Solubilization—emulsification mechanisms of detergency

Abstract

The removal of oily soils from fabrics having high contents of polyester or other synthetic materials occurs largely by a solubilization-emulsification mechanism. A systematic investigation of this mechanism has been conducted during the past several years and is reviewed here. The research has utilized a variety of oily soils containing hydrocarbons, triglycerides, and long-chain alcohols and fatty acids and has included the determination of equilibrium phase behavior, the observation of dynamic behavior which occurs when surfactant-water mixtures contact oily soils, and measurement of soil removal from polyester-cotton fabrics. In most cases, pure surfactants and oils have been used for simplicity, but data showing the applicability of major conclusions to systems containing commercial surfactants are presented. Because typical anionic surfactants are too hydrophilic to achieve the desired phase behavior, the work has employed non-ionic surfactants and mixtures of non-ionics and anionics. One major conclusion is that maximum soil removal usually does not occur when the soil is solubilized into an ordinary micellar solution, but instead when it is incorporated into an intermediate phase such as a microemulsion or liquid crystal that develops during the washing process at the interface between the soil and washing bath. Indeed, for hydrocarbon and triglyceride soils, the washing bath is itself a dispersion of a surfactant-rich liquid or liquid crystalline phase in water for conditions of optimum detergency, i.e. the temperature of the surfactant solution is above — sometimes far above — its cloud point temperature.