The curing processes of SBR with sulfur and CBS at various concentrations are estimated using an oscillating rheometer. The curing reaction, which could be treated as chain reaction including CBS thermal decomposition, is modeled, and rate equations for the reactions are derived. The apparent reaction rates are calculated with a nonlinear least square approximation so that the summation of differential square of relative states obtained from the torque curve of rheometer and the estimated values may become the minimum. The curing processes are analyzed on the basis of simulated using the obtained concentration changes.
It is elucidated that the temperature dependence of the apparent rate constants can be validly expressed with the Arrhenius equation, and this relation gives the rate constant in arbitrary temperature. Therefore, the rate constants of curing processes with sulfur and CBS can be evaluated at arbitrary temperatures, and the curing processes can be estimated even at unsteady temperature distributions in actual rubber products.

View full abstract

In order to elucidate the degradation mechanism of EPDM caused by a amount of chlorine in city water, EPDM used for about 3 years at 45-65°C in the water tank in Osaka City and the unused product were analyzed. The carbon black contained in them was FEF (Fast Extruded Furnace) which particle size is comparatively small. Their morphology changes were observed by SEM. The effect of the diffusion of chlorine was examined by EPMA. The degradation mechanism was studied by FT-IR and ¹³C-NMR. As a result of FT-IR measurement, absorption of C=O bond (1720cm^-1) and C=C bond (1640cm^-1) were detected from the used product. As a result of ¹³C-NMR measurement, in the used product, the peak of methyl group of main chain increased in comparison with the unused product. It was thought that generation of the C=O bond by the oxidation reaction caused the β-scission of the main chain to produce the C=C bond and the methyl group in the used product. Therefore, as the crosslinking density lowered, the used EPDM became brittle and collapsed.

View full abstract