Ines V. Degruy

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.

Microscopical Observations on Partially Acetylated Cottons and Related Fibers

Effects of acetylation on the morphology and submicroscopic structu e of cotton have been studied by light and electron microscopy. The cross-sectional area of partially acetylated (PA) fibers increases with degree of substitution. The average refractive index of PA cotton decreases with increase in acetyl content, as do the indices measured parallel and perpendicular to the fiber axis. Refractive index measurement appears to be a feasible method for estimating the chemical composition of PA cotton. At early stages of esterification, unevenness of reaction along the length of fibers may be demon strated by dyeing and swelling techniques. Acetylation causes the surface of cotton to become smoother, and obliterates the micro- fibrillate pattern characteristic of scoured fibers. PA cotton fibers swell when embedded in methacrylic esters by polymerization. The swelling causes separation of the lamellae of the secondary wall, and permits electron microscopical observations on the interior elements of the fiber to be made on thin cross sections of the specimen. Fragments of PA cotton obtained by wet- beating show progressive loss of the fibrillate character of unacetylated cellulose as the acetyl content increases. At high degrees of substitution, the PA cotton fragments resemble the spongy particles obtained from wet- beaten acetate rayon and Arnel. The results of microscopical examination are considered in terms of fiber structure.

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.

Catalytic Effects and Selective Hydrolysis of Dimethylol Ethyleneurea and Formaldehyde Crosslinks in Finished Cotton

Chemical analyses, physical testing, and selective hydrolysis of the finished fabrics were used to determine differences in chemical structure that resulted from treatment of cotton with dimethylol ethyleneurea (DMEU), formaldehyde, and a mixture of the two with strong or moderate catalysts. The strong catalyst was hydroxymethanesulfonic acid, which was produced by reaction of sulfurous acid and free formaldehyde present in the pad bath. Magnesium chloride was the moderate catalyst used. From combinations of the data the number of crosslinks in the treated cottons was calculated. Stability to acidic hydrolysis indicated the nature of the structures present in the crosslinks. Electron micrographs from application of cupriethylenediamine hydroxide (cuene) solubility and layer expansion techniques provided additional evidence to support these findings. Results are in general agreement with present theories of crosslinking to give wrinkle resistance in cellulosic materials. In addition they furnish new information on the treatment of cotton with a combination of agents that exhibit different reactivities and different stabilities of the crosslinks introduced.

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.

The Microscopy of Fiber and Fabric Finishes and Coatings 1

Finishes and coatings are often applied to textile mate rials in order to alter their physical characteristics by changing the nature of the surface and, therefore, the interaction between elements of the structure. Sometimes these have adverse effects such as, for example, a loss in tearing strength. Various microscopical techniques are described and illustrated which can be useful in examining the distribution of the added material, its penetration into the structure, and the nature of the interaction which exists between the finish or coating and the fibrous substrate, as well as between fibrous elements within the structure.

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.

A Microscopical Technique for Determining Latex Distribution in Tire Cords

A dye-staining technique is described which permits the microscopist to locate the extent of penetration of latex in tire cords. Photomicrographs illustrate the results obtained.

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.