Effect of the highly asymmetric structure on the membrane characteristics and microfiltration performance of PTFE wrapped hollow fiber membrane

This study aims at enhancing the permeate flux and filtration precision of PTFE hollow fiber membrane (HFM) in microfiltration by preparing the PTFE wrapped hollow fiber membrane (wHFM), in which pore size and porosity could be artfully manipulated by an asymmetric microporous structure that HFM as the inner layer was coated with PTFE sheet membrane as the skin layer. Stability of such asymmetric microporous structure and its effect on the filtration performance were carefully studied in consideration of stretching temperature, stretching ratio and wrapping tension. The results show that the highly asymmetric microporous structure was successfully fabricated owing to the interlocking of fibrils at the interface between the skin and inner layers. High stretching temperature, high wrapping tension and low stretching ratio for preparing the inner layer are positive to the stability of asymmetric structure. In addition, an unusual phenomenon that smaller pore can be fabricated at higher stretching ratio is revealed in preparation of the PTFE sheet membrane. Finally, CaCO3 particles are retained by the skin layer of the wHFM, which leads to the high flux and rejection due to the high porosity and bubble point, respectively. We hope such an asymmetric membrane would be potentially useful in separation and purification fields.