Preparation And Properties Of Superhydrophobic PVDF Hybrid Membrane

Polyvinylidene fluoride（PVDF）is an ideal membrane material for the preparation of hydrophobic membranes because it has excellent thermal stability,chemical stability,and low surface free energy.The superhydrophobic PVDF membrane can be prepared by the water mist induced phase separation method,but the mechanical properties and mechanical stability of the membrane are poor,and the surface structure of the membrane is easily damaged,resulting in the loss of superhydrophobicity.In order to improve the mechanical properties and surface durability of the membrane,three kinds of inorganic nanoparticles with high strength and hardness were used as additives to prepare PVDF hybrid membranes by optimized water mist induced phase separation method.Firstly,the membrane preparation conditions of superhydrophobic PVDF membrane prepared by water mist induced phase separation were optimized.The effects of polymer dissolution temperature and maturation time of casting solution on the structure and performance of PVDF membranes prepared by water mist induced phase separation were investigated.The results showed that when the polymer dissolution temperature increases,the gas flux of the membranes increases,water contact angle and tensile strength of the membrane surface decrease;when the maturation time of casting solution is prolonged,the gas flux,water contact angle and tensile strength of the membrane all increase and then decrease.Within the experimental range,the appropriate polymer dissolution temperature was 60℃,and the better maturation time of casting solution was 3d.PVDF/SiO₂,PVDF/MWCNTs,PVDF/Gr hybrid membranes were prepared with silicon dioxide（SiO₂）nanoparticles,multi-walled carbon nanotubes（MWCNTs）and graphene（Gr）as additives,respectively.The effects of the mass content of nanoparticles on the structure and performance of PVDF hybrid membranes were investigated.The results showed that the surface of the three hybrid membranes all have the network structures of adhering spherulite particles.The cross-section of the membranes was symmetrical spherulite particle accumulation structure.When the content of nanoparticles increases,the size of the spherulites decreases,and the porosity and gas flux of hybrid membranes decrease.Among them,tensile strength,peel strength and water contact angle of PVDF/SiO₂ hybrid membranes increase first and then decrease,tensile strength,peel strength and water contact angle of PVDF/MWCNTs hybrid membranes also increase first and then decrease,and both peel strength and water contact angle of PVDF/Gr hybrid membranes increase.After 50 cycles of wear,water contact angle on the surface of the PVDF/MWCNTs and PVDF/Gr hybrid membranes were still above 150°,and water contact angle on the surface of the PVDF/SiO₂ hybrid membranes was above 145°,all of which show good durability.Based on the above research,performance evaluation was performed on the superior membrane samples of the three kinds of hybrid membranes.Compared with the non-added PVDF membranes,the hybrid membranes maintain excellent superhydrophobicity,the mechanical properties was significantly improved,and the durability of the surface structure of the membrane surface structure was improved.The durability of the three hybrid membranes were PVDF/MWCNTs>PVDF/Gr>PVDF/SiO₂.The vacuum membrane distillation experiments of fresh brine showed that the rejection rates of the three hybrid membranes are all above 99.9%,showing good operational stability.Among them,the PVDF/MWCNTs hybrid membrane had the smallest flux attenuation rate.