Crosslinking of high consistency silicone with dicumylperoxide: Predicting curing behaviour employing a rubber process analyser

Abstract

Curing solid poly(dimethylsiloxane) rubber, or high consistency silicone, produces a vast range of useful products, mainly via injection or compression moulding. Predicting how the crosslinking reaction will proceed is one of the bases for reliable processing simulation results, along with the precise determination of the material properties, like specific heat capacity, flow behaviour, and specific volume, for example. In this paper, the well-known rubber quality control device rubber process analyser (RPA) was employed to study the crosslinking kinetics of solid silicone rubber in terms of the concentration of dicumylperoxide. The RPA was applied as a moving die rheometer, and the main processing parameters were initially determined. After several experiments with different curing temperatures and various dicumylperoxide concentrations, a kinetic description of the solid silicone crosslinking was proposed, and thermodynamic reasoning was also introduced. Both temperature and dicumylperoxide concentration affected the optimum cure time, but the effect was less pronounced for high temperatures and high concentrations. A limit on thestate of cure was detected, meaning that the dicumylperoxide capacity to crosslink the silicone network is restricted by the curing mechanism. A suitable description of the crosslinking behaviour was succesfully done at the curing temperature applying the Kamal and Sourour model, becoming convenient to be implemented into rubber injection moulding simulation routines.