Natural Ageing of Automotive Polymer Components: Characterisation of New and Used Car Bumpers

The chemical and morphological structure of new and'post-consumer ten years old poly(propylene) based car bumpers has been investigated and their mechanical properties have been correlated to the chemical and physical degradation of the material. Poly(propylene) matrix and a rubbery ethylene-propylene phase were the constituents of the bumpers. A strong impairment of the mechanical properties has been found in old samples which showed also a distinctive phase separation. The modification of the chemical structure was much less evident: oxidation on the exposed surface involving the poly(propylene) phase has been highlighted in old bumpers, and possible crosslinking. These relatively small changes, however, are esponsible for the pronounced physical ageing. A tentative explanation is a poor interfacial adhesion of rubber particles from which the crazes can propagate further to form cracks.