SOLUBILIZATION EMULSIFICATION MECHANISMS OF DETERGENCY

The removal of oily soils from fabrics having high contents of polyest er or other synthetic materials occurs largely by a solubilization-emu lsification mechanism. A systematic investigation of this mechanism ha s been conducted during the past several years and is reviewed here. T he research has utilized a variety of oily soils containing hydrocarbo ns, triglycerides, and long-chain alcohols and fatty acids and has inc luded the determination of equilibrium phase behavior, the observation of dynamic behavior which occurs when surfactant-water mixtures conta ct oily soils, and measurement of soil removal from polyester-cotton f abrics. In most cases, pure surfactants and oils have been used for si mplicity, but data showing the applicability of major conclusions to s ystems containing commercial surfactants are presented. Because typica l 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 re moval usually does not occur when the soil is solubilized into an ordi nary micellar solution, but instead when it is incorporated into an in termediate phase such as a microemulsion or liquid crystal that develo ps during the washing process at the interface between the soil and wa shing bath. Indeed, for hydrocarbon and triglyceride soils, the washin g bath is itself a dispersion of a surfactant-rich liquid or liquid cr ystalline phase in water for conditions of optimum detergency, i.e. th e temperature of the surfactant solution is above - sometimes far abov e - its cloud point temperature.