A green and efficient deep eutectic solvent strategy for flame retardancy in bamboo

Bamboo has broad application prospects in the fields of construction and decoration; however, its flammability limits its high-value applications. This study develops a green modification process based on a choline chloride-urea-phosphorous acid ternary deep eutectic solvent (DES), which significantly enhances the flame retardancy of bamboo within 2 h under mild conditions of 60°C, while maintaining its mechanical properties. The treatment achieves dual high-efficiency flame retardancy through P-N synergistic action, which quenches free radicals in the gas phase, releases non-flammable gases, and catalyzes the formation of a dense carbon layer in the condensed phase. The results show that KB-PN-4 achieved a LOI of 37.3%, UL-94 V-0, and reductions in THR, HRR, TSP, and pCOP by 8.3%, 20.58%, 22.97%, and 49.03%, respectively. The char residue rate increased by 204.26%. Additionally, both modulus of elasticity (MOE) and compressive strength (CS) retention rates exceeded 93%, indicating that the structural load-bearing capacity was maintained. It provides a simple and efficient solution for the green flame retardant modification of bamboo. • A novel green process using for flame-retardant modification of bamboo. • Modified bamboo KB-PN-4 shows excellent flame retardancy with a LOI of 37.3%. • P-N synergistic effect achieves dual flame retardancy in gas and condensed phases. • KB-PN-4 retains over 93% of its mechanical properties.