Factors Controlling Formaldehyde Release from Durable Press Cotton

Abstract

Formaldehyde release from durable press fabrics treated with dimethyloldihy droxyethyleneurea (DMDHEU) has been investigated in an effort to understand the physicochemical equilibria that control the generation of formaldehyde and its transport from the fabric to the environment. Fabric pH plays a major role in the generation of pendant N—CH20H groups and of formaldehyde by affecting the rates of hydrolysis of the crosslinks formed between cellulose and the finish and of the pendant N—CH2OH groups, respectively. Specific rate constants for the hydrolysis of C-O and C-N bonds have been determined and found to go through a minimum at pH 7, suggesting that formaldehyde release under neutral conditions is very low. Under acid conditions, a high rate of crosslink hydrolysis (C-O scission) and a proportionately low rate of N—CH20H hydrolysis lead to the generation of additional N-CH2OH groups, increasing the formaldehyde release potential of the fabric. Under alkaline conditions, on the other hand, a combination of high C—N and low C—O hydrolysis rates leads to the elimination of N—CH2OH groups, the potential sources of formaldehyde release in the fabric. The sorption equilibrium does not play a major role in formaldehyde release into water, but in a confined gas phase, formaldehyde release to the environment is controlled by the distribution coefficient of formaldehyde between cellulose and air. At ambient temperatures, the distribution coefficient is very large, reflecting the high affinity of formaldehyde for cellulose at low temperatures. Heats of sorption obtained from sorption studies at various temperatures suggest chemisorption of formaldehyde, possibly involving the formation of hemiacetals with cellulose. Since hemiacetals are hydrolytically unstable, formaldehyde is released under conditions of high humidity. At high treatment temperatures, formaldehyde binds with cellulose in an irreversible manner, forming a product that is stable to mild hydrolytic conditions, and is thus removed from the sorption equilibrium.