Shrinkage and Cell Wall Structure of Cotton Fibers

Abstract

THE SHRINKAGE of natural fibers such as cotton, is dependent upon the fine structure of the fiber and its physical condition. The structure, as variously described in the literature, is still debatable but the physical condition of the fibers can be controlled within reasonable limits. A study of the shrinkage resulting from a reduction in moisture content may aid in the determination of the fundamental structure of the fiber. The microscopic structure of the cotton fiber has been described by Balls (1923), Denham (1923), Anderson and Kerr (1938), Hock, Ramsay and Harris (1941), and others. The fine structure as determined by x-ray diffraction has been described bv Berkley (1939). Certain phases of the literature dealing with cellulose and cell wall structure in general have been reviewed recently by Bailey (1938, 1939), Kratky (1940), Mark (1940) and Nickerson (1940), and the need for studies in cotton fiber character were discussed by Conrad and Webb (1935), so no extensive review will be attempted here. Briefly, the cotton fiber is a single cell and contains a primary wall and a secondary thickening as described by Kerr and Bailey (1934) for other plant fibers. The primary wall is the first formed layer and constitutes the thin sheath, approximately 0.5 i in thickness, on the outer surface of the mature cottoIn fiber. The crystalline cellulose is arranged at an angle of 70 to 80 degrees to the fiber axis (Balls, 1923; Anderson and Kerr, 1938). The secondary wall is laid down on the inside of the primary wall next to the lumen. The crystalline cellulose of the secondary thickening lies in a spiral in the fiber, direction of which changes frequentlv from an S to a Z spiral, or vice versa. According to Anderson and Kerr (1938), the direction of the spiral of the first layer is usually opposite that of the succeeding layers, all of which follow in general a given pattern. The pitch of the spiral, that is, the angle between the long axis of the fibrils and that of the fiber, varies with the variety of cotton and the climatic condition under which it is grown (Berkley, 1941; Kerr, 1941; Barre and Berkley, 1942). The samples used in these studies varied in age from ten to thirty days after bloom and represent either the primary wall only, or both the primary and the secondary walls as indicated. The shrinkage of green moist cottoln fibers as a result of drying has received little attention in connection with the studies of quality of raw cotton and