Abstract
Thermally induced phase separation (TIPS) is a technique to prepare commercial membrane. However, the quick polymer crystallization during the quenching process will bring about a dense and thick skin layer and thus decrease permeability markedly. In this paper, a diluent mixture with upper critical solution temperature (UCST) was used to prepare polyvinylidene fluoride (PVDF) hollow fiber membrane. That is, the separation between diluent (propylene carbonate (PC)) and non-diluent (dioctyl terephthalate (DOTP)) occurred during the quenching process when the temperature of the dope was lower than 110 °C. The effects of separation between PC and DOTP and the resulting coalescence of DOTP on the PVDF crystallization process, microstructure, and the permeability of the membranes were analyzed. The results showed that the suitable PC/DOTP weight ratio reduced the thickness of the skin layer near the outer surface markedly and resulted in a porous outer surface, and the microstructure evolution process was proposed. The maximum pure water flux for the prepared membrane is up to 128.5 L·m−2·h−1 even in a dry mode without using a hydrophilizing agent. The rejection rate of the carbonic particle is nearly 100%. This study presents a novel and simple way to fabricate the microporous membrane with the interconnected pore structure.
Highlights
Induced phase separation (TIPS), based on the heat transfer, is one of the techniques for preparing commercial microporous membrane [1,2,3]
Cthe difference of Tc is not obvious for the different propylene carbonate (PC)/dioctyl terephthalate (DOTP) weight increase of Tslight the addition mainly ascribed the effect of PVDFtocontent in PC
The higher the PC/DOTP weight ratio, the higher the polyvinylidene fluoride (PVDF) content in which in turn resulted in an easy nucleation the PVDF/PC
Summary
Induced phase separation (TIPS), based on the heat transfer, is one of the techniques for preparing commercial microporous membrane [1,2,3]. Compared with non-solvent induced phase (NIPS) technique, the membrane via the TIPS had a narrower distribution of pore size, high strength, and ease of regulation of the microstructure [4,5]. Direct polymer crystallization occurred as the temperature of the dope decreased to the crystallization temperature for the S–L phase separation This suggested that could the decomposition of the polymer be avoided, and the microstructure regulation of the membrane became simple for the S–L phase separation. For the L–L phase separation by penetrating boundary polymer-lean phase and polymer-rich phase due to the resulting aggregation of each diluent This suggested that the separation between dioctyl terephthalate (DOTP) and PC and the resulting component in the diluent mixture.
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