Preparation And Performance Study Of Composite Diluent UHMWPE/PVDF Blended Hollow Fiber Membrane

In order to improve the mechanical properties,permeability and rich pore structure of the membrane,UHMWPE/PVDF blend hollow fiber membranes were prepared by TIPS method,with mineral oil/dibutyl phthalate(DBP)as the mixed diluents.The membrane has the fibril network structure by UHMWPE.In order to study the performance of the casting solution,the viscosity of the casting solution was tested by a capillary rheometer,the cloud point of the casting solution was observed by a hot stage polarizing microscope,and the crystallization temperature of the casting solution was measured by a differential scanning calorimeter.The morphology,pore structure,permeability and mechanical properties of hollow fiber membranes were analyzed by field emission scanning electron microscope,gas-liquid interface pore size tester,flux tester,porosity and universal mechanical tester.The solid content of the system was unchanged,but the content of UHMWPE was changed.The blends hollow fiber membranes with different UHMWPE content were prepared.The results demonstrated that with the content of UHMWPE increased,the viscosity of the casting solution increased.The blend system presented a typical"sea-island"structure with UHMWPE/mineral oil as continuous phase and PVDF/DBP as dispersed phase.During cooling,the L-L phase separation between PVDF and DBP,the S-L phase separation caused by PVDF preferential crystallization,the L-L phase separation between UHMWPE and mineral oil,and S-L phase separation caused by UHMWPE crystallization occurred sequentially.The element of F had more in the outer skin layer than inside.With the increase in UHMWPE content,the L-L phase separation region of UHMWPE/mineral oil become smaller,the average pore diameter and porosity decreased,resulting in a decrease in gas flux and water flux.Finally,the rejection rate increased which could up to 80%.And the tensile strength increased by nearly one point five times.In order to further investigate the effects of different cooling temperatures on the morphology and pore structure of the membrane,blends hollow fiber membranes with different cooling temperatures were prepared.The results showed that as the cooling temperature increases,the time of phase separation and crystallization were prolonged.Therefore,the diluent droplets and crystal particles fully grew and aggregated.The average pore size and porosity of the membrane increased.However,some of the large pores subside and the number of UHMWPE micro-fibers decreased,which lead to the membrane permeability improves and mechanical properties decrease.On the basis of this,the influence of spinning temperature on the structure and properties of the membrane was studied.The results illustrated that with the spinning temperature increases,the viscosity of the casting solution decreased,and the average pore size and porosity of the membrane increased,but the porosity did not change significantly.Due to the increase in pore size and porosity,the gas flux water flux increased and the rejection rate reduced.The tensile strength was not significantly reduced,which indicated that the spinning temperature had no significant effect on the tensile strength of the membrane.