Epoxy (EP) vitrimers with excellent mechanical properties that could be efficiently healed under mild temperatures (<150 degrees C) are of great importance to practical applications but are difficult to accomplish yet up to now. In this work, we used l-cystine dimethyl ester (CDE), a disulfide-containing diamine, as the hardener to synthesize a type of EP vitrimer, EPV-CDE. The tensile strength of EPV-CDE reached 81.5 MPa mainly due to the relatively short chains of the CDE hardener and resulting high cross-linking density, and at the same time, EPV-CDE was able to be recycled under a mild temperature at 120 degrees C, with a 93.4% recovery ratio after the first recycling cycle, enabled by the relatively flexible chains and low steric hindrance of the CDE hardener. Compared to most of disulfide-containing EP vitrimers reported in the literature, EPV-CDE demonstrated higher tensile strength and lower activation energy and topology freezing transition temperature. Moreover, the liquid nature of CDE allows the incorporation of up to 25 wt % carbon fiber powder into the EPV-CDE matrix to prepare the EPV-CDE/CF composite, which achieved the tensile strength of 112.5 MPa and maintained excellent recyclability. Even though our EP vitrimer exhibited strong resistance performance to most solvents, it could also be chemically degraded by thiol-containing solvents such as dithiothreitol, offering environmental-friendly substitutes for unsustainable thermoset resins.

将 3,3'-二硫代二丙酸二甲酯(DTDP)结合传统的甲基四氢邻苯二酸酐固化剂对环氧树脂进行固化,制备了环氧树脂复合材料,利用FTIR、TG、DMA、DSC等方法研究了环氧树脂复合材料的固化反应动力学,分析了固化机理,并考察了力学和电学性能.实验结果表明,添加DTDP后,环氧树脂复合材料交联密度提高,故拉伸强度提高,但同时也提升了韧性,其中,EP-DTDP-2 的拉伸强度和断裂伸长率分别达到了 81.3 MPa和 5.7%,比纯环氧树脂分别提升了 16.1%和 104%.交联密度的提高还使环氧树脂复合材料的击穿强度有所提升,其中,EP-DTDP-3 的击穿强度达到最高(37.6 kV/mm),比纯环氧树脂(33.8 kV/mm)提高了11.2%.

Epoxy (EP) vitrimers are currently regarded as ideal substitutes for traditional thermosetting resins, as this class of materials combines the advantages of thermoplastic and thermoset polymers. However, maintaining the high performance of EP vitrimers with excellent healing properties remains a challenge. In this work, a novel hardener combining disulfide and imine bonds through the reaction of Schiff base (4-AFD-VAN) was designed and then used to prepare the EP vitrimer with dual-dynamic covalent bonds. Compared to the single-disulfide-containing vitrimer (EVP-4-AFD), the prepared EP vitrimer (EPV-4-AFD-VAN) exhibited a lower activation energy and a faster stress relaxation. Moreover, EPV-4-AFD-VAN showed a tensile strength of up to 71.5 MPa and maintained a recovery ratio of approximately 90.0% during the three cycles. Similar to traditional thermoset EP, EPV-4-AFD-VAN retained its good solvent resistance, high breakdown strength, and good dielectric properties, which can be chemically degraded in suitable solvents, demonstrating its environmental sustainability.

Epoxy (EP) vitrimer with excellent processing and recyclability is of great potential for industrial application. In this study, we prepared an EP vitrimer based on the low viscosity homogenous mixture of diglycidyl ether of bisphenol A (DGEBA) and a liquid hardener dimethyl 3,3′-dithiodipropionate (DTDP) catalyzed by 2,4,6-tris (dimethylaminomethyl) phenol (DMP30). The optimal curing condition was determined to be 110 °C × 12 h for the original EP vitrimer. Owing to the exchangeable disulfide crosslinks, rapid stress relaxation was found for the vitrimer with a relaxation time of 1.9 s at 160 °C. Moreover, the prepared EP vitrimer possessed excellent self-healing ability and recyclability, with recovery ratio of at least 94.1% during 3 times recycling. The self-healing ability, recyclability and processing performance remain excellent for the vitrimer even after incorporating 30 wt% boron nitride (BN), which can be recycled using DMF as a solvent.

Incorporating inorganic filler is an efficient method to improve the surface charge dissipating performance of epoxy resin (EP), and the key is to strengthen the interfacial interaction between EP matrix and filler. In this work, the polydopamine (PDA) coated barium titanate (BT) was synthesized via commonly used in situ self polymerization of dopamine in BT aqueous suspension, and then BT-PDA particles were introduced into EP matrix to prepare EP/BT-PDA composites. The introduction of PDA coating on the BT surfaces was able to strengthen the interfacial filler-matrix interactions, significantly improving the dispersion of BT-PDA particles in the EP/BT-PDA composites. As a result, the surface charge dissipation was effectively enhanced for the EP/BTPDA composites, as the EP composite filled with 1.0 wt% BT-PDA exhibited the surface potential decreasing rate around twice as fast as that of pure EP.

To restrain the surface charge accumulation of the epoxy resin (EP) applied in the high-voltage power field, one of the efficient methods is to dissipate the charges on the EP surface by incorporating inorganic filler. In this work, we employed amine-functionalized boron nitride nanosheets (mBNNS) based on liquid-phase exfoliation and urea modification to prepare EP composites. Owing to the existence of - NH2 groups on the exfoliated mBNNS platelets, the uniform filler dispersion and good filler-matrix compatibility were achieved in the EP composites. As compared to the pure EP, the EP/mBNNS composites exhibited better charge dissipation performance, comparable dielectric constant and higher breakdown strength. The best charge dissipation performance was achieved in the EP composite by adding only 1.0 wt% mBNNS with the surface potential decreased by 65.5% in 1200 s, much higher than pure EP (28.1%). (C) 2021 Elsevier B.V. All rights reserved.

Increasing attention has been paid to the design of high-performance polymer composites applied in high voltage insulation field, and typical composites are comprised of either micro-scaled or nano-scaled inorganic fillers. In this work, we prepared bulk graphitic carbon nitride (g-C3N4) from melamine via thermal condensation, and silicone rubber (SR)/C3N4 composites were prepared via direct mechanical blending followed by in-situ modification by vinyl tri-methoxysilane (VTMS). The formation of the bulk g-C3N4 from melamine was confirmed by XRD, FTIR and XPS. Increasing the g-C3N4 content improved the mechanical properties of the composites. The role of VTMS in the modification of bulk g-C3N4 was revealed to serve as the molecular bridge between the SR matrix and g-C3N4 filler, which strengthened their interfacial interaction. Therefore, the incorporation of VTMS reduced the defects in the as-prepared composites, which resulted in the enhancement of both breakdown strength and mechanical properties. Moreover, the SR/C3N4-VTMS composites exhibited a higher dielectric constant and a lower dielectric loss at high frequency range compared to the SR/C3N4 composites.

The introduction of filler into the epoxy resin has become one of the most important means to improve the electrical performance. In this work, halloysite nanotubes (HNTs) was modified by a commonly used silane coupling agent KH560, and then blended with epoxy resin to prepare epoxy composites. The successful modification of HNTs was confirmed by TGA and FTIR. The structure and performance including dielectric properties, charge dissipation, breakdown strength and flashover voltage of the as-prepared epoxy composites were investigated to reveal the structure-properties relationship.