Accelerated ageing and hydrolytic stabilization of poly(lactic acid) (PLA) under humidity and temperature conditioning

The accelerated hygrothermal ageing of two commercial poly(lactic acid) grades, a semi-crystalline and an amorphous one, was studied in order to establish a baseline degradation mechanism and kinetics. In particular, the water uptake, the molecular weight, the carboxylic end groups concentration and the thermal properties were monitored during the course of humidity and temperature conditioning at 70 °C and 80% relative humidity (RH), revealing significant extent of chain scission. The effect of four commercial anti-hydrolysis agents of different composition was then examined in order to stabilize the two PLA grades. The additives comprised an epoxy-based chain extender, an aromatic carbodiimide, as well as an aromatic and an aliphatic polycarbodiimide. The epoxy-based additive did not exhibit any stabilizing effect, while the other three carbodiimide-based additives were found efficient as anti-hydrolysis agents at a concentration of 1% especially in the case of the amorphous grade.