Thermal degradation of binary physical mixtures and copolymers of poly(ε-caprolactone), poly(D, L-lactide), poly(glycolide)

The thermal degradation of various aliphatic polyesters such as poly(epsilon-caprolactone) (PCL), poly(glycolide) (PGA), and poly(D, L-lactide) (PLA), their physical blends and copolymers were investigated in a thermogravimetry analyzer under dynamic heating in an inert nitrogen atmosphere. The peak decomposition temperatures of the PCL, PGA, and PLA are 402, 360 and 295degreesC, respectively. The Friedman plots showed a 2.5- to 3-fold increase in the activation energy from lower temperatures to higher temperatures during degradation. This suggested that the governing mechanism changes during degradation from random chain scission to specific chain end scission with increase in temperature. The activation energies for the random chain scission of PCL, PGA and PLA are 18.5, 16.5, and 10.2 kcal/mol, respectively and the corresponding activation energies for the specific chain scission are 55.5, 32.0, and 25.2 kcal/mol. Experiments were also conducted under isothermal holding to evaluate the activation energies for specific chain scission and are 47.5, 28.0, and 22.2 kcal/mol for PCL, PGA, and PLA, respectively. The degradation of the blends and copolymers was also investigated. The presence of PLA in the copolymer destabilized the other polymers (PCL and PGA). However, the presence of PLA in the mixture did not influence the degradation of PGA. (C) 2004 Elsevier Ltd. All rights reserved.