Study of NaCl permeability through a non-porous polypropylene film

Abstract

The possibility of NaCl permeation through a polymeric matrix of polypropylene membranes was studied. A non-porous polypropylene film, which was assembled in a flat sheet module, separates a saturated solution of NaCl from pure water. The changes of water composition were determined by the application of ion chromatography and measurements of the electric conductivity. The studies were carried out for 4 years, and the permeation of salt through the polypropylene film from the feed to pure water was not observed over this period. In the first month the results of studies were affected by the impurities, which were introduced to pure water from the installation walls. Moreover, the electrical conductivity of water was also enhanced by adsorption of components from the ambient air. The used polypropylene film demonstrated a high resistance to polymer degradation. SEM observations revealed that the film was free from micropores and cracks after 4 years of studies. The DSC examinations demonstrated only slight changes in the polymer crystallinity. FTIR spectra recorded for a new film and film assembled in the module were similar. The XPS studies did not demonstrated the presence of NaCl in the surface layer of polymer on the side of brine flow. Moreover, a significant change of material hydrophobocity did not take place over the period studied. A dynamic wetting angle measured for a new film amounted to 103–106° and was decreased to 95° on the water side and to 84° on the brine side after 4 years of contact of the polymer with water and a saturated NaCl solution, respectively.