Antagonism of Natural Anti- and Pro-Oxidants in Synthetic Polyisoprene Rubber Vulcanizates

Abstract

This research was to elucidate the antagonism of natural anti-and pro-oxidants in synthetic polyisoprene rubber (IR) grade 2200 as a model system. Alanine and linoleic acid was chosen as natural anti-and pro-oxidants, respectively. These two amino acids were directly added into the rubber by mixing in two-roll mill. Peroxide vulcanization and three types of the sulfur curing system, i.e., conventional vulcanization (C.V.), efficient vulcanization (E.V.) and semi-E.V. have been studied. Cure properties of the rubber compounds were characterized with moving die rheometer (MDR) at 150 and 170°C for sulfur and peroxide vulcanizing systems, respectively. The compounded rubbers were divided into two parts. The former was pressed on a hydraulic hot press machine and cut to a dumbbell specimen according to ASTM D412 type C. Then, the rubber specimens were subjecting to accelerate the thermal oxidative degradation at 100°C under air-circulating oven with various times. The deterioration of the aged rubber specimens was determined by tensile test. The latter was shaped and characterized by ozone resistance in accordance with ISO 1431/1. For tensile test, the results showed that only the C.V. system of the sulfur cure, the tensile stress at 200% strain of IR comprised alanine and linoleic acid with the ratio of 1:1 was higher predominantly than that of the cured IR control. In addition, the peroxide cured IR mixed with alanine and linoleic acid cannot be passed the heat aging for 96 h. For the ozone resistance, the results exhibited that all specimens appeared uncountable number of crack but only the IR cured by peroxide presented the length of crack less than 1 mm (C-3). It might be concluded from the experiment that anti-oxidative activity of the alanine plays a vital role in the rubber vulcanizate only for C.V. system. However, the existing of both alanine and linoleic acid in the sulfur cured IR was not outstandingly changed for the ozone resistance but not that for the peroxide cured IR.