Preparation And Performances Of PVDF Microporous Membrane Via Immersion Precipitation With Microrolling

Membrane separation technology is a new separation and purification technology,compared with the traditional separation technology,it has some advantages in operation process,separation efficiency,energy saving and so on.In recent years has been widespread concern.In the membrane contactors separation processes and oil/water separation processes,ensuring no wetting was the key to membranes for a long time,which was largely depend on the hydrophobic of microporous membranes.The method of micro-rolling combining with immersion precipitation was proposed for preparing high hydrophobic poly?vinylidene fluoride??PVDF?microporous membranes.The sandblasting roller with artificial microstructure were used as the substrates,while N-methyl pyrrolidone?NMP?was respectively chosen as solvent in the process and Dioctyl Phthalate?DOP?as additive,exploring a simple method for the preparation of highly hydrophobic membranes.In the experiment,the semi-gelled membranes and the etched completely gelled membranes were rolled respectively.First,determining the semi-gelling agent is pure water or solvent NMP aqueous solution in the semi-gelled membrane rolling test,the gel kinetics experiments of each semi-gelling agent were made respectively.The study found,the formation of different structural layers in the microporous membranes corresponds to different gel rates,indicating that the formation of the microporous membrane is a diffusion-mass transfer process and polymer inflated process.Choosing final mass transfer period to the polymer inflated period as half gelation time,to roll the surface of membrane during this time.The results showed:each condition was changed,which made the contact angle of the surface up to 142.3°,the membrane flux was more than 0.2m³·m^-2·s^-1.The rolling of the completely gelled membranes need to erode the membrane surface.Estimate the erosion ability of each etchant by the solubility parameter method,electing etchant composition is NMP/BA or NMP/H₂O,the volume ratio is8:2,7:3,6:4.There are two erosion methods,one is spraying erosion,the other one is immersion erosion.Use conventional methods to prepare PVDF membranes.Roll the surface after etching the membranes with an etchant,the highly hydrophobic PVDF membrane was obtained by re-gelation,the contact angle of the surface up to 138.9°.Comparison the results,the best erosion is NMP/BA which ratio is 7:3,followed by NMP/H2O,the ratio is 8:2.Finally,the continuous preparation process and equipment of highly hydrophobic PVDF microporous membrane were discussed.Three continuous preparation schemes were proposed according to the above experimental procedure,and produced a self-rolling device.Experiments were carried out using the device under better experimental conditions.The obtained membrane has a smooth performance with a contact angle of up to 143.4°,the membrane flux was more than 0.2 m³·m^-2·s^-1.