A Study of Some Physical Problems of Water Condition and Mass Transfer in Cellulose Acetate and Dynamic Membranes

Abstract

The paper presents experimental study of physical water condition and mass transfer in cellulose acetate and dynamic semipermeable membranes by infrared spectrometric and hydrodynamic methods. The authors found that OH-groups of cellulose acetate form a nonequilibrium grid of hydrogen bonds between molecules and their fragments in the amorphous phase of the semipermeable membrane in the air-dried sample. The water molecules adsorbed on active —OH and —C = O groups, particularly in the amorphous phase, create additional negative charge on the molecules of cellulose acetate resulting from the orientation of the water dipoles, which leads to electrostatic repulsion of broken, stranded molecule fragments and straightening of polymer molecule while breaking intermolecular hydrogen bonds. Thermogravimetric studies to find out the structural organization of hydrogen bonds and water condition in the samples of the semipermeable polymeric MGA-95 membrane showed that at temperatures in the air-dry and water-saturated samples the membrane degradation process starts and ends with mass loss and endothermic effect. The research proves the fact of dynamic membranes formation on the ultrafilters from water starch solutions. Due to the changes in condition and volume of water in the dynamic layer of the membrane, it is possible to change kinetic coefficients, i.e. to regulate the process of baromembrane separation of industrial water solutions. Electro-kinetic characteristics of reverse osmosis semipermeable membranes were studied. The experimental curves of the potential depending on sorption of sodium bicarbonate by MGA-95 and LSA-100 membranes were obtained. The discrepancy between the calculated and experimental data did not exceed 10 %. The method devised for determining the membrane potential in the process of sorption of sodium bicarbonate can be used as a testing methodology of polymeric semipermeable membranes.