Sustainable Multiscale Interface Engineering of Bio-Based Poly(Lactic Acid) Nanocomposite Films

Traditional carbon-based additives often exhibit irregular morphology and poor dispersion, which hinder the overall performance of poly(lactic acid) (PLA) composite films. To overcome these limitations, a hybrid nanonetwork structure (CQDs@TiO2) was constructed via the in situ integration of carbon quantum dots (CQDs) derived from wheat straw, an agricultural waste, with titanium dioxide (TiO2), and subsequently embedded into the PLA matrix. Additionally, three representative interface compatibilizers─4,4′-methylenebis(phenyl isocyanate) (MDI), tannic acid (TA), and the ionic liquid [BMIM][BF4] (IL)─were employed to functionalize the nanofillers and tailor interfacial interactions. The effects of these modifiers on the physicochemical properties of both CQDs and CQDs@TiO2 were systematically evaluated, and their influence on the ultraviolet-shielding performance, crystallization behavior, thermal stability, biodegradability, and mechanical performance of PLA composites was comprehensively investigated. Notably, the tensile strength and toughness of PLA/CT-MDI and PLA/CT-IL composites reached 68.28 MPa and 4.53 MJ/m3, representing enhancements of 65.9% and 335.6% over pure PLA, respectively. These improvements were attributed to the synergistic effect between the rigid CQDs@TiO2 nanonetwork and flexible interfacial regulators, which promoted nanofiller dispersion, interfacial adhesion, and structural cohesion. This work demonstrates a versatile interfacial engineering strategy for developing high-performance, biodegradable PLA materials, with potential applications in packaging, biomedicine, and environmental sustainability.