DEGRADATION OF SILANE-CROSS-LINKED AND PEROXIDE-CROSS-LINKED POLYETHYLENE AND ETHYLENE PROPYLENE RUBBER

The degradation behavior and kinetics of degradation of polyethylene (PE), ethylene propylene rubber (EPR), silane-grafted PE (PE(g)S) and EPR (EPR(g)S), and silane and dicumyl peroxide (DCP) cross-linked PE, EPR and their blends, have been studied by thermogravimetry in both nitrogen and air. The effect of silane grafting and subsequent cross-linking on the degradation characteristics is more pronounced in air than in N2. The temperatures at which maximum rates of degradation occur (T(max)), are significantly higher for silane-grafted PE and EPR than the control PE in air. In N2, both cross-linked and control PE follow first-order decomposition kinetics while control and grafted EPR follow half-order kinetics. In air, all the systems except DCP-cured EPR follow first-order kinetics. The activation energies for degradation of silane-grafted and silane-cross-linked materials are significantly higher than those of peroxide-cross-linked materials. The onset temperature of oxidative degradation, as measured by differential scanning calorimetry, is markedly higher and the air ageing properties are also better for silane-cross-linked material than for peroxide-cross-linked material. The increased stability of the silane-cross-linked material has been explained in terms of its polyfunctional network structure.