Abstract
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.
Highlights
Epoxy resin is widely used as insulation material and adhesives in power equipment and electronic packaging [1,2]
The relaxation process caused by carboxyl-terminated liquid nitrile-butadiene rubber (CTBN) and hydroxyl-terminated liquid nitrile-butadiene rubber (HTBN) in the medium temperature range should be attributed to the interfacial polarization
It is worth mentioning that according to literature [10], the values of ε0 and tanδ lies for epoxy/liquid rubber composites in the corresponding temperature and frequency spectrum are smaller than those of pure epoxy resin, and no such relaxation peaks could be found based on our experimental results
Summary
Epoxy resin is widely used as insulation material and adhesives in power equipment and electronic packaging [1,2]. In addition to toughening epoxy resins, liquid rubber will affect other properties such as glass transition temperature and conductivity of matrix. It is necessary to compare the dielectric properties of epoxy resin toughened with different liquid rubbers in order to understand the mechanisms behind it. The mechanisms of the interfacial polarization formed between the rubber phase and epoxy matrix remains unclarified. In what follows we introduce four kinds of liquid rubbers with different polarity and functional groups to epoxy resin: HTPB, epoxidized hydroxyl-terminated liquid polybutadiene (EHTPB), CTBN and HTBN. The DC resistivity and dielectric spectra these epoxy/liquid rubber composites mentioned above are measured By comparing these properties of epoxy resin toughened by those four kinds of liquid rubbers, the effect and mechanism of different polarity liquid rubber on the DC resistivity, ε0 , and tanδ of matrix are analyzed. The results of our research can provide theoretical basis for a better selection of liquid rubber fillers for designing high-performance epoxy/liquid rubber composite insulating materials
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