Study On The Effect Of Hydrothermal On Electrical Properties Of Epoxy Resin Composites

The theory and curves of absorbing moisture of four kinds of epoxy resin composites under the hydrothermal aging were studied in this article. Analysed the varieties of chymist and microcosmic configurations of composites materials under the hydrothermal aging by FTIR and SEM. Moreover, researched the effect of hydrothermal aging on the dielectic properties, resistivity properties, static mechanical properties, dynamic mechanical thermal analysis as well as changing rules. Simulated the hydrothermal aging life of composites by Arrhenius model.The curves of absorbing moisture of MeTHPA/E-51, MeTHPA/WHUT-170, transformed amine/E-51, vinyl ester resin 3201 composites materials under the hydrothermal aging were studied. The results showed that there were three phases in the process of absorbing moisture of materials. The first one was the phase according with Fick law, the speed of absorbing water was controled by the relaxation speed of molecule chains in the second phase, the balance of absorbing moisture in the third phase. There was difference in the third phase between transformed amine/E-51 and other kinds of composites, the difference was the speed of absorbing moisture keeping rise. The diffuse quotiety of MeTHPA/E-51 composites was 8.95×10-6m2/s which was the least in the four kinds of composites under the boiling water, but 1.25×10-5 m2/s of transformed amine/E-51 was the most. Along with the increase of temperature, relaxation speed of molecule chains increased, the time of saturation absorbing moisture was shorter. In addition, when the humidity was 75%, the curves of absorbing moisture was not according with Fick law, then keeped balance.There was no change on the characteristic peaks, not any other new peaks appeared. Before the hydrothermal aging, the surface of composites materials was smooth and even, fiber/resin interface contacted well, after the hydrothermal aging, cavities and bareness fiber appeared on the surface of materials, then the fiber/resin interface ruptured, the fibers were smooth. Chemical changes of composites did not happen in the process of hydrothermal aging, the changes of composites materials properties mainly were caused by debonding, the interface thermal stress damage and other physical changes. The composites material dielectric constant and dielectric loss had increased in the hydrothermal aging process, however, the role of wet and hot at the same time, the dielectric properties were not always increase, there would be some ups and downs and slow growth in the process of hydrothermal aging. With the temperature of hydrothermal aging increases, the dielectric constant and dielectric loss of materials had increased, as the humidity increased, the dielectric constant and dielectric loss of composites materials were also corresponding increase. When the electric field frequency was about 105Hz, the dielectric properties appeared the abrupt change, respectively, the dielectric constant increased, while the dielectric loss decreased, as the frequency continues to increase, dielectric constant decreased, but the dielectric loss increased.As the moisture content increase within the composites materials, the resistivity declined substantially, the temperature and humidity influences were also reflected in the moisture absorption of materials. At the same time, due to the differences of polarity in the resin matrix of composites materials, because the vinyl ester resin was more hydrophilic, its surface resistivity changed more quickly, while the volume resistivity were ups and downs, because of the impact of "cage effect" under the process of free radical curing.Through the contrast on the strength and modulus retention, when the four kinds of composites were under hydrothermal aging materials. The results showed that the aging 144h in boiling water, the strength and modulus retention rate were maximum in the composites cured by MeTHPA, respectively 72% and 79%. By analyzing the dynamic mechanical properties of composites materials with the impact of aging time, found that with the aging time increase, the tg8 peak decreased, then the peak moving to the lower temperature and peak width broaden, and some even two peaks, while the storage modulus of composites materials also fell, the curves of storage modulus-temperature moved to the lower temperature direction.Used the Arrhenius extrapolation for life prediction of MeTHPA/E-51 composites materials, it provided the theoretical basis for the epoxy resin electrical insulation materials used in the hydrothermal aging environment.