupling agent before being dispersed into an epoxy/4,4’-diamino diphenyl methane matrix to prepare a composite material using the bar-coating technique. The modified GO materials with the γ-APS silane (GOS) were characterized by infrared spectrum, Zeta potential, and TG/DSC thermal analysis. The amount of silane grafted on the GO is ~ 3.3 wt.%; the Zeta potential value shifted from the negative to the positive region was observed on the surface potential distribution diagram. Scanning electron microscopy, DSC thermal analysis, and dielectric constant were used to characterize the obtained composite epoxy/GO material properties. The results show that graphene oxide, after modification with γ-APS silane agent, has good dispersion ability in the epoxy resin matrix. Composite material epoxy/GOS presented a high dielectric constant value (εaverage = 6.19, at 1 kHz), increasing thermal stability, which is a suitable material promising for future applications.

Epoxy composite materials filled with rice husk ash

The present research responds to two current tendencies, such as circular economy, involving reuse of industrial waste, and green chemistry, presupposing application of renewable resources and technologies, which minimize the negative environmental impact. The present article is dedicated to the study of the application of rice husk and its ash as a filled for epoxy composite materials. Rice husk represents a multi-tonnage agricultural by-product, subject to recycling, and at the same time, is a valuable source of amorphous silica. Temperature regime of rice husk ash (RHA) production, optimum content and particle size of filler providing maximum modifying effect were determined. The influence of modifying fillers on the complex of operational properties of filled epoxy compositions including hardness, wear resistance, adhesion to steel and aluminium and antifriction properties of epoxy coatings has been established. A comparative analysis of the properties of modified compositions with non-filled ones and with compositions filled with fully amorphous silica, including industrial analogue Aerosil 300, has been carried out. It has been established that the best compatibility with polymer epoxy matrix is possessed by rice husk ash obtained at the combustion temperature of 500оC introduced in the amount of 10 mass parts per 100 mass parts of epoxy polymer.

Multiscale modeling of microstructural and hygrothermal effects on vibrations of CNT-enhanced fiber-reinforced polymer composites

This work presents a multi-scale analytical and computational approach designed to predict the hygro-thermo-mechanical vibrational response of laminated composite structures reinforced with multi-walled carbon nanotubes (MWCNTs). Employing the modified Halpin-Tsai model, this study estimates the elastic properties of the MWCNT-enhanced epoxy matrix, incorporating the impacts of MWCNT agglomeration, orientation, waviness, and size-dependent characteristics. Additionally, the Chamis micromechanical model is utilized to ascertain the independent elastic constants of the nanocomposite lamina, considering environmental variables such as temperature and humidity. Subsequent analysis involves the determination of natural frequencies for both pristine and MWCNT-integrated laminated composite structures via the Finite Element Method (FEM), addressing various design-related parameters. This investigation further explores the macroscopic influences of MWCNT incorporation, boundary condition and layup scheme, along with the temperature, moisture content, and the nanoscopic impact of MWCNTs on the natural frequencies of laminated composite plates. The obtained results of the proposed multiscale modeling are compared with experimental and theoretical observations. It has been demonstrated that while the incorporation of carbon nanotubes (CNTs) can enhance the mechanical properties of nanocomposite laminae, the natural frequencies of these nanocomposite plates are adversely affected by variations in temperature and moisture content. Furthermore, the findings indicate that the microstructural characteristics of CNTs play a crucial role in determining the efficacy of the reinforcement phenomenon. The developed multi-scale methodological framework offers significant potential for the design and optimization of MWCNT-based composite structures across diverse industries, including automotive and aerospace sectors.

Analysis of the impact of exfoliated graphene oxide on the mechanical performance and in-plane fracture resistance of epoxy-based nanocomposite

Graphene oxide (GO) is a versatile material, derivative of graphene, and it has gained significant attention in the field of polymer nanocomposites due to its exceptional properties and unique structural features. These characteristics make it a successful secondary reinforcing agent for enhancing mechanical performance, fatigue resistance, and other various physical and thermal properties of nanocomposites. However, the low fracture toughness of nanocomposite has restricted the overall structural applications. In this research work, the epoxy nanocomposites were prepared with different weights of exfoliated graphene oxide (E-GO) nanoparticles by using a dual mixing probe ultra-sonication for homogeneous distribution and proper dispersion. A substantial enhancement in mechanical performance and fracture toughness of nanocomposite was observed. The good dispersion and interfacial adhesion among E-GO and epoxy matrix were investigated through the critical analysis of the fracture surfaces of the nanocomposite. The enhancement of mechanical performance of E-GO nanofiller-reinforced epoxy composite was observed superior at 1 wt. % of GO60 particle concentration. The maximum increment of mechanical properties such as tensile strength, flexural strength, and work of fracture were 40.763, 39.23, and 12.106 % respectively, whereas maximum tensile modulus and flexural modulus were 19.3724, 27.63 % at 1.5 wt. % of GO60 as compared to the neat composite. However, in the case of fracture toughness and energy, maximum improvement of 1.256 Mpa.m1/2 and 0.472 KJ/m2 respectively was observed at 1 wt. % of GO60. Such enhancement was primarily due to the bolstering of in-plane crack propagation resistance in the nanocomposites. Additionally, the highlight point in thermomechanical properties of the polymer nanocomposite is optimal storage modulus and damping factor such as 4066.75 MPa, and 0.46 respectively, for the GO60 at 1 wt.% nanocomposite. Moreover, GO60 at 1 wt.% demonstrates greater thermal stability, withstanding up to 50% material degradation at 413.65°C.

Enhanced morphological and thermal properties of epoxy composites reinforced with Palm and Prosopis Juliflora fibers

Abstract This study investigates the fabrication and characterization of a hybrid epoxy matrix composite reinforced with Palm and Prosopis Juliflora fibers fabricated using the hand layup technique. Three composite samples were prepared with varying weight percentages of palm and Prosopis Juliflora fiber reinforcements: 5% (Sample A), 10% (Sample B), and 15% (Sample C). Sample B having 10 weight percentage each of Palm fiber and Prosopis Juliflora fiber and 80 weight percentage of Epoxy matrix, exhibited superior performance with a tensile strength of 45.5 MPa and a hardness of 86.5 Shore D. Thermal analysis revealed Sample B’s exceptional thermal stability, with distinct decomposition stages observed through Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA). Void content analysis indicated Sample C had the lowest void content at 4.5%. Energy Dispersive x-ray (EDX) Analysis confirmed homogeneous fiber distribution and strong fiber-matrix adhesion, supported by carbon and oxygen peaks. Fourier-transform infrared spectroscopy (FTIR) spectra showed interactions between functional groups, including alcohols, carboxylic acids, and carbonyl compounds. These findings underscore the composite’s potential for high strength, toughness, and thermal stability applications.

Effects of spherical fillers reinforcement on the efficacy of thermal conductivity in epoxy and polyester matrices: Experimental validation and prediction using finite element method

AbstractThe creation of a theoretical heat conduction model for polymers embedded with spherical inclusions is described in this study. It also contains the experimental confirmation of the suggested correlation for utilizing the model to estimate the effective thermal conductivity (K) of such composites. According to ASTM‐E‐1530, composites are made with varying amounts of aluminium oxide and pine wood dust reinforced in polyester resin. The effective thermal conductivities (Keff) of the composites are then determined using the Unitherm TM model 2022. Ansys 19.R2 software is used to evaluate the effective thermal conductivity of these composites with a uniform filler distribution, while Digimat‐FE software is used determine the thermal conductivity values of such particle filled polymer composites with a random filler distribution. After comparison and validation with experimental data, these values are shown to be fairly good agreement with the theoretical values from the suggested correlation. The investigation is further expanded to determine the thermal conductivities for epoxy composites using wood apple shell dust and coir dust particle. Also epoxy and polyester composites reinforced with SiO2 and TiO2 have been investigated in the similar manner. The main thrust of this report to validate the numerical results of composites by varying numerous polymers. The thermal conductivity all the composites grow monotonically with increase in filler content. The thermal conductivity of silicon dioxide, titanium oxide, and aluminium oxide filled epoxy composites is measured as 1.5, 7, and 35 W/m‐K respectively.Highlights In this study spherical fillers are successfully used as a potential filler material in polyester composites The thermal conductivity predicted by proposed mathematical model of polyester is validated with measured value and found better agreement. The Ansys 19.R2 and digimat software are used to predict the thermal conductivity values of these composites. The mathematical model is further used to predict thermal conductivity of epoxy composites to check the accuracy of the model.

Cross-Linking Reaction of Bio-Based Epoxy Systems: An Investigation into Cure Kinetics.

The cure kinetics of various epoxy resin mixtures, comprising a bisphenol epoxy, two epoxy modifiers, and two hardening agents derived from cardanol technology, were investigated through differential scanning calorimetry (DSC). The development of these mixtures aimed to achieve epoxy materials with a substantial bio-content up to 50% for potential automotive applications, aligning with the 2019 European Regulation on climate neutrality and CO2 emission. The Friedman isoconversional method was employed to determine key kinetic parameters, such as activation energy and pre-exponential factor, providing insights into the cross-linking process and the Kamal-Sourour model was used to describe and predict the kinetics of the chemical reactions. This empirical approach was implemented to forecast the curing process for the specific oven curing cycle utilised. Additionally, tensile tests revealed promising results showcasing materials' viability against conventional counterparts. Overall, this investigation offers a comprehensive understanding of the cure kinetics, mechanical behaviour, and thermal properties of the novel epoxy-novolac blends, contributing to the development of high-performance materials for sustainable automotive applications.

Study on the nuclear shield behaviors of basalt/carbon fibers reinforced PbO blended epoxy matrix composite – A novel material for thermal insulation applications

This study introduces a novel composite material engineered for thermal insulation, specifically in environments requiring radiation shielding. The composite is composed of basalt and carbon fibers reinforced varying with lead oxide (PbO) nanoparticles for five different composite laminates, all integrated into an epoxy matrix. The research primarily focuses on evaluating the composite's thermal insulation capabilities, gamma-ray attenuation effectiveness, and microstructural characteristics. Mechanical testing reveals that the incorporation of basalt and carbon fibers significantly enhances the composite's tensile strength and modulus. Thermal analysis demonstrates the composite's excellent insulation properties, attributed to the synergistic effects of the fibrous reinforcement and the epoxy matrix, which effectively reduce thermal conductivity. Gamma attenuation tests indicate a substantial improvement in radiation shielding effectiveness with the addition of lead oxide nanoparticles. The composite exhibits improved gamma-ray attenuation compared to conventional materials, due to the high atomic number of lead, which enhances photon absorption and scattering mechanisms.Microstructural analysis provides detailed insights into the composite's structure. Morphological images show a uniform dispersion of PbO nanoparticles and strong adhesion between the fibers and the matrix. Elemental analysis confirms the elemental composition, highlighting the successful integration of PbO nanoparticles, which significantly enhances radiation shielding.

A novel tooling-free carbon fibre reinforced polymer (CFRP) manufacturing method, double point incremental forming (DPIF) with direct electrical curing (DEC)

Carbon fibre-reinforced polymers (CFRPs) are essential in various industries due to their exceptional specific mechanical properties. However, conventional CFRP manufacturing involves significant costs related to moulds, ovens, and autoclaves, rendering it expensive for low-volume production and prototyping. This study introduces a novel method, Double-Point Incremental Forming with Direct Electric Curing (DPIF-DEC), which enables CFRP fabrication without the need for moulds, directly from CAD models, but it is not suited for mass production. This technique, enhanced by the addition of 2 wt.% carbon black to the epoxy resin matrix, improves through-thickness electrical conductivity, allowing uniform and rapid curing. DPIF-DEC demonstrates rapid localised curing, real-time process monitoring, and achieves mechanical properties comparable to traditional methods. Additionally, it reduces energy consumption, presenting a cost-effective and environmentally sustainable solution for low-volume and prototype CFRP production, laying the groundwork for future applications in continuous-fibre composite manufacturing directly from CAD models.

Properties of Epoxy Matrix Modified with Boron Nitride

Properties of Epoxy Matrix Modified with Boron Nitride

Constructing Mechanochromic Fluorescent Interphase via Core-Shell Microcapsules: A Route for Interface Reinforcing and Damage Self-Reporting of CFRP Composites.

Perylenediimide-chitosan/γ-poly (glutamic acid) microcapsules sizing (PDI-CS/γ-PGA) core-shell microcapsule is designed and used to establish a novel interphase in carbon fiber/epoxy (CF/EP) composite, and the interfacial property, as well as the damage self-reporting of the composite, is compared with desized carbon fiber (CF-desized)/EP and commercial carbon fiber (CF-COM)/EP composite. The ruptured PDI-CS/γ-PGA microcapsule exhibits strong "turn-on" green fluorescence from the released PDI upon mechanical stimuli. The anchoring of PDI-CS/γ-PGA microcapsule on carbon fiber with PDI-CS/γ-PGA microcapsules sizing (CF@PDI-CS/γ-PGA) surface results in increased chemical activity and roughness, exhibiting a weak green fluorescence signal instead of non-fluorescence on CF-desized and CF-COM surface. The transverse fiber bundle tensile (TFBT) strength of CF@PDI-CS/γ-PGA composite is 80.97% and 31.09% higher than those of CF-desized/EP and CF-COM/EP composite, which is attributed to the mechanical interlocking and chemical bonding interaction between carbon fiber and epoxy matrix by introducing PDI-CS/γ-PGA microcapsule with spherular structure and active groups. After microdroplet testing, the strong "turn-on" green fluorescence signal of the released PDI from the microcapsules is detected in the interfacial debonding regions, realizing the microscopic damage self-reporting of CF@PDI-CS/γ-PGA composite.

Novel recyclable epoxy resin with releasable residual stress and synergistically enhanced dielectric properties and healing ability

It has been a challenge to improve the performance of epoxy insulation in the whole life cycle by achieving the reduction of residual stress during manufacturing, the healing of damages during application, and the recycling after decommissioning. In this paper, a novel recyclable epoxy resin (SEP) with releasable residual stress and synergistically enhanced dielectric properties and healing ability was successfully developed by introducing dynamic thiocarbamate bonds (DTBs). A reduction in residual stresses by 45 % was detected after SEP was annealed at 30 °C below the glassy transition temperature (Tg) for 8 h, during which the mechanical properties remained unchanged. Synergistically improved dielectric properties and damage-healing ability were also observed in SEP. A high healing efficiency of 94.4 % for electrical breakdown damage was found in SEP, meanwhile its dielectric properties were superior to commercial epoxy resin. Additionally, SEP featured good recyclability, including reprocessability and degradability. All those excellent properties were ascribed to the dissociation and recombination of DTBs triggered by thermal stimulation. This work provides an effective solution to a series of issues throughout the full lifecycle of epoxy materials.