Enhancement of mechanical and thermal properties of Poplar through the treatment of glyoxal-urea/nano-SiO2

Glyoxal is a cross-linking agent that could effectively improve dimensional stability and water resistance with compromising the mechanical properties of wood materials. This study explores relevant disadvantages of glyoxal-treated wood, and in an effort to overcome the drawbacks, an environmental-friendly glyoxal-urea (GU) resin is synthesized from urea and glyoxal, and combined with nano-SiO2 to treat Poplar wood. Results showed that the mechanical properties of the GU resin-treated wood were significantly increased compared to those of wood treated with glyoxal alone, and that incorporation of nano-SiO2 in the GU resin further improved performance. The fracture morphology of GU/nano-SiO2-treated wood was also characterized, indicating increased elasticity. Scanning electron microscopy and energy dispersive X-ray (SEM-EDX) results showed that GU and nano-SiO2 existed not only in the wood cell lumens, but also in the cell walls. Fourier transform infrared spectroscopy (FT-IR) test results showed the formation of GU resin and the incorporation of GU resin into the wood samples. Thermal analysis results demonstrated that thermal properties were improved after the incorporation of GU and nano-SiO2 compared to samples solely glyoxal-treated. Improvement can most likely be attributed to increased cross-linkage length among the celluloses, and/or the filling effect of GU/SiO2 in the voids in wood cell walls.