Lipid Detergency as Observed by the Quartz Microbalance Method

Abstract

Removing solid lipids with surfactants in an aqueous solution is observed with a quartz crystal microbalance. The pH of the bathing solution is adjusted to 7.0-12.0 at 25 and 30°C. Concentrations of four anionic and nonionic surfactants vary from far below the CMC to ten times the CMC. The alkalinity of the solution at pH 9.0-12.0 causes swelling of the lipids by about 10%, but adding surfactants results in swelling up to 10-20%, followed by lipid removal by solubilization. This removal takes place at concentrations lower than the CMC. From this fact and the dependence on surfactant concentration of the removal rates by the two kinds of surfactants, we can infer that micelles of anionic surfactants do not participate in the removal, while those of nonionic surfactants do participate.Removing various lipids from textiles is an important process in scouring and cleaning. This process is complex, comprising mechanical abrasion, rolling up, and chemical solubilization of liquefied lipids. Among these mechanisms, the last one is crucial for scouring to control lipid content in textiles. It is also important for the performance of heavy duty detergents in daily use. Some studies have been devoted to the real time observation of the removal process of solid lipids: liquefaction or the swelling of the lipids by water and surfactant, and subsequent removal, have been observed by radiotagging, gravimetric, FTIR spectroscopic, ellipsometric, and quartz crystal microbalance (QCM) methods [ 1, 2, 3, 5, 7].These observations are confined to specific conditions for a particular lipid, surfactant, and concentration, etc. It is informative to study the process from a comparative view point with regard to lipid and surfactant species, surfactant concentration, degree of swelling of lipids, and removal rate.In a series of studies on soil removal, we reported a real time observation of some solid proteins by protease [6]. We used the QCM technique for these observations by monitoring the weight increase and accompanying decrease of protein coated on the gold electrode of a QCM as the frequency change around 9 MHz. In this study, we report the removal process of tripalmitin (TP), trimyristin (TM), and cetyl alcohol (CA) from the surface of the electrode of the QCM by anionic surfac-~i tanits-sodium dodecylbenzc~nesulfonate (DBS) and sodium dodecyl sulfate (SDS)---and nonionic surfactantsdodecyl heptaethyleneoxide (C,2(EO)~) and hexadecyl I heptaethyleneoxide (C 16(EOh)-in an aqueous medium of pH 7.0-12.0 at 25 and 30'C. In this paper, we discuss the swelling behaviors of the lipids and variations in the removal rates to interpret the process. j Experimental Reagent grade TP, TM, and CA were supplied by Tokyo Kasei Kogyo Co.. Ltd.. and used as received.Analytical grade TP from the same company was used to test the effect of impurities. The melting points of TP, TM, and CA are 66, 56-57, and 49°C, respectivety. DBS, supplied as sodium n-dodecylbenzensulfonate by Wako Pure Chemical Industries, and SDS, supplied by Nakarai Tasque, In...

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