Colloid Chemical Changes in Rubber and Fatty Oils

Abstract

Abstract In attempting to solve many of the problems in connection with the chemistry of rubber and of the fatty oils, it is usually found necessary to employ the main principles of colloid chemistry. It is, however, impossible definitely to classify rubber, as either lyophobic or lyophilic in nature. Raw rubber, such as pale crepe or smoked sheet, is in the presence of organic solvents of lyophilic nature, whereas it is entirely lyophobic when dispersed in water. Rubber latex shows an intermediate behavior between lyophobic and lyophilic systems. After neutralization of the electrical charge of the particles, i. e., at the so-called isoelectric point and slightly beyond it, the rubber particles do not flocculate. From this behavior it may be imagined that latex is a lyophilic system, but it is found that a comparatively small excess of electrolyte causes complete flocculation of the rubber, i. e., the salting-out of the rubber particles. Freundlich and Hauser (Kolloid Z., 1925, Erg. Bd. 36) have shown that the rubber particles in latex are made up of a liquid interior and a semi-solid external layer. The protein and resin content of the latex are supposed to be present in this external layer of the particles. Von Weimam (Bull. Chem. Soc. Japan, 3, 157 (1928)) has found that if latex is treated with solvents or solutions which are dispergators (dispersing agents) of protein compounds, and which thus cause a dispersion of the proteins from the external layer of the particles, the emulsion of the rubber hydrocarbon, normally lyophobic in character, will immediately assume a lyophilic nature and the whole system will gelatinize to a solid mass. It seems to be probable that in latex the rubber hydrocarbon is in a lyophilic state and that the partly lyophobic nature of latex is due to the lyophobic character of the protecting protein layer. Immediately this is dispersed, the lyophilic nature of the rubber hydrocarbon becomes evident. Concentrated lithium iodide solution acts as a suitable protein dispergator. As proteins have partly lyophobic and partly lyophilic nature, it is possible that the protein itself forms a gel skeleton containing the rubber hydrocarbon particles dispersed in it. In this case the rubber hydrocarbon may be of a lyophobic nature. Against this hypothesis is the fact that the gelatinization occurs in the presence of protein dispergators and not in the presence of protein coagulators.