Epoxidised Natural Rubber – A Substitute for Silane Coupling Agent in Safe Silica-Filled Natural Rubber
Formulations
Abstract- Natural rubber (NR) vulcanizates prepared using nonregulated nitrosamine generating accelerators such as tertiarybutyl benzothiazolesulfenamide (TBBS) and tetrabenzyl thiuramdisulfide (TBzTD) are reported to be safe and noncarcinogenic. The difficulties during processing of silica-filled NR compounds could be overcome by incorporating silane coupling agent to the silica-rubber mix to improve the interactions between rubber and silica. The work reported in this paper is an attempt to replace the expensive silane coupling agent (Si69) with a modified form of natural rubber, i.e. epoxidised natural rubber (ENR) in safe accelerators incorporated formulation. The silica-filled ENR modified NR vulcanizates show lower optimum cure time compared to silane modified vulcanizate. Silica-filled NR vulcanizates modified with ENR show improved mechanical properties compared to the unmodified silica-filled natural rubber vulcanizate.
Keywords- Non-regulated nitrosamine, Epoxidised natural rubber, Coupling agent, Cure time, Vulcanizate
I. INTRODUCTION
Most of the conventional accelerators used in rubber formulations are derived from secondary amines. The chemicals derived from secondary amines, when exposed in air, form nitrosamines in presence of atmospheric nitrosating agents. Some of the nitrosamines are carcinogenic (regulated) [1-3]. One of the options to eliminate toxic hazards of rubber products is to use nitrosamine safe (non-regulated) chemical ingredients in rubber compounding [4]. Silica is one of the important reinforcing filler used in the rubber industry. Because of the polarity, silica exhibits higher filler-filler interaction and therefore poor rubber-filler interaction. Several modifications of silica filler such as heat treatment, chemical modification of the filler surface groups, grafting of polymers on to the filler surface and use of promoters or coupling agents have been reported to improve the rubber-filler interaction [5, 6]. Silane modification is the most widely practised technique for improving silica-rubber bonding [7, 8]. One of the widely used silane coupling agent is bis-(3-(triethoxysilyl)-propyl)-tetrasulfide (TESPT) [9]. Howe ver, the high cost of silane coupling agent is a limitation to its widespread acceptance
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