Microstructure construction of polypropylene-based hollow fiber membranes with bimodal microporous structure for water flux enhancement and rejection performance retention

摘要

The low porosity, low pore connectivity and poor hydrophilicity of polypropylene hollow fiber membranes (PPHFMs) reduced membrane performance and limited its application in water treatment. Hence, the bimodal microporous structure including two different grades and independent pore size distributions was constructed in hydrophilic polypropylene (PP)/poly(ethylene-co-vinyl alcohol) (EVOH)/maleic anhydride grafted polypropylene (PP-g-MAH) hollow fiber membrane (PP/EVOH/MAH-HFM) via melt blending combining with melt-spinning and stretching (MS-S). The addition of PP-g-MAH formed compatible interfaces to optimize the bimodal microporous structure in PP/EVOH/MAH-HFM. The porosity and pure water flux of PP/EVOH/MAH-HFM with stretching ratio of 200% respectively increased to 81.5% and 322.7 L/(m(2).h), which respectively increased by 27.3% and 118.0% compared to PPHFM with stretching ratio of 200% due to the large micropores in bimodal microporous structure. The rejection performance of PP/EVOH/MAH-HFM was also retained due to the small micropores in bimodal microporous structure. The reactive groups in EVOH and PP-g-MAH significantly improved the hydrophilicity of PP/EVOH/MAH-HFM, while also improving the antifouling property of membrane. Moreover, the formation mechanism of bimodal microporous structure was systematically investigated in combination with physical modeling and FESEM method. This work supplied a new membrane structure and provides a new perspective for the fabrication of high performance polypropylene-based hollow fiber membranes by MS-S.