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The use of radioisotopes as tracers offers unique opportunities in the study of soil retention, soil removal, and the mechanism of the action of detergents. Because of the high sensitivity with which radioactive materials can be determined, this method makes possible the use of artificial samples in which the level of soil loading is comparable to that of natural soils. Simultaneous determination of both soil removal and redeposition can be made at levels of redeposition which have no significant effect on the removal. Very small surfaces such as individual threads and fibers can be studied. Since activity measurements can be made without disturbing the sample either chemically or mechanically, such properties as particle size and surface area are unchanged by the measurement and their effect on the cleaning process can be studied. Likewise the effect of multicycle soiling and washing tests on soil build-up can be evaluated. The fact that the activity of a tagged component of a soil can be directly related to its mass makes possible the study of the important relationship between reflectivity and mass as a function of different variables including particle size and shape, method of soiling, and mechanism of removal during cleaning. This is especially useful in the important practical case of carbon and carbonaceous soils on textile substrates which can be determined only with considerable difficulty by chemical or other means. Soil determinations by means of activity are not affected by colored substrates or by fluorescent dyes in detergent formulation; soil removal patterns for invisible soils can be obtained by autoradiography. Two or more components of a soil can be tagged with different isotopes and their behavior studied simultaneously.
Ashcraft, E. B.
Advisory Chemist, Westinghouse Research Laboratories, Pittsburgh, Pa.