ABSTRACT
Different types of curing systems play important roles in the thermal degradation of natural rubber vulcanisates. In this study, natural rubber vulcanisates were cured with conventional (CV), efficient (EV) and Dicumyl Peroxide (DCP) curing systems at 160°C using a laboratory-size two roll mill. The tensile, tear and swelling were tested before and after ageing for 2, 4, 6, 9 and 12 days at 100°C. Fourier transform infrared (FTIR) measurements and thermogravimetric analyses (TGA) were performed to assess the thermal degradation behaviour of the natural rubber vulcanisates. The results indicated that the tensile modulus (M100), tensile strength, elongation at break and tear strength of the CV system were better compared to EV and peroxide systems before ageing. After ageing, the CV system vulcanisates, which contained predominantly polysulfidic linkages, showed drastically reduced tensile strength and elongation at break and tear due to crosslink breakage. Crosslink reformation into a stable network inhibited their ability to undergo strain-induced crystallisation at longer durations of ageing. The EV system vulcanisates showed comparable swelling index percentages before and after ageing while the peroxide curing system exhibited increased swelling uptake with longer ageing times. The presence of alcohol, amides and carbonyl groups after ageing was observed with FTIR measurements. Based on the TGA and DTG curves, the peroxide curing system vulcanisates showed higher thermal stability than the CV and EV curing system vulcanisates.
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