The Possible Contribution of Shape to the Swelling and Moisture-sorption Behavior of Cotton Fiber at the Saturation Point

Abstract

11'10ISTURE sorption and swelling of cotton fiber are complex phenomena depending in degree upon a considerable number of more or less independent variables which do not lend themselves to control.In the following discussion it is attempted to analyze the effect of a change in one of these variablesnamely, the shape-on the moisture behavior of the cotton fiber. Although some quantitative relationships are derived, it must be kept in mind that, because of the assumptions necessary and the number and the complexity of the variables involved, the conclusions drawn can at best be considered only qualitative in nature in specific random cases. They should, however, serve to show in a general way the effect on swelling and related phenomena contributed by fiber shape.The extent to which a cotton fiber can swell when immersed in water may in some cases be restricted by the cuticle or primary wall [3,5,6,7,8,11,20,29], which behaves like a membrane around the outside of the fiber. It has been suggested that a mature fiber cannot swell beyond the maximum volume it had as a living, unshrunken cell in the green boll [6,20], except with strong swelling agents. Since the change in the length of a fiber on swelling is negligible ( 1 or 2 percent) [9, 10], the change in volume can, as a first approximation, be considered proportional to the change in its cross-sectional area.Swelling thus presumably involves a change in shape of the fiber so as to cause an increase in the area of the cross section with little or no change in the perimeter. It can be shown mathematically that when the primary wall is distended to its full capacity-that is, its maximum volume-the cross section of the fiber would be circular. A very flatshaped (immature) fiber with a given perimeter would have a small cross-sectional area and would theoretically swell to many times its original volume before reaching the maximum area. On the other hand, a nearly round fiber could swell very little before reaching this limit, while a perfectly round fiber could not swell at all unless the perimeter of the cross section increased-that is, unless the primary wall stretched.For the purpose of discussion the first assumption necessary is that the cotton fiber is uniform in crosssectional area both throughout its length and, for any given sample, from fiber to fiber. The effect of the lumen or of any possible open spaces inside the fiber has been ignored. It has also been assumed that the cellulose within the fiber wall is identical in all cases and that it behaves like a fluid * to the extent

Part II: Centrifuge Studies

“…According to Skau [7], the effect of tension on a yarn is to decrease the percentage swelling of the fibers and the yarn. Also, Nickerson [2] has shown that a yarn under stress exhibits a lower desorption regain―8.19% for a yarn under a deadweight load of 60% of its breaking strength, as compared to 8.78% for the unstressed yarn, both yarns being equilibrated at 21°C and 65 % relative humidity.…”

The Swelling of Cotton in Water

“…Theoretical calculations by Skau [14] indicate that as the fiber swells in water a change in circularity is to be expected and that the thin-walled fibers would be expected to show ( 1 ) a greater percentage of swelling, (2) a higher degree of deformation, and (3) a higher rate of sorption because of the larger surface per unit volume. Again there were no experimental data to support these views.…”

Cross-Sectional Shape of Cotton Fibers Belonging to Different Species

“…Shape is also associated with certain physical properties of textile fibers such as luster [ 1 ], friction [3], structural uniformity [ 10], water and moisture sorption [ 18], behavior during dyeing and mercerizing [6], draping ,qualities of fabric [4], etc. The cross-sectional shape of cotton fiber has been studied by different workers [5, 1 l, 12, 13, 14, 17].…”