Adsorption of oleic acid soap in styrene-butadiene latex

Abstract

Abstract A study has been made of adsorption of isomers in soaps made from commercially available oleic acids to rubber by separating and analyzing the serum from styrene-butadiene (S-BR) latex. Both the cis and trans forms of potassium 9-octadecenoate (potassium oleate and elaidate) adsorb strongly to the rubber particles. The rubber phase was separated from the serum without disturbing the soap distribution by successive filtration through Millipore filters of diminishing pore size. These filters had been thoroughly washed to remove surface-active wetting and plasticizing agents and treated with methylene blue to block active sites which would otherwise adsorb emulsifier. Potassium erucate (C22−) was added as an internal standard to the rubber-free serum, which was then acidified and extracted with ethyl ether. The extraction glassware was rinsed with cyclohexane to remove adsorbed fatty acid. Methyl esters of the recovered emulsifier-erucic acid mixture were quantitatively analyzed by gas liquid chromatography. The results show selective adsorption of certain isomers on the rubber particles. In cases where only enough emulsifier was present to cover the rubber surface, the octadecenoic isomers were greatly depleted in the serum indicating preferential adsorption. Addition of emulsifier to the latex increases the quantities of selectively adsorbed isomers in the serum until with large excesses, the serum soap composition approaches that of the original emulsifier.