Effect Of Surfactant On The Film Formation Process Of PVDF Hollow Fiber Membrane

Polyvinylidene fluoride(PVDF)is one kind of fluorinated membrane materials,which has low surface energy and excellent performance.PVDF membrane has been widely used in the field of membrane separation including water purification,bioseparation,chemical sensing and energy storage,because of the advantages of high separation efficiency,low energy consumption and other excellent performance.However,in the process of the membrane preparation,the traditional ultrafiltration membrane is easy to form a relatively dense layer.Presence of a dense skin renders the membrane unsuited to sieving-based separation processes and high permeation fluxes dare demanded.Therefore,regulating the separation membrane structure and change the performance of membrane separation become one of the important !methods.In this paper,polyvinylidene fluoride(PVDF)hollow fiber membranes were fabricated by NIPS using dual surfactants(Span80 and Tween80)as the additive.Exactly,the dual surfactants have the specific value of Hydrophilic-Lipophilic Balance(HLB).Here we evaluated the Hydrophilic-Lipophilic Balance offset value(AHLB)on the membrane relative properties such as the pure water flux,SEM etc.As results indicated,in the membrane preparation process of NIPS,the surfactant could activate the interface of polymer concentrated phase when the casting dope transits from the stable region to the unstable region.Also,when the value of HLB approached to 10,the interfacial activation of the dual surfactants was obvious,eventually leading to more pores on the skin layer.Meanwhile the membrane intrinsic resistance was the lowest.They are also featured by the most probable aperture moving toward the maximum pore size.Most importantly,compared to the separation membrane without the surfactant,the pure water flux increased by 277%,reaching up to 1015 L/(h·m2).This research introduces a new pore-making strategy of the surfactant interfacial activation on polymer concentrated phase,which involves a novel film-forming mechanism in NIPS.Because of the dual surfactants can activate the interface of the metastable concentrated phase region of the casting dope.Under the unchanged condition of the HLB(HLB=10),in this part,the effect of surfactant content on the water flux,skin structure(SEM),and other properties of the membrane are investigated.As results indicated,similar to the principle of the critical micelle concentration(CMC),the surfactant interfacial activation on the metastable concentrated phase region has a critical value.In view of the film-forming system of this paper,the critical point is 1.5 wt.%.When the surfactant content increases to 1.5 wt.%,the pure water flux increases by 277%.Meanwhile,the skin of the obtained membrane has the most pores.However,after the surfactant content goes beyond critical point,the properties of the membrane have no significant difference.In summary,this method makes full use of the property of CMC to regulate the opening of skin,introducing a novel strategy to prepare membrane.