The effects of non-solvent on surface morphology and hydrophobicity of dip-coated polypropylene membrane

Polypropylene (PP) has been widely used for fabrication of hydrophobic microporous membrane due to its good thermal and chemical stability. However, the hydrophobicity of PP is inadequate to prevent membrane wetting which hinders its application in long-term operation of membrane contactor and other hydrophobic membrane processes. Endowing the membrane with superhydrophobicity has become an attractive way to improve wetting resistance. In this work, superhydrophobic PP membrane was prepared by coating with roughened polymer film. A simple technique of two-step dip-coating was used for deposition of the non-solvent solution and polymer solution. The effects of five non-solvent types were investigated, including ethanol, isopropyl alcohol (IPA), acetone, methyl ethyl ketone (MEK), and cyclohexanone. All non-solvents increased the surface roughness, leading to an improvement of membrane hydrophobicity. Superhydrophobic PP membranes with high water contact angle (WCA) of 150.4° and 151.3° have been successfully prepared by using IPA and MEK, respectively. Morphology characterization revealed that both modified membranes had more uniform and larger number of smaller aggregates which might minimize surface area in contact with liquid, resulting in increased contact angle. As the coating was conducted separately, the utilization of non-solvent could be more effective. (paper)