Preparation of ultra-flame retardant wood materials with mechanical reinforcement and water resistance through biomimetic mineralization of carbonated apatite

Abstract The preparation of wood products with mechanical reinforcement, flame retardancy, and water resistance is still a problem to be solved. In this work, carbonated apatite (CAp) was biomimetically mineralized in wood vessel by the method of gradient impregnation. The CAp@wood75G sample with the weight gain of 75% showed the greatest bending strength due to the formation of organic-inorganic composites. With the high bending strength, the CAp@wood75G sample exhibited elevated limiting oxygen index (LOI) of 60.4% and passed the UL-94 V-0. In cone calorimetry, the peak of heat release rate and total heat release for CAp@wood75G sample were lessened by 68.2% and 53.1% respectively, compared with that of natural wood sample. Furthermore, the LOI of CAp@wood75G was still as high as 38.4% with V-0 rating after immersed in water for 24 h. Furthermore, the flame retardant mechanism was explored and generalized. The CAp was decomposed to produced CO2 and H2O to dilute the combustible gases in the air, and catalyzed wood to form the barrier of heat and oxygen during burning. Moreover, CAp produced inorganic salts which played the protective layer role. To conclude, this efficient processing method by bioinspired mineralization was eco-friendly and effective.