Studies in the changes in fine structure of cellulosic fibers during mild acid hydrolysis

Abstract

Changes in the accessibility of the fine structure of cellulose as a result of mild acid action on standard cellulose, cellulose mercerized with and without the application of tension, viscose rayon, and cuprammonium rayon have been studied with respect to changes in DP, fiber density, fiber crystallinity, moisture regain, oxidative susceptibility, and equilibrium adsorption of Chrysophenine G, Chlorazol Sky Blue FF, and Procion Brilliant Red 2Bs. Results indicate that the mild acid action on all the cellulosic fibers studied, appears to proceed in three different stages. In the initial stages the acid action is rapid and results in a sudden decrease in DP, moisture region, oxidative susceptibility, and adsorption of dyes with a simultaneous increase in fiber crystallinity and fiber density. The subsequent acid action is slower than that in the initial stages during which the extent of lowering in the values of fiber characteristis is much less, and during the final stages of acid action there is a tendency for the leveling-off of all the fiber characteristics. The extent of reduction in the values of the fiber properties and the stages during hydrolysis at which the changes take place in different cellulosic fibers depend mainly on the rate of removal of hydrolyzable fraction and the extent of crystallization of cellulose chains taking place during the acid action.