Effect of Thermal Cycling on the Dielectric Properties of Epoxy Resin

This paper adopts a linear temperature change method to subject epoxy resin to thermal cycling within a temperature range of -40 °C to 70°C at different rates of temperature change (1 °C/min and 10 °C/min), exploring the effects of thermal cycling duration and rate of temperature change on the glass transition temperature and dielectric properties of the epoxy resin. The results indicate that with an increase in cycling duration, both the dielectric constant and dielectric loss of the epoxy resin first decrease and then increase. Moreover, under a temperature change rate of 10 °C/min, this trend shows a smaller decrease in the early stages of cycling and a more significant increase in the later stages. Analysis reveals that thermal cycling promotes dynamic adjustment of internal chain segments in the epoxy resin, resulting in a denser structure and enhanced binding capacity to polar groups, which increases the glass transition temperature and improves the dielectric properties of the epoxy resin in the early stages. However, as the number of cycles increases, molecular chains break under the long-term effects of thermal expansion and contraction, gradually deteriorating the dielectric properties. Furthermore, a faster rate of temperature change prevents the internal chain segments of the epoxy resin from adjusting sufficiently, and the increased stress impact makes the epoxy resin more prone to degradation.