Antibacterial composite films fabricated from curcumin-loaded lignin micro-nanoparticles and cellulose

Degradable regenerated cellulose (RC) composite films have prospects to replace plastic packaging. However, limitations such as lack of functionality, poor mechanical properties, inherent color, and the absence of antibacterial activity restrict their practical application. Herein, butyric anhydride esterified alkali lignin (BAL) encapsulated curcumin micro-nanoparticles were synthesized to develop high-antibacterial composite films. Uniform dispersion of the B-CMPs within the cellulose matrix is critical for enhancing the film's properties. Furthermore, the esterified lignin contributes to the photodynamic bactericidal properties of curcumin by reducing the light absorption of lignin's native chromophoric groups. Results suggest that in the presence of B-CMPs, the RC composite film exhibits a high visible light transmittance of 80.4 % and a tensile strength of 68 MPa. Under blue light excitation, an inhibition rate of 91 % and 92 % against Escherichia coli and Staphylococcus aureus, respectively, was obtained. In addition, the composite films exhibited improved barrier properties with water vapor permeability of 1.12 × 10^-12 g·cm·cm^-2·s^-1·Pa^-1 and enhanced hydrophobicity (contact angle 82.3° vs. 46.2° for pure RC). These findings demonstrate that reducing reactive groups in lignin via esterification significantly enhances the functional integration of curcumin, yielding composite films with a superior balance of properties. This work offers novel insights into the high-value utilization of lignin toward developing packaging films to meet the growing demand for sustainable packaging materials.