Effects of accelerators on the cure characteristics and mechanical properties of natural rubber compounds

Abstract

The effects of different accelerators on the cure characteristics and mechanical properties of sulphur-cured natural rubber (NR)-based compounds are investigated. Three accelerator systems, with mercaptobenzothiazole disulphide (MBTS) as primary accelerator and diphenylguanidine (DPG) and Zn-2-mercaptobenzothiazole (ZMBT) as secondary accelerators, were incorporated into a premixed NR compound referred to an industrially used rubber mat formulation by using the melt mixing method. The cure characteristics, rubber crosslink density and mechanical properties were the focus in the present study. It is observed that the synergistic effect of the MBTS/DPG combination imparts the shortest scorch time, highest cure rate and highest crosslink density compared with the MBTS/ZMBT and MBTS/ZMBT/DPG combinations. Mechanical tests indicate that the tensile strength and modulus of MBTS/DPG are enhanced owing to improved cure activation in initiating sulphuric crosslinking, but the tear strength is decreased compared with the others. This study demonstrates that the MBTS/ZMBT/DPG system is the most effective in enhancing tear strength by 4.5 % compared with MBTS/DPG system, as well as other mechanical properties. Analyses on tear behaviours and scanning electron microscope (SEM) micrographs of the fractured surfaces of tear test samples correspond well with the results of tear strength.