Preparation of highly-densified modified poplar wood by evacuating the micro-pores of wood through a gas expansion method

This study proposed an impregnation method that can dredge the internal liquid flow paths of poplar(Populus L.) wood to achieve a high degree of densification. The permeability of poplar wood was improved by opening the circulation paths from the inside-out through the decomposition and expansion of sodium bicarbonate. A high concentration of sodium silicate was achieved by a vacuum-impregnation process. An in situ reaction produced silica that filled the tiny pores of the cell walls, and some filled the larger pores, such as tube pores and cell cavities. Combined, this resulted in highly-densified modified poplar wood. Macroscopic and microscopic morphological observations showed that the filling rate of the agent inside the poplar wood was extremely high, with a WPG (weight percentage gain) of 65.2 %. Due to the densification of poplar wood, the mechanical properties were greatly improved. The FT-IR (fourier transform infrared) and XRD (X-ray diffraction) results showed that some sodium silicate was chemically bonded to the cell walls, and the penetration of the agent into the crystalline region slightly decreased the relative crystallinity of the modified poplar wood. The poplar pores were filled with a large amount of the inorganic material, and the flame retardant and smoke suppression performance was greatly enhanced. The total heat release was reduced due to a decrease in the amount of combustible components. The good heat absorption and insulation ability of the inorganic material allowed the poplar wood to more easily form a char layer, which hindered the release of smoke and the spread of fire. Densified poplar is a green high-strength flame retardant material that may be widely used in interior furniture and wood-based construction materials to realize the high-value utilization of poplar wood.