Jarrell H. Carra

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.

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.

Yarn Untwisting as a Rapid Test of Cotton Swelling in Various Reagents

Approximately 80~ of the yarns and fabrics produced in this country are treated with reagents to ln~rify. mercerize, dye. or impart any of a variety of special finishes for specific end uses. The effectiveness of most of these treatments is largely governed by the extent to which the cellulosic substance swells in the reagent systems. In some cases, e.g. mercerization, a high degree of swelling is often desirable for optimum results; whereas most treatments to impart crush resistance appear to require low swelling to produce finishes that are suitable. These generalizations are largely based on empirical observations, and the swelling effect of new reagent systems, particularly those being tried in the

Liquid Ammonia vs. NaOH Mercerization as Pretreatment for the Cotton- Butadienediepoxide Reaction. Spectral and Microscopical Studies

Native, mercerized, and ammonia-treated cottons were reacted with butadienediepoxide (BDO), and their fine struc tural changes were followed by x-ray diffractograms, infrared absorption spectra, refractive indices, and in micro scopical cross sections. Conventional mercerization and liquid NH3 pretreatment of native cotton generally produced a more isotropic fiber. But the nature and mode of decomposition of cellulose swelling complexes formed with either NaOH or liquid NH3 differed, as evidenced by differences in crystalline lattices and the optical properties of reaction products. Optical density increased only in the direction of the fiber axis with NH3 but also perpendicularly to the fiber axis with NaOH. Subsequent treatment of NH3-cellulose controls with mercerizing strength NaOH converted their crystalline lattices to Cellulose II. BDO reaction and postmercerization affected the refractive index only in the direction of the fiber axis (η||). Generally, BDO reaction reduced η|| of all but the NH3-cellulose I control; and postmercerization further reduced η|| of only BDO-reaction products that retained the cellulose I lattice. Birefringence of postmercerized BDO-reaction products derived from NH3-cellulose I was lower than that of comparable BDO-reaction products from conventionally mercerized cotton. Before and after BDO reaction, cross sections of most fibers in reaction products from native and NH3-treated cottons with the cellulose I lattice were elliptical, while comparable cross sec tions from conventionally mercerized cotton were round. Changing the catalyst from 2% to 15% NaOH generally increased the number of circular fibers in BDO-treated cottons having the cellulose I structure. All control cottons dissolved in cupriethylenediamine, but BDO-reaction products were insoluble and cross sections appeared solid. Gen erally, reaction products from cottons pretreated with liquid NH3 had a softer hand and dyed more uniformly than did comparable products from conventionally mercerized cotton.

Fibrous Structure and Properties of Cotton-Poly(Butyl Methacrylate) Copolymers Prepared by Post-Irradiation Initiated Reactions

Graft copolymerization reactions of butyl methacrylate from aqueous methanol solutions with radiation-activated cotton cellulose fibers and fabrics were investigated. The effects of the initial concentration of long-lived free radicals (formed on the cellulose molecule at different radiation dosages) on the rate and extent of copolymerization of butyl methacrylate, with radiation-activated cellulose, and on the distribution of poly(butyl methacrylate) in the fibrous structure were determined. Copolymerization with cotton, containing the lowest initial concentration of free radicals of about one free radical per five to six cellulose molecules, gave a fibrous cotton copolymer which tended to have a layered structure. As the initial concentration of free radicals in cotton was increased, a fibrous copolymer with a higher degree of compactness of structure was obtained. The textile properties of fabric copolymers, which were crosslinked with dimeth yloldihydroxyethyteneurea, were determined.

Microscopical Analysis of Chemically Modified Textile Fibers

Properties of textile fibers are altered to achieve specific qualities by treatment with various chemical finishes. These finishes produce changes that may be observed through direct or indirect microscopical procedures. In developing and evaluating finished fabrics, it is advantageous to determine sites of interaction of the finish and the fiber, since it is generally intended that finish chemicals be located in a particular area of the fabric structure. Microscopical techniques have been developed to show locations of these finishes. Scanning electron microscopy provided a means for showing deposition of finish on fabric and fiber surfaces, and energy dispersive X-ray analysis was used to show the presence of specific elements on or within fibers.

Effect of Cellulase on Cotton Fiber Microstructure Part I: Degradation by Cellulase in Fungal Growth Filtrates

Electron microscopical studies of changes in cotton fiber microstructure, after ex posure of the fibers to the cellulase in filtrates prepared from cultures of Myrothecium verrucaria, showed evidence of the transverse, jagged cuts into the cellulose structure previously seen by cytical microscopy. The degradation appeared localized in areas along the length of the fiber which were not related to any recognized component of fiber structure. Micrographs of fragmented, degraded fibers showed etching of the macro- fibrils of the sheets of secondary wall and a sharpening of the image of the individual microfibrils. Continued enzyme attack produced smaller fragments and hydrocellulose- like particles. Measurements of changes in tensile strength, swelling in alkali, and in glucose yield were correlated with changes in microstructure. The extent of fiber degradation by cellulolytic culture filtrates was limited and could be continued only if fibers were swollen between filtrate exposures. No evidence of damage to the cellulose structure was seen which could not be explained hy hydrolysis at the β-1,4-glucosidic linkage.

A Microscopical Study of the Reaction Products of Halogenated 1,2-Epoxides with Diethylaminoethyl(DEAE)-Cotton and Aminoethyl-Cotton(Aminized)

Reaction products of diethylaminoethyl (DEAE)-cotton and aminoethyl-cotton (aminized) with 1,2-epoxy-3-chloropropane (epichlorohydrin), 1,2-epoxy-3,3-dichloropropane, 1,2-epoxy-3,3,3-trichloropropane, and 1,2-epoxy-4,4,4-trichlorobutane, 1,2-epoxypropane, 1,2-epoxyhexafluoropropane, and 1,2-epoxy-3-bromopropane were studied microscopically. The methacrylate layer-expansion technique was used to evaluate the extent of chemical reaction. Epichlorohydrin appeared to be the most efficient cross-linking agent. The chlorinated epoxides capable of dehydrohalogenation after epoxide ring openings appeared to be good cross-linking agents. Electron mcirographs demonstrate the effects of the above treatments on fiber morphology.

Electron-Microscope Study of the Effects of Various Solvents on Reactions of Diethylaminoethyl-Cotton with Epichlorohydrin

Reaction products of diethylaminoethyl (DEAE)-cotton with epichlorohydrin in both protic and aprotic solvents, have been examined in the electron microscope. Evaluation of degree of cross-linking and uniformity of reaction was made on the basis of expansion patterns obtained by polymerization of methacrylate within the fibers treated in the various solvents. In general, fiber structures from the aprotic systems appeared to be more homogeneous and solid than those from the protic media.

Structural Aspects of the Walls of Cateye Cotton

Aspergillus flavus boll infection is revealed in a bright, greenish-yellow fluorescence of cotton seeds. The lint on these seeds has been studied microscopically to determine the characteristic properties of the infected fibers. Photomicrographs andelectron micrographs show the extent of wall damage caused by the A. flavus fungus. Cross sections examined in the light microscope revealed a “doughnut” fiber shape, unlike the usual kidney-bean shape of normal cotton. A possible mechanism for this phenomenon is suggested.