ИСТИНА

Bio-based semicrystalline polylactide (PLA) has a growing value as a substitute for fossil-based polyesters in technical applications and as a biocompatible material in medicine. Poor toughness is generally recognized as a limitation for the expansion of PLA usage in the applications that require elastic-plastic deformations at high stress levels. An identified research challenge is to develop new insights and approaches to guide the mechanical properties of PLA to a level that will make it suitable for industrial usage. Presented research reveals that under certain environmental aging conditions, below and close to glass transition temperature Tg and under a wide range of relative humidity, melt-spun highly crystalline PLA monofilaments demonstrate a long-term preservation of the toughness, outlasting the hydrolytic degradation. Environmentally triggered structural changes and 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. The mechanism behind the observed durability of PLA material is attributed to the relaxation of the confined amorphous phase presumably as a result of local chain scission. A self-developed model was elaborated to predict the long-term mechanical behavior of the fibers. New model is based on the well-known Maxwell model and assumes a mean relaxation time in combination with a relaxation coefficient and allows to derive master curve from one measurement series at a single strain by fitting the data to the model equation. The proposed model turned to be extremely sensitive in revealing changes in the mechanical performance of the treated polymer samples. Presented results offer possible design strategies toward tough neat PLA materials for sustainable technologies.