Processing of Pinus sylvestris L. into a heat-insulating, thermally stable, and flame-retarded material by combining the flame-retardant impregnation and densification treatment

Abstract Flame-retardant impregnation and densification are two major modification techniques to improve the fire safety of wood. Here, these two techniques were combined to prepare flame-retarded wood, aiming at further fire hazard reduction. The delignated Pinus sylvestris L. was impregnated with boric acid (BA) and graphene oxide (GO) solutions, then densified to prepare densified flame-retarded wood named BGO-DW sample. The results revealed that the BGO-DW sample obtained a limiting oxygen index (LOI) value of 47.4 %. Its backside temperature after 1200 s heating was 49 % lower than that of unmodified wood. Besides, the peak heat release rate (PHRR) and total heat release (THR) values of BGO-DW sample were 72 and 62 % lower than those of unmodified wood due to its shorter pyrolysis interval and lower peak mass loss rate (PMLR), as supported by thermogravimetric (TG) analysis. The flame retardancy of BGO-DW sample could be attributed to the formation of compatible char containing C=C aromatic structure, C–O–C cross-linked structure, and boron trioxide (B2O3) structure. These features of BGO-DW sample offer a new method to improve thermal stability, heat insulation, and flame retardancy for wood and wood-based products.