Wetting and detergency

Abstract

Wettability in real systems is difficult to define in quantitative terms. The usefulness of the contact angle is limited when measuring the wettability of nonideal surfaces. Immersion and sorption methods can provide more useful information on the wettability and the rate of wetting of fibers and fabrics. Wetting of fibers and soil is essential for soil removal, but detergency is a complex process with many variables and the relationship between wetting and detergency is not simple. Liquid (oily) soils and particulate soils have different detergency mechanisms. Oily soil detergency depends on the wetting rate of the substrate and sorption of water in the fibers and fiber coatings. The main mechanism of oily soil removal involves diffusion of water to the soil-fiber interface and rolling up of soil. Other mechanisms are less important. Kinetic studies of oily soil removal reveal (a) an induction period during which water diffuses into the soiled substrate, (b) separation of soil from the hydrated soil-fiber interface, and (c) a final period of nearly insignificant soil removal. Detergency of particulate soil is not dominated by the wettability of fibers, but depends mainly on the location of the soil particle and its adhesion to the fiber surface. The strength of the adhesive bond depends on the attractive forces and the contact area between soil and fiber. The adhesion and retention of particulate soil depends on soiling conditions and increases with the force of the impact of the soil particle contacting the fiber surface. © 1981, Walter de Gruyter. All rights reserved.