Further study to improve variability of natural rubber

Abstract

Studies had been made on the nature and magnitude of variabilities in processing properties (vulcanisation and rheological properties) of natural rubber (NR). A novel study was also made to find out whether the commonly reported validities in processing properties had actual effects on practical mixing. These were studied by means of the instrumented torque rheometer fitted with small mixer head. Samples were prepared from 3 clones of NR, viz. GT 1, RRIM 600 and KRS 156 and were collected over the period of 3 years. In order to study the effects of non-rubber constituents of NR, 2 types of samples were prepared which were WNR (containing whole nonrubbers) and PNR (nonrubbers removed). The results showed that both WNR and PNR exhibited clonal and seasonal variations in viscosity over the shear rates of measurements of 0.1-200 s(-l), although the variation became smaller at higher shear rates. Their vulcanisation behaviours were, however, consistent, rather independent of clonal or seasonal differences. The cure times of the two type of NR samples were, however, slightly different. The cure times were also not affected by mastication of NR. Both WNR and PNR exhibited significant storage-hardening over the period of 3 months. Variations in rheological properties of WNR and PNR, both before and after storage, could not be accounted for by molecular weight, molecular weight distribution and gel content of the rubbers. The significant findings of the present studies, which have not been reported previously, were that, contrary to the previous reliefs, the observed variations in processing properties showed no practical effect on the mixing properties of NR with carbon black.