Enhancing the properties of PBAT/PLA composites with novel phosphorus-based ionic liquid compatibilizers

Biodegradable polybutylene adipate terephthalate/polylactic acid (PBAT/PLA) composites with good interfacial adhesion, mechanical properties, flame retardancy and melt processability are demanded by the plastics sector. To simultaneously achieve these attributes, researchers are actively seeking novel compatibilizers for these polymers. Herein, two ionic liquids (denoted as IL1 and IL2), comprising phosphonium cations (PR4+) with different length alkyl substituents (R) and phosphorus containing asymmetric anions (RPO32−), were successfully synthesized and applied as compatibilizers to prepare PBAT/ILs/PLA composites by melt blending and injection molding. Owing to chain entanglement between the long alkyl chains of PR4+ and RPO32− with the PLA and PBAT polymer chains, as well as interactions between the anion -PO32− groups and ester groups on PLA and PBAT, the toughness, flame retardancy and processability of the composites were all enhanced. Adding the ILs resulted in the more uniform dispersion of PLA in the PBAT matrix. The elongation at break of composites containing 0.4 wt.% IL1 or IL2 increased by 329.9 % and 168.5 %, respectively, relative to pristine PBAT/PLA composites. At an IL content of 0.7 wt.%, both of PBAT/IL1/PLA composites and PBAT/IL2/PLA composites possessed excellent flame retardancy (a limiting oxygen index of 28.1 and 27.3, respectively). Furthermore, the melt fluidity of the PBAT/ILs/PLA composites increased with increasing IL content. This work conclusively demonstrates that ionic liquids can serve as excellent compatibilizers for high performance biodegradable PBAT/PLA composites.