Phase behavior, dynamic contacting and detergency in systems containing triolein and nonionic surfactants

Abstract

Systems containing the pure triglyceride triolein, pure nonionic surfactants and water have been studied. At low temperatures both the lamellar liquid crystalline phase L α and the isotropic liquid phase termed D′ or L 3 solubilize little triolein and have interfacial tensions with triolein of a few tenths mN m −1. However, above a particular temperature in each system phase compositions change rapidly. For the C 12E 3 system, the oil phase, at low temperatures mainly triolein and surfactant, experiences an abrupt increase in water solubilization and becomes an oil-continuous microemulsion. In contrast, for the C 12E 5 system, oil phase composition changes little, but the D′ phase suddenly becomes capable of solubilizing triolein and exhibits behavior similar to that of microemulsions in hydrocarbon systems although surfactant concentration is considerably higher than in typical microemulsions. Behavior intermediate between these two situations occurs in the C 12E 4 system. The differences in phase behavior are reflected both in the dynamic behavior seen by videomicroscopy when a surfactant-water mixture contacts triolein and in removal of triolein from polyester/cotton fabric during washing. Behavior of the C 12E 5 system is similar to that reported previously for hydrocarbon systems with maximum soil removal found near the apparent phase inversion temperature (PIT) and an intermediate D′ phase seen in contacting experiments near the PIT. For the C 12E 3 and C 12E 4 systems the dynamic behavior is different and soil removal is lower than with C 12E 5. For mixtures of triolein and n-hexadecane typical microemulsion phases D are found at low triolein contents and the D′ phase having low solubilization of both oils at high triolein contents. For intermediate compositions the phase behavior includes a narrow four-phase region where both D and D′ phases coexist with excess oil and water. Detergency experiments for a mixture containing equal parts by weight of the two oils showed greater overall soil removal than for pure triolein and a slightly greater removal of the hydrocarbon than of the triglyceride at all temperatures. The former result probably stems from the lower interfacial tensions found for the mixed soil, the latter from preferential solubilization of hydrocarbon into surfactant-rich phases initially present or formed during the washing process.