Rational Design of a Multifunctional Macromolecular Ionomer for Enhancing the Toughness, Flame Retardancy, and Antibacterial Properties of Poly( <scp>l</scp> -lactic acid) Composites

Improving the toughness, antibacterial properties, and flame retardancy of poly(l-lactic acid) (PLLA) is crucial for its use in plastic packaging. However, few studies have achieved simultaneous enhancement with a single additive due to poor interfacial compatibility and low efficiency. To overcome these challenges, a multifunctional additive poly(butylene succinate)-based polyurethane ionomer (PBSUI) was synthesized. Specifically, the flexible polyester segments in PBSUI enhance toughness, while its unique ionic units provide antibacterial performance and flame retardancy. Thanks to this unique structure, the long-standing challenge of achieving good compatibility between additives and PLLA has been effectively addressed. Notably, the PLLA/PBSUI9 blend achieved an elongation at break of 212%, which is 20 times higher than that of pure PLLA, while maintaining a moderate tensile strength of 39.7 MPa. Moreover, the fire safety of PLLA is significantly enhanced even with a low addition of PBSUI. When the PBSUI content reaches 5 wt %, the limiting oxygen index (LOI) value increases to 25.8%, and the UL-94 rating achieves the highest level V-0. In addition, the PLLA/PBSUI blends exhibit excellent antibacterial properties. Even with only 3 wt % PBSUI, the antibacterial activity against both Escherichia coli and Staphylococcus aureus exceeds 99.9%, demonstrating strong potential for practical applications.