Abstract
Gas transport properties (i.e., permeability, diffusivity, and solubility) and the crystallinity/crystalline structure of poly(lactic acid) (PLA) membranes were systematically investigated. PLA membranes with different crystalline structures were prepared by regulating the heating and cooling conditions during their membrane preparation. The PLA membrane that was thermally-treated at 70°C was amorphous, while the membrane heated at higher than 80°C had crystalline structures. As the treatment temperature increased, the crystallinity increased and the PLA crystal growth branched out in a radial fashion. Regardless of crystallinity, the order of the gas permeability, diffusion, and solubility coefficients was the same for all membranes; permeability coefficient: H2>CO2>O2>N2>CH4; diffusion coefficient: H2>O2>N2>CO2>CH4; solubility coefficient: CO2>CH4>O2>N2>H2. Interestingly, unlike common crystalline polymer membranes, the permeability coefficient in a crystalline PLA membrane was larger than that in an amorphous PLA membrane. The gas permselectivity in the amorphous and crystalline PLA membranes was larger than 120 for H2/N2, 6 for O2/N2, 23 for CO2/N2, and 27 for CO2/CH4 and less than 1 for CH4/N2.
