Textile Research Journal

Fabrics varying widely in fiber parameters and in yarn and fabric construction were treated with wash-and-wear resin formulations. Wash-and-wear ratings after tumble drying, crease recovery values, and breaking and tear strengths were determined.

It was found that the wash-and-wear ratings of cotton fabrics after tumble drying were not systematically affected by the fabric construction, except that light, open-weave fabrics performed poorly. The crease recovery of resin-treated cotton fabrics was also relatively insensitive to construction. Both of these properties could, of course, be im proved by increasing the resin concentration.

As a consequence of the relative insensitivity of wash-and-wear appearance ratings and crease recovery to construction variables, the principal emphasis in the design of functional wash-and-wear fabrics should be placed on gaining maximum strength. The breaking strength, at any one resin concentration, was found to be essentially linearly related to the weight of the fibers in the stressed yarn system, with the fiber strength ( Pressley, 5 mm between jaws) the only important secondary effect. The tear strength, too, was related in a gross manner to the fiber weight in the torn yarn system; it was, however, also improved by increasing the openness of the fabrics, by reducing the number of yarns per inch, by use of more open weaves, or by assembly of the fibers into fewer, coarser yarns rather than more numerous, finer yarns. The reduction of tear strength for a given improvement in wash-and-wear rating due to increased resin concentration seemed to be greater in fabrics woven from finer than those woven from coarser yarns and, in some cases, in open weaves as compared to plain weave fabrics. Quite generally, effects of fabric construction on crease recovery and strength observed in the untreated fabrics were reduced to various degrees by resin treatment.

Rate equations for the development of wrinkle recovery improvement by the reaction of wrinkle-resistant finishes with cotton were calculated from a theory derived from previous work. The implications of this theory are that covalent cross-linking is required to obtain improvement in the wrinkle recovery of cotton, but only a small fraction . of the cellulose reactant necessary to obtain a given level of wrinkle recovery is involved . in cross-linking. The rest is employed in reducing hydrogen bond interaction between cellulose molecules by intramolecular or intrachain reaction. Rate data are obtained for the reaction of a melamine-formaldehyde compound and a cyclic ethyleneurea' formaldehyde compound on 80 X 80 cotton. The theoretical rate equations give results in agreement with the experimental data. The rate constants obtained vary with the . concentration of the cellulose reactant as predicted by the theory. The rate constants vary with temperature in accordance with the Arrhenius law. These results lend support to the theory on which the rate equations are based. Further support is obtained using rate data, taken from the literature, on the reaction of formaldehyde with cotton in an .acetic acid-water mixture. The effect of catalyst and catalyst concentration on the reaction rates is considered. A theory considering metal salt catalysts to act as Lewis acids forming an activated complex with the cellulose reactant is developed which is consistent with the data obtained on the effect of catalyst cpncentration on the rate constants. A consideration of the decrease in the tensile strength of cotton which accompanies wrinkle recovery improvement brought about by reaction with a difunctional agent emphasizes the role of hydrogen bond interaction between cellulose molecules. A relationship between tensile strength loss and the concentration of reacted finish on the fabric is derived on the basis that the effect occurs only in the amorphous region. The relationship obtained is similar to that between the wrinkle recovery and the concentration of reacted reagent of the earlier work [25, 26]. That both of these relationships could be derived taking only the formation of covalent cross-links into consideration and dis- ' regarding the effect of the agents on the hydrogen bonding in the amorphous region of cellulose is shown to be an indication that the ratio of covalent cross-links formed to hydrogen bond cross-links broken is a constant. According to this concept, some tensile strength loss is a necessary consequence of wrinkle recovery improvement.

The results of a study on the susceptibility to acid hydrolysis of the products from the reaction of amido-methylol compounds with cotton are reported. A correlation was found between electron displacement and ease of hydrolysis. Substituent groups in the amido-methylol compounds play an important role in the electron displacement. Electron- releasing groups attached to either the amido nitrogen or the carbonyl carbon facilitate acid hydrolysis; electron-attracting groups hinder hydrolysis, Various hydrolysis mech anisms are considered for explaining the observed inductive and resonance effects. A mechanism wherein initial electrophilic attack is at the ethe al oxygen a fission of the link with cellulose is through carbonium ion formation appears co pletely satis factory in explaining the observed facts.

Progress in developing cotton fabrics having high recoverable stretch, durable loft, warmth, and other highly desirable properties is reported. Three general methods for making stretch and bulked cotton yarns and fabrics are described: (i) use of cross- linking agents to set or maintain crimp in cotton yarn; (ii) slack mercerization of cotton fabrics to cause shrinkage; and (iii) the crimping and heat setting of thermoplastic cotton yarns (ethers and esters of cotton cellulose). The first method employs the chemical reactions of the type widely used by industry in manufacturing wash-wear products. Stretch and bulked cottons might present opportunities equal to those already provided by wash-wear products.

Dimethylol ethylene urea was applied to cotton in aqueous solutions containing high concentrations of nonvolatile, nonreactive, water-soluble compounds. The fiber appears to remain in the distended state after evaporation of water, and the fabric cured at high temperature exhibits high wet but low dry wrinkle recovery properties similar to those previously observed in cotton cross-linked in the wet state. Moisture regain and water of imbibition are maintained at high level in the cotton fiber cross-linked by the new process. Premercerization without intervening drying enhances these effects. The application of the new technique for other purposes, including the introduction of water- insoluble finishing agents inside cotton fibers, is suggested.

The changes in crease recovery and water absorption of untreated and modified rayon and cotton fabrics have been studied as a function of relative humidity at 25° C. The crease recovery of rayon was found to be very dependent on relative humidity and water content whereas that of cotton was almost independent. The effects of "dry"-state and "wet"-state cross-linking and other special treatments on the crease-recovery-water- content relationships were studied. All of the modified fabrics exhibited a deep minimum in crease recovery, which is attributed to the glass transition of the fibers. The minimum occurs at the water content which lowers the T, of cellulose to 25° C, the temperature of the experiment. This water content is also marked by a minimum in fiber resiliency. The change in the crease-recovery-humidity relationship produced by cross-linking gen erally parallels the change produced in the corresponding fiber resiliency relation, thereby supporting the interdependency of fiber resiliency and fabric crease recovery.

The rate of crease recovery up to 5-min recovery time was determined for all the fabrics at different humidities. Over this time range, the recovery data were linearly related to log time. Although no minimum in crease recovery could be discerned for untreated rayon and cotton fabrics, the glass transition point was marked by a maximum in recovery rate.