The Study Of The Structure And Properties Of Cellulose Acetate Ultrafiltration Membranes With Blending Modification

At present,ultrafiltration technology is one of the most popular water treatment technologies,which has the advantages of high efficiency,energy saving and low cost.In this study,cellulose acetate(CA)was selected as the membrane matrix due to its excellent properties,especially biodegradability,and the ultrafiltration membrane was fabricated through the method of immersion precipitation phase transformation.In order to improve the performances of cellulose acetate ultrafiltration membrane during water treatment processes,such as low permeability,poor mechanical property and easy to be polluted,the cellulose acetate composite ultrafiltration membrane with excellent performance were prepared by blending with hydrophilic filler,and the interaction mode and bonding mechanism between the polymer blends were investigated.Graphene oxide(GO)was used as hydrophilic filler to modify CA ultrafiltration membrane because of its rich oxygen-containing functional groups.With the increase of GO content,the hydrophilicity,water flux and antifouling performance of CA/GO composite membranes were improved obviously.When the GO content is 0.09 wt%,the water flux of the composite ultrafiltration membrane reached the maximum value of 147.78 L/(m²·h),which is 49.29%higher than that of the pure membrane(98.99 L/(m²·h)).Whereas,GO nanosheets tend to stack due to their strong tendency for polymerize.To solve this problem,the composite nano filler HKUST-1@GO was fabricated by modifying GO using MOF,and the effect of HKUST-1@GO on the performances of composite ultrafiltration membrane was compared.The results show that MOF@GO can effectively improve the porosity and pore size of the membranes,reduce the roughness of the membrane surface,and improve the hydrophilicity of the membrane surface.Under the same amount of GO,the performance of CA/MOF@GO composite ultrafiltration membranes is better than that of CA/GO membranes.When the content of GO(HKUST-1@GO)is 0.12wt%,the pure water flux and FRR value is 183.51 L/(m²·h)and 88.13%,respectively,which also has the highest antifouling ability.Taking CA/GO and CA/MOF@GO composite ultrafiltration membrane as the research object,the blending modification of ultrafiltration membrane was further investigated by studying the compatibility,rheological properties and bonding forms between the blends.The results confirm that the non-newtonian fluid index of all the casting solution is less than 1,and the membrane solutions are pseudo-plastic fluid.The results show that there is a good compatibility between the hydrophilic filler and CA casting solution,that is,?[?]m>0.The filler and polymer are entangled and influenced by hydrogen bond,which can not only improve the original performance of the membranes,but also endow the membranes with the unique performance of the filler.The lignocellulose(LCNFs)with different lignin content shows linear structure and high crystallinity.The diameter of LCNFs is also affected by lignin content,and the diameter of LCNF₄ is 3?40nm.The effects of different LCNFs on the structure and properties of composite ultrafiltration membrane were investigated by blending it with CA membrane solution.The results show that the pore size of CA/LCNF₄ is 45.97 nm,the pure water flux and FRR are 188.23 L/(m²·h)and 86.07%,respectively.Meanwhile,CA/LCNF₄ possesses the highest tensile strength of 7.08 MPa and strain-at-break of 12.21%,which is higher than that of CA membrane.In order to further improve the comprehensive performance of the membrane,HKUST-1@LCNFs was added to the casting solution to prepare CA/MOF@LCNFs.Compared with other composite ultrafiltration membranes,M6 has the best comprehensive performance.Its pure water flux is 207.32 L/(m²·h),FRR is 90.56%,tensile strength and elongation at break are 7.83MPa and 13.12%,respectively.The study proves that HKUST-1@LCNFs has great potential in the application of membrane blending modification.