In Situ Polymerization and Flame Retardant Mechanism of Bio‐Based Nitrogen and Phosphorus Macromolecular Flame Retardant in Plywood

Abstract

To improve the flame retardant performance of plywood and reduce the reagent loss and moisture absorption of the flame retardant, a bio-based supramolecular flame retardant is prepared by vacuum-pressure impregnation and high-temperature in situ polymerization in plywood. The best value of bonding strength appears at 170 °C, and the limiting oxygen index (LOI) of 170BF-B plywood is 42.3%. After hot pressing, the moisture absorption rate of the 170BF-B veneer is only 18.51%, while the loss resistance rate achieves 83.45%. Its residue at 700 °C is 91.36% higher than that of poplar veneer. In the combustion process, the peak value of heat release rate (PHRR) and heat release rate (HRR) of 170BF-B plywood are only 10.69% and 37.11% of that of untreated plywood. After combustion, an intumescent flame retardant layer exhibits a graphitization trend. In the flame retardant layer, there are not only functional groups, such as P═O, PO₄ ^3- , POC decomposed by flame retardant but also characteristic functional groups of wood fiber, like C═O, CH, etc. The prepolymer BF-B, which is composed of phytic acid, urea, and dicyandiamide polymerized with chitosan or lignocellulose to form a supramolecular flame retardant connected with POC and PON functional groups, thus improving the flame retardant and anti-loss property by in situ polymerization.