Evaluation of Physico-Chemical Interactions between Linear Alkylbenzene Sulfonate (LAS) and Alcohol Ethoxylates

Linear alkylbenzene sulfonate (LAS) is the most widely used surfactant in household products. The dominance of LAS is particularly apparent in laundry detergents, dishwashing liquids, household cleaners, and institutional/industrial cleaners, where it accounts for over 3 million tons per year worldwide consumption. However, detergency performance of LAS is decreased in hard water due to lower solubility and surfactant loss in the presence of calcium and magnesium ions. In this study behavior of an aqueous binary surfactant mixture composed LAS and nonionic surfactants was investigated. Ethoxylated alcohols (C(12)-C(14)) with 7 EO and 2 EO units were mixed with LAS in laundry detergent formulations, and performance factors including detergency, solubility, and efficiency and effectiveness of surface tension reduction were examined. Analysis of surface tension data indicated strong molecular interaction between LAS and nonionic surfactant. The results indicated that the addition of low amounts of the nonionic surfactant lowers significantly CMC of the mixed surfactant system, and causes the formation of mixed micelles containing predominantly nonionic molecules which provide water hardness protection for LAS. The overall improvement in detergency appears to be due to: lower CMC of the mixed surfactant system which improves soil solubilization, solubilization of Ca(LAS)(2), and reduction of free calcium ions which frees up soluble LAS in solution to adsorb at fabric-soil interfaces for enhanced soil removal.