Processing of Pinus sylvestris into remarkable heat- insulating, thermally stable, and flame-retarded materials by combining the flame retardant impregnation and densification treatment

Abstract

Flame retardant impregnation and densification treatment as wood modification techniques both can improve the fire safety of the wood. Here, these two techniques are applied to prepare flame-retarded wood, aiming at further fire hazard reduction of wood. The delignated Pinus sylvestris wood was impregnated with boric acid (BA) and graphene oxide (GO) solutions to form BA-GO protective layer, then densified to prepare densified flame-retarded wood named BGO-DW sample. The results reveal that the BGO-DW sample obtains a limiting oxygen index (LOI) value of 47.5%, accompanied by a 56.1% reduction in thermal conductivity and a 48.6% decrease in equilibrium backside temperature at 1200 s compared to natural wood. Besides, the peak heat release rate (PHRR) and total heat release (THR) values of the BGO-DW sample are 72.0% and 62.5% lower than those of natural wood, which can be ascribed to the shorter pyrolysis interval and lower peak mass loss rate, as supported by thermogravimetric (TG) analysis. The outstanding flame retardancy of the BGO-DW sample is attributed to the generation of char rich in C = C aromatic structure, C–O–C cross-linked structure, and B2O3 glassy structure via the dehydration, carbonization, and cross-linking reactions. These fascinating features of densified flame-retarded wood offer a new method to enhance the thermal stability, heat insulation, and flame retardancy of wood.