Highly porous 3D PLLA materials composed of nanosheets, fibrous nanosheets, or nanofibrous networks: Preparation and the potential application in oil–water separation

•We develop a novel method about generating porous PLLA.•We can understand the gradual precipitation method systematically according to this work.•The method may be flexibly extended to fabricate varieties of other porous materials.

Gradual precipitation method was used to generate porous PLLA materials with adjustable morphology and micropores. By adjusting the solvents and concentrations of polymer solution, we could conveniently get PLLA nano-units, which further formed porous materials with tunable porosities (91.4–97.5%). It was found that nanosheets, fibrous nanosheets, and nanofibrous networks were produced from solutions with the PLLA in DMF, acetone and EtOAc, respectively. The mechanism of solid–liquid phase separation and liquid–liquid phase separation were responsible for the formation of nanosheets and nanofibrous networks respectively. The nano-/micro-dual-scale structures on the porous materials surface and the trapped air in pores significantly improved the water contact angle up to 145°, compared to 74° of the solvent-cast PLLA bulk film. Due to hydrophobicity, high porosity and excellent capillary effect, the oil absorption ratio of the porous materials reached more than 2900% which was significantly higher than the absorption capacity of materials obtained by traditional thermal induced phase separation method. Furthermore, the materials have good oil fixation property and excellent stability in shape after oil absorption. In combination with the biodegradable properties, the materials were potential environmentally used as oil absorbents and as oil–water separation materials.

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