Preparation of nanoporous poly (L-lactic acid) microspheres with controllable morphology via thermally-induced phase separation

This article describes a facile method to prepare nanoporous poly (L L-lactic acid) microspheres via a thermally- induced phase separation method with controllable diameters. It was found that the morphology and diameter of PLLA microspheres were easily controlled by adjusting solvent ratio, quenching temperature, and PLLA concentrations. The results revealed that by using a ternary solvent system consisting of 1,3-dioxolane as a good solvent, 2-butanone as mid-solvent, and water as a poor solvent, the diameter of PLLA microspheres can be easily controlled by changing the ratio of 1,3-dioxolane and water. The diameter of PLLA microspheres prepared ranged from 28.8 +/- 5.9 mu m to 63.8 +/- 12.5 mu m. Moreover, the evolution of PLLA spherulitic structures grown from polymer solution was confirmed as well through varying solvent ratios and PLLA concentrations. The presence of water as a non-solvent governed the phase separation mechanism of the phase separation process. At the same time, the diameter of the spherulites is affected by the ratio of 1,3-dioxolane controlling the polymer crystallization process in the polymer-rich region. Interestingly, the surface of these spherulites contains nano- pores due to the stacking of lamellar crystals of PLLA during polymer crystallization which contributed to its superhydrophobicity and superoleophilicity. Hence, the prepared PLLA spherulites were utilized as PLLA microspheres with nanoporous surfaces for the adsorption and removal of oil in oil/water and oil-in-water emulsion. This facile method provides a novel pathway to prepare nanoporous PLLA microspheres with controllable diameters for eco-friendly oil/water and oil-in-water separation applications.