Mary L. Nelson

Liquid-Ammonia and Caustic Mercerization of Cotton Fibers: Changes in Fine Structure and Mechanical Properties

Cotton fibers blended to give three levels of fiber maturity were mercerized in anhydrous liquid ammonia and in sodium hydroxide solution, slack and under tension. Both reagents produced similar changes in the cottons, but to differing degrees. Both ammonia and caustic treatments produced changes in morphology (swollen fibers, decrease in convolutions) and in fine structure of the cellulose (increased accessibility as measured by increased moisture regain, iodine sorption, accessibility to deuterium exchange, and decreased density). X-ray diffraction showed increased amorphous fraction and partial recrystallization into cellulose III and cellulose II lattice after treatment with ammonia and caustic, respectively; the x-ray orientation angle was decreased by treatments under tension. Both reagents produced increased fiber elongation-at-break with slack treatment and increased fiber tenacity with tension treatment; caustic mercerization produced a slight increase in fiber tenacity after slack treatment.

The Iodine Sorption Test. Factors Affecting Reproducibility and a Semimicro Adaptation

The iodine sorption test is a convenient though empirical method of measuring cellulose accessibility, but results show considerable variability. The relative importance of some experimental factors with respect to reproducibility of test results was, therefore, examined. Agitation during equilibration and use of a standard concentration of iodine solution and a standard sample weight were shown to be important. A fixed shedule of equilibration times and some degree of temperature control are also necessary. No increase in precision was obtained by direct titration of iodine in the sample, compared to the usual indirect determination by titration of supernatant solution and blank. The procedure can be scaled down from the usual 300-mg sample to 60-mg samples without loss of precision.

Improvements in the Acid-Hydrolysis Method of Determining the Crystallinity of Cellulose

In a study of the acid-hydrolysis method [5] for the determination of the degree of crystal linity of cellulose fibers, a technique has been developed for the solvent removal from the hydrolysis residues of all but traces of the humic substances which are formed from the soluble hydrolysis products and which interfere with the crystallinity determination. Although ammonium hydroxide and pyridine were effective solvents, hot 50-percent aqueous monoethanolamine was found to be the most practicable means of removing these humic sub stances. Its effectiveness was demonstrated (a) by showing that the weights of the extracted residues were the same as the weights of residues corrected by computations based on data from experiments with glucose; (b) by varying the liquid-solid ratio during hydrolysis and showing the uniformity of the weights of the resulting ethanolamine-extracted residues; and (c) by obtaining equal extrapolated values for degree of crystallinity from parallel extracted and un extracted but mathematically corrected hydrolysis series. Data are presented to show that preliminary extraction with either 1-percent sodium hydroxide or ethanolamine to remove the noncellulosic constituents does not change the crys tallinity values of samples of cotton and cotton linters. A revised crystallinity procedure is described which incorporates the improvements de scribed above.

Reactivity and Fine Structure of Cotton Mercerized in Sodium Hydroxide or Liquid Ammonia

The effect of liquid ammonia mercerization on the fine structure and reactivity of cotton sliver and yarn was compared with that of sodium hydroxide mercerization. X-ray diffractograms showed considerable decrystallization by both swelling agents, with little difference between them, and no effect of tension. The swelling produced by both reagents decreased the density of the cotton, with the percentage decrease being dependent on tension, method of removing the swelling agent, and fiber maturity, rather than on type of reagent. Accessibility to moisture, deuterium exchange, and iodine was increased by all treatments, but in general, increases with caustic soda were greater than with ammonia. Differences in enhanced reactivity towards acid hydrolysis and crosslinking with formaldehyde, attributable to mercerizing agent, were small, but in partial acetylation, greater reactivity resulted from caustic mercerization.

Properties of Durable-Press Cotton Fabrics Related to Swellability

Fabrics with a wide range of durable-press properties were prepared by treating cotton printcloth with dimethyloldi hydroxyethyleneurea (DMDHEU) by pad-dry-cure, mild-cure, and steam-cure processes and with formaldehyde by vapor-phase, Form D, and Form W processes. Swellability in aqueous media, as measured by water retention, iso propanol retention, alkali centrifuge value, and yarn untwisting number, is discussed in relation to durable-press appear ance ratings and wrinkle recovery angles. Such measurements of accessibility as moisture sorption isotherms, internal surface area, iodine sorption, and differential dye sorption are also presented. Some inferences regarding spatial location of crosslinks and its relation to wet and dry fabric recovery properties are discussed.

Effects of Heat-Drying on the Physical and Chemical Properties of Cottons

The poor spinnability of some lots of gin-dried cotton has been attributed to over heating of the seed cotton. To determine what changes in the lint might be responsible, two series of gin-dried cottons and one series that was flash-heated in the laboratory were studied. Appropriate physical and chemical properties of the lint were measured, such as fiber length distribution, single-fiber and fiber-bundle strength and elongation, moisture regain, nepping potential, fiber friction, microscopical swelling, alkali swelling, wet tability, fluorescence, copper number, carboxyl content, pH, infrared spectra, and wax properties. Limited spinning and weaving tests allowed yarn and fabric properties to be measured. Nearly all tests showed no evidence of radical permanent changes in lint properties. The one significant finding was an altered fiber length distribution in some heated lots such that the proportion of shorter fibers was increased while the percentage of long fibers was slightly decreased. This change appeared to be correlated with poorer yarn appearance and uniformity, a slight reduction in yarn and fabric strength, and poorer resistance to flex-abrasion. A blend of unheated lint with enough short (cut) fibers to give a fiber-length distribution approximately the same as that of a gin-overheated lot produced yarns and fabric with properties in close agreement with the overheated lot whose fiber-length distribution was approximated by the blending. Laboratory tests showed that fiber strength was lower when tested immediately after heating—that is, when the moisture regain was temporarily greatly reduced. From this finding it is deduced that the change in length distribution is the result of excessive fiber breakage when lint is subjected to mechanical agitation at too low a moisture content.

Effect of Grinding on the Crystallinity of Cellulose Fibers, as Indicated by the Acid-Hydrolysis and Other Techniques

A study was made of an effect previously noted, that grinding cotton fibers in a Wiley mill causes a reduction in degree of crystallinity as determined by the acid-hydrolysis method. It is shown on samples of purified linters and cut cotton, ground under conditions of increasing severity, that even mild grinding—for example, through a 2-mm. sieve—causes a detectable reduction in indicated degree of crystallinity, and that as the severity of grinding increases the degree of crystallinity drops correspondingly. This drop is not caused by passage of more of the finely ground particles from the more severely ground samples through the filters. When the ground samples were moistened with water and allowed to dry, a portion of the lost crystal linity was regained. The acid-hydrolysis results are supported by accessibility, heat of wetting, and moisture adsorption measurements, which, with few exceptions, indicate increasingly larger amounts of amorphous material in the samples receiving the more severe grinding. While the x-ray diffraction patterns did not reveal any effect of the most severe grinding, it is assumed that the changes were not sufficient to permit their detection by this means. Some implications of the results on the interpretation of cellulose structure are discussed.

Mechanical Properties of Cotton Yarns Mercerized in Liquid Ammonia and Sodium Hydroxide

Yarns spun from high- and low-maturity cottons were mercerized in liquid ammonia in a continuous process, and in liquid ammonia and sodium hydroxide in skein form under various tensions. Both swelling agents produced similar changes in mechanical properties (breaking strength, tenacity, elongation-at-break, and initial modulus) under comparable conditions. Mercerization under high tension increased breaking strength and tenacity and decreased elongation-at-break. Slack mercerization in caustic resulted in elongations-at-break substantially higher than did ammonia treatment. A major difference between reagents was noted during treatment. When skeins were swollen slack and then restretched, much greater force was required to restretch ammonia-swollen skeins, and they could not be stretched as much as those that were caustic-swollen. Measurements of length changes in yarns during swelling, tensioning, and deswelling gave quantitative data to substantiate this observation. Differences in mechanism of swelling are discussed in relation to these findings.

Closed-Boll Cotton Part I. Properties of Never-Dried Cotton Fibers Before and After Aqueous Formaldehyde Treatment

Cotton lint from closed bolls harvested at various stages approaching maturity had very high initial moisture content, water retention, and dye sorption. Values decreased as fibers matured. Equilibrium moisture contents of never-dried cotton by desorption to 93 and 87% relative humidity were much higher than those for rewet air-dried fibers. Tensile elongations of never-dried fibers were greater than those of rewet air-dried fibers only in the more mature samples. Under the condi tions employed, treatment of never-dried cotton with aqueous acidified formaldehyde solution did not preserve the very high sorptive properties.

Closed-Boll Cotton Part II. Restoration of the Never-Dried State by Treatment with Propylene Oxide 1

Never-dried and dried cotton fibers from closed bolls harvested at various stages of growth were treated with propylene oxide. Both sets of treated fibers, which were tested after drying and rewetting with water, had moisture-sorption and tensile properties close to those of never-dried cotton. Com parison of treated fibers to untreated dried fibers showed that water-retention values were doubled by the treatment, regains at 87% RH were increased by a third, and fiber-bundle and single-fiber elonga tions were more than doubled. Bundle tenacity and single-fiber breaking load were also increased