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The effect of peroxide and co-agent amount on the cure behavior, network structure, and dynamic mechanical properties of ethylene-propylene elastomers were studied by moving die rheometer, equilibrium swelling and dynamical mechanical measurements. The increase in peroxide and co-agent concentrations resulted in an increase in total cross-link density, Ctot. The model calculation results based on torque measurements considered the changes in Ctotas a function of peroxide and co-agent content; it linearly depended on initial peroxide content when the co-agent content was constant. The torque measurements were also carried out to investigate the cross-linking efficiencies of the peroxide and the co-agent triallyl isocyanurate (TAIC); the efficiencies were evaluated as 77–95% and 33%, respectively, but the use of TAIC didn't affect the scorch time and rate constants of EPDM compounds significantly. The incorporation of TAIC into the network enhanced the network heterogeneity, the glass transition temperature shifted towards higher temperature and the peak values of the loss factor gradually decreased, both of which were caused by restricted segmental mobility due to the increase in cross-link density. [ABSTRACT FROM AUTHOR]

The influence of three different co-agents, triallyl isocyanurate (TAIC), trimethylol propane trimethacrylate (TMPTMA) and high vinyl poly(butadiene) (HVPBd), on the curing characteristics, including the cure kinetics, of peroxide-cured EPDM compounds and the mechanical properties of the resulting EPDM vulcanizates were studied. The results showed that the addition of each co-agent could improve the cure extent of the EPDM samples; the hardness and modulus of the EPDM vulcanizates were also improved. In particular, the compound containing TAIC obtained the highest cure extent. However, the addition of TMPTMA negatively affected the scorch safety, especially below 165°C. From the cure kinetics of the EPDM compounds, obtained by using the cure data from a moving die rheometer, it was found that the Deng–Isayev, first-order and Hsich models showed better agreement with experimental data compared to the Kamal–Sourour model. The reaction rate constants were gradually increased with the elevated temperature, and TMPTMA could significantly promote the curing reaction rate, TAIC secondly, while HVPBd showed no effect. In addition, the apparent activation energy of all EPDM compounds, calculated by the Deng–Isayev model, was estimated slightly higher than that of the other three kinetic models. However, due to the addition of the three co-agents, the activation energy of the curing reaction decreased, with the EPDM compound with TAIC showing the lowest activation energy. [ABSTRACT FROM AUTHOR]

The fire-resistant noncorrosive ethylene-vinyl acetate copolymers with vinyl acetate (VA) content > 40 wt.% (EVM)/acrylonitrile-butadiene rubber (NBR)/magnesium hydroxide (MDH) composites were prepared, and the influence of MDH contents on flame retardancy, thermal stability, filler dispersion, and mechanical properties were studied. The flame-retardant effect of three different flame retardants [micro-sized MDH (mMDH), nano-sized MDH (nMDH), and micro-sized aluminum hydroxide (mATH)] was also investigated by cone calorimetry, thermal gravimetric analysis, and rubber process analysis in this paper. The decrease of the heat release rate and total heat release, the increase of residual mass, and the enhancement of thermal stability of the composites were all due to the flame-retardant effect of the MDH. The EVM/NBR vulcanizates had the best flame retardancy when the mMDH content was 180 phr. It was also found that the nMDH, mMDH, and mATH at the same loading had no obvious influence on the limiting oxygen index, while the combustion behaviors measured by the cone calorimeter had significant differences. The addition of ATH prolonged the time to ignition. The mMDH showed a better flame retardancy for EVM/NBR vulcanizates than the nMDH. [ABSTRACT FROM AUTHOR]