METALLOCENE-BASED POLYOLEFIN FOAMS - EFFECTS OF OXIDATIVE IRRADIATIONON MECHANICAL-PROPERTIES

Metallocene-based polyolefin (MPO) foams are being considered for a wi de range of applications because of their uniform composition and low toxicity. In this study, stress relaxation and dynamic rheological exp eriments are used to probe the effects of oxidative irradiation on the structure and final properties of these novel MPO foams. Experiments conducted on irradiated foams of two different densities reveal signif icantly different behavior. Gamma irradiation of the lighter foam caus es structural degradation due to chain scission reactions. This is man ifested in faster stress relaxation rates and lower values of elastic moduli and gel fraction in the irradiated samples. The incorporation o f O-2 into the polymer backbone, verified by FTIR analysis, confirms t he hypothesis of chain scission occurring at the labile peroxide linka ges. In contrast, the denser foam shows a small amount of cross-linkin g and a concomitant improvement in mechanical properties after oxidati ve irradiation. (C) 1998 Elsevier Science Ltd. All rights reserved.