Converting poplar sawdust waste into antioxidant lignocellulose film

Alkali lignin (AL) exhibits favorable ultraviolet (UV)-shielding performance, yet its poor antioxidant activity significantly restricts practical applications in packaging materials. In this study, AL with high antioxidant and UV-shielding effects was prepared from renewable poplar sawdust by preheating with dilute acid and ultrasonication, and it was used as a filler to be added to regenerated cellulose (RC) matrix to prepare a new high-performance bioactive packaging film (RC-AL). Results demonstrated that AL (5–10%) incorporation endowed RC films with near-complete (100%) UV-shielding in the 200–300 nm range. The RC-AL film containing 10% AL achieved a 93.2% 1,1-diphenyl- 2-trinitrophenylhydrazine (DPPH) radical removal rate. Oxygen barrier properties remained stable with AL addition, while maximum moisture barrier enhancement (33.3%) occurred at 7.5% AL loading. Optimal mechanical performance was observed at 5% AL content (68.8 Mpa), showing a 35.7% increase in tensile strength (TS) and 38.4% reduction in elongation at break (EB). This work successfully converts renewable poplar waste into value-added bio-composite films, providing an attractive route to environmental sustainability for agroforestry by-products.