Thermal behaviour of poly(lactic acid) in contact with compressed carbon dioxide

BACKGROUND: The thermal behaviour of poly(lactic acid) (PLA) in contact with compressed CO2 was studied using high-pressure differential scanning calorimetry. In particular, the effect of annealing below and above the glass transition temperature (T-g) on the glass transition, cold crystallization and melting temperatures was studied systematically as a function of annealing time and pressure. RESULTS: The effect of compressed CO2 on the thermal properties of PLA is time dependent. Annealing below T-g decreases the temperature and enthalpy of cold crystallization. Similar, but more evident, behaviours are observed when annealing above T-g. Crystallization temperature and enthalpy during cooling decrease with increasing pressure, and the peak is narrower. CONCLUSION: Annealing PLA in the presence of compressed CO2 accelerates cold crystallization, but retards crystallization during cooling. (C) 2009 Society of Chemical Industry