Effects of environment and composition on degradation of guayule rubber

Abstract

SYNOPSISBales of antioxidant-stabilized guayule rubber underwent significant losses in bulk viscosity when stored under ambient conditions at an Arizona processing facility. Previous work implicated the unsaturated fatty acid esters present in entrained resin as promoters of such degradation. Aging studies as functions of storage temperature and unsaturated acid ester content were carried out on both hulk rubber and rubber-resin solution (miscella) for cultivar AZ-101. The rate of thermooxidative degradation, determined as a function of Mooney viscosity, was increased by the addition of unsaturated ester. Anaerobic degradation was not affected in this way. The activation energy of chain thermolysis was found to be 116 f 6 kJ/mol (28 k 1 kcal/mol). A t temperatures above 60°C, chain recombination successfully competed with chain scission in lower viscosity rubber. The rate of thermooxidative degradation was substantially higher in a typical process miscella. A hindered amine antioxidant significantly reduces chain scission under these conditions. 0 1996 John Wiley & Sons. Inc.

Protein influences on guayule and Hevea natural rubber sol and gel

“…The thermal-oxidative stability of Hevea natural rubber 19 has been attributed to the presence of non-rubber constituents including proteins 20 and/or amino acids. 21 Hevea natural rubber shows much better thermal stability than that from guayule, as seen here (Table VI) and elsewhere, 22,23 and the difference is usually attributed to the much lower protein levels in guayule rubber compared to Hevea rubber. However, neither the reduction in the amount of protein present in Hevea rubber S fractions nor the concentration of protein in G fractions impacted PRI in this study (Table VI).…”