Examination of the parameters governing oily soil removal from synthetic substrates

The rate of removal of mineral oil soils from model polyester sub‐strates by the roll‐up mechanism shows a marked dependence on nonionic surfactant concentration even above the critical micelle concentration (cmc). Similarly, although the solid/water interfacial tension is observed to be constant, the equilibrium oil/water inter‐facial tension in these systems consistently decreases as the nonionic surfactant concentration is increased. The dependence of removal time and oil/water interfacial tension on surfactant concentration above the cmc is most pronounced for nonionic surfactants having relatively high cmc. At a given concentration, surfactants exhibiting the lowest equilibrium oil/water interfacial tension generally provide the most effective soil removal, suggesting that the reported depen‐dence of removal time on surfactant concentration is related to the commensurate lowering of the oil/water interfacial tension. Nonyl phenol ethoxylates perform exceptionally well with mineral oil on polyester substrates because of the combination of a low oil/water interfacial tension and high solid/water adhesion tension. Regardless of surfactant structure, mineral oil on Teflon FEP maintains a high contact angle in the water because the solid/oil interfacial tension is less than the solid/water interfacial tension. Oil removal in such systems occurs only by an inefficient necking and drawing process. Oleyl alcohol displays a high contact angle in the water on both Teflon FEP and Mylar substrates for reasons similar to that of mineral oil on Teflon FEP. Partial oil removal occurs from both substrates in selected built systems, presumably because a low oil/ water interfacial tension promotes necking and drawing. Given sufficient time, unremoved oils develop a liquid crystalline phase which results in slow oil removal via dispersion. Triolein soils also possess a relatively low solid/oil interfacial tension and similarly exhibt a high contact angle (in water) on both Teflon FEP and Mylar substrates in unbuilt surfactant systems. Builder addition lowers the oil/water interfacial tension and thereby prompts necking and drawing action.