Constitution and Variability of Rubber from Individual Trees

Abstract

Abstract A special procedure of collecting rubber latex directly from the tree by dropping it directly into alcohol to coagulate and preserve it has been described. The color, hardness, solubility in benzene or chloroform and viscosity of the soluble portion of this alcohol-coagulated rubber has been found to vary widely in the case of rubber from 24 individual trees in a Costa Rica rubber estate. While it is shown that rubber from individual trees show wide variations, the results from bulked latex and crepe are close to the average results found for the 24 trees. The results from the present investigation show that rubber direct from the tree contains soluble and insoluble fractions like those found in crepe and smoked sheet. Lower polymers in crepe and smoked sheet are also present in the latex as it emerges from the tree. It was found that some trees yielded a rubber almost completely soluble in benzene or chloroform, while in others, the soluble portion was as low as 61 per cent, with the average being 80 per cent. High viscosity of the sol and insoluble gel both lead to hard tough rubber. The alcohol coagulums varied widely in color from almost white in the ease of some trees to various shades of cream in most of the others. A new and unexpected finding was that four of the 24 trees yielded a distinctly grey mottled coagulum. This grey color apparently comes from the presence of clotted grey lutoids not apparent in the latex itself. The constitution of sol and gel rubber is discussed and data are presented on the solubility and viscosity of the solutions obtained from the gel fraction. From these data it is concluded that the difficultly soluble gel is a three dimensional network structure with either oxygen or carbon-to-carbon linkages between the polyisoprene chains.