Preparation and characterization of novel porous PVDF-ZrO2 composite membranes

Poly(vinylidene) fluoride (PVDF)-ZrO2 composite membranes were prepared by casting and immersion into a water bath of ternary suspensions obtained by adding additional amounts of ZrO2 particles to PVDF solutions. Methods to obtain an intimate dispersion of the inorganic particles in the PVDF solutions were developed. A large variety of supported and unsupported membranes were prepared by varying some of the preparative parameters such as: the PVDF solvent (N-methyl-2-pyrrolidone or triethylphosphate), the total concentration and the PVDF/ ZrO2 ratio in the ternary dispersion. Membranes were also cast from a binary solution of PVDF and solvent for comparison purposes. All the obtained membranes were characterized by scanning electron microscope observations and ultrafiltration tests. The effect of the above-mentioned preparative parameters on the structure, flux and dextran retention properties of the membranes is discussed.

A large variety of membranes with different permeate fluxes and dextran retentions were prepared from ternary suspensions of PVDF and ZrO2 in two different polymer solvents, namely NMP and TEP. The structure of the membrane cross-sections is not practically affected by the presence of the ZrO2 but strongly depends on the PVDF solvent. The UF performance of the membrane can be properly varied by changing the PVDF solvent or the ZrO2 concentration ratio in the ternary suspension. By using a non-woven as casting support the skin layer surfaces are deeply altered as pore with typical sizes of microfiltration membranes are formed. Suspensions composed of PVDF-ZrO2-TEP produce membranes with very low porosity. This fact along with the modifications induced by the presence of the amphoteric oxide may open new avenues towards the preparation of new PVDF based nanofiltration membranes.