Abstract
Cotton, rayon and polynosic fibers were treated with formaldehyde under the wet conditions. The apparent dry density of the crosslinked fibers decreased linearly with increasing amount of combined formaldehyde, for each cellulose species. The apparent dry density of the crosslinked rayon and polynosic fibers decreased more markedly than that of the crosslinked cotton fibers. Swelling of the crosslinked fibers in aq. NaOH was studied. The degree of swelling of the crosslinked fibers increased with increasing amount of combined formaldehyde in water and dilute aq. NaOH while it decreased in conc. aq. NaOH. The critical concentrations of aq. NaOH at which the swelling tendency in relation to the amount of combined formaldehyde was reversed were 10-12.5%, 3-5%, and 6-7.5% for cotton, rayon and polynosic fibers, respectively. The swelling behavior is explained by the double network structure of cellulose made up by crystalline and hydrogen-bond networks in the amorphous region, and by the destruction of the crystalline network at the critical concentration of aq. NaOH.
