Preparation of ECTFE membranes with bicontinuous structure via TIPS method by a binary diluent

The ECTFE membrane with bicontinuous structure was prepared by a binary diluent via thermally induced phase separation method. The effect of binary diluent composition on membrane structure was investigated systematically. The Flory-Huggins interaction parameters between ECTFE and diluents were investigated to analyze the mechanism of phase separation. Dibutyl sebacate (DBS) was selected as the primary diluent due to the high boiling point and strong interaction with ECTFE, while triphenyl phosphite (TPP) was selected as the secondary diluent because of the good compatibility with DBS. As the weight ratio of DBS to TPP was 3/2, a uniform bicontinuous structure was obtained. A typical upper critical solution temperature behavior was displayed and the monotectic concentration was as high as approximately 50 wt.%. Finally, an ECTFE hollow fiber membrane with a bicontinuous structure was prepared by the binary diluent and revealed high mechanical strength (tensile strength of 2.40 MPa) and filtration performance (water flux of 313 L m(-2) h(-1) at 0.1 MPa).