Study on the dielectric properties of the epoxy resin toughened with different molecular weight HTBN

Epoxy resin (EP) is one of the most popular insulation materials used in the electrical equipment. Adding different liquid rubbers into EP is the common way to increase the toughness, but the dielectric properties of the EP change while the toughness increasing. In this paper, the hydroxyl-terminated liquid nitrile rubbers (HTBN) with different molecular weight were used as fillers to toughen the EP. Through comparing and analyzing the changes of the glass transition temperature and the permittivity of the EP specimens with different kinds and same concentration of HTBNs, the influence of the HTBN´s molecular weight to the properties was gained. The glass transition temperatures of the two kinds of specimens are very close to each other, so the glass transition temperature is mainly affected by the adding amount of HTBN. Addition of HTBN brings a new polarization into the composite. This polarization makes a mutation step in the real part and a relaxation peak in the imaginary part of permittivity curve. For the relaxation time of the new polarization, the composite with bigger molecular weight of HTBN is less than another HTBN. For the intensity of the new polarization, the composite with bigger molecular weight of HTBN is greater than another HTBN. The research result shows that the molecular weight of the filler is an important factor to the dielectric properties of the EP toughed with HTBN.