20—A STUDY OF THE SORPTION OF FORMALDEHYDE FROM AQUEOUS SOLUTION BY CELLULOSE

Abstract

The concentration of an aqueous solution of formaldehyde has been found to diminish after introduction of cellulose and the lowering is attributed to preferential sorption. The sorption is manifested only slowly at room temperature, requiring over 24 hours at 25°C to reach equilibrium, but the phenomenon is reversible and cellulose is recovered unchanged after rinsing for a sufficient time in water. The rate of sorption is approximately doubled for each 10° rise between 5 and 45°C (giving an energy of activation of 13 kilocalories per mole for both cotton and viscose rayon) and is slightly increased at high and low values of pH. The equilibrium is little affected by changes of temperature or hydrogen ion concentration, by pretreatment of the cellulose, or by the presence of additives in the formaldehyde solution, but it is greater in regenerated than in native cellulose, and it increases with increase of formaldehyde concentration (conforining to isotherms of the Langmuir type) and over a limited range is approximately proportional to the square root of the concentration. As accompaniments of sorption, the wet strength and birefringence of regenerated cellulose decline (but recover on steeping in water). The system is compared with the uptake of direct dyes by cellulose, and a theory is advanced that the sorption of formaldehyde depends on a diffusion process and ultimately on chemical substitution of accessible hydroxyl groups by hemiacetal groups, i.e., formation of methylolcelluloses.