Preparation of composite fiber membranes with asymmetric wettability and oil-water separation performance
Objective Emulsified oil is known to be difficult to separate due to the close combination of water and oil,and Janus composite membrane with multiple wettability is studied aiming to effectively separate the emulsified oil.In this study,the Janus structure is constructed by two layers of fiber membranes with different wettability,and the difference of micro-nanometer size is used to solve the problem of high separation efficiency and low flux of composite membranes,so as to prepare composite membranes with both high separation efficiency and high flux.Method Janus composite membranes with micro-and nano-structures were prepared from cellulose nanofiber membranes as hydrophilic layer and polypropylene meltblown nonwovens as hydrophobic layer by hot pressing method.The prepared cellulose-polypropylene composite nanofiber membranes were characterized using scanning electron microscope,capillary flow pore size analyzer and contact angle tester.The composite membranes were also tested for pore size,Laplace force,separation performance,repeatability and generalizability.Results The cellulose nanofiber membrane prepared by electrostatic spinning technology using cellulose as raw material.The results showed that when the spinning voltage was 25 kV,the spinning rate was 5 mL/h and the spinning time was 16 h,the cellulosenanofiber membranes showed the bestperformance,with an average pore size of 5.029 μm and a thickness of 0.281 mm.The cellulose nanofiber membrane showed amphiphilicity in air,oleophobicity under water,and hydrophilicity under oil,which can be used as a hydrophilic material for Janus structure.Polypropylene meltblown nonwovens exhibits hydrophobicity and lipophilicity in air,hydrophobicity under oil,and lipophilicity under water,and can be used as a hydrophobic material for Janus structure.The Janus membrane was then prepared by laminating cellulose nanofiber membrane and polypropylene meltblown nonwovens in combination with hot pressing process.The areal density of polypropylene meltblown nonwovens,hot pressing temperature and hot pressing pressure were found to affect the performance of the composite membrane.According to the experiments,when the grammage of polypropylene meltblown nonwovens was 30 g/m2,the hot pressing temperature was 130 ℃,and the hot pressing pressure was 30 N,the separation efficiency and flux of the composite membrane are the most balanced,with 98.8％and 9 789.9 L/(m2·h),respectively.The composite membrane demonstrated excellent reuse performance,and after 10 cyclic use,its separation efficiency still maintained at 98％,and the flux 9 444.5 U(m2·h).The composite membrane showed significant separation effect on these oils to be mentioned,for which the separation efficiency was more than 98％,and the flux was more than 9 000 L/(m2·h).Conclusion In this study,Janus composite membranes with cellulose nanofiber membrane as hydrophilic layer and polypropylene meltblown nonwovens as hydrophobic layer were prepared.The composite membranes prepared under optimum process conditions achieved the best separation efficiency and flux of 98.8％and 9 798.8 L/(m2·h),respectively.The composite membranes had excellent reusability,and the separation efficiency could still maintain 98％and the flux reached 9 444.5 L/(m2·h)after 10 cyclic use.The composite membranes had significant separation effects on all five common emulsified oils.This idea achieves a balance between separation efficiency and flux,and has theoretical value and practical significance for the development of emulsified oil separation membranes.
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