Analysis of the Effect of Blending Different Molecular Weight Polyetheramines on the Thermal and Electrical Properties of Epoxy Composite Foam Insulation Materials
Liu Hechen1, Dong Peng1, Zhou Songsong2, Liu Yunpeng1, Wei Liwei1, Li Le1
1. Hebei Key Laboratory of Green and Efficient New Electrical Materials and Equipment North China Electric Power University Baoding 071003 China; 2. China Electric Power Research Institute Beijing 100192 China
Abstract Epoxy-based composite foam (syntactic foam) uses hollow microspheres of low-density material as the lightweight phase and epoxy resin as the matrix phase. It has high porosity, low density, few internal defects, and good insulating properties, with good application prospects as a core insulating material. However, due to the large size of the insulating core, SF materials are prone to thermal concentration in the casting and curing process. It causes problems such as core burning and cracking within the material, greatly impacting the performance of the core after curing. By modifying the resin matrix in the SF material, the starting temperature of the epoxy resin-based cross-linking reaction and the reactivity of the curing agent are reduced. Thus, the curing speed of the SF material curing reaction and the amount of heat released can be reduced, alleviating the core burning phenomenon. The characteristics of low viscosity, low reactivity, and high elongation of polyetheramines are combined with those of low density and high viscosity of SF systems. By blending polyetheramine curing agents of different molecular weights to obtain epoxy-based SF systems with suitable curing rates and heat release, the electrical and thermomechanical properties of the materials were also comprehensively evaluated to obtain suitable matrix formulations for insulation core applications. The internal temperature of the blended system during curing (40 ℃) is measured using thermocouples to clarify the actual temperature variation during curing. In addition, good electrical and thermal properties are required as core insulating material. It also needs to have a low water absorption rate. Breakdown strength, dielectric loss angle, leakage current, and thermal weight loss were measured for different SF materials, and the change in water absorption was tested for SF materials over 96 h. The interface between the microspheres and the resin matrix affects the performance of the SF materials. The degree of interfacial bonding between the microspheres and the resin matrix was observed by scanning electron microscopy (SEM). The results show that SF material systems with lower curing reaction rates can be obtained by blending polyetheramines of different molecular weights. The internal peak curing temperature decreases from 185 ℃ to 113.5 ℃. With the gradual increase of the high molecular weight curing agent (D-2000), the electrical and thermal properties show different decrease degrees (breakdown voltage decreases from 28.53 kV/mm to 22.74 kV/mm; leakage current increases by 11.38 μA to 41.24 μA; and the 5 % thermal weight loss temperature decreases by up to 17 ℃). In addition, SEM tests determine that the different curing agent systems have little effect on the interfacial bond strength of the microspheres and the resin matrix. The influence of the interface on the change in material properties is excluded. As the proportion of high molecular weight D-2000 curing agent increases, the activation energy of the curing reaction gradually increases, and the reaction rate decreases. It can significantly reduce the core temperature during curing and reduce the heat concentration phenomenon during curing. With the addition of the D-2000 curing agent, SF material thermal decomposition temperature, electrical properties, and water absorption slightly decrease but still meet the practical application.
Liu Hechen,Dong Peng,Zhou Songsong等. Analysis of the Effect of Blending Different Molecular Weight Polyetheramines on the Thermal and Electrical Properties of Epoxy Composite Foam Insulation Materials[J]. Transactions of China Electrotechnical Society, 2023, 38(10): 2589-2601.
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