<p>In this study, vinyltriethoxysilane (VTES) was grafted onto lignin (VL) via an aqueous alcohol solution method to fabricate a biodegradable composite film. The modified lignin was then melt-blended with poly (butylene adipate-co-terephthalate) (PBAT) in a catalyst-free system, and the blends were processed into PBAT/VL composite films with varying VL loadings via film blowing. When the VL content was 10%, the resultant P₉₀VL₁₀ composite films showed a 23.99% increase in tensile strength and a 6.66% improvement in elongation at break compared to the PBAT films. Meanwhile, its ultraviolet transmittance was reduced by 62.83%, and the crystallinity increased from 15.61 to 16.47. Notably, the melting temperature remained stable, and the composite films retained excellent biodegradability. Two types of laboratory-simulated accelerated aging tests were performed to analyze the sensitivity of the composite films to temperature, irradiance, and oxygen concentration. Based on these test results, a multi-factor coupled aging kinetic model for the composite films was established. The findings demonstrated that the incorporation of modified cotton straw lignin could reduce the sensitivity of PBAT composite films to temperature, irradiance, and oxygen concentration, thereby significantly enhancing their weather resistance. This improvement expands the applicability of PBAT in the packaging field while lowering the overall production cost, offering a feasible and economically advantageous alternative for sustainable packaging solutions.</p> Graphical abstract <p></p>