Study On Manufacturing And Mechanism Of Thermochromic Wood

Thermochromic wood is a kind of new wood functional materials. Comparison with others wood products, thermochromic wood owns two new functions, that is, reversible color-change and thermal energy transformation with increasing or decreasing temperature. It is importantly academic and practical significance for exploring a new field of intelligent furnature material, promoting development of wood science and innovation of wood product to research and manufacture thermochromic wood, a new kind of wood functional material. Samples of Chinese white poplar were impregnated using wood thermochromic gent including thermochromic dye, chromogenic agent and 1-tetradecanol though method of ultrasonic impregnation. The ingredients of wood thermochromic agent were selected, its manufacturing process was investigated, its color-change and combining mechanism were studied and its photo-discoloration and surface properties were analyzed in the test. The main research conclusions were listed as follow:1 Study on ingredients of wood thermochromic agent(1) Research results showed that thermochromic dye 2, thermochromic dye 8 and crystal violet lactone were respectively selected in the black-red, orange-yellow and blue wood thermochromic agent according to color difference (△E*1) between thermochromic wood and objective. For all color wood thermochromic agent, biphenyl A was selected according to color-change value (△E*2) which means color difference before and after color-change of samples and 1-tetradecanol was selected according to color-change temperature (T) and time (t) of thermochromic wood.(2) The optimum mixture ratio of thermochromic dye and chromogenic agent respectively was 1:8,1:12 and 1:6 for black-red, orange-yellow and blue wood thermochromic agent. That of all color wood thermochromic agent, however, was that mixture ratio of thermochromic dye and 1-tetradecanol was 1:402 Study on manufacturing process of thermochromic wood(1) Comparison with method of thermal diffusivity and ultrasonic impregnation, the ultrasonic impregnation method was selected using to manufacture thermochromic wood according to color-change value (△E*2) in the test.(2) The optimum manufacture process was impregnation temperature 55.0℃, impregnation time 4.0h, and power of ultrasonic 140.0W for black-red thermochromic wood. That of orange-yellow and blue thermochromic wood was impregnation temperature 75.0℃, impregnation time 4.Oh, and power of ultrasonic 120.0W.(3) The new material, thermochromic wood, was finally made in the laboratory. Its initial color-change temperature was 26.0℃, the final one was 32.0℃. Its surface color respectively changed from black-red, orange-yellow and blue to wood color with temperature increasing form 26.0℃to 32.0℃. Otherwise, that respectively changed from wood color to black-red, orange-yellow and blue with temperature decreasing form 32.0℃to 26.0℃.3 Study on phto-discoloration property of thermochromic wood(1) The lost rate of color-change value (△E*2) was least to blue thermochromic wood, which indicated that phto-discoloration property of blue thermochromic wood was best. The next was orange-yellow thermochromic wood, and the last was black-red thermochromic wood.(2) Before all thermochromic wood changed color, the brightness index (L*3), red-green index (a*3), yellow-blue index (b*3) and lost of surface color (△E*3) gradually increased with prolonging time of Xenon-light irradiation to black-red thermochromic wood. The brightness index (L*3), red-green index (a*3) and yellow-blue index (b*3) gradually decreased and lost of surface color (△E*3) gradually increased to orange-yellow thermochromic wood. The brightness index (L*3), yellow-blue index (b*3) and lost of surface color (△E*3) gradually increased and red-green index (a*3) gradually decreased to blue thermochromic wood.(3) After all thermochromic wood changed color, brightness index (L*4), red-green index (a*4), yellow-blue index (b*4) and lost of surface color (△E*4) gradually increased with prolonging time of Xenon-light irradiation.(4) The results of FTIR analysis showed that hydroxyl groups (O-H) of molecular structure were partly oxidized to carboxylic acid (COOH) on the surface of thermochromic wood when they were radiated by Xenon-light. Otherwise, some free radicals also were oxidized to carbonyl groups (C=O). At the same time, the pyridine ring and ether (C-O-C) structure were broken down during the process of Xenon-light irradiation. Phto-discoloration of thermochromic wood was closely correlated with the change of chemical function groups on their surface.4 Study on surface property of thermochromic wood(1) The wettability of black-red thermochromic wood was best, the next was blue thermochromic wood and the last was orange-yellow thermochromic wood. The value of static contact angle respectively was 52.0,53.4 and 55.3 and the K value, lost rate of dynamic contact angle, respectively was0.2362,0.2221 and 0.2069.(2) The surface free energy of black-red thermochromic wood was highest, the next was blue thermochromic wood, and the last was orange-yellow thermochromic wood. The value of surface free energy respectively was 29.85 mN/m,28.30 mN/m and 21.05 mN/m.(3) The numbers of polar functional groups was different on black-red, orange-yellow and blue thermochromic wood surfaces. For example, the numbers of hydroxyl groups were most on the black-red thermochromic wood surface, its wetability was best and surface free energy was biggest, the next was blue thermochromic wood and the last was orange-yellow thermochromic wood. So different numbers of function groups resulted in change of wettability and free energy for three color of thermochromic wood.5 Study on color-change mechanism of thermochromic wood(1) The molecular structure of wood thermochromic agent was slightly changed, that is, its molecular structure was not restructured before and after color-change, which indicated that color-change mechanism of thermochromic wood was because of gain and loss electron of molecular structure.(2) The activation energy of blue thermochromic wood was biggest in the phase-transition. The next was orange-yellow thermochromic wood. The last was black-red thermochromic wood. The value of activation energy respectively was 13.58KJ/mol,12.37KJ/mol and 11.72KJ/mol.(3) The reaction order of all thermochromic wood was nearly 1, which expressed that the phase-transition mechanism of all thermochromic wood is the same.(4) The value of thermal property parameters of black-red, orange-yellow and blue thermochromic wood were lower than that of wood thermochromic agent, which showed that wood can reduce maximum energy of phase-transition and transition energy from semi-crystalline state to soluble state.(5) The value of thermal property parameters was least to black-red, orange-yellow and blue thermochromic wood manufactured though 1-tetradecanol. The next was 1-hexadecanolare and the last was 1-octadecanol.(6) With the increasing of heating rate, the initial temperature (To) of phase-transition gradually deceased, but peak temperature (Tp) and final temperature (Tc) of phase-transition and enthalpy (△H) gradually increased.(7) The relationship between color-change time and environment temperature was remarkable negative linear correlation to black-red, orange-yellow and blue thermochromic wood. The formula of them respectively was y1=-12.321x+830.64, y2=-12.929x+876.71 and y3=-8.1929x+578.5.6 Study on combinative mechanism of thermochromic wood(1) The longitudinal growth rate was most for black-red, orange-yellow and blue thermochromic wood. The next was redial direction and the last was tangential direction. The value of longitudinal, radial and tangential growth rate respectively was 30.34%,16.66%, 15.79%; 18.67%,7.65%,7.01% and 20.39%,13.13%,12.12%.(2) The FTIR result showed that there are chemical and physical combination between thermochromic agent and wood. The hydroxyl (O-H) absorption intensity decreasing indicated that hydrogen bonds between thermochromic agent and wood were formed, which expressed chemical combination. At the same time, methyl group (C-H) absorption intensity increasing indicated that mechanical adsorption came about between thermochromic agent and wood, which expressed physical combination.