Morphological investigation of poly(Lactic acid) asymmetric membrane

Abstract

The use of biodegradable material in membrane technology will be a great solution in reducing unbiodegradable waste in the landfill. The main objective of this preliminary study is to investigate the morphology and mechanical properties of poly(lactic acid) (PLA) flat sheet membrane as the solvent evaporation time was varied and its potential for gas separation process. Dichloromethane was used as a solvent for preparing 15wt% PLA membrane dope solution. The membranes were produced by a simple dry/wet phase inversion technique using a pneumatically controlled casting system with various solvent evaporation times between 10 to 90 s to promote the formation of the desired structure prior to immersion into a water coagulation bath. Prior to the gas permeation test, the prepared membrane were coated with silicone rubber coating to reduce the membrane surface defect and improved the gas separation performance. The membrane surface morphology was examined using scanning electron microscopy (SEM). This preliminary study revealed that the produced membrane possessed an asymmetric structure with a very thin dense layer, a porous substructure and the porosity of the skin surface was reduced as the evaporation time increased. This showed that the membrane had a better molecular rearrangement and this was further supported by the slight improvement of the membrane mechanical strength. Pressure-normalized fluxes of oxygen and nitrogen and the separation factor of O2/N2 measured showed that PLA asymmetric membrane has a potential as a membrane material for gas separation. Further improvement is required in term of morphology with defect-free layer to ensure the PLA membrane can perform at its best in a gas separation process.