Mechanical, Thermal, and Electrical Properties of BN-Epoxy Composites Modified with Carboxyl-Terminated Butadiene Nitrile Liquid Rubber

Low viscosity and low temperature curing reactive POSS/epoxy hybrid resin with enhanced toughness and comprehensive thermal performance

The mechanical and high-temperature resistance properties of epoxy resins cured at low temperatures (Tcuring ≤ 100 °C) are often inferior, and the most toughening modification methods for epoxy resins tend to compromise thermal resistance, which significantly limit the practical applications of it. Therefore, this work reported a low viscosity and low-temperature curing epoxy hybrid resin system (OPEP), adopting E-51 as a resin matrix, liquid anhydride (MHHPA) as a curing agent, tertiary amine (DMBA) as a curing accelerator, and reactive octa-epoxy terminated polyhedral oligomeric silsesquioxane (OG-POSS) as a toughening modifier. Results demonstrated that the OPEP system has excellent processability with low viscosity and long processing window period and satisfies the practical requirements of low-temperature curing. The OG-POSS exhibits superior compatibility and reactivity with the resin matrix, and its addition slightly reduces the Eα of the curing reaction and has a certain promotive effect on the curing of epoxy resin. In addition, the curing reaction rate of the OPEP resin complies with the Šesták-Berggren autocatalytic kinetics model. The impact strength, flexural strength, tensile strength, and elongation at break of the OPEP resin reached a maximum of 15.55 kJ m-2, 121.65 MPa, 90.36 MPa, and 2.48%, representing increases of 55.97%, 3.1%, 64.68%, and 26.51% compared to those of the pure resin, respectively. Notably, due to the heat-resistant inorganic silicon cage structure of OG-POSS, the thermal decomposition temperature (Td5), glass transition temperature (Tg), and heat distortion temperature (THDT) of the OPEP0.02 resin were 313.2 °C, 123.7 °C, and 102.0 °C, showing increases of 13.0 °C, 2.3 °C, and 6.8 °C compared to the pure resin, respectively, which is difficult to achieve for the general thermosetting resin toughening modification method. This research utilized organic-inorganic nanohybrid materials (POSS) to optimize the toughness and thermal stability of the resin in a coordinated manner, providing guidance for the preparation of high-performance epoxy resins that cure at low temperatures.

Fracture of Epoxy Matrixes Modified with Thermo-Plastic Polymers and Winding Glass Fibers Reinforced Plastics on Their Base under Low-Velocity Impact Condition

The work is aimed at studying the impact resistance of epoxy oligomer matrices (EO) modified with polysulfone (PSU) or polyethersulfone (PES) and glass fibers reinforced plastics (GFRP) based on them under low-velocity impact conditions. The concentration dependences of strength and fracture energy of modified matrices and GFRP were determined. It has been determined that the type of concentration curves of the fracture energy of GFRP depends on the concentration and type of the modifying polymer. It is shown that strength σ and fracture energy E_M of thermoplastic-modified epoxy matrices change little in the concentration range from 0 to 15 wt.%. However, even with the introduction of 20 wt.% PSU into EO, the strength increases from 164 MPa to 200 MPa, and the fracture energy from 32 kJ/m² to 39 kJ/m². The effect of increasing the strength and fracture energy of modified matrices is retained in GFRP. The maximum increase in shear strength (from 72 MPa to 87 MPa) is observed for GFRP based on the EO + 15 wt.% PSU matrix. For GFRP based on EO + 20 wt.% PES, the shear strength is reduced to 69 MPa. The opposite effect is observed for the EO + 20 wt.% PES matrix, where the strength value decreases from 164 MPa to 75 MPa, and the energy decreases from 32 kJ/m² to 10 kJ/m². The reference value for the fracture energy of GFRP 615 is 741 kJ/m². The maximum fracture energy for GFRP is based on EO + 20 wt.% PSU increases to 832 kJ/m² for GFRP based on EO + 20 wt.% PES-up to 950 kJ/m². The study of the morphology of the fracture surfaces of matrices and GFRP confirmed the dependence of impact characteristics on the microstructure of the modified matrices and the degree of involvement in the process of crack formation. The greatest effect is achieved for matrices with a phase structure "thermoplastic matrix-epoxy dispersion." Correlations between the fracture energy and strength of EO + PES matrices and GFRP have been established.

Enhancement of Mechanical Properties and Bonding Properties of Flake-Zinc-Powder-Modified Epoxy Resin Composites

As a typical brittle material, epoxy resin cannot meet its application requirements in specific fields by only considering a single toughening method. In this paper, the effects of carboxyl-terminated polybutylene adipate (CTPBA) and zinc powder on the mechanical properties, adhesion properties, thermodynamic properties and medium resistance of epoxy resin were studied. A silane coupling agent (KH-550) was used to modify zinc powder. It was found that KH-550 could significantly improve the mechanical properties and bonding properties of epoxy resin, and the modification effect of flake zinc powder (f-Zn) was significantly better than that of spherical zinc powder (s-Zn). When the addition amount of f-Zn was 5 phr, the tensile shear strength and peel strength of the composites reached a maximum value of 13.16 MPa and 0.124 kN/m, respectively, which were 15.95% and 55% higher than those without filler. The tensile strength and impact strength reached a maximum value of 43.09 MPa and 7.09 kJ/m², respectively, which were 40.54% and 91.11% higher than those without filler. This study provides scientific support for the preparation of f-Zn-modified epoxy resin.

Structure and Properties of Epoxy Polysulfone Systems Modified with an Active Diluent

An epoxy resin modified with polysulfone (PSU) and active diluent furfuryl glycidyl ether (FGE) was studied. Triethanolaminotitanate (TEAT) and iso-methyltetrahydrophthalic anhydride (iso-MTHPA) were used as curing agents. It is shown that during the curing of initially homogeneous mixtures, heterogeneous structures are formed. The type of these structures depends on the concentration of active diluent and the type of hardener. The physico-mechanical properties of the hybrid matrices are determined by the structure formed. The maximum resistance to a growing crack is provided by structures with a thermoplastic-enriched matrix-interpenetrating structures. The main mechanism for increasing the energy of crack propagation is associated with the implementation of microplasticity of extended phases enriched in polysulfone and their involvement in the fracture process.

Thermally conductive h-BN/EHTPB/epoxy composites with enhanced toughness for on-board traction transformers

The dry-type on-board traction transformer (DOBTT) has the characteristics of huge heat generation and high heat dissipation requirements, so it has higher requirements for heat dissipation performance of epoxy resin (EP) insulation. However, the toughness of the existing high thermal conductivity EP composite after being modified by inorganic particles is greatly reduced, and it is very easy to crack under the occasion of frequent vibration such as electric multiple units or electric locomotives, so it cannot be directly applied to the DOBTT. In this article, the composite using h-BN to improve the thermal conductivity, and epoxidized hydroxy-terminated polybutadiene (EHTPB) liquid rubber to improve the toughness was prepared. After characterization and testing, it was found that when the EHTPB content was between 10 and 15 phr, the elongation at break of the EP/h-BN/EHTPB composite could be increased by 47.9% and the impact strength could be increased by 47.8% compared with that without EHTPB. The thermal and electrical performances were still satisfactory, which has a potential in application of on-board electrical equipment.

Mechanical Characterization of Graphene—Hexagonal Boron Nitride-Based Kevlar–Carbon Hybrid Fabric Nanocomposites

Polymer nanocomposites have been gaining attention in recent years. The addition of a low content of nanomaterials into the matrix improves mechanical, wear, thermal, electrical, and flame-retardant properties. The present work aimed to investigate the effect of graphene and hexagonal boron nitride nanoparticles on Kevlar and hybrid fiber-reinforced composites (FRP). Composites are fabricated with different filler concentrations of 0, 0.1, 0.3, and 0.5 wt.% by using a hand layup process. Characterizations like tensile, flexural, hardness, and impact strength were evaluated separately, heat deflection and viscosity properties of the epoxy composites. The dynamic viscosity findings indicated that a higher concentration of filler material resulted in nano-particle agglomeration. Graphene filler showed superior properties when compared to hexagonal boron nitride filler. Graphene showed optimum mechanical properties at 0.3 wt.%, whereas the hBN filler showed optimum properties at 0.5 wt.%. As compared to Kevlar composites, hybrid (carbon–Kevlar) composites significantly improved properties. As compared to graphene-filled composites, hexagonal boron nitride-filled composites increased scratch resistance. Digimat simulations were performed to validate experimental results, and it was observed that hybrid fabric composites exhibited better results when compared to Kevlar composites. The error percentage of all composites are within 10%, and it was concluded that hybrid–graphene fiber composites exhibited superior properties compared to Kevlar composites.

Research on Improving the Partial Discharge Initial Voltage of SiC/EP Composites by Utilizing Filler Surface Modification and Nanointerface Interaction

SiC/EP composites are promising insulating materials due to their high thermal conductivity, stable chemical properties, and nonlinear electrical conductivity. However, the compatibility of micron-sized SiC particles with the organic polymer matrix is poor, and defects such as air gaps may be introduced at the interface, which reduces the partial discharge resistance of the composite materials. In order to improve the partial discharge initial voltage (PDIV) of SiC/EP composites, in this paper, SiC/EP composites with different proportions were prepared by surface modification of filler and compound of micro/nano particles. Firstly, a method of secondary modification of SiC particles was proposed, which was first modified by alkali washing and then silane coupling agent KH560, and the effectiveness of the modification was verified. Therefore, the interface bonding ability between the filler and the matrix was improved, the air gap defects at the interface were reduced, and the PDIV of the composite material was improved. When the filling ratio is 10 wt%, the PDIV was enhanced by 13.75%, and when the filling ratio was further increased, the improvement was reduced. In contrast, the introduction of nanoparticles into the composites can effectively improve the PDIV of composite materials. In this study, nanoparticles were used to form a shell-core structure in epoxy resins to exert their huge specific surface area and active surface properties, thereby changing the overall crosslinking properties of the composites. Through experimental research, the optimal micro-nano particle compounding ratio was explored. Under the optimal mixing ratio, the PDIV of the composite material can be increased by more than 90%.

Bio-Based Eucommia ulmoides Gum Composites with High Electromagnetic Interference Shielding Performance

Herein, high-performance electromagnetic interference (EMI) shielding bio-based composites were prepared by using EUG (Eucommia ulmoides gum) with a crystalline structure as the matrix and carbon nanotube (CNT)/graphene nanoplatelet (GNP) hybrids as the conductive fillers. The morphology of the CNT/GNP hybrids in the CNT/GNP/EUG composites showed the uniform distribution of CNTs and GNPs in EUG, forming a denser filler network, which afforded improved conductivity and EMI shielding effect compared with pure EUG. Accordingly, EMI shielding effectiveness values of the CNT/GNP/EUG composites reached 42 dB in the X-band frequency range, meeting the EMI shielding requirements for commercial products. Electromagnetic waves were mainly absorbed via conduction losses, multiple reflections from interfaces and interfacial dipole relaxation losses. Moreover, the CNT/GNP/EUG composites exhibited attractive mechanical properties and high thermal stability. The combination of excellent EMI shielding performance and attractive mechanical properties render the as-prepared CNT/GNP/EUG composites attractive candidates for various applications.

Research on the Compound Optimization Method of the Electrical and Thermal Properties of SiC/EP Composite Insulating Material

In this paper, in order to improve the electrical and thermal properties of SiC/EP composites, the methods of compounding different crystalline SiC and micro-nano SiC particles are used to optimize them. Under different compound ratios, the thermal conductivity and breakdown voltage parameters of the composite material were investigated. It was found that for the SiC/EP composite materials of different crystal types of SiC, when the ratio of α and β silicon carbide is 1:1, the electrical performance of the composite material is the best, and the breakdown strength can be increased by more than 10% compared with the composite material filled with single crystal particles. For micro-nano compound SiC/EP composites, different total filling amounts of SiC correspond to different optimal ratios of micro/nano particles. At the optimal ratio, the introduction of nanoparticles can increase the breakdown strength of the composite material by more than 10%. Compared with the compound of different crystalline SiC, the advantage is that the introduction of a small amount of nanoparticles can play a strong role in enhancing the break-down field strength. For the filled composite materials, the thermal conductivity mainly depends on whether an effective heat conduction channel can be constructed. Through experiments and finite element simulation calculations, it is found that the filler shape and particle size have a greater impact on the thermal conductivity of the composite material, when the filler shape is rounder, the composite material can more effectively construct the heat conduction channel.

Bioinspired Dielectric Film with Superior Mechanical Properties and Ultrahigh Electric Breakdown Strength Made from Aramid Nanofibers and Alumina Nanoplates

Materials with excellent thermal stability, mechanical, and insulating properties are highly desirable for electrical equipment with high voltage and high power. However, simultaneously integrating these performance portfolios into a single material remains a great challenge. Here, we describe a new strategy to prepare composite film by combining one-dimensional (1D) rigid aramid nanofiber (ANF) with 2D alumina (Al₂O₃) nanoplates using the carboxylated chitosan acting as hydrogen bonding donors as well as soft interlocking agent. A biomimetic nacreous ‘brick-and-mortar’ structure with a 3D hydrogen bonding network is constructed in the obtained ANF/chitosan/Al₂O₃ composite films, which provides the composite films with exceptional mechanical and dielectric properties. The ANF/chitosan/Al₂O₃ composite film exhibits an ultrahigh electric breakdown strength of 320.1 kV/mm at 15 wt % Al₂O₃ loading, which is 50.6% higher than that of the neat ANF film. Meanwhile, a large elongation at break of 17.22% is achieved for the composite film, integrated with high tensile strength (~233 MPa), low dielectric loss (<0.02), and remarkable thermal stability. These findings shed new light on the fabrication of multifunctional insulating materials and broaden their practical applications in the field of advanced electrics and electrical devices.

Analysis of the Electrical and Thermal Properties for Magnetic Fe3O4-Coated SiC-Filled Epoxy Composites

Orderly arranged Silicon carbide (SiC)/epoxy (EP) composites were fabricated. SiC was made magnetically responsive by decorating the surface with iron oxide (Fe₃O₄) nanoparticles. Three treatment methods, including without magnetization, pre-magnetization and curing magnetization, were used to prepare SiC/EP composites with different filler distributions. Compared with unmodified SiC, magnetic SiC with core-shell structure was conducive to improve the breakdown strength of SiC/EP composites and the maximum enhancement rate was 20.86%. Among the three treatment methods, SiC/EP composites prepared in the curing-magnetization case had better comprehensive properties. Under the action of magnetic field, magnetic SiC were orderly oriented along the direction of an external field, thereby forming SiC chains. The magnetic alignment of SiC restricted the movement of EP macromolecules or polar groups to some extent, resulting in the decrease in the dielectric constant and dielectric loss. The SiC chains are equivalent to heat flow channels, which can improve the heat transfer efficiency, and the maximum improvement rate was 23.6%. The results prove that the orderly arrangement of SiC had a favorable effect on dielectric properties and thermal conductivity of SiC/EP composites. For future applications, the orderly arranged SiC/EP composites have potential for fabricating insulation materials in the power electronic device packaging field.

Synergistical Performance Modification of Epoxy Resin by Nanofillers and Carboxyl-Terminated Liquid Nitrile-Butadiene Rubber

Epoxy composite materials are widely used in power equipment. As the voltage level increases, the requirement of material properties, including electrical, thermal, and mechanical, has also increased. Introducing thermally conductive nanofiller to the epoxy/liquid rubber composites system is an effective approach to improve heat performance, but the effects of thermally conductive nanofillers on relaxation characteristics remain unclarified. In this paper, nano-alumina (nano-Al₂O₃) and nano-boron nitride (nano-BN) have been employed to modify the epoxy/carboxyl-terminated liquid nitrile–butadiene rubber (epoxy/CTBN) composites system. The thermal conductivity and glass transition temperature of different formula systems have been measured. The effect of the nanofillers on the relaxation behaviors of the resin matrix has been investigated. Results show that the different kinds of nanofillers will introduce different relaxation processes into the matrix and increase the conductivity at the same time. This study can provide a theoretical basis for the synergistic improvement of multiple properties of epoxy resin composites.

Dielectric Relaxation Characteristics of Epoxy Resin Modified with Hydroxyl-Terminated Nitrile Rubber

Utilizing liquid rubber to toughen epoxy resin is one of the most mature and promising methods. However, the dielectric relaxation characteristics of the epoxy/liquid rubber composites have not been studied systematically, while the relaxation behaviours are a critical factor for both micro and macro properties. In this paper, hydroxyl-terminated liquid nitrile rubber (HTBN) is employed to reinforce a kind of room-temperature-cured epoxy resin. The dielectric spectrum is measured and analysed. Results show that two relaxation processes are introduced in the binary composites. The α relaxation of HTBN shows a similar temperature dependence with the β relaxation of epoxy resin. The interfacial polarization leads to an increase of complex permittivity, which reaches its maximum at 70 °C. In addition, affected by interfacial polarization, the thermionic polarization is inhibited, and the samples with filler ratios of 15% and 25% show lower DC-conductivity below 150 °C. In addition, the α relaxation and thermionic polarization of epoxy resin obey the Vogel‒Fulcher‒Tammann law, while the interfacial polarization and DC-conductivity satisfy with the Arrhenius law. Furthermore, the fitting results of the Vogel temperature of α relaxation, glass transition temperature, apparent activation energy of interfacial polarization and DC-conductivity all decline with HTBN content. These results can provide a reference and theoretical guidance for the assessment of dielectric properties and the improvement of the formulation of liquid-rubber-toughened epoxy resin.

Effect of Toughening with Different Liquid Rubber on Dielectric Relaxation Properties of Epoxy Resin

Liquid rubber is a common filler introduced to epoxy resin to improve its toughness for electrical insulation and electronic packaging applications. The improvement of toughness by adding liquid rubber to epoxy resin leads to the variation of its dielectric properties and relaxation behaviors and it has not been systematically studied yet. In this paper, four kinds of liquid rubber with different polarity were selected and the corresponding epoxy/liquid rubber composites have been prepared. By analyzing the temperature and frequency dependence of dielectric spectra, we found that a lower relative dielectric constant and dielectric loss of the epoxy/liquid rubber composites could be achieved by reducing the polarity of liquid rubber filler. These results also confirm that the polarity of liquid rubber plays a critical role in determining the α transition relaxation strength of rubber molecules at about -50 °C, as well as the relaxation time of interfacial polarization. In addition, the conductivity of rubber phase with different polarity were investigated by studying the apparent activation energy of interfacial polarization calculated from the Arrhenius plot. This study can provide a theoretical basis for designing high-performance epoxy/liquid rubber composite insulating materials for industrial use.

Modified Epoxy Resin Synthesis from Phosphorus-Containing Polyol and Physical Changes Studies in the Synthesized Products

Epoxy resins are commonly used to manufacture the molding compounds, reinforced plastics, coatings, or adhesives required in various industries. However, the demand for new epoxy resins has increased to satisfy diverse industrial requirements such as enhanced mechanical properties, thermal stability, or electrical properties. Therefore, in this study, we synthesized new epoxy resin (PPME) by modifying phosphorous-containing polyol. The prepared resin was analyzed and added to epoxy compositions in various quantities. The compositions were cured at high temperatures to obtain plastics to further test the mechanical and thermal properties of the epoxy resin. The measured tensile and flexural strength of epoxy compositions were similar to the composition without synthesized epoxy resin. However, the heat release rates of the compositions exhibited tendencies of a decrease proportional to the amount of PPME.