Molecular Structure Design Of Additives For Ultrafiltration Membrane Performances Regulation

With the increasingly problem of water shortage,the protection and recycling of water resources is particularly important for human beings.Membrane technology has been applied in the desalination of seawater,water and wastewater treatment,removal of novel pollutants in water.Membrane separation technology provoid an effient way in alleviating water resources crisis.Membrane pollution is an bottleneck problem to be solved in the membrane application and development.As a result,membrane modification to obtain high flux,high selectivity,anti-fouling membrane material is an important scientific problem.In this thesis,we reviewed the modification technology of membrane,and introduced the preparation methods of polymer and the environmental application of ultrafiltration membranes.We build a series of different additives with different molecular structure via ATRP to modify cellulose acetate membrane.We explore the influence of the molecular structure design of the additives on membrane surface properties and structural function.The influences of the additive molecular structure design on the membrane pore size,surface hydrophilicity were studied systematically in a macro and micro way.Humic acid and E.coli was used as a model pollutant for membrane anti-fouling test,three different size of polystyrene particles were used for the membrane molecular intercept test.The results of this research can provide a theoretical guidance and support for the preparation of membranes with specific functions and structures regulated by the molecular structure design of polymer additives.The main conclusions and innovations of this thesis are as follows:(1)The relationship of the changes of additive molecular structure(side chain length and density)and internal structure and surface properties of modified membranes was illustrated.Two polymer additives(AS In every 100 AGU units,4long chain with 41 hydrophilic monomers AL,22 short chain with 8 hydrophilic monomers AS)grafted with the same hydrophilic monomer but in different structure were synthesized by ATRP reaction under precise control,and then,different modified cellulose acecate membrane ML and MS were prepared.The results showed that changing the polymer chain length from dense short chain into scattered long chain can improve the surface hydrophilicity of membrane,as well as antifouling property,the relative flux recovery achieved over 90%.The result showed that additive with long chain of low substitution make the most of hydrophilic monomer to achieve the biggest modification ability.This study can provide guidance for the preparation of high efficiency hydrophilic additives in membrane modification and reduce the production cost of membranes in industrial applications.(2)A method for regulating membrane pore size for pollutants seperation via changing the functional additive structure(side chain length)is proposed.Three hydrophilic additives(side chain length of A1?A2?A3 were 18?38?58)were successfully prepared by ethyl cellulose macromolecular initiator,then,three different hydrophilic modified CA membranes M1,M2 and M3 were prepared successfully.The result showed that the change of the side chain length of additives can be an effective method to prepare the membrane with the desired uniformed pore.With the increase of the side chain length of the additive polymer,the membrane pore size increased.In the interception experiments of polystyrene microspheres with different particle sizes,PS microspheres with particle size > 20 nm can be intercepted by M1,PS microspheres with particle size > 50 nm can be intercepted by M2,PS microspheres with particle size > 100 nm can be intercepted by M3,the result comfirmed the pore size regulate.Meanwhile,The hydrophilicity,water flux,antifouling property of the membrane also improved with the increase of chain length of the additive.