Polyelectrolyte complexes of sulfoethyl cellulose–chitosan: effect of the structure on separation properties of multilayer membranes

Membranes of a Simplex type with diffusion layers from sulfoethyl cellulose (SEC) and chitosan were investigated. Aromatic poly (amide imide) (PAI-O) synthesized by the low-temperature polycondensation from dicarboxyphenylphtalimide dichloranhydride and 4,4′-diaminodiphenyl ether was used for the support preparation of the composite membrane. Porous support films with an average pore size in the skin layer of 8 nm, were obtained from PAI-O under conditions of a phase-inversion process. Transport characteristics of membrane samples obtained were tested in processes of the aqueous ethanol pervaporation. All membranes are selective in the isolation of water from 96 wt% ethanol solution. In the case of the SEC layer at the top of composite membrane the selectivity is very high and a water concentration in the permeate reaches 100 wt%. The most selective membranes contained PEC based on counter-ions with the same degree of substitution of hydroxyl groups. The structure and morphological features of multilayer films studied by X-ray diffraction method, scanning electron microscopy and energy-dispersive X-ray microanalysis were discussed in view of a ratio of ionogenic groups of polyelectrolytes and a concentration of their solutions. The boundary of the counterion layers was visualized, as well as the polyelectrolyte complex (PEC). A formation of the PEC layer in the film obtained on a glass plate was shown to occur with the ordering of chitosan chains resulting both hydrated and anhydrous polymorphs, while the formation of the same film on the PAI-O substrate led only to the anhydrous form of chitosan.