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 (ΔE_td) were evaluated at different weight loss values from TG data using the procedure recommended by MacCallum et al. The ΔE_td values of the PLLA/PDLA, PLLA, and PDLA films were in the range of 205-297, 77-132, and 155-242 kJ mol⁻¹ when they were evaluated at weight loss values of 25-90% and the ΔE_td value of the PLLA/PDLA film was higher by 82-110 kJ mol⁻¹ than the averaged ΔE_td value of the PLLA and PDLA films. The mechanism for the enhanced thermal stability of the PLLA/PDLA film is discussed.