Research On The Structure Regulation And Surface Modification Of PVDF/PA6 Blend Membrane Prepared Based On TIPS Technology

Poly?vinylidene fluoride??PVDF?,a crystal polymer with higher thermal stability,chemical resistance and better mechanical strength,has been used as the main membrane material.During the using process,the membrane have low water flux,weak anti-fouling property and short operating time due to the hydrophobic of PVDF.Therefore,Hydrophilic modification of PVDF is very significant.Blending modification and grafting modification are common methods.The membrane prepared via the thermally induced phase separation?TIPS?technique,possessed higher mechanical strength,narrow pore size distribution and less factors of influencing microstructure.Presented effective method to tailor the microstructure of membrane and enhance the hydrophilicity,permeability,anti-fouling performance,mechanical property of membrane via the combination of TIPS and blending modification and grafting modification.The PVDF/PA6 flat blend membrane was prepared via TIPS process using water-soluble diluent mixture.The effects of different PVDF/PA6 on the membrane forming process,membrane microstructure and membrane properties were investigated.The results showed that dope solution system occurred S-L phase separation with the addition of PA6.The microstructure of membrane changed from the spherulites to the somewhat opened cellular pores,which can be attributed to the co-effect of TIPS and NIPS.The membrane formation mechanism about S-L phase separation of TIPS by combining the pore-forming effect of PA6 and restricting PVDF crystallization to form somewhat opened cellular pore was proposed.Also,the introduction of PA6 reduced the shrinkage of the membrane,increased the porosity and hydrophilicity,improved the rejection of petroleum ether-in-water emulsion and Congo Red?CR?,enhanced the anti-fouling capacity,and the pure water flux increased from 12.8 L m^-2h^-1?M0?to 298.3 L m^-2h^-1.The morphology of PA6 within the matrix changed from the dispersed phase?particle or fiber?to the continuous phase?network fiber?with the addition of PA6,which in turn the breaking strength increased from 1.91 MPa?M0?to 5.85 MPa?M3?,breaking elongation increased from 18.04%?M0?to 39.4%?M2?and the corresponding mechanisms of strengthening and toughening were developed from the PA6 of crystal particle,fiber and network fiber,respectively.The poly?vinylidene fluoride??PVDF?/polyamide6?PA6?hollow fiber membrane was prepared via thermally induced phase separation?TIPS?process based on the PVDF/PA6 of flat membrane.The effect of the PVDF/PA6 and the air gap on the membrane microstructure and membrane properties were investigated.The results showed that the introduction of PA6 reduced the thickness of the membrane surface,and the spherulites can be observed from membrane due to the instant chill of the dope solution.The membrane hydrophilicity,the pure water flux of external pressure increased from 6 L m^-2h^-1?M0-1?to 150 L m^-2h^-1?M2-1?and the morphology of PA6within the matrix changed from particle to fiber with the addition of PA6.The amino of PA6 provides a reaction site for graft modification on the surface of hollow fiber membrane.Tanning acid,a kind of organic material with more phenolic hydroxyl group,was used as the modifier.Grafted TA on the surface of PVDF/PA6 hollow fiber membrane via the reaction of amino?PA6?and the phenol?TA?.The effect of TA on the microstructure of upper surface and matrix was discussed.The hydrophilicity,permeability,anti-fouling capability and anti-fouling mechanism of the membrane were investigated.The results of Raman spectroscopy were proved that the amino reacted with the phenol to obtain PVDF/PA6 hydrophilic modified membrane.The result of nano-IR showed that a layer of TA was distributed on the outer surface of the membrane.The hydorphilicity and anti-fouling property of N2 were improved.This is reasonable because the phenolic hydroxyl group was distributed on the outer surface of N2.In addition,the phenolic hydroxyl group of TA was complex with Fe³⁺,further increased the density of membrane surface and the rejection of negative dye.