Mineralizing wood with chitosan–silica to enhance the flame retardant and physical-mechanical properties

Herein, based on the principle of biomineralization and a layer-by-layer self-assembly (LBL) method combined with a sol-gel method, a chitosan–SiO2 film was formed on the wood surface. Polycationic chitosan was used as a mineralization inducer and self-assembled multilayer polyelectrolyte on the substrate surfaces. This inducer accelerated the deposition of silicon dioxide (SiO2) in the cell wall and intercellular space of the wood and a chitosan–SiO2 film was formed, which was confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The appearance of Si–O–Si and Si–O–C peaks in the Fourier transform infrared (FTIR) spectra, which were confirmed by X-ray photoelectron spectroscopy (XPS), indicated the formation of an organic–inorganic structure on the mineralized wood. Thermogravimetric analysis showed that the carbon residue ratio of the control wood was 10%. In contrast, with an increase in the number of self-assembled layers, the carbon residue ratio of the mineralized wood increased, reaching a maximum of 58%. The highest peak in cone calorimetry (CONE) indicated that heat release rate of the mineralized wood was significantly reduced after mineralization, with microcalorimetry experiments demonstrating a similar outcome. Moreover, the moisture absorption and physical and mechanical strength of the mineralized wood were reduced and increased, respectively. Based on the principle of biomineralization, combining LBL with sol-gel method provides a new idea for the preparation of wood-inorganic composites and the preparation process is non-toxic, non-hazardous, green.