Elaborating Mechanisms behind the Durability of Tough Polylactide Monofilaments under Elevated Temperature and Humidity Conditions

Melt-spun poly( l -lactic acid) (PLA) monofilaments with excellent toughness have been subjected to environmental weathering under varying temperatures in the range of 50–70 °C, that is, below and close to the glass transition temperature T g, and at 20–95% relative humidity in order to follow the evolution of their mechanical performance. Environmentally triggered structural changes and the hydrolytic degradation of the monofilaments have been evaluated by analysis of their thermal and mechanical properties as well as their long-term relaxation behavior using a self-developed model. Despite structural changes, the fibers demonstrate a long-term preservation of the toughness under environmental conditions of physical aging. The mechanisms behind the observed durability of the PLA material are attributed to the relaxation of the confined amorphous phase presumably as a result of the local chain scission. Conditions when hydrolytic degradation leads to mechanical failure correspond to an absolute humidity of 90 g/m 3 independent of the temperature of the aging. Presented results reveal a persistence of the mechanical performance of PLA fibers upon aging under moderate conditions, thus offering possible design strategies toward tough and durable PLA materials for sustainable technologies.