Microemulsion Formation and Detergency with Oily Soil: IV. Effect of Rinse Cycle Design

Abstract

AbstractThe objective of this work was to apply a microemulsion‐based formulation for the removal of motor oil in laundry detergency at low salinity. To produce the desired phase behavior, three surfactants were used: alkyl diphenyl oxide disulfonate (ADPODS), sodium dioctyl sulfosuccinate (AOT) and sorbitan monooleate (Span 80). The mixed surfactant system of 1.5% ADPODS, 5% AOT and 5% Span 80 (13 parts ADPODS, 43.5 parts AOT, and 43.5 parts Span 80 of the total actives) was found to form a middle phase microemulsion (Type III) at a relatively low salinity of 2.83% NaCl. When this formulation was diluted, detergency performance increased with increasing total surfactant concentration and leveled off above about 0.1% total actives on the three types of fabrics studied (pure cotton, 65/35 polyester/cotton blend, and pure polyester). Detergency was found to improve with increasing hydrophilicity of the fabric with cotton being cleanest after washing and polyester the most difficult to clean. To achieve a specified oil removal, less rinse water can be used if a higher number of lower‐volume rinses are employed. An interesting characteristic of microemulsion‐based formulations is that a substantial fraction of oil removal occurs during the rinse cycle. In this work, this removal is shown to be due to the low oil/water interfacial tension during initial rinsing and is therefore strongly correlated to residual surfactant concentration in the rinse steps. As a result, the number of rinses and the volume of water per rinse can profoundly affect detergency in these systems.