Formation kinetics of the poly (phthalazinone ether sulfone ketone) (PPESK) asymmetric membrane via wet phase-inversion process has been studied experimentally. The membrane morphology has been observed using an online optical microscope - CCD camera experimental system. The precipitation front movement, X, has been measured. Three different linear correlations between the value of X2 and the gelation time, t, have been identified. This observation is different from a commonly accepted conclusion which assumed a single linear correlation between X2 and t for the whole gelation process. Compared to the morphology evolution of the membrane, it is realized that these three correlations correspond to the three consecutive gelation steps: formation of the top layer, formation of the transition layer and formation of the support layer. The effect of two additives, PEG1000 and Tween80, on the formation kinetics as well as the membrane flux has also been studied. The results present here may provide better understanding of the asymmetric membrane formation process.
Since the initial development by Loeb and Sourirajan , asymmetric membranes have been widely used in numerous applications, such as in food and pharmaceutical processing, chemical separation, waste water handling, drug delivery, artificial organs, and so on. Although many polymer materials have been synthesized and used in asymmetric membrane preparation, there still is a large need to develop new polymeric materials with high temperature resistance and chemical stability. As we shown in our previous paper, poly (phthalazinone ether sulfone ketone) (PPESK) is a novel developed copolymer with a very high glass transition temperature being of around 280 ˚C . Figure 1 shows the chemical structure of this copolymer. It contains different component ratios of bis(4-fluorodiphenyl) ketone and bis(4-chlorodiphenyl) sulfone with respect to a certain amount of 4-(4-hydroxyphenyl)-2,3-phthalazin-1-one. This polymeric material shows an excellent tolerance to commonly used acids, bases and oxidants. By introducing other groups on to its polymer chain, the hydrophilicity and charging characteristics of this polymer can be altered. Several attempts have been conducted to use this novel polymer in membrane applications, including the gas separation membrane, electron transport membrane, ultrafiltration membrane and nanofiltration membrane[3-9]. However up to now, details on the membrane formation process with this copolymer have not been reported yet. Better understanding of the membrane formation process can provide insight into the relationship between the membrane material, the membrane formation condition, and the membrane performance.