Apparent dissociation constant of cellulose gum acid

Abstract

Gums are widely used in the paper, textile and petroleum industries. Gums, such as carboxymethyl cellulose (CMC) is synthetically derived from cellulose are used for microencapsulation of medicinal and food products. The aim of the study was to determine its ionization properties and acidic property. The dissociation behaviour of cellulose gum has been investigated by potentiometric titration. The apparent acidity constant, pKa and the intrinsic acidity constant, pK0, have been determined from potentiometric titrations of carboxymethyl cellulose [degree of substitution (DS) = 0.70-0.85] in salt-free aqueous solutions of various concentrations at 20 °C. Furthermore effect of different neutralizing agents were tested on the titration curves. It was found that the extended Henderson-Hasselbalch equation reproduced measured data well and the dissociation suppressed progressively either by decreasing CMC concentration or with increasing counterion size. The concentration dependence of pH for different values of degree of dissociation (α), was found in the following form for CMC (degree of substitution = 0.70-0.85), [pH]0α = 5.04 + 2.72 log [α/(1-α)].