Florine A. Blouin

The Effects of Gamma Radiation on Cotton: Part I: Some of the Properties of Purified Cotton Irradiated in Oxygen and Nitrogen Atmospheres

Two series of samples of purified cotton were irradiated in oxygen and nitrogen atmospheres with gamma rays at six dosage levels ranging from 100.000 to 100.000.000 roentgens. Some of the chemical and physical properties of the irradiated cellulose were determined by means of various widely used techniques of cellulose chemistry. It was found that high energy gamma irradiation of cotton resulted in carbonyl group formation, carboxyl group formation, and chain cleavage in the approximate ratio of 20 : 1 : 1 ; increased solubility in water and in dilute alkali ; decrease in tensile strength of the fibers ; small but unusual changes in moisture regain: relatively unchanged infrared absorption spectra ; and the same type of degradation in a nitrogen atmosphere as in an oxygen atmosphere, with oxygen producing only slight enhancement of the reaction.

The Effects of Gamma Radiation on Cotton: Part V: Post-Irradiation Reactions1

Purified cotton cellulose dried to less than 0.5% moisture was irradiated in a nitrogen atmosphere with high-energy gamma radiation from cobalt-60 at selected dosages up to 6 × 106 roentgens. Post-irradiation chain cleavages of the cellulose molecule on exposure to air were indicated by decreases in the viscosity of the irradiated cellulose with increasing time after irradiation. Post-irradiation reactions of the irradiated cellulose with acrylonitrile were investigated. Low yields of graft polymer were obtained on treatment of the irradiated cottons with pure acrylonitrile, 5% acrylonitrile in water, and 32% acrylonitrile in N,N-dimethylformamide. The effect of temperature in the 23°-100° C range on these treatments was investigated. High yields of graft polymer were obtained when the irradiated cottons were treated with acrylonitrile solutions in concentrated aqueous zinc chloride. The mechanical properties of selected fibrous graft polymers of cellulose–polyacrylonitrile were determined. Some irradiations were carried out in the presence of oxygen and moisture for comparison of these post-irradiation reactions. Results were discussed with relation to the production of long-lived free radicals in the cotton cellulose by high-energy gamma radiation.

Gel Permeation Properties of Cellulose II: Comparison of Structures of Decrystallized Cotton Cross . Linked With Formaldehyde by Various Processes

Application of gel permeation chromatography, which has been shown to be an effective means of measuring changes produced in the accessibility of decrystallized cotton cellulose by one form of formaldehyde cross-linking [9, 10], has been extended to the study of alterations of the structure of decrystallized cotton produced by intro duction of formaldehyde cross links under various other reaction conditions. These include reaction in aqueous solution (Form W), in the vapor phase (Form V), in acetic acid solution (Form D), each with high and low concentrations of formaldehyde, and in a bake-cure process (Form C). The properties determined by gel permeation chroma tography are the effective internal solvent volume derived from measurements of selective permeability to solutes of decreasing molecular weight and the limit of per meability to solutes of increasing molecular size. Striking differences were revealed in both the nature and magnitude of the alterations of accessibility resulting from differ ent reaction conditions employed for formaldehyde cross-linking. Corresponding changes were observed in gross properties of the cellulose polymer gels, such as the extent of swelling measured by the volumes occupied by the swollen gels per gram of dry solids. Accessibility was increased by reactions in aqueous solution which produced cellulose having larger internal volumes and permeability limits than the unmodified, decrystallized , cellulose. The reaction catalyzed by hydrochloric acid in the acetic acid medium formed products having larger internal volumes, but somewhat lower limits of permeability. Both the internal volume and the permeability limit were decreased by the bake-cure process which produced a polymer having much lower accessibility than the unmodified, decrystallized cellulose.

Polymerization-Crosslinking of N-Methylolacrylamide in Cotton Fabric

Several variations of polymerization-crosslinking of N-methylolacrylamide (NMA) in cotton were explored to clarify factors critical to achievement of resilience with superior retentions of strength and abrasion resistance in fabric. Per sulfate catalysis simultaneously initiated both polymerization and crosslinking reactions of NMA in cotton fabric; the results from dry-cure reactions fell in the conventional range of textile performance properties achieved by treatment of cotton fabric with agents such as dimethyloldihydroxyethyleneurea. Wet-cure reactions carried out in scaled bags at or above 100°C resulted in low resilience, high retentions of strength-abrasion resistance, and large increases in stiffness, the last attributed to fiber bonding in yarns. Wet-cure reactions conducted at or below 80°C caused little stiffness, and only in these cases was a subsequent catalyzed dry-cure reaction effective in raising resilience with good retentions of strength and abrasion resistance. Inclusion of alkali metal phosphates in the persulfate-initiated reaction of NMA with cotton in a pad-dry-cure caused retentions of abrasion resistance to be very substantially improved and retentions in breaking and tearing strengths to be significantly improved at durable-press appearance ratings of 4.5. These results are attributed to relatively sequential but rapid polymerization and crosslinking reactions, to reduction in formation of oxymethylene crosslinks, and possibly to reduced molccular degradation of the cellulose.

Gel-Permeation Properties of Cellulose Part III: Measurement of Pore Structure of Unmodified and of Mercerized Cottons in Fibrous Form

The gel permeation technique, initially investigated for measuring the pore structure of cotton cellulose decrystallized by ball-milling, has been adapted for application to the study of cotton in fibrous form. The crystalline cotton has an apparent internal solvent volume, in pores permeable by solutes of decreasing molecular weights, approximately 53% of that of decrystallized cellulose. The molecular-weight limit of permeability was 2900, compared to approximately 1900 for the decrystallized material. Mercerization of the fibrous cotton increased the apparent internal solvent volume by approximately 60%, but decreased the limit of permeability to a molecular weight of about 2200. These results illustrate the utility of the chromatographic gel permeation method for measuring changes in the pore structure of fibrous cotton produced by various modifications.

RADIATION STABILIZATION OF GLYCOSIDES BY AROMATIC GROUPS.

During the Co60 y-irradiation of glycosides, no localized absorption of the radiation in the aglycon portion occurs. Therefore, in view of the selective radiation cleavage of the glycosidic bond, this group of carbohydrates appeared suitable for studying the factors that influence energy transfer within the molecule. This paper describes the effects of y-irradiation on substituted and unsubstituted glycosides in the solid state. The results demonstrate that considerable protection of the glycosidic group may be achieved over distances extending beyond one D-glucose molecule.

POST-IRRADIATION GRAFTED VINYL CELLULOSE COPOLYMERS

Purified cotton cellulose fibers, yarns, and fabrics were grafted with vinyl acetate, acrylonitrile, and methyl methacrylate, using a post-irradiation grafting technique. The cottons were irradiated dry and in nitrogen with gamma rays from a cobalt-60 source to a dosage of 106 roentgens (R) and treated at about 23°C with a 15% monomer solution in 70, 75, or 80% aqueous zinc chloride. The rates of graft polymerization of these vinyl monomers onto cotton fibers were studied, and the radiochemical yields obtained were 6400 to 75,000 molecular actions per 100 ev. The rate of reaction and maximum yield were also dependent on the physical state of the cotton. Yarns and fabrics con taining approximately 50 and 25% grafted polymer, respectively, were prepared for property evaluations. Grafted yarns showed a marked increase in elongation-at-break and a decrease in average stiffness, Polyacrylonitrile-cotton yarns exhibited significant rot resistance. The vinyl grafted yarns were thermoplastic. Two different distribu tions of the vinyl polymers were observed on examination of cross sections of grafted fibers. The molecular weights of the vinyl polymers were very high (1-3 X 106). Both the polyvinyl acetate- and the polyacrylonitrile-cotton fabrics exhibited marked improve ments in abrasion resistance.

Vinyl Cellulose Copolymers Part I: Effect of Method of Preparation on the Properties of Polyacrylonitrile-Cotton Copolymers1

Polyacrylonitrile-cotton copolymers were prepared by post-irradiation, simultaneous- irradiation, ceric ion, and ferrous ion/hydrogen peroxide-initiated graft copolymerization reactions. Molecular weights of the grafted polyacrylonitrile ranged from 33,000, when the simultaneous-irradiation method and dimethylformamide solvent were used, to 1,200,000 when the post-irradiation method and 75% aqueous zinc chloride solvent were used. The location of the grafted polyacrylonitrile ranged from principally the outer layers of the fibrous structure to uniform distribution within the structure. All of the textile properties of cotton yarns and fabrics, which had been graft-copolymerized with acrylonitrile, were apparently not wholly dependent on the molecular weight of the grafted polyacrylonitrile, the fraction of the cellulose molecules containing grafted polyacrylonitrile, or the distribution of the polymer within the fibrous structure. Of the properties evaluated, only the flat abrasion resistances of cotton fabrics, copolymerized with acrylonitrile using radiation methods and aqueous zinc chloride solvent, were significantly greater than those of copolymers prepared by other methods. The wrinkle recoveries of fabrics, containing the polyacrylonitrile which had the lowest molecular weight, were greater than those for fabrics grafted with polyacrylonitrile which had higher molecular weight. The relationships between the site on the cellulose molecule of the graft copolymerization reaction to the method of initiation and the properties of the cotton copolymers were considered.

Vinyl-Cellulose Copolymers Part II: Fibrous Structure and Properties of Poly (Alkyl Methacrylate)—Cotton Copolymers Prepared by Radiation-Initiated Reactions

Graft copolymerization reactions of methyl, ethyl, butyl, hexyl, and lauryl methacrylates and 1,3-butylene dimethacrylate with fibrous cotton cellulose were initiated by the simul taneous irradiation procedure, using 60Co γ-radiation. The fabric properties of the poly(alkyl methacrylate)—cotton copolymers (methyl, ethyl, butyl, and hexyl) were determined at two degrees of grafting. The flex abrasion resistance of the poly(hexyl methacrylate)—cotton copolymer at 37% add-on of polymer was more than ten-fold that of the cotton fabric control. The flat abrasion resistance of the poly(ethyl methacrylate) —cotton copolymer was ten-fold greater than that of the fabric control. Examination of electron microphotographs of thin sections of the copolymers embedded in aqueous polyvinyl alcohol indicated that layer opening of the fibrous structure occurred during graft copolymerization and that the degree of layering and size of the opening was related to the molecular weight of the monomer being reacted. The radiochemical yields of the reactions ranged from 4,600 to 44,000 molecular actions per 100 eV at a dosage of 0.5 MR.

An Effect of a Pretreatment of Fabric upon the Development of Durable-Press Properties in Cotton Fabrics by the Wet-Fixation Process

A critical factor in the development of durable-press performance in cotton fabrics by the wet-fixation process is the presence of trace amounts of residual base in the cotton. In relatively large quantities the base neutralizes the acid catalyst employed for fixation and decreases the extent of reaction of the hexamethylolmelamines. In lesser amounts the base has little or no effect upon the development of add-on and resilience but deters the development of breaking strength and abrasion resistance in the fixed and cured fabrics. Evidence obtained in this study shows that in the wet-fixation type of process high levels of resilience are developed readily and are a function of reactions occurring in the early stages of fixation but subsequently modified by curing. On the other hand, high levels of breaking strength and abrasion resistance are developed only after extensive penetration of reagents into the fiber structure; these properties are a function of reactions occurring in the later stages of fixation. These strength properties are enhanced by use of reagent systems (i.e., hexamethylolmelamines) whose moderate reactivities allow good penetration.