Using the Ozawa method to study the thermally initiated curing kinetics of vinyl ester resin

In this study, a thermal initiator of 1,1-bis(t-hexylperoxy)-3,3,5-trimethyl cyclohexane was introduced to thermally initiate the curing of vinyl ester resin, and then a dynamic differential scanning calorimetry method was applied to investigate the thermally initiated curing procedures. Thermally initiated by the thermal initiator under heating, the end double bonds of vinyl ester resin macromolecules were opened to accomplish the crosslinking, polymerizing, and curing. The increasing thermal initiator advanced the curing procedures and shifted the initial temperature, exothermic peak temperature, and final temperature to a low temperature zone. The curing kinetics of thermally initiated vinyl ester rein was studied using the Ozawa method and deduced by assuming a constant activation energy. The thermally initiated curing kinetic equations, e.g., dα/dt = e30.16(1 − α)2.88α0.01e−106.60/RT, dα/dt = e29.43(1 − α)2.72α0.16e−105.17/RT, dα/dt = e29.43(1 − α)2.85α0.03e−104.48/RT, dα/dt = e29.41(1 − α)2.87α0.01e−104.11/RT, dα/dt = e27.70(1 − α)2.64α0.05e−99.63/RT, and dα/dt = e26.26(1 − α)2.32α0.30e−96.16/RT, respectively corresponding to the weight ratios between the thermal initiator and the vinyl ester resin at 0.5:100, 1:100, 2:100, 3:100, 4:100, and 5:100, were obtained. The increasing thermal initiator significantly influenced the thermally initiated curing kinetic parameters, such as the exothermic peak temperature, the fractional extent conversion, the rate of conversion, the overall order of reaction, the activation energy, the preexponential factor, and the reaction rate constant, and the thermally initiated curing kinetic equations. The data calculated from the kinetic equation agreed well with the experimental data, showing that the Ozawa method could evaluate the curing kinetics effectively.