The Reaction of Formaldehyde with Cellulosic Fibers
1956
The acid-catalyzed reaction of formaldehyde with cellulose has been studied under conditions comparable to those of formaldehyde treatments carried out in textile finish ing plants. Cotton, Fortisan, and viscose rayon fabrics were treated at different pad- bath pH values (2.0, 2.2, and 2.4) and formaldehyde concentrations, at different tempera tures (110°, 120°, and 130° C.), and for different periods of time. At the higher pH values of 2.2 and 2.4, the cross-linking reaction seems to take place primarily in the amorphous regions of the fibers; at the lowest pH, a very rapid reaction occurs in the amorphous regions, accompanied and followed by diffusion of formaldehyde into the crystalline regions which controls the observed reaction rate. Both the rate and extent of reaction appear to depend on the state of internal order of the cellulosic material, being least for cotton, the material of highest crystallinity. Fortisan and viscose rayon have about the same degree of crystallinity, but the reaction with Fortisan is more rapid which causes the extent of reaction at later times to be greater than that observed for viscose rayon. Two possible explanations are either that the higher orientation of Forti san facilitates the cross-linking process or that recrystallization occurs during acid hy drolysis, and viscose rayon has a relatively higher rate of recrystallization. The results of X-ray diffraction studies carried out on the variously treated cellulosic fibers are con sistent with the proposed reaction mechanisms.
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