EFFECTS OF ENVIRONMENT AND COMPOSITION ON DEGRADATION OF GUAYULE RUBBER

Bales of antioxidant-stabilized guayule rubber underwent significant l osses in bulk viscosity when stored under ambient conditions at an Ari zona processing facility. Previous work implicated the unsaturated fat ty acid esters present in entrained resin as promoters of such degrada tion. Aging studies as functions of storage temperature and unsaturate d acid ester content were carried out on both bulk rubber and rubber-r esin solution (miscella) for cultivar AZ-101. The rate of thermooxidat ive degradation, determined as a function of Mooney viscosity, was inc reased 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 +/- 6 kJ/mol (28 +/- 1 kcal/mol). At temperatures above 60 degrees C, chain recombination successfully competed with cha in scission in lower viscosity rubber. The rate of thermooxidative deg radation was substantially higher in a typical process miscella. A hin dered amine antioxidant significantly reduces chain scission under the se conditions. (C) 1996 John Wiley & Sons, Inc.