The Study Of Polyethersulfone Ultrafiltration Membranes

Polyethersulfone(PES)is one of the most prospective polymers to form ultrafiltration(UF)and nanofiltration(NF)membranes due to its favorable characteristics,i.e.mechanical stability,wide pH tolerance,fairly excellent resistance to chlorine and organic solvents.Besides,PES membrane has been widely used in the field of medical treatment especially for the blood purification due to its excellent biocompatibility.Most PES membranes are prepared by nonsolvent induced phase separation(NIPS),which are characterized by a finger-like and macrovoids structure.These finger-like pores and macrovoids actually act as a structural defect,which usually weaken the mechanical strength and undermine the integrity of membranes.Therefore,it is necessary to avoid the formation of macrovoids during the phase inversion process.In this paper,a certain amount of nonsolvent additives(NSAs)are added to the casting solution to avoid the formation of macrovoids.Besides,different membrane forming conditions were studied to show their influence on the properties and structure of membranes,where flat and hollow fiber membrane with sponge like cross-section structure were prepared and were analyzed through scanning electron microscopy(SEM),contact angle test,pure water flux test,retention to BSA test,mechanical strength test and so on.The specific research results of this paper are described as follows:1.The effect of different PES/NSA/dimethylacetamide(DMAc)systems was discussed to show their influence on structure and properties of PES flat sheet membrane,especially the PES/alcohol-A/DMAc system.The results show that increasing the mass ratio of alcohol-A,coagulation bath temperature(CBT)and concentration of polymer facilitate the formation of sponge like structure.Besides,PES/alcohol-B/DMAc system,PES/alcohol-C/DMAc system,PES/alcohol-D/DMAc system are all lower critical solution temperature(LCST)systems.The membranes prepared from these systems all have high mechanical strength with sponge like structures.Due to the higher water flux,alcohol-A was chosen to be the nonsolvent additive to prepare PES hollow fiber membranes.2.The PES hollow fiber membranes were prepared via NIPS from a spinning dope containing PES/alcohol-A/poly(vinyl pyrrolidone)(PVP)K30/DMAc.The results show that,as the outer coagulation bath temperature increases,the cross-section structure of PES hollow fiber membranes changes from double-layer finger-like pores to one-layer finger-like pores with sponge like structure.When ethanol aqueous solution and DMAc aqueous solution are used as outer coagulation bath,the cross-section structure of PES hollow fiber membranes changes from double-layer finger-like to one-layer finger-like structure,and pure water flux has a tendency to increase,retention to BSA changes a little and mechanical strength has a tendency to increase as the concentration of ethanol and DMAc increases.When the inner coagulation bath is 74 wt%DMAc aqueous solution and the outer coagulation bath temperature is 52?,the sponge like structure accounts for the largest proportion of hollow fibers.3.As the concentration of PES increases from 14 wt%to 18 wt%,structure of hollow fibers changes from totally sponge like to finger-like structure,pure water flux decreases sharply,retention to BSA increases,mechanical strength increases firstly and then decreases.4.Different kinds of additives in outer coagulation have different effects on structure and properties of hollow fiber membranes.All of the PES hollow fiber membranes have one layer finger-like pores near the inner wall,and the membrane with T-1 has the largest proportion of sponge like structure.The membrane with T-1 has the max pure water flux(521.7 L m-2 h-1),the membrane with T-5 has the max retention to BSA(84.3%%),membrane with T-7 has the max tensile strength and break elongation.