Study of aspects of the changes in several properties of cotton fibers during moistening

Abstract

A study is made of the effects of the moisture content of cotton fibers on their frictional, dielectric, and strength characteristics. It is established that the paths of the curves of equations obtained to describe these effects are related to changes in the structural-relaxational state of cotton cellulose and the presence of different forms of sorbed moisture.The main tendencies seen in the changes that occur to several properties of cellulosic materials during moistening were established by the middle of the Twentieth Century. However, it should be mentioned that the interpretation of many of those changes has been of a rather general and conjectural nature, since polymer science was still in its formative stages at that time. Thus, the changes just alluded to need to be studied by using better research methods and analyzing them based on modern representations on the interaction of cellulose with water. That interaction has drawn a considerable amount of attention in recent years. The goal of the study being discussed here was to quantitatively evaluate the effect of moistening on certain practically important properties of cotton fibers and determine how the property changes are related to changes in the structural-relaxational state of cotton cellulose and the presence of different forms of sorbed moisture.A modernized version of tensile-testing machine 2099 R-5 was used to measure the breaking load and elongationat-rupture of the warp fibers of cotton fabric "mitkal'". Since at least 80 parallel measurements were made in each series of tests, the coefficient of variation for the given type of test was roughly 5%.Krumm's method [1] was used to evaluate the shear strength of the fibers during friction against steel. The dielectric characteristics of the cotton fabric were determined by the capacitance method with an E8-4 digital capacitance meter having a standard frequency of 1 kHz. The test specimen was a fabric disk (d = 20 m) precompacted at 400 MPa. When permittivity was being calculated, a correction was introduced in accordance with the recommendations in [2] to account for the effect of moisture in vapor form inside the macroscopic pores of the fibrous material.The necessary moisture content was created in all of the experiments by conditioning the specimens in dessicators above aqueous sulfuric-acid solutions of a prescribed concentration. Figure 1 shows the dependence of the tensile characteristics of the warp fibers of the cotton fabric on the fibers' moisture content. By analogy with plasticized polymers, moistened cotton cellulose exhibits an improvement in its elastic properties in the form of increases in such indices as the fibers' elongation in tension (Fig. 1a). The increase is due to weakening of the forces of interaction between the macromolecules as a result of hydration of the hydroxyl groups in the cellulose. That facilitates rearrangement of the units of the molecules under the influence of external mechanical fields.One distinguishing feature of the moistening of cotton-based textil...