Numerical Model for the Prediction of Final Mechanical Properties of EPDM Vulcanized with Peroxides - Part I: Basis of the Numerical Model and Experimental Campaign

In the paper, a simple but effective mathematical model having kinetic base, to predict the vulcanization degree of rubber vulcanized with peroxides, is presented. The approach takes contemporarily into consideration, albeit within a simplified scheme, the actual reactions occurring during peroxidic curing, namely initiation, H-abstraction, combination and addition, and supersedes the simplified approach used in practice, which assumes for peroxidic curing a single first order reaction. After a suitable re-arrangement of the first order system of differential equations obtained from the actual kinetic system adopted, a single second order non-linear differential equation is obtained and numerically solved by means of a Runge-Kutta approach. Kinetic parameters to set are evaluated by means of a standard least squares procedure where target data are represented by experimental values available, i.e. normalized rheometer curves. In order to assess numerical results, a wide experimental campaign is conducted, varying curing agents, vulcanization temperatures and concentration of the peroxides. Both rheometer curves to compare with those provided by the numerical model and stretch-strain curves of the vulcanized samples are obtained, to have a precise insight into the most suitable parameters to use during curing.