P/N/S synergistic lignin nanoparticles enhance the excellent flame retardancy, flexibility, UV resistance, and full biodegradability holocellulose nanocomposite films

Bamboo holocellulose emerges as a significant candidate in the field of bio-based functional materials, owing to its rapid growth cycle, high strength, and antioxidant properties. However, its flammability poses a significant critical challenge, thereby hindering the widespread application of this carbonized polymer. In this study, we present a straightforward and efficient ternary deep eutectic solvent (TDES) pretreatment strategy. Specifically, the TDES treatment was employed to chemically introduce P/N/S groups into holocellulose and lignin, resulting in the production of flame-retardant holocellulose (HC-SP) and lignin (Lignin-SP), respectively. By adjusting the ratio of these two components, nanosuspensions and nanocomposite films were fabricated through a co-grinding process. The incorporation of Lignin-SP imparted the P/N/S-containing holocellulose nanofibril composite films with exceptional flame retardancy (with a limiting oxygen index exceeding 52.5 %), substantial tensile strength (reaching 152.3 MPa), robust UV-blocking capability (blocking over 98.9 % of UV radiation), and biodegradability (degrading within 70 days). This straightforward preparation strategy for all-biobased green flame-retardant packaging materials holds promising application potential in the fields of flame-retardant food packaging.