Study of process of cure of EPDM rubbers in moving die rheometer

Rheometers, especially moving die rheometers (MDR), are widely used for evaluating the kinetic parameters of the cure of rubbers. Experiments are run under isothermal conditions at three temperatures and the reaction is followed by measuring the torque as a function of time. The kinetic parameters can be determined, except the enthalpy of cure. However, the total heat generated by the overall cure reaction can be obtained by calorimetry. Using numerical models and taking all the known facts into account, i.e. the heat transfer by conduction and heat evolved from the cure reaction, profiles of temperature and of state of cure developed through the samples in the MDR have been calculated. The profiles of state of cure were calculated at various times, especially at the time necessary for the torque modulus to attain the value of 95%, and thus a comparison is made between these two pieces of information. Three EPDM compounds were used, containing 2, 9, and 19% peroxide and having different cure enthalpies. The effect of a change in the thickness of the rubber sheet and in the value of the heat transfer at the die/rubber interface was also determined. Rather good correlation was obtained between the results obtained from MDR and the values of the state of cure. The thickness of the sample plays an important role on the process of cure.