Effects of borides on flame retardant and decay resistance properties of resin modified wood

This study employed phenol-melamine-urea-formaldehyde (PMUF) resin and borides to impregnate Chinese fir from planted forests, systematically investigating the influence of borides on the flame retardancy and decay resistance performance of PMUF resin modified wood. The results indicate that after incorporating borides, the oxygen index of the composite modified wood increased by 24.2 % compared to the resin modified wood, achieving a V-0 level. Meanwhile, the two peak heat release rates of the composite modified wood decreased by 39.6 % and 32.1 % respectively, and the total heat release and total smoke release decreased by 19.3 % and 43.7 % respectively. Raman spectroscopy analysis showed a higher degree of graphitization in the composite modified wood. Pyrolysis-gas chromatography/mass spectrometry analysis revealed that borides inhibited the generation of volatile phenolic compounds and effectively prevented the ring-opening fracture of pyran rings in cellulose. Decay resistance tests show that resin modified wood achieves a strong decay resistance grade I, while the decay resistance performance of composite modified wood slightly decreases but still reaches the decay resistance grade Ⅱ. Combined with scanning electron microscopy, differential scanning calorimetry, ¹³C solid-state nuclear magnetic resonance, dynamic mechanical and nanoindentation analysis, it was indicated that the addition of borides reduced the crosslinking density of the resin, interfered with the curing process of the resin, and led to a decrease in the cell wall modulus and hardness of the composite modified wood. This research provides a new theoretical basis and technical guidance for the inorganic-organic combined modification of wood.