Effect of acetyl content on the sorption isotherm of water by cellulose acetate: comparison with the thermal analysis results

In this study, the sorption isotherms of water vapor by cellulose acetate for various acetyl contents were measured. The BET adsorption theory was modified for the system which has two different kinds of energy levels in the water adsorption sites, i.e. a hydroxyl group and an acetoxyl group, and applied it to the experimental results in order to examine the effect of acetyl content on the sorption isotherm of water using the parameters which represented the total number of adsorption sites, Vm, the interaction energy between water and the adsorption sites, K, and the number of adsorbed layers, n. Vm and K decreased with an increase in acetyl content and n remained constant. The apparent activation energies of the water desoption were also determined using differential thermal analysis. They are nearly constant with an increase in the acetyl content.