Anna T. Moore

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).

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.

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.

Structure and Properties of Chemically Modified Cotton1

Photomicrographs of chemically modified cotton fibers, illustrating the alterations in the fine structure that were caused by the treatments, are shown. An attempt is made to correlate structural changes in the fiber with changes in such fiber and fabric properties as breaking strength, elongation, and dry and wet wrinkle recovery.

New information on the morphology of the gossypol pigment gland of cottonseed

Exploratory electron microscope studies of the cottonseed pigment gland demonstrate a complex internal structure in which discrete particles ranging in size from one micron to less than 0.2 micron diameter are held within a membranous meshlike network. This structure is extremely sensitive to water, and it may be the rapid swelling of the network which results in the explosive release of pigment particles from the gland on exposure to moisture. Pigment particles are spherical, of a wide range of diameters, and exhibit no birefringence in the gland or when extruded. Calculations of specific surface based on sizes of particles and density of purified gossypol (1.34) indicate surface area per gram of gossypol particles of the order of 8 square meters. Further work is indicated to determine details of the structure of the platelets, which constitute the wall of the gland, and to establish the relationship of gossypol and gossypurpurin to morphological features within the gland.

The Surface of Cotton Fibers: Part IV: Distribution of Dry Soil

The location of soiling agents such as colloidal and activated carbon, floor soil. a syn thetic soil, and a clay on gray and modified plain weave cotton fabrics soiled under con trolled conditions was determined by light and electron microscopical examination. Cross and fine geometry of fabric and fiber play a major role in determining the dis tribution of soil in most cases. The mechanical entrapment of soil particles and ag glomerates between fibers near the surface of the fabric is repeated in the accumulation of soil in the natural or induced irregularities of the native and modified fiber surface. The presence of soft films on the fiber surface extends the quantity of soil and its dis tribution. Sorption of the soil particles on apparently smooth areas of the fiber also occurs to a significant extent.

A Program of Microscopical Research on Soiling in Cotton

Blanche R. Porter, Charles L. Peacock, Anna T. Moore, Verne W. Tripp, and Mary L. Rollins Southern Regional Research Laboratory, New Orleans, Louisiana Toward the ultimate goal of a built-in resistivity to soiling, investigations have been initiated to develop basic information on the mechanism of soiling of cotton fibers. Electron microscope studies of surface replicas of individual fibers have shown the frequency, depth, and size of wrinkles and grooves which are characteristic of untreated cotton, and the relation of these irregularities to entrapment of soil particles of certain ranges of particle size. The effects of bleaching and mercerization on soiling have been compared, and the changes brought about by certain commercial soil retardants or other treatments on fiber surface roughness have been observed. The relation of these findings to the ease of soiling are currently being studied, but tests are incomplete. Preliminary observations indicate that soil resistance involves geometric or physical saturation of soil sites on the fiber surface that normally would be occupied by soil particles. The comparative excellence of soil retardants of the colloidal metallic oxide type lends credence to this theory. Water repellants of the substituted ketene type and the silicone and acrylic resins used in these experiments, although they effectively cover the natural fiber surface rugosities, also, apparently, present a &dquo;tacky&dquo; surface for holding soil. This is a progress report of initial phases of a rather complex study. Findings and conclusions will be reported in detail at the completion of the investigation.

Natürliche und künstliche technologische Fasern

It is most appropriate that the first session of an International Conference on Electron Microscopy, devoted exclusively to technological fibres, should be held here at Berlin where the pioneering work of this kind was conducted over twenty years ago (1). Moreover, a gathering of many workers from the field of applied research provides a useful opportunity to assess the extent of the general progress.