Recovery and purification of small rubber particles from skim latex

Abstract

Skim latex is a by-product of the production of concentrated latex. Skim latex contains about 3-10% DRC (dry rubber content) and composes of mainly small rubber particles. The rubber fraction recovered by coagulation of skim latex with sulfuric acid contains higher amounts of non-rubber component than ordinary solid natural rubber. Therefore, skim rubber is evaluated to be a low-grade rubber. In this work, and attempt was made to get the highly purified skim rubber using various purification methods: 1) Enzymatic deproteinization of skim latex in the presence of NaCl, 2) Saponification of skim latex with NaOH, 3) Phase separation of rubber by incubation of skim latex with dry yeast, 4) Deproteinization of skim rubber by saponification in toluene solution. Enzymatic deproteinization in the presence of NaCl and the saponification of skim latex with NaOH gave a clear phase separation as cream phase and serum phase. The resulting cream phase of both methods was concentrated to 2-3 times DRC. The average particle size increased from 0.1 um to about 3 um after enzymatic treatment, while it was unchanged after the saponification. The nitrogen content of the purified rubber by enzymatic deproteinization and saponification was reduced from 2.7 to 0.6 and 0.3%, respectively. The purified rubber contained high ash content and slightly lower in ester content. After the washing of cream phase by centrifugation, the nitrogen content was further reduced to 0.04 and 0.03% for the enzymatic treatment and the saponification, respectively. Ash, ester and gel contents were lower than that of the original rubber. The incubation of skim latex with dry yeast at pH7 in the presence of 0.2% SDS caused an increase in particle size of small rubber particles in skim latex from 0.1 um to about 1-5 um after 48 h and an unchange in the nitrogen content. Centrifugation of yeast at bottom. The recovery of rubber particles of 45% can be achieved. Saponification of cream phase reduced thenitrogen content to 0.71%. Deproteinization by saponification of skim rubber in toluene solution (10% rubber concentration) was carried out with NaOH at 70 ํC. The nitrogen and ash contents decreased to 0.03% and 0.3%, respectively. This purified skim rubber showed the lower green strength than original skim rubber. Mooney viscosity was unchanged. Wallace plasticity (pฺ) and Plasticity retention index (PRI) were improved