The Composition and Characteristics of the Rubber in Hevea Latex

IMPORTANCE OF THE SERUM SUBSTANCES The importance of the non-rubber components of latex, and particularly the protein components, in deciding the behavior towards coagulating agents was recognized at a relatively early date. Indeed, some investigators regarded the coagulating effect as being exerted only by way of the protein, the addition of the coagulants leading initially to its precipitation from solution in the serum, and thereby to the aggregation of the rubber globules. To-day the stability of latex as an aqueous dispersion of rubber globules is still regarded as being dependent on the non-rubber components of the latex. The material actually responsible for its stability, however, is now known to be adsorbed on the surface of the globules, and the physical behavior of the latex globules towards extraneous influences depends on the adsorbed film rather than on the rubber. This is remarkable, as the adsorbed layer, based on the approximation that one gram of protein covers a surface area of 107 cm.2, probably constitutes only 0.6% of the weight of the rubber globules, or thereabouts. The protective layer is not immovably attached, although in fresh latex it is possibly more firmly held than in preserved latex. It should be noted that the adsorbed coating normally represents only a small fraction of the total hydrophilic surface-active substances in the latex, and the stability of latex is less influenced by decrease in the proportion of the non-rubber components than might at first be expected. Latex purified by triply centrifuging shows little, if any, increased tendency to coagulation.