Preparation of Poly(lactic acid) Flat Sheet Membranes by Liquid Induced Phase Separation

Biodegradable and biocompatible polymers have been evaluated as materials for membrane separation based processes due to their flexibility and highly aggregated value in biomedical, food and packaging applications. Polylactides is a promising class of biodegradable polymers mostly due to its mechanical properties and ease in processing. In this work, flat sheet Poly(L-lactic acid) (PLLA) membranes were made by liquid induced phase separation (LIPS) technique using water as non-solvent and N-methyl-2-pyrrolidone (NMP) as solvent. Processing conditions as polymer concentration of the casting solution, time of exposure in humid atmosphere and composition of coagulation bath were evaluated. The effects of these variables were analyzed in the performance, morphology and mechanism of phase separation during membrane formation. The PLLA-water-NMP system miscibility gap was estimated by cloud points and viscosity of polymer solutions were measured. Membranes were characterized by precipitation kinetics by light transmission, hydraulic permeability and scanning electron microscopy. Porous microfiltration membranes could be formed with permeabilities of 62.87 Lm(-2) h(-1). It could be concluded that the morphology of PLLA membranes is a result of a complex interplay between solid-liquid and liquid-liquid demixing during phase separation.