Construction And Function Of Wood-based Phase Change Composites

In recent years,energy crisis and environment pollution have become increasingly serious.The realization of sustainable and green development is what the whole world pays attention and strives.Phase change materials are widely applied in the filed of thermal energy storage,due to its storing thermal energy capacity during phase change.It palys an important role in the temperature control of building,electronic device and texile.Organic solid-liquid phase change materials are widely used because of its advantages,such as large latent heat,good thermal reliability and stability,no super cooling and no phase separation,nontoxic and noncorrosive.However,there are some problems:liquid leakage during solid-liquid phase change process,low photothermal conversion efficiency,low thermal conductivity and hygroscopicity.Therefore,solving these problems is the key to broaden the application of organic solid-liquid phase change materials.In this paper,novel wood-based phase change composites are fabricated by impregnating phase change materials into the wood-based materials after carbonized process or deligninfication.In addition,multifunctional wood-based phase change composites are developed by endowing the wood-based phase change composites the reversible thennochromic ability,fluorescence,magnetic property,superhydrophobic property,and high thermal conductivity.It not only broadens the application range of wood-based phase change composites in the fields of light,heat and magnetism;It also solves the problems of low photothermal conversion efficiency,hygroscopicity and low thermal conductivity of wood-based phase change composites in practical application.The applications of multifunctional wood-based phase change composites in thermal energy storage and temperature control are also expored.The specific research contents are as follows:(1)Mechanism study of thermochromic property and heat energy storage.The thermochromic delignified wood-based phase change composites composed of thermochromic compound and delignified wood are fabricated by vacuum-assisted impregnation method.The characteristics of delignified wood as support material in the aspects of wetting properties,mechanical properties,thermal energy storage capacity,thermal insulation properties,and the mechanism of thermochromic material were explored.The phase change temperature and heat fusion of thermochromic delignified wood-based phase change composites is 34.31? and 119.20 J/g,respectivity.In addition,the composites have good reversible thermochromic ability and can visibly show the phase change progress and temperature by color change,which is convenient for people's production and life and it can make the phase change composites more decorative.In addition,it has low thermal conductivity(0.22 W/mK)and thermal insulation ability.Thus,it could have potential applictions in the fields of storage,decoration,and building energy conservation.(2)Mechanism study on heat and light energy storage.Under the current theme of energy conservation and environmental protection,it is important to prepare composites with both thermal energy storage and light energy storage,which can effectively relieve energy pressure.The self-luminous wood composites are fabricated by impregnating of phase change materlas and long afterglow luminescence materials mixture into delignified wood.The thermal energy and light energy storage capacity and stability of self-luminous wood composites were investigated.The heat fusion of composites is 146.70 J/g.It can absorb ultraviolet and visible light,and emit 520 nm green light in the dark for 11 h.In addition,the synergistic effect between long afterglow materials and phase change materials is also explored.The addition of long afterglow materials is beneficial to improve the thermal conductivity of the composites and improve the working efficiency of phase change materials(The thermal conductivity of composites is 0.47 W/mK).The self-luminous wood composites with both thermal energy storage and light energy storage can provide theoretical basis and experimental basis for the development of superior energy storage devices in the later stage.(3)Preparation and fluorescence of lignin-based carbon dots.In the early experimental process,it has been proved that delignified wood as a support material can effectively solve the liquid leakage problem of phase change materials.However,the utilization of extracted lignin is usually low.Therefore,to improve the lignin utilization,the removed lignin as precursor is prepared into CQDs by solvothermal method.Then,the fluorescent CQDs and phase change materials are impregnated into delignified wood to fabricate a multifunctional wood photoluminescent and photothermic material for thermal energy storage.The fluorescence and thermal energy storage properties were investigated.The composites exhibit strong red and NIR luminescence with emission at 650 nm with a shoulder peak at 710 nm under 580 nm(visible light)excitation.It not only realizes the efficient functional application of lignin,but also endow the wood-based phase change composites fluorescence,which broadens the application of composite materials in the field of thermal energy and light energy.(4)Preparation and functional realization mechanism of magnetic wood-based heat energy storage materials.Wood-based phase change composites were fabricated via impregnation of a compound composed of 1-tetradecanol and Fe3O4 nanoparticles into delignified balsa wood.More importantly,introducing Fe3O4 nanoparticles endows the composites with a magnetic property and magnetothermal effect,whereby the temperature increases under an alternating magnetic field.Also,the addition of Fe3O4 nanoparticles improves the solar-to-thermal conversion efficiency.The magnetic wood-based phase change composites not only solve the problem of liquid leakage and low solar-to-thermal conversion efficiency,but also broaden the application in magnetic fileld.(5)Mechanism study on superhydrophobic wood-based heat energy storage materials.To broaden the outdoor application range of wood-based composite phase change materials,the form-stable and superhydrophobic phase change composites are fabricated by spraying superhydrophobic coating on the surface of phase change composites(water contact angle of 155°).The superhydrophobic phase change composites not only further prevent liquid leakage and improve thermal energy capacity in humid environments,but also endows the composites with self-cleaning functionality.Therefore,superhydrophobic phase change composites effectively solve the hygroscopicity problem,and also provides a reference for other porous matrix-based phase change materials to solve hygroscopicity problem.(6)Mechanism study on high thermal conductivity of wood-based phase change materials.To solve the low thermal conductivity and liquid leakage problem of organic solid-liquid phase change materials,3D low-cost and high thhermal conductivity,carbonized wood-based phase change composites are fabricated by vacuum-assisted impregnation of TD into carbonized wood for thermal energy storage.The micro-structure,specific surface area and thermal conductivity of carbonized wood are explored,which investigated carbonized wood as supporting material can solve the problem of liquid leakage and low thermal conductivity.In this paper,the mechanism of energy storage and function of the thermochromic,heat/light energy storage,fluorescence,magnetic,superhydrophbic,high thermal conductivity wood-based phase change composites are explored.It not only endows wood-based phase change composites multifunctional,but also provides some research ideas and experimental basis on solving problems in practical application.