Flame Retardancy of Densified Wood Modified by Bio-Material Based Flame Retardant

Densified wood (DW) is a carbon-negative and energy-saving structural material with promising applications in high-rise timber buildings. However, its fire safety issues restrict its applications. In this paper, a bio-material, phytic acid, based flame retardant PPBNOH was prepared to improve the flame retardancy of DW. The structure characteristics, thermal stability, flammability, combustion behavior and mechanical performance of flame-retardant DW (PPBNOH/DW) were studied. Results show that the decomposition of PPBNOH catalyzes char formation and enhances thermal stability. Thus, PPBNOH/DW has a 57% reduced peak mass loss rate and a 27.9% increased char yield. Both the wood dense structure and PPBNOH catalyzation synergistically promote the formation of phosphorus-containing, crosslinked and aromatic char during wood combustion, which hinders heat/mass transfers and enhances flame retardancy. Thus, PPBNOH/DW has a 53.2% limiting oxygen index, a V-0 rating of UL-94 test. It presents delayed ignition time, reduced heat release characteristics and lower heat of combustion (5.37 MJ kg⁻¹) in the cone calorimeter test. BNOH improves the smoke suppression performance of PPBNOH/DW with a 38.6% reduced total smoke production. The compatible and thermally insulating char also enhances the high-temperature heating resistance of PPBNOH/DW as it has the highest remaining mechanical strengths after heating.