Preparation And Properties Of Reversible Thermochromic Veneer

Reversible thermochromic wood is a kind of new functional material, which responds tochange of temperature by color change and energy conversion. The color can transformbetween warm and cool and it meets the individual needs of furniture and decoration aesthetic.The application of thermochromic in wood materials, is one of main method to realize thefunction of wood materials, which could improve value-added and market competitiveness ofthe wood products.In my research, the method was by changing the composition and proportion of thereversible thermochromic agent to determine the optimum ratio of reversible thermochromicagent. By analyzing the thermochromic properties of reversible thermochromic veneer, theperformance test method of reversible thermochromic veneer was explored. With the methodof in-situ polymerization, the reversible thermochromic agent with the best proportion wasmicroencapsulated, and then the technology of microcapsule was explored. By mixing theprepared microcapsule with impregnation resin, the reversible thermochromic veneer wasprepared, and the properties of thermochromic veneer were discussed including thermochromicproperties and thermal stability. The main results are summarized as follows:1Preparation of reversible thermochromic composite materials（1） Color developer and solvent had significant effect on thermochromism properties ofreversible thermochromic composite materials. The high aliphatic alcohols such as1-dodecanol （DD）,1-tetradecanol （TD） and1-hexadecanol （HD） were more suitable forthermochromic materials than other high aliphatic acids including stearic acid （SA）. And thecolor change of thermochromic materials was more obvious by taking bisphenol A （BPA） ascolor developer than by SA and p-nitrophenol （p-NP）.By taking DD, TD and HD as solvent,thermochromic rose-red （TRR） as color former, the color change temperature intervals of thethermochromic composite materials were10²0℃,26³8℃,44⁵4℃, respectively. （2） For the thermochromic composite materials, the optimal mass ratio of TRR, BAP andTD was1:6:60. Under this condition, the reversible color change of thermochromic compositematerials occurred rapidly, and the intervals of achromic and chromic temperature were33³7℃,27³3℃, respectively.（3） The thermochromism mechanism was electron transfer mechanism. According to theresults of FT-IR spectrogram, there was a carbonyl group （C=O） in the wavenumbers of1766cm^-1in the color former TRR, a characteristic peak of esters. For thermochromic compositematerials, the lactone ring ruptured in the low temperature, the lactone peak disappeared.2Properties and testing methods of reversible thermochromic veneers（1） According to the grade evaluation the color difference unit of National Bureau ofStandards （NBS unit）, the achromic and chromic temperature could be confirmed. Theachromic temperature and range of achromic temperature of thermochromic veneers whichbased on the thermochromic composite materials of TRR, BPA and TD were31℃and27～23℃in the decolorization process, while the chromic temperature and range of chromic temperaturewere25℃,29℃～19℃in the colorization process.（2） The color changes depended on temperature and thermal history, which was namedcolor hysteresis. The colors appearing on heating were in general not equal to those on cooling.（3） The light stability was not good enough and the ultraviolet light absorbers couldimprove the light stability. The loss of total color difference of the thermochromic veneers withno ultraviolet light absorbers increased with the prolonging Xenon-light irradiation time. Thelight stability of the thermochromic veneers with UV-326was better than the ones withUV-531. With the increasing of additive amount up to2.0%, the change of total colordifference was small, that is, the light stability was good.（4） The method of colorfastness to light in the National Standard GB/T15104-2006couldn’t suit for testing the light stability of reversible thermochromic veneers. It is necessaryto study the test condition for light stability of the thermochromic veneers, which wasinfluenced by irradiance, temperature and relative humidity.3Preparation technology of reversible thermochromic microcapsule The type of emulsifiers and emulsifier dosage, emulsifying rotate speed, emulsificationtime, wall/core materials ratio and pH value had great influence on the structure, morphologyand particle size of thermochromic microcapsules. Polyvinyl alcohol0588（PVA-0588） wassuitable for emulsifier in the emulsification process of thermochromic composite materials.The optimum technology parameters for thermochromic microcapsules were as follows:emulsifier dosage3.0%, emulsifying rotate speed14000rpm, emulsification time30min,wall/core materials ratio4:2and pH value5.0. Under this condition, the microcapsules hadgood color and color change effect, the size distribution of microcapsules was narrow and theaverage diameter was3⁵μm.4The application of thermochromic microcapsule in the veneers（1） The thermochromic microcapsule emulsion with melamine formaldehydeimpregnating resin could be used for the reversible thermochromic veneers which had goodthermochromic properties.（2） In the reversible color change process, there was a phenomenon named colorhysteresis, that is, the decolorization and colorization curves were continuous, but had form aclosed loop. The achromic and chromic temperature were33℃,25℃and the interval ofachromic and chromic temperature were25³5℃,27¹9℃, respectively.（3） The reversible thermochromic veneers had good resistance to fatigue performance.The lightness index （L*）, red-green index （a*）, yellow-blue index （b*） and the total colordifference （E） had no significant changes after10thermocycling （-20—100℃）.