The effect of feldspar loading on curing characteristics, mechanical properties, swelling behaviour and morphology of natural rubber vulcanizates

Abstract

Feldspar is being used herein as a filler in natural rubber vulcanizates. Two different types of natural rubber, SMR L and ENR 50 having 0 and 50 mol% of epoxide groups and semi-efficient vulcanization were used. The scorch time, (t2) and cure time, (t90) of both rubber vulcanizates slightly increased with increasing feldspar loading. At a similar feldspar loading, the ENR 50 vulcanizates showed shorter t2 and t90 than SMR L vulcanizates. Besides t2 and t90, maximum torque, (MHR) and torque difference (MHR - ML) were also investigated. Results indicate that MHR and MHR - ML increase for both rubbers with increasing feldsparloading. Swelling test results showed a reduction in the swelling percentage for both rubbers with increasing feldspar loading. At a similar filler loading, SMR L vulcanizates showed lower swelling percentage than ENR 50 vulcanizates. The mechanical properties such as tensile strength (up to certain filler loading), tensile modulus and hardness increased with increasing feld-spar loading for both rubbers. However, at a similar feldspar loading, the mechanical properties of SMR L vulcanizates are higher than ENR 50 vulcanizates.