On the acetalization of regenerated cellulose with dialdehydes

The effects of acetalization with the divalent aldehydes glyoxal and glutaraldehyde on rayon staples of various structures were studied. The swelling in aqueous 25% sodium hydroxide was measured after centrifuging. The knot strength was taken as a measure of the fiber brittleness. The acetalized glyoxal was determined by Head's method, and the amount of glutaraldehyde liberated by hydrolysis of the acetalized fiber with acid was determined polarographically. The results were as follows: (1) The amounts of acetalized glyoxal formed increased with increasing steeping liquor concentration, curing temperature, and curing time, but the percentage of glyoxal reacted did not exceed 65% of that applied. (2) For a constant amount of aldehyde applied to the fibers, more acetalized glyoxal was obtained (a) with lower moisture in the fiber after predrying, (b) by treatment with a higher concentration of aldehyde in a single step rather than at lower concentrations in many steps, and (c) with lower pickup at higher concentration. Therefore, the aldehyde concentration in the fiber at the final stage of curing may determine the acetalization reaction equilibrium. (3) The amounts of free and semiacetals formed increased initially and then decreased with higher total amounts of acetalized glyoxal. (4) The fine structure of all‐skin rayon may be favorable to the reduction of water imbibition and also to the prevention of brittleness at the same degree of acetalization. (5) Glutaraldehyde was more reactive than glyoxal and more favorable to prevention of brittleness in the fiber. (6) Super rayon crosslinked with glutaraldehyde had relatively high strength, including knot strength, and resistance to alkali, so that blending it with cotton, which benefits from mercerization, is a possibility.