Abstract
Filling epoxy resin (EP) with boron nitride (BN) nanosheets (BNNSs) can effectively improve the thermal conductivity of BN/EP nanocomposites. However, due to the few hydroxyl groups on the surface of BNNSs, silane coupling agent (SCA) cannot effectively modify BNNSs. The agglomeration of BNNSs is severe, which significantly reduces the AC breakdown strength of the composites. Therefore, this paper uses atmospheric pressure bipolar nanosecond pulse dielectric barrier discharge (DBD) Ar+H2O low temperature plasma to hydroxylate BNNSs to improve the AC breakdown strength and thermal conductivity of the composites. X-ray photoelectron spectroscopy (XPS) shows that the hydroxyl content of the BNNSs surface increases nearly two fold after plasma modification. Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) show that plasma modification enhances the dehydration condensation reaction of BNNSs with SCA, and the coating amount of SCA on the BNNSs surface increases by 45%. The breakdown test shows that the AC breakdown strength of the composites after plasma modification is improved under different filling contents. With the filling content of BNNSs increasing from 10% to 20%, the composites can maintain a certain insulation strength. Meanwhile, the thermal conductivity of the composites increases by 67% as the filling content increases from 10% (SCA treated) to 20% (plasma and SCA treated). Therefore, the plasma hydroxylation modification method used in this paper can provide a basis for the preparation of high thermal conductivity insulating materials.
Highlights
Breakdown strength and thermal conductivity of insulating materials are important factors affecting the safe and stable operation of electrical equipments
When the boron nitride (BN) content exceeds a certain amount, serious agglomeration will occur, which will lead to a decrease in the AC breakdown strength of the composite, limiting the improvement in the thermal conductivity and practical application of epoxy resin composites [8,9]
The results showed that the N2 (C3Πu → B3Πg) spectral emission intensity produced by bipolar pulse discharge was approximately 4–5 times that of unipolar pulse discharge, which indicated that bipolar pulse discharge was more conducive to exciting active substances
Summary
Breakdown strength and thermal conductivity of insulating materials are important factors affecting the safe and stable operation of electrical equipments. The thermal conductivity of epoxy resin is low, and the heat generated during operation of a device cannot be dissipated in time, resulting in a decrease in the dielectric strength and insulation life of epoxy resin [1,2]. The higher the content of BN, the higher the thermal conductivity of the epoxy resin composite [6,7]. When the BN content exceeds a certain amount, serious agglomeration will occur, which will lead to a decrease in the AC breakdown strength of the composite, limiting the improvement in the thermal conductivity and practical application of epoxy resin composites [8,9]. It is important to improve the breakdown strength of high thermal conductivity nanocomposites
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