Study On The Morphology And Performance Of PES And PES Blend Membranes

In this work, the phase separation behavior and the rheological properties of thecasting solution of Polyethersulfone (PES) prepared with dimethyI lacetamide(DMAc) were studied, and PES flat-sheet membranes and hollow fiber membraneswere prepared. Moreover PES and Phenolphthalein polyethersulfone(PES-C) wereblended, and PES/ PES-C blend membranes including flat-sheet membranes andhollow fiber membranes were prepared, The mechanism about pores forming on theskin layer of PES/PES-C blend membranes is put forward.The research is as follows:1. The phase separation behavior of PES/DMAc/nonsolvent systems wasinvestigated.The phase separation behavior of PES dope was studied according to the linerizedcloud point (LCP) correlation. It was found that the phase separation behavior of thetwo systems, i.e., PES/DMAc/H₂O and PES/DMAc/C₃H₆(OH)₂, both agree with theLCP correlation. The binodal lines of the two systems were calculated according tothe LCP correlation. The binodal lines of the PES/DMAc/(H₂O+DMAc) andPES/DMAc/(C₃H₆(OH)₂+DMAc) systems were also calculated according to the LCPcorrelation. It was found that the bimodal lines of the systems shifted away the PES/DMAc axis with increasing the content of DMAc into the nonsolvent/DMAc mixture.Moreover the shift of the binodal line is more remarkable when the coagulationability of the nonsolvent is weaker. Furthermore, the phase separation behavior ofPES/DMAc/(H₂O+C₃H₆(OH)₂) system also agrees with the LCP correlation, and theeffects of H₂O and C₃H₆(OH)₂ on the composing of cloud point are additive.2. The rheological properties of PES/DMAc solutions were investigated.The solution behaves shear-shinning characteristics within the concentration studiedfrom 18% to 28%. Non-Newtonian index decreases and the zero shear viscosityincreases with increasing the concentration of PES. Dependence of zero shear viscosity on concentration of PES is formulated. Non-Newtonian index increases andthe zero shear viscosity decreases with solution temperature rising from 20℃to 100℃. The viscous flow activation energy is calculated after Arrhenius equation.3. The structure and properties of PES flat-sheet membranes and hollow fibermembranes were investigated.The PES membranes prepared from the casting solution containing low molecularweight additive such as propylene glycol and high molecular weight additive such aspolyethylene glycol (PEG). The effects of the concentration of casting solution,additives, pre-vaporizing time, the composing of coagulation bath on the structureand properties of PES flat-sheet membranes and hollow- fiber membranes werestudied. Moreover the effects of the composing and pressure of coagulation bathinside hollow fiber membranes and the concentration of coagulation bath outerhollow fiber membranes on the structure and properties of PES hollow fibermembrane were also studied.For PES flat-sheet membranes, the pure water flux, porosity and average pore sizesdecrease, and retention to bovine serum albumin (BSA) increases with increasing theconcentration of PES. The pure water flux and average pore sizes increases, porositychanges little, and the retention to BSA reaches the maximum with increasing theconcentration of low molecular weight additive, propylene glycol. The sizes andamount of pores on the membranes are changed when high molecular weight additivesuch as PEG is added in the casting solution so that the properties of membrane arealso changed. The pure water flux, porosity and average pore sizes increase and theretention to BSA reaches the maximum when the concentration of PEG is 3% withincreasing the concentration of PEG. The pure water flux and average pore sizesincrease slightly and porosity changes little, and the retention to BSA reaches themaximum with extending pre-vaporizing time. The pure water flux, porosity andaverage pore sizes increase and the retention to BSA decreases with increasing theconcentration of DMAc in the casing solution. For PES hollow fiber membranes, the inner diameter and outer diameter of hollowfiber membranes increase, the thickness of wall decreases, the pure water flux,porosity and average pore sizes increase and the retention to BSA decreases withincreasing the pressure of coagulation bath inside hollow fiber membranes. The innerdiameter, outer diameter and thickness of wall of hollow fiber membranes changelittle, the pure water flux, porosity and average pore sizes reaches the minimum andthe retention to BSA reaches the maximum when the concentration of coagulationbath outer hollow fiber membranes is 20% with increasing the concentration ofcoagulation bath outer hollow fiber membranes.4. The compatibility and rheological properties of PES/PES-C blend solutions wereinvestigated.The compatibility of PES/PES-C blend solutions was investigated by dilute solutionviscometry and phase difference microscope method. The results show that PES/PES-C blend system is miscible at any blend ratios. But the system is instable whenblend ratio of PES and PES-C is 1.The rheological properties of PES /PES-C blend solutions were investigated. Theblend solution behaves shear-shinning characteristics. Non-Newtonian increases andreaches the maximum when the blend ratio of PES and PES-C is 1. The zero shearviscosity of blend solutions increases with increasing the concentration of PES-C.Non-Newtonian index decreases and the zero shear viscosity increases when blendratio is 1 with increasing the concentration of blend solutions, and the dependence ofzero shear viscosity on concentration is formulate& The viscous flow activationenergies at different concentrations of blend solutions are calculated after Arrheniusequation.5. The structure and properties of PES/PES-C blend membranes were investigated.PES and PES-C were blended to prepare PES/ PES-C blend membranes includingflat-sheet membranes and hollow fiber membranes. The effects of the blend ration ofPES and PES-C and other factors on the structure and properties of PES/PES-C blend membranes are studied. The mechanism about pores forming on the skin layer ofPES/PES-C blend membranes is put forward.For PES/PES-C blend membranes including tim-sheet membranes and hollow fibermembranes, the pure water flux, porosity and average pore sizes decrease and theretention to BSA increases with increasing the concentration of blend solution. Thepure water flux, porosity and average pore sizes increases and the retention to BSAdecreases with increasing the blend ratio of PES and PES-C until it is close to 1. Thepure water flux, porosity and average pore sizes decreases and the retention to BSAincreases with the temperature of blend solution rising.The mechanism about pores forming on the skin layer of PES/PES-C blendmembranes is put forward after the experimental data. The blend ratio of PES andPES-C and temperature of the casting solution after the mechanism could be changedto adjust compatibility of blend solution, the pore sizes and porosity of membranes sothat the membranes with different properties and applications are prepared.Zhu Sijun (Material Science and Technology)Supervised by Prof. Wang Qingrui...