The Effect of Additives and the Stability of Multilamellar Vesicles in a Commercial Surfactant System

I n the detergent industry, the surfactant 'linear alkylbenzene sulfonate' (LAS), is used in the manufacture of compact detergent powders. High-active LAS (ca. 78 wt% LAS in water) is a liquid crystalline material with paste-like properties. Industrial techniques, which use additives to process the LAS paste into a suitable material for down-stream unit operations, transform the planar lamellar phase that is initially present into multilamellar vesicles (MLVs). Previous studies have shown that certain salts when sheared with high-active LAS at 60°C result in the formation of densely-packed MLVs. In this paper we compare the stability of shear-induced MLVs in high-active LAS samples prepared using different additives and processing temperatures. Uniquely amongst the salts tested, sodium sulphate and sodium sulphite were found to be ineffective in promoting the formation of MLVs in high-active LAS at 60°C. MLVs are more stable when formed with sodium disilicate than sodium chloride. MLVs formed with sodium disilicate at 60°C appear more stable than when formed at lower temperatures.