Sorption and desorption of water vapour by membranes of the polyelectrolyte complex of chitosan and carboxymethyl cellulose

Sorption of water vapour by chitosan/carboxymethyl cellulose polyelectrolyte complex membranes prepared at two different pHs was studied. A linear dependence of the water uptake (W) on time was observed for W values lower than 0.5 g of water per gram of membrane. For higher values of W diffusion becomes controlled by the relaxation of the chains, and second-order kinetics is observed. An equation that satisfactorily reproduces this behaviour is proposed. Desorption experiments were carried out at different temperatures and the W versus time curves obtained exhibited the same general pattern and were also adjusted by this equation. The approximate average diffusion coefficients were evaluated at each temperature and the apparent activation energy for the diffusion process is reported.