textile research journal

Abstract

This paper contains a discussion of the water-adsorption properties of a class of long-chain materials with many polar groups, which includes most textile fibers. The process discussed is distinguished from the adsorption by substances such as metal and metallic oxide catalysts in that it is not strictly a surface phenomenon, the adsorbent swelling as water is adsorbed. It differs from simple hydrate formation in that the water uptake is a continuous function of relative humidity, although in theory this behavior can be considered to be caused by the existence of an infinitely large number of possible hydrates. And, finally, it is distinguished from adsorption by liquids by the fact that the adsorbent possesses, and retains during the adsorption process, a certain amount of dimensional stability. In the first part of the paper a summary is given of some experimental data. This summary is not a complete review of previous work but is rather an outline of the data on the various phe nomena associated with the adsorption process. The purpose of this section is to give as much information on the fundamental adsorption process as possible rather than to give data for a large number of representative substances. For this reason many references, especially to chemically modified fibers (which contrast individual members of this class but do not contribute new infor mation on the fundamental adsorption process), are omitted. In the second section a review of previous theoretical treatments is given and a new theory of the adsorption isotherm for this class of substances is proposed. This treatment is derived by the methods of statistical mechanics and expresses the adsorption isotherm in terms of the relative humidity, regain, and molecular parameters in the simplest case. The application of the theory to experimental data shows surprisingly good agreement between theoretical and experimental isotherms, considering the approximations involved. In some cases missing data are estimated from known data for similar substances. The third section contains a discussion of adsorption hysteresis in terms of the theory developed here and the theory of absolute reaction rates, as well as a discussion of the constants of the isotherm.