Kinetics of Oily Soil Release

Abstract

The kinetics of detergency of liquid and mixed (liquid-solid) oily soil from cellulosic and synthetic fabrics has been investigated. A three-step soil-release mechanism is postulated involving (a) an induction period during which soil re moval is slow, (b) a rapid soil-removal period during which the amount of soil retained decreases linearly with the loga rithm of washing time, and (c) a final period during which soil retention is essentially constant. The soil-release rate is related to the diffusion rate of water into the soiled fabric. The ability of a fabric to release soil is not related to the rate at which the liquid front of a hydrophilic liquid (water, an aqueous detergent, ethylene glycol, etc) advances on the unsoiled fabric, but to the diffusion of water into the entire capillary system of the fabric. Diffusion of water into the fiber bundle facilitates soil release. Studies were made of the release of oily soil as affected by amount of soil (0.7-87% owf), wash temperature, agitation, and viscosity of oily soil in contact with an aqueous detergent. It is shown that soil which forms a highly viscous emulsion with water or an aqueous detergent solution is especially difficult to remove by aqueous detergency. Soil removal under conditions emphasizing spontaneous soil release is compared to practical laundering, and the effect of agitation is discussed. Mechanical work causing dynamic shear and flexing can be the dominant factor in oily soil removal from hydrophobic fibers with smooth surfaces and these compensate for a slow spontaneous soil release.