Structural And Performance Regulation Of Ultrafiltration Membranes Produced From Blending With Block Copolymers Of Different Conformations

Anti-fouling modification has attracted lots of interest in the field of membrane materials and membrane separation.Until now,the methods including coating,grafting,chemical functionalization treatment,plasma treatment,blending,and so on,have been developed for preparation of fouling-resistant membranes Due to its simple operation and good compatibility with real production,the blending has been accepted as one of the most widely used methods.Among the modifiers used before,amphiphilic block copolymers are regarded as one of the excellent modifiers for separation membranes due to their good hydrophilicity and good durability in membrane matrix materials.Although amphiphilic block copolymers have been widely used in the modification of membranes,little work has been directed to systematically study the influence of block copolymer configuration on membrane performance.As thus,this paper proposes to study the block copolymer configuration and composition on the anti-fouling properties of the blended membrane and the structural adjustment.Firstly,di-block copolymers(PS-b-PEO)and tri-block copolymers(PS-b-PEO-b-PS)of similar composition were prepared via living/controlled polymerization.The compositions and molecular weights of block polymers were carefully analyzed by using nuclear magnetic resonance hydrogen spectroscopy(~1H-NMR)and gel permeation chromatography(GPC).Secondly,the synthesized block copolymers were added to casting solution containing the polyethersulfone(PES),and blend membranes were prepared via non-solvent induced phase inversion(NIPS).The morphologies and surface roughness of prepared membranes were analyzed by scanning electron microscope(SEM)and atomic force microscope(AFM).The reservation and surface segregation of block copolymers in membranes were determined by X-ray photoelectron spectroscopy(XPS),infrared spectroscopy(FTIR)and nuclear magnetic resonance hydrogen spectroscopy(~1H-NMR).Finally,the pure water flux,rejection rate and anti-pollution performance of the membrane were tested.The effects of di-block and tri-block copolymers on the surface hydrophilicity,roughness,pore size,retention rate,and anti-fouling performance at the same dosage and the same polymer compositions were carefully compared.We found that:(1)PS-b-PEO and PS-b-PEO-b-PS significantly changed the structure of the surface and cross-section of the PES membrane.The permeability and fouling-resistance of prepared membranes were largely improved;(2)Under the same blending ratio,PS-b-PEO-b-PS/PES blend membrane showed larger water flux while PS-b-PEO/PES blend membrane has higher rejection;(3)PS-b-PEO-b-PS/PES blend membrane presented better hydrophilicity and fouling-resistance performance because PS-b-PEO-b-PS forms loop-like conformation on the membrane surface.The conclusions obtained in this thesis will provide useful information on the preparation of blend membranes with both higher selectivity and better fouling resistance.