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 °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′_max and the lowest tan(delta) were found for 0.7% of DCP at 150 °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 °C. The activation energy of cross-linking E_A obtained by Arrhenius plot had maximum at 0.5-0.6% of peroxide. While at 190-200 °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 °C) the increasing peroxide content caused increase in cross-linking kinetics. However at higher temperatures (190-200 °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 °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.