THERMAL PROPERTIES AND CRYSTALLIZATION BEHAVIOR OF HIGHLY DEPROTEINIZED NATURAL RUBBER

Natural rubber was deproteinized with a proteolytic enzyme and surfactant to reduce nitrogen content less than 0.02%. The deproteinized rubber was further purified by acetone-extraction followed by transesterification with sodium methoxide. The density of rubber decreased and the thermal expansion coefficient increased by deproteinization and transesterification. The glass transition temperature, Tg, was slightly reduced after deproteinization and transesterification. These were explained in relation to the decrease in gel content of the rubber. The equilibrium melting temperature, T ^o(m) was practically unchanged by these treatments. The low-temperature crystallization between -30 and -10 °C was significantly influenced by free fatty acids present as a mixture and fatty acid groups linked to the rubber chain. The crystallization behavior was independent of Tg and T ^0(m)values.