Enhanced thermal stability of poly(lactide)s in the melt by enantiomeric polymer blending

Poly(L-lactide) (i.e. poly(L-lactic acid) (PLLA)) and poly(D-lactide) (i.e. poly(D-lactic acid) (PDLA)) and their equimolar enantiomeric blend (PLLA/PDLA) films were prepared and the effects of enantiomeric polymer blending on the thermal stability and degradation of the films were investigated isothermally and non-isothermally under nitrogen gas using thermogravimetry (TG). The enantiomeric polymer blending was found to successfully enhance the thermal stability of the PLLA/PDLA film compared with those of the pure PLLA and PDLA films. The activation energies for thermal degradation (DeltaE(td)) were evaluated at different weight loss values from TG data using the procedure recommended by MacCallum et al. The DeltaE(td) values of the PLLA/PDLA, PLLA, and PDLA films were in the range of 205-297,77-132, and 155-242 U mol(-1) when they were evaluated at weight loss values of 25-90% and the DeltaE(td) value of the PLLA/PDLA film was higher by 82-110 U mol(-1) than the averaged DeltaE(td) value of the PLLA and PDLA films. The mechanism for the enhanced thermal stability of the PLLA/PDLA film is discussed. (C) 2003 Elsevier Science Ltd. All rights reserved.