Objective  Considering the problems such as formaldehyde emission from wood resin modifier and high hygroscopicity of inorganic material modified wood, the easily available silica powder was used as the main raw material to prepare composite silicon wood modifier, which was water-soluble, high permeable, environmental friendly and fireproof. Through vacuum pressure impregnation and heat-treatment, the physical, mechanical and fire retardant properties of woods were effectively improved.

  Method  Silicone oil composite silicon modifier (SC₂) and coupling agent hybrid silicon modifier (HS₂) were prepared respectively. Plantation poplar wood was impregnated, then the impregnated wood was heat-treated at a high temperature. The physical, mechanical and fire retardant properties of composite silicon modified wood and its heat-treated wood were finally tested and analyzed.

  Result  After heat-treatment, the mass and oven-dry density of all samples decreased, and the oven-dry density loss rate and mass loss rate of heat-treated silicone oil composite silica modified wood (TW-SC₂) were the largest. Compared with silicone oil composite silicon modified wood (W-SC₂), the moisture absorption rate of TW-SC₂ increased. The moisture absorption rate of the heat-treated coupling agent hybrid silica modified wood (TW-HS₂) was significantly lower than that of the coupling agent hybrid silicon modified wood (W-HS₂), and the moisture absorption resistance was significantly improved. Compared with the untreated wood (W), the mechanical properties of all the modified wood apparently improved, and were better than TW-SC₂. The ignition time of W-HS₂ was 8 s later than that of W, its fire performance index increased from 0.043 to 0.140 m²s/kW. The ignition time of TW-HS₂ was 9 s later than that of W, and its fire performance index increased by 64.3% compared with W-HS₂. Compared with W, the total heat release of TW-HS₂ reduced by 29.4%, the peak heat release rate decreased, and the peak time of the second heat release rate was delayed. The total smoke release of W-HS₂ or TW-HS₂ was larger than that of W, the HS₂ impregnation modification combined with heat-treatment can further promote the flame retardancy of wood. The thermal degradation rate of the modified wood was significantly lower than that of W, and the thermal stability was improved, indicating that the HS₂ modifier had a significant effect on promoting char formation.

  Conclusion  Taking silica as raw material, the coupling agent hybrid silicon modifier HS₂, which was environmentally friendly and highly efficient, was prepared through organic hybridization. The combined modification process of vacuum pressure impregnation and heat-treatment can effectively improve the mechanical and fire-retardant properties of plantation poplar wood, realize green modification with broad application prospects.