Properties of Poly(lactic acid)/Poly(butylene adipate-co-terephthalate)/Nanoparticle Ternary Composites

Poly(lactic acid) (PLA) can be toughened by flexible poly(butylene adipate-co-terephthalate) (PBAT) at the cost of a certain degree of strength and modulus loss. In an attempt to achieve balanced overall properties, PLA ternary composites containing both PBAT and rigid nanoparticles, i.e., montmorillonite clay (MMT) or nanosized precipitated calcium carbonate (NPCC), were prepared by twin screw extrusion and subsequent injection molding. Mechanical testing demonstrated that the composites containing MMT exhibited higher tensile strength and modulus but lower elongation compared to the composites containing NPCC. Using maleic anhydride (MA) grafted PLA as a compatibilizer, the elongation of the ternary composites was substantially increased, possibly due to improved dispersion of the nanoparticles. The injection molded ternary composites were shown to have a skin-core layered structure. The skin and core layers were found to possess different microstructure, thermal behavior, and mechanical properties. The microstructure difference led to a sequential fracture behavior during tension testing: the fracture of the core layer was followed by the skin layer. The skin layer, with a higher degree of PLA chain alignment and conformational ordering than the core layer, exhibited a higher glass transition temperature, lower cold crystallization temperature, and a higher degree of perfection in crystalline structures.