High pressure differential scanning calorimetry of poly(lactic acid) in presence of CO2 up to 100 MPa
For the processing of sustainable polymers with compressed CO2 to produce innovative products, knowledge of the thermodynamic properties of the polymer-CO2 system is essential. In this work, the thermal behaviour of three different poly(lactic acid) (PLA) grades, 2003D, 3251D and 8052D, from NatureWorks was determined experimentally using high pressure differential scanning calorimetry (HP-DSC) at CO2 pressures up to 100 MPa. After the HP-DSC had been extensively calibrated using potassium, sodium and indium, the thermal transition temperatures of the biopolymers were determined as a function of CO2 pressure. The melting and crystallization temperatures of the PLA grades were found to be up to 84 K lower in the presence of CO2. In addition, the crystallinity of the three biopolymers was investigated. It was shown that the degree of crystallinity was dependent on both the melting temperature and the CO2 pressure. In fact, a striking parabolic dependency which is also correlated with D-lactide content and molar mass was observed.