Preparation of PVDF Microporous Membranes via Combining TIPS with Rolling Embossing for Water-in-Oil Emulsions Separation

Abstract

Superhydrophobic microporous membranes have great application prospects in oil–water separation. The stability of micro-rough structures on the surface of hydrophobic membranes is a challenge in the oil–water separation process. In this regard, it is crucial to develop a simple method to prepare stable superhydrophobic membranes. This article prepared superhydrophobic polyvinylidene fluoride (PVDF) membranes, employing a combination of thermally induced phase separation (TIPS) with rolling embossing. The gel state of the membrane surface is the key core for the success of the process, for which the effect of pre-evaporation time on the membrane properties was explored. A turning point in the gel curve occurred at a pre-evaporation time of 1.5 min, when the gel state of the membrane was most suitable for rolling. The surface of the embossed membrane shows a micron–submicron hierarchical structure reminiscent of the lotus leaf surface, and the surface of the membrane presents a water contact angle of 151° and a solid contact angle of 9.5°. The micrometer submicron hierarchical structure exhibits excellent mechanical stability in friction experiments, with a water contact angle only reduced by 7.9° after 50 sandpaper frictions. Cross-flow filtration was significantly superior to dead-end filtration in oil–water separation, the embossed membrane maintained a high flux of 1234 L•m⁻²•h⁻¹ and a retention rate (α) of 99.10%. Meanwhile, the embossed membrane can remove 100% of mechanical impurities and water from waste diesel fuel. This study provides certain ideas and methods for the preparation of superhydrophobic microporous membranes.