Preparation Of PVDF/PVDF-CTFE Blended Hydrophobic Membrane

Polyvinylidene fluoride(PVDF)is currently one of the most popular materials for preparing porous hydrophobic membranes.A variety of membrane preparation methods such as solution phase separation(NIPS)can be used to prepare porous hydrophobic membranes with excellent performance.PVDF has good mechanical strength,but the hydrophobicity and alkali resistance of the material itself is not high,which limits the application scope and cleaning methods of the membrane,especially due to the low hydrophobicity.When PVDF hydrophobic membrane is applied to membrane distillation and other hydrophobic During the membrane separation process,membrane wetting is prone to affect its service life.Polyvinylidene fluoride chlorotrifluoroethylene(PVDF-CTFE)copolymer contains more CF bonds,so it has higher hydrophobicity and alkali resistance,but the mechanical properties of the material itself are poor,and the prepared hydrophobic membrane is used in applications is restricted.In order to obtain a porous hydrophobic membrane with the advantages of both polymers,this article uses a blending method to blend PVDF-CTFE with PVDF,and prepare PVDF hollow fibers with PVDF-CTFE higher hydrophobicity and alkali resistance through the NIPS method.In this paper,the EDS blend membrane interface analysis method is used to study the film formation process of the PVDF/PVDF-CTFE system solution phase separation.It is found that there is a competition mechanism in the precipitation of different hydrophobic polymers in the casting liquid,that is,when the casting liquid When it comes into contact with water as a coagulation bath,the more hydrophobic vinylidene fluoride trifluoroethylene copolymer preferentially precipitates to form an interface(membrane surface and pore wall surface),and the less hydrophobic polyvinylidene fluoride lags behind to precipitate.Form the sponge structure behind the interface.The results show that due to the competitive precipitation mechanism,when the polyvinylidene fluoride trifluoroethylene is added at 40wt%,the total amount of polyvinylidene fluoride trifluoroethylene material is less than 50%,but it has become the interface of the porous hydrophobic membrane.The main material,the prepared PVDF porous hydrophobic membrane has a water contact angle of 95°,which is about 20°higher than that of pure PVDF hydrophobic membrane.After 3hours of strong alkali treatment,the mechanical properties of the porous hydrophobic membrane basically do not change,showing PVDF-CTFE material has the characteristics of hydrophobicity and alkali resistance;in terms of membrane strength,the tensile breaking strength of the hydrophobic membrane is 2.9MPa,and the membrane rupture pressure is 0.42 MPa,which shows the good mechanical properties of PVDF as the main material.In this paper,the study of system kinetics,alkali resistance and hydrophobicity and oleophobicity of porous hydrophobic membranes confirmed the feasibility of the EDS new blend membrane interface analysis method to study the membrane formation mechanism,and provided a new idea for the preparation of blend membranes.Aiming at the low flux of PVDF/PVDF-CTFE blended porous hydrophobic membrane,this paper uses orthogonal experiment method and single factor variable method to explore the optimal conditions for preparing porous hydrophobic membrane.By comparing the performance of the prepared porous hydrophobic membrane with PVDF porous membrane and PVDF-CTFE porous membrane,it is shown that the blended porous hydrophobic membrane prepared in this paper has higher hydrophobicity and strength,but also has advantages in membrane flux.