Polymer International 38 zyxwvutsr (1995) 45-52 zyxwvuts Sorption and Desorption of Water Vapour by Membranes of the Polyelectrolyte Complex of Chitosan and Carboxymethyl Cellulose C. Peniche-Covas," W. Arguelles-MonaP* zyx Centro de Biomateriales, IMRE, University of Havana, Havana 1O400, Cuba zyxw & J. San Roman Instituto de Ciencia y Tecnologia de Polimeros, Juan de la Cierva 3,28006 Madrid, Spain (Received 14 February 1995; accepted 20 March 1995) Abstract: Sorption of water vapour by chitosanfcarboxymethyl cellulose poly- electrolyte complex membranes prepared at two different pHs was studied. A linear dependence of the water uptake zyxwvu (w) on time was observed for W values lower than zyxwvuts 0.5g of water per gram of membrane. For higher values of W diffu- sion 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. Key words: polyelectrolyte complex membranes, water vapour sorption and desorption, chitosan, carboxymethyl cellulose. I NTRO DU CTlO N the chemical and physical properties of the membrane induced by changing local conditions (such as PH).~ Polyelectrolyte complexes zyxwvutsr (PECs) result from the inter- In spite of the relatively high moisture sorption of action of macromolecules carrying complementary ion- PECs, water sorption kinetic studies on these kind of izable groups. They have been proposed for the design materials are scarce. A study of successive differential of drug delivery systems,' protein separation,2 anti- sorption of water vapour on to poly(acry1ic acid)/ coagulant coating^,^ and membranes for separating poly(4-vinylpyridine) complexes revealed that water materials4 or even as skin s~bstitutes,~ among other sorption was controlled not only by a diffusion mecha- applications. nism, but also by the relaxation of polymer chains.' The It has been stressed that perhaps the main expecta- results of sorption of water by 1 : 1 and 1 : 2 complexes tion of PEC membranes is the possibility to control the of poly(acry1icacid) and poly(4-vinyl-N-ethylpyridinium rate and selectivity of fluxes for solutes by changes in bromide) suggested that the two complexes had an ana- logous morphology and that they underwent similar * To whom correspondence should be addressed. structural changes during sorption. The sorption rate Polymer International 0959-8 103/95/$W.O0 zyxwvut 0 1995 SCI. Printed in Great Britain 45