High-temperature study of radiation cross-linked ethylene-octene copolymers

Abstract

Three ethylene–octene copolymers (EOC) with a wide range of octene content (17, 30, and 38 wt%) and with the same melt flow index of 1 g/10 min were cross-linked by e-beam radiation (in range 30–120 kGy). The testing methods comprised of rheology, a high-temperature creep test, an analysis of the gel content, and a dynamic mechanical analysis (DMA) test. It was discovered that copolymers with a high octene content attain a higher level of cross-linking density. Cross-linking influenced properties below Tm only marginally as seen from the DMA results. However, the properties above Tm were highly influenced as detected by high-temperature creep and rheology. Above Tm, without the presence of crystals, only the chemical bonds holding the amorphous chains together manifested a gradually decreasing creep at 150 °C with an increasing irradiation level. The loss factor (tanδ at 0.1 Hz) at 150 °C revealed a decreasing trend (or higher cross-linking level) with an increasing octene content. High-temperature results were supported by an increasing gel content with increasing octene content. Samples irradiated to 30 kGy dissolved completely in xylene but showed significantly changed rheological characteristics indicating only an increase in the molecular weight and branching. Analysis according to the Charlesby–Pinner equation revealed increased cross-linking to the scission ratio G(X)/G(S) for EOCs with a higher octene content. While the q0 value which relates to cross-linking changed only slightly, a significant decrease in the p0 value which relates to chain scission was discovered. © 2016, Springer-Verlag Berlin Heidelberg.