Effects of nonrubber components on the crystallization behavior of natural rubber

Abstract

The crystallization behavior of highly purified natural rubber (NR) was investigated by polarized light microscopy. NR was purified by enzymatic deproteinization followed by transesterification to remove nonrubber components present in the rubber. Nucleation rate and growth rate were estimated from a number of spherulites of different sizes observed in the course of crystallization for the purified NR. The slope of a linear line drawn in a plot of the logarithmic growth rate vs. 1/TΔT for the purified rubber was identical to that for the untreated rubber, suggesting that the lateral surface free energy was not a function of the nonrubber components. In contrast, nucleation was found to be promoted in the presence of nonrubber components, such as the fatty acids. This demonstrated that the crystallization of NR was significantly promoted by the nucleating effect of the fatty acids.