Enhancing the thermal stability of silica-mineralized wood via layer-by-layer self-assembly

Abstract

Employing a combination of a layer-by-layer self-assembly and sol gel methods, a negatively charged silica sol was successfully deposited into the cell wall and cell cavity of wood by the electrostatic attraction of cationic polyelectrolytes. The physical and mechanical properties, microscopic morphology and the chemical structure of the silica-mineralized wood were characterized using mechanical testing, scanning electron microscopy (SEM–EDS), Fourier-transform infrared spectroscopy and X-ray diffraction (XRD). The thermal performance of the treated wood was investigated using a cone calorimeter, thermogravimetry analysis (TG). SEM images and XRD results showed that the mineralization layer of the treated wood had various forms of amorphous nano-SiO2 particles, which could be attributed to multi-layers of polyelectrolytes. The mechanical strength of the mineralized wood was greatly improved. Based on the TG results, the major thermal degradation (mass loss at about 50%) began at higher temperatures for the silica-mineralized wood. Fire resistance testing demonstrated that the maximum heat release rate of the modified wood was less than that of the untreated wood, indicating that the silica mineralized layer had effectively altered the combustion mechanism. In addition, this work also considered the hydrophobic properties of silica-mineralized wood. In conclusion, the thermal stability and dimensional stability of silica-modified wood was insignificantly improved.