The structure and properties of poly(vinylidene fluoride)/ultrahigh-molecular -weight polyethylene blend hollow fiber membranes via TIPS with mixed diluents

Abstract

To synchronously improve mechanical properties and permeability of poly (vinylidene fluoride) (PVDF) membranes, PVDF/ultrahigh-molecular-weight polyethylene (UHMWPE) blending hollow fiber membranes were prepared by a thermally induced phase separation method, with mineral oil and dibutyl phthalate as mixed diluents. To study the fluidity, phase separation and crystallization behavior of the membrane-forming system, the element distribution state, morphology and pore structure of the membrane were observed by energy -dispersive X-ray testing microanalysis, field-emission scanning electron microscopy, gas-liquid interface pore size measurements and porosity measurements. Finally, the permeability, separation and mechanical properties were measured by gas flux, pure water flux, talc powder rejection rate and tensile experiments. The results showed that solid-liquid phase separation caused by PVDF preferential crystallization, liquid-liquid phase separation between UHMWPE and mineral oil, and solid-liquid phase separation caused by UHMWPE crystallization occurred sequentially during cooling. The connectivity of membrane was enhance by UHMWPE microfiber. When water flux of the blending membranes reached 8000 L/m2/h/MPa, the strength also reached 11.8 MPa. The membranes had outstanding permeability and mechanical property simultaneously. With UHMWPE content increased, the porosity and average pore size decreased, which caused a decrease in the flux and an increase in the rejection rate.