Lignin nanoparticles for sustainable and biodegradable packaging films

Abstract A simple, green, and scalable procedure to manufacture spherical lignin nanoparticles is demonstrated in this work. Softwood kraft lignin (S-lignin) was fractionated using acetone which was recoverable and reused in the following step to produce lignin nanoparticles (S-LNPs). Deionized water was used as anti-solvent to precipitate S-LNPs under ultrasonication. The size of S-LNPs was found to be in the range from 40-300 nm with an average of 120±18 nm. S-LNPs had lower ash content at 0.05% as compared to 1.22% of S-lignin. More importantly, S-LNPs had significant increased phenolic to aliphatic hydroxyl ratio. Home-composable polybutylene succinate (PBS) was selected to develop sustainable materials for flexible film applications. Composite films of PBS/S-lignin and PBS/S-LNPs were manufactured via conventional blown film melt-extrusion. Both composite films appeared brownish. At 0.5 wt% loading content, the PBS/S-LNPs composite films possessed comparable mechanical properties to the neat PBS film with several advantages including (a) a superb UV-blocking ability of 69% and 64% enhancement in shielding of UV-B and UV-A, respectively; (b) retardation of thermo-oxidative reaction with 42 % improvement in onset oxidative temperature; and (c) antibacterial activity (R) values of 2.5 for gram-negative (E. coli ATCC8739) and 1.5 for gram-positive (S. aureus ATCC 6538p). For a meaningful approach in fully biodegradable and sustainable plastic products, the spherical lignin nanoparticles produced in this work can be alternative multifunctional bio-additives for UV protection, antioxidation and antibacterial applications.