Thermal and hydrolytic degradation kinetics of PLA in the molten state

Poly(Lactic Acid), PLA, is an extremely interesting polymer for industrial applications in which degradability is required. However, it presents considerable processing issues due to its sensitivity to stocking and processing conditions. In particular, the decrease of molecular weight at high temperature during processing in the molten state induces a reduction of viscosity.In this work the degradation of a commercial grade of PLA in the molten state was studied through the analysis of the rheological properties as a function of time and drying conditions.In particular, measurements of the complex viscosity were taken during time at a frequency of 1 rad/s in the temperature range at which the polymer is usually processed (from 180 °C to 220 °C) on samples stored at ambient humidity and on samples subjected to drying.A kinetic model of degradation of PLA which keeps into account the contribution of hydrolysis and thermal degradation was applied to the experimental data and the parameters of the model were obtained as a function of temperature for the commercial grade analysed.