Flexure-resistant and additive-free poly (L-lactic acid) hydrophobic membranes fabricated by slow phase separation

PLLA membranes with excellent ductility were successfully prepared by a simple solvent evaporation-induced precipitation method, without any additive. The excellent mechanical properties are mainly attributed to the interconnecting pore morphology and the plastic deformation of the pore wall during the stretching process. The interconnecting pore morphology is determined by delaying non-solvent diffusion and molecular chain pre-nucleation. It was found that the average pore size gradually decreased from 19.25 μm to 6.71 μm as the concentration of the polymer solution increased from 0.03 g/ml to 0.10 g/ml, and the elongation at break of the membrane can reach 130.8%. The crystallinity is between 33.4% and 44.5%, and the crystal form is a perfect α crystal. Membrane with interconnecting pore structure contributes to the formation of 91.2% porosity. Furthermore, the solvent evaporation-induced precipitation method can also form surfaces containing micro-nano structures which significantly improves surface hydrophobicity. The combination of high porosity and hydrophobicity makes the membrane potentially applicable to the field of oil-water separation.