Fabrication And Properties Of Photoresponsive And Thermoresponsive Wood Materials

Humans tend to draw guidance and inspiration from nature when they encounter problems.People investigate the structure and function of living organisms,and then apply these characteristic principles to provide new ideas for design,to promote the improvement of product function or the development of new product functionality.In the course of evolution,organisms experimented with form and function for at least 3 billion years before humans first harnessed the power of tools like stone and bone.Wood has evolved over time to optimize its structure and unique properties.From meter-level tree trunks,meter-level tree rings,millimeter level wood fibers,micron-level wood cells to nanometer level cellulose molecules,wood has distinct,complex and ordered multi-scale hierarchical structures.It is commonly known that wood has three major components which are cellulose,hemicellulose,and lignin.The network of the components and the space of parallel hollow tubes construct the multi-scale porous structure,which offers the penetrability,accessibility and reactivity of wood materials.As a result,the unique composition and subtle hierarchical structures of wood lay the foundation for their further functionalization.In this paper,by taking advantage of the unique microstructure and physical and chemical properties of wood materials and by combining wood materials with stimulate response materials,we prepared multi-type thermoresponsive and photoresponsive wood materials.The purposes of this paper are by realizing wood materials functionalization through bionic design to broaden the application field of wood materials and improve the utilization value of wood materials and provides a new way of thinking and theoretical reference for the subsequent development of new functional wood materials.The main contents of this paper can be summarized as follows:(1)The smart thermoresponsive wood was developed by depositing thermochromic materials on wood surfaces.The as-fabricated wood composites can reversibly change their colors with the changing temperature.The natural wood texture was completely unaffected by the transparent film through the visual inspection.Samples possessed good thermoresponsive properties and excellent thermal stability.By using 3-Aminopropyltriethoxysilane(APTES),the interaction among thermochromic materials and wood surface can be reinforced by covalent bonds.The modified sample possessed superior reversible thermoresponsive property,and its thermochromic response rate was higher than the other samples.Furthermore,the surface properties of wood materials changed from hydrophilic to hydrophobic after chemical modification.(2)The inorganic-organic hybrid photoresponsive wood was fabricated by incorporating the phosphomolybdic acid(PMA)/polyvinylpyrrolidone(PVP)composites into the multi-scale hierarchical structure of wood.The UV-Vis and XPS results indicated that the photoreduction reaction occurred and part of Mo6+ was converted to Mo5+,demonstrating that the heteropoly blues were formed during the visible light irradiation process.By using chitin to modify the sample,the phosphomolybdic acid(PMA)entrapping into a mixture of chitin/polyvinyl pyrrolidone(CS/PVP),which is anchored on the wood surface.Owing to the superior sensitivity,accurate response and environmental protection,the future of the photoresponsive wood with visible light response looks bright with many promising application areas such as sensor,smart home and solar energy conversion.(3)A novel wood-based photocatalyst was prepared by a simple one-pot way.The scanning electron microscopy showed that the synthesized bismuth molybdate nano-eggshells were evenly grown on the surface of wood substrate.Additionally,its morphologies were strongly dependent on the initial pH of precursor solution and the presence of wood substrate.The photocatalytic activity of the samples was evaluated based on the decomposition of rhodamine B under visible light irradiation.The improved photocatalytic activity could be attributed to the higher light absorption intensities,the superior adsorption capacity and a lower recombination rate of charge carriers of the sample.(4)We have demonstrated a facile route to fabricate UV light absorbing photoluminescence wood composite(UAW)by assembling photoresponsive materials into polymethyl methacrylate/wood mixture.The UV absorbing UAW samples displayed good reversible photoluminescence process with a coloration time of 3.63 s under UV light,and a fading time of 1.06 s under visible light.The UV-Vis absorption spectra and the UV blocking measurements proved that the UAW possessed much better UV intercepting and absorbing ability than that of pristine wood and transparent wood.After the water immersion test,the volume of pristine wood increased almost three times bigger than that of UAW.And the fracture strength of UAW after the water immersion test was 20 times higher than that of pristine wood.(5)Energy saving materials are economically and environmentally beneficial as they effectively reduce energy consumption and greenhouse gas emissions.Energy saving wood composite was prepared by injecting a methyl methacrylate dispersion containing a mixture of VO2(M)@SiO2 core-shell nanocomposites and thermochromic microcapsules into wood templates.The energy saving wood composite exhibited outstanding temperature regulatory ability by shielding needless infrared radiation,resulting in thermal comfort.Energy saving wood composite possess excellent waterproofing and thermogravimetric stability.Structurally colored wood was fabricated by building a structurally colored film on a wood-based substrate.The reflectance spectra and the model room test results demonstrated that the sample possesses the reflective heat insulation ability.