Thermal degradation of poly-L-lactide - Studies on kinetics, modelling and melt stabilisation

The kinetics of changes in molecular weight during thermal treatment of crude and purified poly-L-lactide (PLA) were studied in sealed ampouls in nitrogen atmosphere in the temperature range of 180-230 degrees C. The changes in molecular weight were modelled by using a two-parameter model, consisting of a statistical degradation step and a recombination step. From the results, the catalytic effect of tin-(II) on degradation and recombination reaction can be seen, as well as the effect of tin concentration on the existing ring-chain equilibrium. The thermal stabilisation of Poly-L-lactide during processing in the melt is possible by the addition of tropolone. (C) 1997 Elsevier Science Limited.