Application of cellophane films as nanofiltration membranes

The prospects for use of commercially produced cellophane as a membrane material for organic solvent nanofiltration have been studied. The effect of cellophane film conditioning with aqueous ethanol mixtures with a gradually varying concentration (from ethanol to water and from water to ethanol) has been examined. It has been shown that such treatment increases the ethanol permeability by more than two orders of magnitude in comparison with the untreated sample. The obtained value of the ethanol permeability coefficient for the treated cellophane is comparable with that for highly permeable glassy polymers. The study of cellophane swelling in aqueous ethanol solutions has revealed that the formation of porous structure takes place during the cellophane treatment process as a result of an increase of the interchain distances in the film. The observed high permeability of ethanol is associated with the fact that the porous structure formed is preserved when water is replaced by ethanol. The main factors affecting the membrane flux are the viscosity of the liquid and degree of cellophane swelling in this liquid. It has been also shown that the rejection coefficients of some dyes with molecular mass in the range of 350 to 626 Da from ethanol agree well with the hydrophobicity/hydrophilicity of the solutes. The rejection coefficients of anionic dyes in the case of water are significantly higher than in ethanol (R(EtOH) = 55% -> R(H2O) = 97% for Orange II and for Remazol Brilliant Blue R) despite the higher swelling degree of cellophane in water. This behavior is explained by the increase of the solvation shell of the solute molecules and narrowing of the transport channels, in good agreement with the assumption of the sieving mechanism of separation by nanofiltration.