Fabrication and characterization of poly (vinylidene fluoride) (PVDF) flat sheet membranes with diluent mixtures.

In order to obtain the separation membranes possessing outstanding water permeability and mechanical property, poly (vinylidene fluoride) (PVDF) flat sheet membranes were fabricated via the low-temperature thermally induced phase separation method (L-TIPS) by the ternary system of PVDF/dibutyl phthalate (DBP)/dioctyl phthalate (DOP). The effects of PVDF concentration, the concentration ratio of diluent mixtures, cooling rate and coagulation bath temperature on membrane structures and performance were studied. The results showed that with the increases of PVDF and DOP concentration, the spherulite structure of the membrane was gradually transformed into a bicontinuous structure. The pure water flux and porosity of membrane decreased, but the tensile strength and elongation at break of membrane increased with the increase of PVDF. When the coagulation bath temperature and the casting solution temperature were similar, and the cooling rate was slowed down, the pure water flux and the average pore size of the membrane increased, while the porosity is almost unchanged. Therefore, when the mass fraction of PVDF was 40% in the casting solution and the casting solution system was cooled under the condition of 20 °C air bath cooling and 60 °C of coagulation bath temperature, the separation membranes were prepared which possessed good water permeability and the fine mechanical property, the pure water flux was 325.65 L/(m²⋅h) and the tensile strength could reach 1.80 MPa. [ABSTRACT FROM AUTHOR]