Chemical Bonding and Reaction Rates of Wrinkle-Resistant Finishes on Cotton

Abstract

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.