Viscoelastic and mechanical properties of large- and small-particle natural rubber before and after vulcanization

Insights into viscoelastic and mechanical properties of large- and small-particle natural rubber (NR) were gained for developing new rubber products. NR latex was first subjected to centrifuging to separate large rubber particles (LRP) and small rubber particles (SRP). The LRP and SRP solid rubbers were prepared to investigate their molecular weight characteristics and mechanical and viscoelastic properties. Before vulcanization, the LRP rubber was found to be better in both tensile strength and elasticity, as a result of natural branch-point networks formed by aggregation of phospholipid groups at the terminating end (α end) of the LRP rubber chains. After vulcanization, the SRP vulcanizate was, on the other hand, found to perform better in all respects. This could be explained by the accelerating effect from the proteins bound to the initiating end (ω end) of the SRP rubber chains in the crosslinking process during vulcanization.