How high pressure CO2 impacts PLA film properties

This work investigated the sorption and the diffusion properties of CO2 under high pressure and the further modifications induced in Poly(lactic acid) (PLA) thin layers. Poly(ethylene terephtalate) (PET) was also considered for comparative purposes. Firstly, from thermodynamic equilibrium, the CO2 sorption isotherm (two sorption-desorption cycles, up to 25 bar, at 25 degrees C) gave strong evidence of a physisorption mechanism and of a hysteresis phenomenon. Infrared spectroscopy analysis confirmed that no chemical reaction occurred. Secondly, from the kinetics aspect, the CO2 diffusion coefficient was found around 10(-13) m(2).s(-1) and was slightly faster for sorption compared to desorption. Additionally, when CO2 sorption occurred, the PLA structure and its functional properties were modified due to plasticization and swelling. CO2 plasticization reduced the glass transition temperature of PLA and accelerated the physical ageing of the polymer. These results are therefore of significant importance in industrial processing and applications which involve close contact between CO2 and PLA.