Swelling Capacities of Fibers in Water

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Abstract
Swelling in water is one of the important fundamental properties of cellulosic fibers, and is also a factor in determining the proper fiber for a specific utilization. An example of this is the selection of cottons for self-sealing fabrics. Since existing techniques for measuring swelling capacities, as they have been used, are tedious and time-consuming, it was desired to find a rapid method which would be sensitive enough to establish, with certainty, small dif ferences in swelling capacity due to variety, conditions of growth, and state of maturity such as might be decisive in the choice of a cotton for an application dependent upon swelling. In Part I of this study a method is discussed for determining swelling capacities of cotton and other fibers. It is based on the measurement of the rate of loss of moisture from a moisture- saturated sample. Experimentally, this method is exceedingly simple—the fiber samples, fully swollen and containing excess water, are dried very slowly and weighed periodically. It is shown that for a time the moisture is lost at a nearly constant rate. Eventually, however, the drying rate changes and thereafter steadily diminishes. It is believed that this change occurs only after all nonswelling water external to the fiber has evaporated. The moisture regain at this point of transition in the desiccation rate is considered to be indicative of the maximum water-holding capacity of the cellulose— i.e., the swelling capacity. The moisture regain values determined are in general agreement with the regain values estimated from adsorption isotherms at 100% relative humidity. The maximum regain values from the desiccation rate technique, when expressed in terms of volume increases, agree with the swelling capacities as determined by microscopic measurements. Although the experimental method is simple and direct and more rapid than microscopic methods, the long drying periods required make it suitable mainly for use in research when time is not an important consideration.

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