Study On The Structure And Properties Of PES Membranes By Two-steps Formation

PES is a good membrane materials which possess excellent properties, such as high mechanical strength, good chemical stability and resistance to heat, pressure and erosion, Its temperature of glass transition is 225. PES is used to make ulfrafiltration membrane and nanofiltration membrane. Hemofiltration (HF) is an important applied field, membranes can be used for HF, which requires that the clearance rate of toxins such as urea and creatintine should be high and water flux should be moderate. Membranes made by single-bath coagulation method either have high clearance rate and high water flux or have low clearance rate and low water flux.The dual-bath coagulation method suggested by J.A.van't Hof could be used in membranes with high selectivity clearance rate of low-molecular weight substances and moderate water flux theoretically. Therefore it may be applied in the field of hemofiltration.To improve and optimize the performance of the PES ultrafiltration membrane applied in the HF, here the flat membranes and hollow fiber (HF) membranes are made in certain conditions based on the dual-bath coagulation method where PES is used as the membrane material, DMSO as solvent and PVP &PEG as additives This paper includes five parts as follow:1. The effects of PES concentration and temperature in casting solution on the structure and properties on PES ultrafiltration membranes are studied. As the concentration of PES solution increases, the pure water flux decreases and the clearance rates of low-molecular weight substances such as urea and creatintine first increase, then decrease, and increase slightly at last. As the temperature increases, the water flux first decreases evidently, then increases slightly and the clearance rates of low-molecular weight substances first increase, then decrease shaply.2. The effects of pre-evaporation time on the structure and properties of PESmembranes by two-step formation. As the pre-evaporation time increases, the water flux first decreases then increase, at the 23rd second it reaches the minimum value; the clearance rates of urea and creatintine increase first then decrease and increase a little at last. As the pre-evaporation time increases, the holes on the membrane surface becomes smaller and less, dense layer is becoming more evident with large and deep holes in supporting layer; and porosity increases as well- as average hole diameter decreases.3. The effects of the component and the time in the first coagulation bath on the structure and' properties of PES membranes are studied. The dense top layer as well as porous supporting layer can be made by duel-bath coagulation method simultaneously. When 2-propanol (IPA)is used as a coagulation reagent, it has better dissolving ability with solvent than 1-butanol and 1-pentanol. As the time in the first coagulation bath increases, the water flux decreases and the clearance rates of urea and creatintine both first increase, then decrease and increase a little at last.4. The effect of the temperature and concentration of the second coagulation bath on the structure and properties of PES membranes are studied. As the temperature of the second coagulation bath increases, the water flux increases and the clearance rates of urea and creatintine first increase then decrease and increase a little at last. As the DMSO concentration (wt/wt) in the second coagulation bam increases, the water flux and the clearance rates of urea and creatintine first decrease men keep in a relatively low level and increase at last.5. The effects of spinning conditions on the structure and properties of PES HF membranes by two-steps formation are studied. The spinning conditions include spinning methods, the pressure and types of filling liquid, the PES concentration, the molecular weight of PVP and PEG and the coagulation length in the first coagulation bam. The spinning method should be Dry-spray wet-spinning method is adopted. As the pressure of filling liquid increases, the inrier and outer...