The Reaction of Formaldehyde with Cellulosic Fibers

Abstract

The effects of an acid-catalyzed formaldehyde treatment on such mechanical proper ties as breaking strength and crease recovery have been determined for three cellulosic fabrics: cotton, Fortisan, and viscose rayon. Samples of these materials, treated under a selected set of conditions, were compared with three "controls": untreated fabric, fabric treated with distilled water under the conditions of the formaldehyde treatment, and fabric treated with the acid solution used in the formaldehyde treatment under the same conditions. The two-dimensional load-elongation behavior of the fabrics was investi gated, and comparisons were made with the results of corresponding one-dimensional tests. The mechanical properties of single fibers and yarns taken from the variously treated fabrics were also measured.In general, cotton fabrics showed a deterioration in mechanical properties due to formaldehyde cross-linking with respect to the acid-treated control, while correspond ingly, Fortisan and viscose rayon were improved by such treatment. In the case of cotton fibers and fabrics, it was found that the formaldehyde treatment had reduced the fiber and fabric elastic moduli with respect to the acid-treated control, although the formaldehyde treatment had also reduced correspondingly the fiber and fabric breaking strains. The deterioration in mechanical properties caused by hydrochloric acid was most marked in the case of Fortisan. It was found that generally the properties of single fibers, yarns, and fabrics are closely related.The improvement in crease recovery caused by the formaldehyde treatment was great est for cotton, less for Fortisan, and least for viscose rayon. These different responses to the cross-linking reaction appear to be related to the different states of internal order of the three cellulosic fibers. Crease-recovery tests carried out on all the variously treated fabrics showed that marked improvements in crease recovery were usually ob tained only with those treated at an initial pad-bath pH of 2.0, which indicates that a high degree of cross-linking of the hydroxyl groups in the amorphous regions of the fibers is necessary to achieve high degrees of crease recovery.