PLA/PBAT/CaCO₃ Composites with Balanced Super-Toughness and Stiffness through Dynamic Vulcanization and Double Interfacial Compatibilization

The incorporation of biodegradable poly(butylene adipate-co-terephthalate) (PBAT) into poly(lactic acid) (PLA) is a simple method to improve the toughness of PLA; however, the toughening efficiency of PBAT is limited, and direct blending adversely impacts the stiffness of the material. In this paper, the surface of nano-CaCO3 was modified with 3-Glycidoxypropyltrimethoxysilane (KH560) in order to prepare CaCO3-g-KH560. A two-step extrusion process using multifunctional epoxy oligomers (ADR) as cross-linking agents was used to prepare PLA/PBAT/CaCO3 ternary blends with a subinclusion structure. In the first extrusion, ADR and CaCO3 nanoparticles were mixed in PBAT. During the second extrusion, the epoxide groups cross-linked the PBAT dispersing phase, as well as co-cross-linked the PLA continuous phase at the PLA/PBAT interface. Fourier Transform Infrared Spectroscopy (FTIR) confirmed this speculation. Additionally, Dynamic mechanical analysis (DMA) and Scanning electron microscopy (SEM) analyses showed that the co-cross-linking reaction improved the interfacial compatibility of PLA/PBAT. Energy dispersive spectrometer (EDS) and Transmission electron microscopy (TEM) analyses confirmed the uniform dispersion of CaCO3 in the PBAT phase. The synergistic toughening of ADR and CaCO3 allowed for the notched impact strength and tensile strength of the prepared blend to reach 74.5 kJ/m2 and 55.7 MPa (11 times and 1.3 times higher than PLA/PBAT with same ratio, respectively). Compared to elastomer toughening alone, the subinclusion structure improves the rigidity of the composite owing to improved interfacial interactions and a distinct energy loss mechanism. This paper provides a methodology for the preparation of PLA with balanced toughness and stiffness.