Studies in the Reaction of Formaldehyde with Unmodified, Modified, and Dyed Celluloses

Abstract

The kinetics of the reaction of formaldehyde with cotton cellulose have been studied, using acidified formaldehyde solutions containing large amounts of calcium chloride The fiber substance was steeped up to 8 hr at 16°-60° C, then treated with boiling water and conditioned. The formaldehyde yield (combined formaldehyde, CF) was then esti mated colormetrically. The reaction is resolved into two simultaneous reactions, one faster than the other. The initial fast reaction obeys first-order kinetics, while the slower reaction in the later stages appears to obey zero-order kinetics. The rate of the former increases with the concentration of the ingredients of the reaction mixtures and with rise of temperature. Further, the fast reaction reaches equilibrium within a short period from the start of the reaction. The equilibrium combined formaldehyde increases with temperature up to 42.5° C exhibiting an apparent heat for the fast reaction of ca 7 kcal/mole. The rate of the slower reaction decreases with temperature. The over-all rate of reaction is determined also by the rate of acid hydrolysis of cellulose and the rate of diffusion of the reactants into the fiber substance and water molecules away from the site of the reaction. The combined formaldehyde value at any time is directly pro portional to the formaldehyde concentration under all conditions studied, while at 16°C it is also proportional to the concentration of hydrogen chloride. Further, with increase in calcium chloride concentration it increases to a maximum and then decreases or re mains unchanged. It is concluded that the initial fast reaction is restricted to the hydroxyl groups on the surface of the fiber substance, while the slower reaction seems to take place with the free hydroxyl groups in the interior of the material.