Cross-linking kinetics study and high temperature mechanical properties of ethylene-octene copolymer (EOC)/dicumylperoxide(DCP) system

Ethylene-octene copolymer (EOC) was cross-linked by dicumyl peroxide (DCP) at various temperatures (150-200 degrees C). Six concentrations of DCP in range 0.2-0.7 wt.% were investigated. Cross-linking was studied by rubber process analyzer (RPA). From RPA data analysis real part modulus s', tan(delta) and reaction rate constant K were investigated as a function of peroxide content and temperature. The highest s',, and the lowest tan(delta) were found for 0.7% of DCP at 150 degrees C. The quantitative analysis confirmed that the DCP-EOC cross-linking was occurring as first order reaction. The highest cross-linking kinetics constant K was found for 0.6% of peroxide at 200 degrees C. The activation energy of cross-linking EA obtained by Arrhenius plot had maximum at 0.5-0.6% of peroxide. While at 190-200 degrees C temperature range there was no detectable degradation for 0.2% of peroxide, for 0.4-0.7% of peroxide there was increasing level of degradation with increasing peroxide content. Generally, at low temperatures (150-180 degrees C) the increasing peroxide content caused increase in cross-linking kinetics. However at higher temperatures (190-200 degrees C) increase in kinetics (for 0.2-0.5% of peroxide) was followed by decrease. Especially in 0.6-0.7% peroxide level range the cross-linking is in competition with degradation which lowers the overall cross-linking kinetics. Gel content of the cross-linked EOC samples was found to be increasing with increase in peroxide content, which is caused by the increased cross-link network. Cross-linked samples were subjected to creep studies at elevated temperature (150 degrees C) and the result was found in agreement with the gel content and RPA results. Storage modulus and tan(delta) values obtained by Dynamic Mechanical Analysis (DMA) also support the RPA results. (C) 2011 Elsevier Ltd. All rights reserved.