Ricardo H. Wade

Structural Changes in Cotton: Effect of Premercerization Conditions on Subsequent Cross-Linking

Structural changes due to tension applied to caustic-swollen yarns were studied. It was found that the cross-linking of yarns which had been mercerized slack, at normal length, or slack and then restretched to normal length produced differences in tenacity and X-ray orientation. It was concluded that this was due to structural rearrangements induced by the application of load to fiber systems. Differences in wet pickup of the cross-linking resin were shown to produce differences in the fiber fragmentation pattern but not in the layer-expansion pattern. Only a fraction of the added cross-linking resin was considered to have contributed to the properties usually attributed to cross-linked yarns. The regions believed responsible for the effect of cross-linking are the less ordered lattices close to the crystalline structures. The strength retained after cross-linking was dependent on the tension and the method of its application. Differences in the degree of conversion of cellulose I to cellulose II were noted in the slack-mercerized yarns treated with different alkali metal hydroxides. These differences, with the exception of lithium hydroxide, correlated with swelling effectiveness of the alkalis used.

Synergistic Effect of Mixed Bases in the Conversion of Cotton Cellulose I to Cellulose II The Role of Cations as Cocatalysts for Crystal Lattice Rearrangement

Several aqueous bases were found which swell cotton yarn greatly, but, after their removal from the cotton, leave the x-ray diffraction pattern unchanged from that of native cellulose I. Such bases include 9.5% lithium hydroxide and 35% benzyltrimethylammonium hydroxide. However, the addition of as little as 1.5% lithium hydroxide or 5% sodium hydroxide, to the benzyltrimethylammonium hydroxide causes substantial conversion of cellulose I to cellulose II. This synergistic effect is attributed to the decrystallizing action of the organic base which, by breaking down the cellulose I lattice, facilitates the action of lithium, sodium, and potassium hydroxides in forming alkali cellulose lattices leading to cellulose II. Rubidium and cesium hydroxides failed to produce this effect when added to the organic base. Cellulose swelling, decrystallization, and recrystallization appear to be distinct steps in lattice conversion. These steps may present greatly different requirements as to optimum cation size and coordination, such requirements being more readily met by mixtures of cations than by any one species. In the absence of the quaternary base, but at alkali concentrations giving maximum fiber swelling, no lattice conversion was produced by lithium or cesium hydroxides, a high degree of conversion occurred with sodium hydroxide, and the other alkalies were intermediate in effect. The strength, elongation, energy-to-rupture, and tenacity of treated yarns varied greatly with the cations present in the alkali. In contrast to yarn, fiber bundles underwent slow and partial conversion to cellulose II by the quaternary base.

Fibrous Cellulose Esters by Trifluoroacetic Anhydride Method

derivatives. The use of trif1uoroacetic anhydride as an esterification &dquo;impeHent&dquo; was reported lry liourne, et al. [11 J and Tedder [5]. Only a few cellulose esters have reportedly hee.n prepared by this method ( 1 J, and these were soluble derivatives. %Ve have found that the trinuoroacetic anhydride ’’impt’l1em’’ method is generally mdre applicable to the partial esterincation of cotton with retention of the fibrcnts form than a study of the literature would indicate. Furthermore, the method has certain adB’antag~s: no additional catalyst is needed, the e~t(’rifyin~ acid is efficiently used and need not he in the

The Role of Alkali Metal Hydroxides in the Benzylation of Cotton Cellulose

The preparation of fibrous benzyl cellulose having a D.S. of 0.5-1.7 has been studied. Cotton yarn was reacted with benzyl chloride in the presence of alkali metal hydroxides under various conditions. A process was developed in which yarn could be benzylated to a D.S. of 0.6 within 30 min, while retaining 100% to 120% of the breaking strength and 315% to 345% of the elongation of untreated yarn. The order of effectiveness of alkali metal hydroxides in activating cotton for benzyla tion was found to be CsOH > RbOH > KOH > NaOH > LiOH, contrary to earlier reports. The rate of benzylation was increased by a factor of 2-4 in going from lithium or sodium hydroxides to potassium, rubidium or cesium hydroxides. This order is the same as the known order of effectiveness of the alkali hydroxides in converting cellulose to cellulosate ions, but is opposite to the relative degree of swelling they produce. It is concluded that benzylation of cotton proceeds by an SN2 type displacement of chloride by cellulosate ions. The primary function of the alkali is to convert cellulose to cellulosate ions, and swelling of the cellulose is of secondary importance.

Use of Trifluoroacetic Anhydride in Partial Acetylation of Cotton Cellulose

Trifluoroacetic anhydride (TFAA) has been found to be an effective esterification promoter in the preparation of experimental quantities of partial cellulose acetates in which the fibrous structure of the original cotton is retained. In this reaction TFAA acts as an impellent and no additional catalyst is required. A method of preparation has been devised, and the effects of time, temperature, and molar ratio of the components in the reaction system have been studied. Optimum reaction conditions are mild with no great degradative effects. Cotton in the form of yarn has been reacted, and the composition and physical characteristics of the modified yarns have been determined.

Iodide Ion Catalysis in the Benzylation of Cotton Cellulose

The presence of alkali metal iodides accelerated the reaction of benzyl chloride with alkali cellulose. The alkali metal iodide was added to the mercerizing alkali used to activate the cotton yarn. The degree of benzylation observed with iodide present was 74% to 110% greater than with iodide absent. A D.S. of 0.7 could readily be obtained within a reaction period of thirty minutes at 115°C. The breaking strength retention at this D.S. was 93% to 119%, based on unmercerized, untreated yarn. Other salts tended to retard benzylation. Borax and neutralized boric acid were ineffective as catalysts, contrary to previous reports. Catalysis by iodide salts is considered to be due to the in situ formation of benzyl iodide from benzyl chloride within the cellulose fibers, the organic iodide being a more active alkylating agent than the chloride. Hydrotropic effects of the alkali iodides appear to be of secondary importance in the catalysis.

Nature of the Swollen State as Determined from Tensile Properties After Cross-Linking Effect of Swelling and Tension on the Fine Structure of Cotton

Changes in internal fiber structure of cotton during swelling and tensioning were determined from the effects of these changes on physical properties imparted by cross-linking with dimethylolethyleneurea (DMEU). Cotton yarns were swollen with various agents and subjected to tension during swelling and subsequent washing. Dimethyl sulfoxide (DMSO), aqueous benzyltrimethylammonium hydroxide (BTOH), and solutions of KI and KCNS in NaOH were used as swelling agents. The effect on structure caused by repeated cycling between slack and original length during the base-swollen stage was judged from the effect of subsequent low-level cross-linking on physical properties. Resin pickup and distribution in the yarns were controlled by high-speed centrifugation. The type and concentration of swelling agent are related to the form and degree of tension needed during the swelling steps to produce optimum properties after cross-linking. Improvement of physical properties after cross-linking was found to correlate with increased crystallite orientation over a part of the range studied. The relationship between degree of conversion of native cotton to Cellulose II and energy-to-rupture values is discussed. The characteristic features of low- level cross-linking previously observed in the fiber fragmentation patterns of yarns treated with DMEU, centrifuged to a low wet pickup, and cured, were also seen in the samples repeatedly swollen and restretched prior to DMEU treatment, centrifuging, and curing.

Preparation and Some Properties of the Anthranilate of Cotton

A new and unusula reaction with cellulose is presented. lastoie anhydride dissolved in DMF or DMSO is caused to react with cotton sheeting by a pad, dry, and cure process. The product is a partial cellulose 2-aminobenzoate. The aromatic ammo groups attached to the cellulose offer possibihties of further reactions. ’ N1’.~V reactions of rc·llttlusc· art* of ~rc;tt interest i«r modifying the C)1(-Illictl attcl j>lij.;I<~iil properties of cotton to expand its many end uses. Of special interest are the timited number of ce))u!ose reactions that are rapid and practica! and that are tunulc;;;racl;ttive. Reaction of cotton BBitli isatoic an!iBdride tit> into this category. ’

Preparation and Properties of Cotton Cellulose Diazonium Salts

Remarkably stable, yet reactive diazonium salts of cotton cellulose fabric have been prepared under ambient conditions by the action of dilute acid and nitrite solutions on cellulose ortho-aminobenzoate. These salts, which may be stored for four to six weeks, coupled readily with phenolic and aromatic amino compounds to produce deeply dyed fabrics.