Composite coatings of inorganic nanomaterials with polyelectrolytes are promising materials for wood modification. Endowing wood with flame retardancy behavior can not only broaden the range of applications of wood, but also improve the safety of wood products. In this work, chitosan/sodium phytate/TiO2-ZnO nanoparticle (CH/SP/nano-TiO2-ZnO) composite coatings were coated on wood surface through layer-by-layer self-assembly. The morphology and chemical composition of the modified wood samples were analyzed using scanning electron microscopy and energy dispersive spectrometry. The thermal degradation properties and flame retardancy of the samples treated with different assembly structures were observed by thermogravimetric analysis, limiting oxygen test, and combustion test. Due to the presence of an effective intumescent flame retardant system and a physical barrier, the CH/SP/nano-TiO2-ZnO coatings exhibited the best flame retardant performance and required only approximately six seconds for self-extinguishing. The coated samples had a limiting oxygen index of 8.4% greater than the original wood.
Natural wood surface is hydrophilic and can easily absorb moisture. Inorganic nanometer-scale metal oxides can be controlled and fabricated on wood surface to serve as a protective coating. In the present study, a superhydrophobic surface consisting of zinc oxide (ZnO) nanorod array was successfully attached on wood via a cosolvent hydrothermal method at low temperature. By means of X-ray diffraction pattern and Fourier transform infrared spectroscopy, the presence of the hexagonal wurtzite phase of ZnO was detected and characterized. Field-emission scanning electron microscopy showed uniform, large-scale rod-like ZnO crystal whiskers on the wood surface. The wettability of the wood surface after treatment became superhydrophobic, with a water contact angle of 153 ° . The prepared coating also showed an anti-contamination effect against milk, cola, soya sauces and coffee.
In special applications, such as hospitals and rehabilitation centers, hygienic wood surface with antimicrobial performance is recommendable. In the present study, the antimicrobial property of wood was increased by grafting with 2-(dimethylamino)ethyl methacrylate (DMAEMA). The reaction proceeds via radical polymerization, and analysis via Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and thermogravimetric analysis confirmed the successful grafting of DMAEMA to wood. The tertiary amino groups of the immobilized P(DMAEMA) were then quaternized by an alkyl halide, and the quaternary ammonium groups at the surface in high concentration proved to be antibacterial. The test against Escherichia coli by means of the optical density method revealed that the bactericidal effect of the modified surface is higher than that of wood and the monomeric precursors of grafting.
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