Crystal nucleation and growth of natural rubber purified by deproteinization and trans-esterification

Abstract

The crystallization of highly purified natural rubber (NR) was investigated by polarized light microscopy. NR was deproteinized with proteolytic enzyme in the presence of surfactant and further purified by acetone-extraction followed by transesterification to remove all mixed and linked fatty acids present in NR. The rubber was fractionated and characterized by size exclusion chromatography,1H and13CNMR spectroscopy. Fractionated rubbers were crystallized at 252-258 K, in which spherulite was observed. The estimated nucleation and growth rates depended on supercooling. Surface free energies were determined for highly purified NR. Nucleating effect of fatty acids on the crystallization was proved by change in the surface free energy after removing and/or adding fatty acids.