Mary L. Rollins

Some Observations on the Constitution of the Primary Wall of the Cotton Fiber

The primary wall of fully matured cotton fibers has been isolated and its morphology and composition studied by electron microscopic examination and by chemical analyses. The pri mary wall appears to contain about 50% cellulose; protein, wax, and pectic substances occur in lesser amounts; cutin or suberin and mineral matter are also present. The concentration of noncellulosic substances in the primary wall is much greater than in the whole fiber. Electron microscopic examination of the primary wall indicates that it consists of a network of cellulose fibrils, having diameters of 100-400 Å, surrounded by the noncellulosic constituents. The oriented fibrillar systems observed with the polarizing microscope have not been seen in the electron micrographs of the specimens studied. There is an apparent increase in the diameter of the fibrils of the primary wall and in the denseness of the network as the fiber matures. The existence of layers in the cellulose network has been observed.

Studies on the Cross-Linking of Cotton Cellulose: Part II: Microscopical Observations

1. Anslow. W. P., Karnofsky, D. A., Jager, B. V., and Smith. H. W., J. Pharmacol. Exptl. Therap. 93, 1-9 (1948). 2. Reeves, W. A., Drake, G. L., McMillan, O. J., and Guthrie, J. D., TEXTILE RESEARCH JOURNAL 25, 41-46 (1955). 3. Reeves, W. A., Perkins, R. M., and Chance, L. H., TEXTILE RESEARCH JOURNAL 30, 179-192 (1960). 4. Schoene, D. L. and Chambers, V. S. (to U. S. Rubber Co.), U. S. Patent 2,524,399 (1950). 5. Stahmann, M. A., Golumbic, C., Stein, W. H., and Fruton, J. S., J. Org. Chem. 11, 719-735 (1946).

A Scanning Electron-Microscope Study of Washer-Dryer Abrasion in Cotton Fibers

Untreated and chemically modified cotton fabrics which had been laboratory-abraded by machine-washing and tumlle drying were studied with the scanning electron microscope. Generally, abrasion patterns were not different from those normally associated with any wet or dry abrasion. Greater differences were observed between washing machine-abraded and dryer-abraded samples than between treated and untreated samples abraded by the same method.

The Swelling of Cotton in Water A Microscopical Study

A method is described for comparing microscopically the cross-sectional areas of the same cotton fiber in wet and dry conditions, for evaluation of swelling. Results indicate the change in cross-sectional area of raw cotton fibers to be between 21 % and 34% of the dry area regardless of variety of cotton or degree of maturity of the fiber. Immature samples show slightly less mean swelling than mature samples, but this is believed to be due to the presence of fibers with no secondary thickening at all which tend to shrink in cross-sectional area rather than swell. In the immature fibers deformation (defined as change in circularity) is slightly more than that of mature fibers. This, coupled with the fact that in a given weight of immature fibers there are approximately twice as many fibers as in a like weight of mature fibers, helps to explain the greater closing capacity of yarns made from immature cotton. Flax and a sample of viscose rayon show twice the swelling of cotton, Fortisan two-thirds as much, and nylon no cross- sectional swelling at all.

The Surface of Cotton Fibers Part I: Native Fibers

The topography of unmoditied cotton fibers has been examined microscopically by means of surface replica techniques. The outstanding characteristic of the surface is a system of roughly parallel ridges and grooves spiraling around the fiber at an acute angle (usually 20 30 ) to its axis. The pattern of the surface is a reflection of the spiral fibrillar structure of the cellulose beneath the primary wall of the fiber. The average height and distance between ridges is approximately 0.5 micron. and many of the ridges are 10 or more microns in length. The surfaces of most native cottons are quite similar, although statistically significant differences in the average distance between ridges were found between certain samples The surface of fibers from unopened bolls is relatively smooth, but assumes the roughness of the typical fiber on drying for the first time. A characteristic surface formation ap peared to be associated with fibers known to have undergone compression. Drastic abrasion largely obliterates the normal appearance of the fiber surface.

Applications of Nitrogen Dioxide Treatment to the Microscopy of Fiber Cell Wall Structure

DURING the course of studies in this laboratory on the oxidation of cellulose, air-dried cotton fibers were treated with gaseous nitrogen dioxide using the. cyclic method described in 1942 by Yackel and Kenyon [43] .~ According to the original work, the fibrous material obtained by this method contains no nitrogen but differs from the original cotton in that part or all of the primary hydroxyl groups of the cellulose molecule are oxidized to carboxyl. A notable property of cellulose which has been so treated is its rapid and complete solubility in dilute alkaline solutions.

Abrasion Phenomena in Durable-Press Cotton Fabrics A Microscopical View

The abrasion characteristics of representative durable-press cotton fabrics were evaluated by selected laboratory-abrasion and laundering tests and the breakdown pattern of individual fibers was surveyed by electron-microscope photographs. Samples compared were from such treatments as wet-fix, poly-set, face-coating, fiber encapsulation, and graft polymerization. Although degree of abrasion resistance, as measured by Accelerotor weight loss or Stoll flex cycles, varied with different treatments, the damage types exhibited by individual fibers differed little from treatment to treatment. In most samples having acceptable degrees of wrinkle recovery and crease retention, the major mechanism of failure was fracture of the entire fiber in a brittle break. In untreated cotton, the characteristic feature of wet abrasion was fibrillation of the fiber surface; wet abrasion of cross-linked fibers often resulted in peeling of thick slabs and ribbons of fused fibrils from the body of the fiber. Characteristic of dry abrasion of untreated fibers was smoothing of fiber surface, general crushing of the fiber, accumulation of lumps of fiber material, and occasionally a pinching-out of wedged-shaped fragments from the side of the fiber in a typical mechanical fatigue break. In cross-linked fibers, differences between dry and wet abrasion were small. Most characteristic of cross-linked fibers was abrupt fracture of otherwise undamaged fibers and brittle shattering of the fiber as in the crushing of glass. Addition of softeners and thermoplastic polymer coatings to the cross-linking treatment improved abrasion resistance, apparently by physical protection of the fiber surface from abrassive forces, but the final mechanism of the failure was nearly always of the same type-mechanical fracture of the fiber. Observations of characteristic damage types in laundering tests in a household-type washing machine were also included. Surfaces of fibers from washed and line-dried fabrics resembled more closely those of fibers from fabrics tumble-dried than of those washed and tumble-dried.

The Surface of Cotton Fibers Part II: Modified Fibers

Microscopical studies of surface replicas of chemically finished or modified cotton fibers have shown that the characteristic surface of native cotton is often altered by various commercial and experimental treatments. While removal of the wax from the fiber sur face has little effect, scouring usually uncovers the fine cellulose fibrils of the primary or even secondary walls. Mercerization does not eliminate the rugosities of the native fiber surface. Additive finishes, including starch, carboxymethyl cellulose, colloidal silica, and acrylic polymer resins change the original fiber topography to an extent dependent on the amount applied. In general, particulate additives tend to concentrate in the grooves of the fiber surface when applied in dilute formulations, but cover most of the fiber surface at higher concentrations. Chemical modifications which increase the fiber cross sectional area make the fiber surface smoother, hut extensive swelling of the cellulose derivative during its preparation appears to create roughness in some modifications. Crease resistant finishes do not alter the fiber topography significantly.

Microscopical Observations of Abrasion Phenomena in Cotton

Native and chemically treated cotton fibers abraded hy laboratory instruments and other means were examined by light and electron microscopy. Characteristic patterns of abrasion damage for a variety of experimental conditions have been estahtished. and reasons are suggested for the abrasion response of the fibers. Marked differences were noted in the abrasion behavior of most cottons when tested in the dry and wet states, but these differences are minimized by resin treatments that cross-link the cellulose.

Some Applications of Microscopy to Cotton Research

treatments applied. Control tests with the aid of the microscope, made during the development of a process, assist the investigator in modifying his methods to attain a specific end. At the Southern Regional Research Laboratory the microscope is being employed in the study of improvements in wartime cotton products. Since individual fibers are often affected by treatments used to alter the characteristics of yarns or fabrics, it is necessary to consider the variability and the range of magnitude of the physical properties, including fine-