Alkali-digested alfalfa lignocellulose for sustainable UV-blocking packaging films

Plastic packaging has become ubiquitous since its introduction; however, its persistence in the environment and long-term ecological effects have increased the search for sustainable alternatives. Biopolymers have been widely studied; however, a plentiful, renewable, and sustainable biomaterial derived from non-food resources is needed. To this end, lignocellulose from agricultural residues meets these criteria and offers a promising solution. In this study, lignocellulose from alfalfa field residues was extracted using 20% NaOH and used to develop biodegradable packaging films. The alfalfa lignocellulosic residue (ALR) was solubilized, crosslinked, and plasticized with 68% ZnCl₂ solution, CaCl₂, and sorbitol, respectively, at 83 °C. The resulting solution was cast into films, regenerated with ethanol, framed, washed, and dried. Mechanical and barrier properties, including tensile strength, elongation at break, and water vapor permeability, were evaluated and optimized using a Box-Behnken Design. The optimal formulation (0.5 g ALR, 263.5 mM CaCl₂, and 0.84% sorbitol) resulted in a tensile strength of 5.7 ± 0.8 MPa, elongation at break of 8.3 ± 0.5%, and water vapor permeability of 1.4 ± 0.2 × 10^-10 g.m^-1.s^-1.Pa^-1. In addition, the films exhibited strong UV-Vis-IR light-blocking capacity and antioxidant activity, making them suitable for packaging light- and oxidation-sensitive food products. The films followed Peleg's water-absorption kinetics and completely biodegraded within 35 days in soil. Overall, this research presents a sustainable strategy for converting alfalfa agricultural residues into biodegradable packaging films, thereby reducing plastic pollution, promoting a circular bioeconomy, and generating socioeconomic benefits for farmers.