Facile preparation of isotactic polypropylene microporous membranes with bioinspired hierarchical morphology for nano-scale water-in-oil emulsion separation

A facile method namely combined hot rolling embossing with thermally induced phase separation （TIPS） for the preparation of superhydrophobic-superoleophilic isotactic polypropylene (iPP) microporous membranes with bioinspired hierarchical structure on its surface was developed. Influences of the pre-evaporation time of liquid membranes, the micro-structure on rollers, the temperature of rollers, and the temperature of cooling bath on morphology, as well as wettability, permeability, pore size distribution, and tensile property of the membranes were evaluated. The water contact angle, the sliding angle and the time for the oil droplet to spread on the surface of the iPP membrane prepared under the optimal conditions were 154°, 3.6° and less than 0.3 s respectively. The prepared iPP membrane could be used to separate water-in-oil emulsions stabilized by surfactant, with an oil flux up to 1108 L m−2 h−1 at 0.09 MPa. In terms of separation efficiency the water content in the permeated oil was as low as 46 ppm. Moreover the prepared iPP membrane exhibited good stability and excellent recyclability (20 uses). Thus we envision that such a facile method will become a candidate to continuously prepare superhydrophobic-superoelophilic polymer (iPP, PVDF etc) microporous membranes on a large scale and low cost.