Preparation of deproteinized natural rubber by saponification

Abstract

Natural rubber from Hevea Brasiliensis latex contains about 6% non-rubber components such as proteins, lipids, carbohydrates, inorganic constituents and etc. Some of proteins (1-2%) act as a surfactant to stabilize latex. However, extractable proteins in latex-product are responsible for the Type I allergic reaction. It is necessary to establish a new method for commercial production of solid deproteinized natural rubber (DPNR) of protein-free or containing the residua! nitrogen or extractable protein less than 0.02% and 20 mg/g rubber, respectively. In this paper, an attempt was made to produce solid DPNR by saponification. Fresh latex (FL) and HA-latex was incubated with NaOH (1-5% w/v) in the presence of surfactant at 70 ℃ for 3 hrs. The resulting latex was treated in two ways: Method 1: Decomposed proteins were washed by single or double centrifugation. Triton X-100 (isooctylphenoxypolyethoxyethanol) stabilized 10% DRC latex and partial coagulation was observed for SDS (Sodium dodecyl sulfate). The addition of Triton X-100 showed a synergistic effect with NaOH to decrease the nitrogen content in DPNR. The addition of 0.2% Triton X-100 in the saponification reaction and before the second washing, stabilizes the latex during centrifugation step. In this case, the nitrogen content decreases to 0.0036% with a slight increase in the ash content. The nitrogen content lower than 0.02% can be achieved at NaOH concentration higher than 4% under these conditions. Method 2: Decomposed proteins were washed with water after coagulation of latex with Ca(NO₃)₂ NaCI or H₂SO₄ by using a high speed mechanical stirrer. The direct coagulation of saponified latex by H₂SO₁ in the presence of sodium stearate produced low nitrogen and ash content solid DPNR. Green strength of DPNR decreases slighly from original value. Ordinary antioxidant able to applied to DPNR to replace natural antioxidant.