Optimization of natural rubber latex deproteinization by enzymes

Abstract

Deproteinized natural rubber or DPNR is the purified form of natural rubber which contains proteins and other non-rubber impurities and posses the good processibilities in many applications especially engineering and medical application. The purpose of this study is to optimize the condition for DPNR production from both; concentrated latex 60%, and clonal field latex by commercially available enzymes, Papain and Alcalase and also study the proper­ ties of DPNR obtained in the step of raw rubber, compound and vulcanizate comparing with the non-treated rubber and industrail used rubber, TTR5L and crepe rubber. The results show that both of Papain and Alcalase exhibit high potential in deproteinization by removing total nitrogen approximately 70-75% of initial content at optimal condition. Concentrated latex 60% is a better starting material than field latex in its consistent and lower nitrogen content resulting in the lower and satisfactory high quality raw rubber compositions : 0.05-0.06 g% N, 0.02-0.04 g% ash, 0.006 g% dirt, 0.07-0.10 g% volatile matter, 54-57 Po and 65-77 PRI with light color and the acceptable processibilities according to international specification. While the DPNR produced from field latex posses higher but acceptable amount of nitrogen and other impurities in raw rubber composition. For field latex, among 3 clones; PB 5/51, GT 1, RRIM 600 tested, PB 5/51 is the most suitable clone for DPNR production because it contains the lowest nitrogen content and lighter color at the initial step throughout the process. Cure characteristic of DPNR under the compounding formulation used for footwear outsole are not significantly different from non-treated rubber and seem to be independent on the clonal effect. This noted that cure rate of low-nitrogen rubbers apparently increase when the retained %N < 0.12 g% which implies the maximum value needed for the high cure rate property of DPNR. The typical characteristic of DPNR vulcanizate are their higher stress-strain properties but slightly lower in hardness and 30% modulus.