Influence of Cross-Sectional Shape of Raw Cotton on Dimensional Changes in Mercerization Without Tension

Abstract

The relation of the cross-sectional shape of the raw fiber to the changes that occur upon mercerization without tension was studied for a number of cotton varieties representing a wide range of maturities.Perimeters and diameters of fiber cross sections were measured by the use of an especially designed instrument. Areas also were measured.It was found that the percent increase in area and the percent decrease in perimeter caused by loose mercerization are dependent upon the cross-sectional shape of the original raw fibers. Flat fibers shrank more in perimeter and increased more in area than did round fibers. This was partly explained as being due to a change toward circularity. THIS PAPER reports data, obtained during an investigation of the fundamental swelling properties of cotton, which show that the cross-sectional shape of the raw cotton fiber is related to the changes that occur in mercerization without tension.The undried fibers from a fresh, undried boll of cotton, which are tubular in form, consist of a thin primary wall surrounding a secondary wall, the thickness of which depends upon the maturity of the fiber. The central opening, or lumen, ranges from very small for thick-walled (mature) fibers to a large proportion of the whole cross-sectional area for thinwalled (immature) fibers [5]. As the fiber dries, the lumen collapses. This gives the fiber cross section various shapes, ranging from almost circular for mature fibers to flat for immature fibers.It has long been known that treatment of the raw cotton fiber in strong swelling agents, as in the mercerization process, causes the fiber to swell toward a circular cross-sectional shape by the thickening of the secondary wall. It has been shown that the primary wall tends to limit the swelling, and that the resulting pressure closes the lumen [7,15] . This restricting action was attributed to the alignment of the fibrils of the primary wall, which are nearly perpendicular to the axis of the fiber [4]. The primary wall, however, may be ruptured by very strong swelling agents [9]. The relation of cross-sectional shape to swelling in water was studied by Skau [14] and Moore [ 12] . Skau predicted that, although thin-walled fibers might reach their maximum swelling in water, thick-walled fibers might be prevented from doing so by the constricting action of the primary wall and might develop a real swelling pressure. Observations by Moore et al. [12] indicate that the shape of the fiber cross sections is changed little with swelling in water. This led to the belief that the secondary wall offered considerable resistance to deformation by swelling.Calvert and Summers [6] showed that upon washing out the mercerizing agent and drying, the fiber shrank in diameter, but retained the more or less circular cross-sectional shape assumed in the mercerizing solution. There was a decrease in both crosssectional area and perimeter from the swollen stage; but, compared to the raw fiber, the area of the cross section was larger and the perimeter was smaller.Marsh [11] ] ...

A Study of the Distribution of Perimeter, Cell-Wall Area and Thickness, and Shape in Raw and Slack-Mercerized . Single Cotton Fibers

“…Studies on the cross-sectional shape of cotton fibers and its association with gravimetric fineness, luster, staple length, and maturity have been reported [1,5,7,8,13]. Physical modifications have been carried out to achieve a circular shape of cotton fibers, which improves their luster and dyeability, and reduces their tendency to soil [10,11,14]. The changes in shape and/or in area affect the physical properties of cotton fibers to a great extent.…”

Axial Drag Coefficients of Cotton Fibers

“…The geometric contours of cotton fibers resemble more or less flattened twisted ribbons [8]. Taylor [10J has previously determined the aerodynamic drag forces on individual cotton fibers in crossflow.…”

Cross-Sectional Parameters of Cotton Fibers

“…The term &dquo;diameter&dquo; has little meaning when applied to cotton fibers because of the extreme variability in the cross-sectional shape of cotton. The undried fiber is tubular and when dried may assume many shapes ranging from almost circular for mature fibers to flat for immature fibers [5]. In addition, this shape can be altered by chemical or physical treatments ~1-3).…”