Morphology And Structure Of PSF-DMAc-IBA System Flat Sheet Membrane

Immersion precipitation based on the phase inversion techniques has been the most popular and typical method for the preparation of asymmetric polymeric membranes for about 30 years. The morphology and structure of membrane formed by this technique depends on the composition and concentration of the dope solution and coagulation bath, as well as some other conditions, e.g., humidity and temperature. The concept of highly asymmetric membrane that is also made by immersion precipitation was brought forward by Wrasidlo in 1986. This membrane has an integral structure that comprises a skin and a highly porous asymmetric support. The pore size in the membrane increases along the direction from the skin to the deep of the sublayer. The ratio of pore sizes at the top and underside surface of flat membrane is more than 125. There is a three-dimensional open network of interconnecting fibrous strand and open interstitial flow channels in the highly asymmetric membrane. So its permeability is much higher than common ultrafiltration membranes. And the retention property is also excellent, while the fluid resistance is smaller.As a membrane material used in blood purification, polysulfone (PSF) has advantages in aspects of biocompatibility, chemostability, and mechanical strength, which make it popular in the field of biomedical materials. Hence, research and development on the PSF highly asymmetric membrane is meaningful and necessary.In this thesis, thermodynamic properties of multicomponent PSF solution systems are studied firstly. PSF -DMAc - alcohols ternary systems and PSF -DMAc - IBA - PVP quadribasic system were measured by experiment of the cloud point. The improved calculation method verifies the experiment results. As a result, the sequence of the precipitation ability of nonsolvents is water > glycerol > 1,2-propylene glycol (PG) > ethanol > iso-propanol (IPA) > iso-butyl alcohol (IBA) > iso-amyl alcohol (IAA). The glass transition and the gelation boundaries of PSF-DMAc-IBA system are deducted for the first time. Then, the whole thermodynamic ternary phase diagram of this system is made for the first time.Secondly, when water and IBA were chosen as coagulation solution, characteristic of phase separation (instantaneous demixing and delayed demixing) of multicomponent PSF systems are determined by light transmission in the process of performance membrane. By using the mass transfer mathematic model and the diffusion formula, the composition paths of PSF-DMAc system and PSF-DMAc-IBA system at the initial moment of immersion in different coagulation baths are computerized.The mechanism of macrovoids formation is discussed in this thesis. By adjusting the thermodynamic factor gij and dynamic factor @ij, macrovoids within the membrane can be controlled. Hereby, additives (IBA or PVP) are used in the experiment of membrane formation.Finally, according to the thermodynamic and dynamic characters of multicomponent PSF systems, the formula and preparation conditions of integral highly asymmetric flat membrane are designed as follows: the dope consists of 15% PSF, 64.8% DMAc, 15.2% IBA and 5% PVP. And the corresponding membrane verified the previous experiment and calculation results. The integral highly asymmetric flat membrane can be obtained under following experimented conditions: Temperature: 20 ± 2℃; Thickness of cast film: 250 urn; Atmosphere humidity: about 60%; Duration time before immersed in the wet phase: 10s. When water or IBA was chosen as coagulation solution, the structure of three-dimensional open network of interconnecting fibrous strand and open interstitial flow channels in thehighly asymmetric membrane were obtained, and the membrane has favorable hydropilicity. But when IBA was used as coagulation solution, the water permeability of the membrane is poor, which indicated that there is no open pore on the surface or in the sublayer of the membrane. This integral highly asymmetric flat membrane has better permeability and the ratio of pore sizes on the topside to that on the underside of the flat memb...