Effect of the State of Cure on the Hardness and Resistance to Liquids of EPDM Rubbers

The effect of the state of cure and peroxide content on EPDM rubbers has been studied by considering some properties of the final material such as the hardness and the resistance to liquids. EPDM rubbers with 2 and 10% peroxide were cured, and the state of cure was evaluated using a numerical model which takes into account heat conduction through the rubber and heat generated by the overall cure reaction. The kinetics of heat evolved by the cure reaction was determined by calorimetry. The state of cure represents the heat evolved up to time t as a fraction of the total heat evolved from the cure reaction. The resistance to toluene was measured through the kinetics of the liquid absorbed and desorbed; these processes are controlled by diffusion with change in dimensions and the two parameters of interest are the diffusivity and the amount absorbed at equilibrium. The hardness and the resistance to liquids reached a maximum value for a state of cure of 90%, and they increased with the peroxide content.