Metallocene-based polyolefin foams: effects of oxidative irradiation on mechanical properties

Metallocene-based polyolefin (MPO) foams are being considered for a wide range of applications because of their uniform composition and low toxicity. In this study, stress relaxation and dynamic rheological experiments 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 significantly different behavior. Gamma irradiation of the lighter foam causes structural degradation due to chain scission reactions. This is manifested in faster stress relaxation rates and lower values of elastic moduli and gel fraction in the irradiated samples. The incorporation of O-2 into the polymer backbone, verified by FTIR analysis, confirms the hypothesis of chain scission occurring at the labile peroxide linkages. In contrast, the denser foam shows a small amount of cross-linking and a concomitant improvement in mechanical properties after oxidative irradiation. (C) 1998 Elsevier Science Ltd. All rights reserved.