Hevea Latex: Effect of Proteins and Electrolytes on Colloidal Behavior

Abstract

1. Three protein fractions have been isolated from fresh and ammoniated latex serum. The usual color and precipitation reactions have been carried out, and they place these proteins in the classification of conjugated glycoproteins. Proteins from fresh latex differ in composition from, and are less sensitive to, coagulating influences than protein from ammonia-preserved latex. 2. Coagulation tests using latex coagulants were performed on the protein hydrosols. It was found that, as the concentration of electrolytes decreased, coagulation of the proteins was inhibited, whereas coagulation readily took place when salts were present in sufficient concentration. 3. Normal ammoniated latex has been subjected to extensive dialytic treatment in specially constructed apparatus. As the ash content of the total solids from the latex approached a value of 0.1 per cent, the mechanical stability decreased and the chemical stability increased. Addition of excess acid or alkali to dialyzed latex yielded stable latices which were highly resistant to spontaneous coagulation. 4. Quantitative coagulation studies, using methyl alcohol and salts of varying types and made on dialyzed latex adjusted to various pH conditions, show that small amounts of a dissolved salt greatly aid coagulation. Considerable variation in the effectiveness of different salts was found. In acid latex of pH 2.5 the charge on the latex particles was reversed from negative to positive, and the salt effect was shown to be different from that experienced in the case where the pH was on the negative side of the isoelectric point. 5. The amount of alcohol required to coagulate dialyzed latex depends on the pH of the latex. It is shown that the amount of alcohol required for coagulation increases on each side of the isoelectric point, which was determined to be at a pH of 4.15. 6. The protective mechanism of proteins has been discussed on the basis of the electrical charges induced on the surface of the latex particles by the presence of the protein layer. The zwitter-ion effect induced by the presence of free amino and carboxyl groups in the rubber proteins is of fundamental importance in determining the colloidal characteristics of latex.