Gradient curing process in the mixed epoxy system and property analysis of the cured products

To improve the high-temperature mechanical properties of room temperature cured epoxy resin, a mixed curing agent was used and the curing process was studied under a temperature ramp. The tests including gelation time, differential scanning calorimetry, dynamic thermomechanical analysis, and flexural strength were taken to evaluate the changes in pot life, reaction process, heat resistance, and mechanical properties, respectively. The analysis then focused on the extent of cure. Meanwhile, the effects of non-reactive diluent on the curing process and product properties were analyzed. Results showed that the resin system containing the mixed curing agent possessed an exquisite characteristic when the temperature rose slowly to 363 or 393 K. The system could be preliminarily solidified in an hour and a half at normal temperature, and then in the heating-up environment, curing reactions initiated by different types of curing agents took place, caused the curing degree to exhibit certain gradient and increase to greater than 95% quickly. The glass transition temperature and the mechanical stability at high testing temperatures of the cured products were therefore improved. When dibutyl sebacate was added into the system as the diluent, the curing reaction was postponed, the curing degree was slightly increased; however, the glass transition temperature and mechanical properties at high temperatures were apparently decreased.