Revisiting the Contribution of Additives to the Long-Term Mechanical Stability and Hydrolytic Resistance of Highly Crystalline Polylactide Fibers

Additives are widely used to improve the processability, toughness, and hydrolytic resistance of poly(lactic acid) (PLA)-based materials. This study compares neat PLA fibers and fibers made from PLA blends with either poly(butylene succinate) (PBS) as a plasticizer or poly(d-lactic acid) (PDLA) as a nucleating agent. The fibers have been characterized with regard to their physical and structural properties after fabrication as well as after artificial aging at elevated temperature and humidity conditions. All samples have been fabricated using industrial melt-spinning equipment, resulting in a high crystallinity of about X_C = 80% and a good initial toughness. Long-term relaxation behavior has been assessed with a self-developed lifetime prediction model, which is successfully verified for semicrystalline blended fibers. Despite slight improvement of the fiber elasticity and ductility, both types of blended fibers demonstrated a reduced hydrolytic resistance. These results suggest a design strategy for neat durable PLA fibers through processing-induced high crystallinity and orientation, which provide improved hydrolytic stability while preserving tough mechanical performance.