Citric acid-treated lignin as a functional regulator for PBS/PBAT biodegradable films

A biodegradable composite film was fabricated using poly(butylene succinate) (PBS) as the main matrix, poly(butylene adipate-co-terephthalate) (PBAT) as the toughening component, and citric acid-treated lignin as a low-cost bio-based filler. Under fixed conditions of a PBS/PBAT mass ratio of 80/20 and a lignin loading of 1 wt%, the effects of different citric acid treatment ratios on the structure and properties of composite films were systematically investigated. SEM and rheological analyses revealed that citric acid treatment mitigated the visible aggregation of lignin and improved the melt structural stability of lignin-containing PBS/PBAT films compared with the films filled with untreated lignin. XRD results demonstrated that the fundamental crystalline structure of the composite films remained unchanged. Among all fabricated samples, the PPCL-2 composite film exhibited the best overall performance, with a tensile strength of 26.8 MPa and remarkably enhanced elongation at break. In addition, this composite film possessed well-balanced water vapor and oxygen transmission rates, exhibited a UV transmittance lower than 0.1% within the wavelength range of 230-340 nm, and displayed accelerated mass loss and structural degradation under simulated composting conditions. Preliminary seedling growth tests indicated that soil containing residual PPCL-2 degraded films exerted no obvious short-term inhibitory effects, with a 7 d germination rate of 97.33 ± 2.31%, and fresh and dry weights comparable to those of the control group. The above results confirm that the PPCL-2 composite film is a promising biodegradable material with well-balanced overall performances, which offers a low-cost and feasible technical route for fabricating high-performance biodegradable films.