Preparation and properties of poly (butylene succinate-co-butylene terephthalate)/poly (L-lactic acid) composite films reinforced with coal gangue as a functional filler.

Poly (butylene succinate-co-butylene terephthalate)/poly (L-lactic acid) (PBST/PLLA) composite films based on industrially compostable polyester matrices have attracted increasing attention owing to their favorable mechanical properties and packaging potential. In this work, PBST/PLLA was used as the polymer matrix, and an epoxy chain extender was introduced to improve the compatibility between the two phases. Surface-modified coal gangue was further incorporated as a functional filler to regulate the properties of the composite films. The results demonstrated that the dispersibility and interfacial adhesion of modified CG (CGKH1.0) in the matrix were significantly improved. Compared with the composite film material containing unmodified CG (CG-9), the tensile strength and elongation at break of the CGKH1.0-9 film increased by 16.2% and 29.5%, respectively. Meanwhile, CG incorporation improved the CO2 barrier and light-shielding performance, while KH550 modification partially reduced the additional water vapor permeability caused by unmodified CG: the water vapor transmission coefficient (Pwv) and carbon dioxide transmission coefficient (Pco2) of the CGKH1.0-9 film were lower than those of the pure PBST/PLLA film, and it also exhibited improved resistance under UV irradiation, hygrothermal aging (85 °C/85% RH), and aqueous hydrolytic environments. This work demonstrates that coal gangue can be transformed into a functional filler for PBST/PLLA composite films, providing a feasible strategy for the high-value utilization of coal gangue in polymer composites.