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ABSTRACT
The objective of the present work was to study the vulcanization of epoxidized natural rubber (ENR) latex using terephthalic acid (TA) as a novel crosslinker. The influence of TA on the physical properties including the swelling behaviour, tensile strength and thermal stability of the cured ENR, which was compressed at 180°C for 30 minutes, was studied. The optimum mechanical properties were observed for particular ratios of ENR/TA. In addition, the effect of cassava starch (CSt) and glycerol on the swelling ratio in toluene, the tensile strength, elongation at break and biodegradation of the cured ENR were also investigated. The ester linkage at 1730 cm^sup -1^ of the cured ENR was confirmed by ATR-FTIR. The swelling in toluene of the modified ENR decreased as a function of the proportion of TA. The thermal stability of the modified ENR was enhanced significantly after chemical modification as observed by TGA. A ratio of 7 phr of TA gave good mechanical strength of the vulcanized ENR compared to other TA contents. The ENR cured with TA easily degraded in natural soil compared to NR conventionaly vulcanized with sulfur.
KEYWORDS: Crosslinking; Natural rubber, Terephthalic acid, Latex, Chemical modification.
INTRODUCTION
Epoxidized natural rubber (ENR) is a derivative product of natural rubber (NR) and it is a material of great interest due to a double functionality for cross-linking (double bonds and epoxy sites)[1-3]. After NR is changed into ENR by an epoxidation reaction, it still displays most of the properties of NR and is able to undergo strain crystallization, maintaining high tensile properties and hence resistance to crack propagation for epoxidation of up to 50 mol%[3]. Before use, it must be vulcanized with many crosslinking agents as noted in previous studies such as sulfur[4], peroxides[5] and diacid[2]. Sulfur reacts preferentially with rubber containing double bonds rather than rubber in the presence of epoxide groups[4]. The problem that has been found to affect ENR cured with sulfur is low efficiency in the degree of vulcanization due to two main causes 1) epoxide groups contiguous to double bonds might act as an activator and 2) the reaction of sulfur with double bonds is a radical addition mechanism, which is slowed down by side reactions between adjacent double bonds. In addition, ENR...