The influence of substrate on the mechanism for oily soil removal

A paper chromatographic technique using fabric as the stationary phase was used to study the mechanism by which oily soils are removed from the substrate in a state almost without mechanical and/or hydrodynamic actions from the standpoint of surface and colloid chemistry. Using a cotton fabric, rayon fabric, polyester fabric, cellulose filter paper, and thin layer of fine crystal cellulose as the stationary phase for the substrate, the R(f)'-values of oleic acid (OA) as a model of oily soil have been studied in sodium dodecyl sulfate (SDS) aq. solutions as a function of the concentration. In every substrate, the R(f)'-value, a measure of the detergency, started to rise at a concentration of SDS significantly lower than its critical micelle concentration (cmc), which implies that the oily soil removal has begun at this low concentration. The R(f)'-value increased with the increase in SDS concentration. The concentration necessary to increase the R(f)'-value to 1 was 12 x 10(-3) mol dm(-3) SDS for polyester fabric and 7.0 x 10(-3) mol dm(-3) SDS for the other cellulose substrates. With these chromatographic observations, the partition coefficients, K-values of the OA between the fiber and water and between the fiber and micelle have been determined. K-values for polyester are higher than that for cotton or rayon, which suggests that it is more difficult to remove OA from polyester. The removal of OA from a substrate largely occurs by a molecular complex formation between OA and SDS at a low concentration below the cmc, and by solubilization of OA into or around a micelle above the cmc.