| The effects of technical parameters on the properties of heat treated wood,especially the species of fast-growing Chinese fir, are studied for suitable heat treatment processes of different end uses.Based on documents and prior work, under the protection of vapor, nine treating levels are used for the heat treatment. The effects of primary factors on heat treatment fir wood and its properties are studied. By comparing the properties between the thermo treated wood (also named Thermowood) and controls, the conclusion is as follows:(1) The mechanical properties of thermo treated wood tend toward decrease, but the declining amounts of MOE, MOR, impact bending, and compressive strength parallel to the grain are different. With the treatment temperature raising, MOE of thermowood hardly decreases, MOR decreases in the range of from 8.7 to 41.3 percent, impact bending declines to 40.79 percent and to 38.15 percent at 220℃,and compressive strength parallel to the grain fall to from 10.39 to 22.8 percent.(2) When treatment temperature rises from 160℃up to 220℃, The density of treated wood becomes litter lesser and color darker regularly than that of untreated wood. In addition, lightness of wood is lower but chroma higher after treatment; The dimension stability of thermowood is improved remarkably. For examples, the decrease of air-dry shrinkage ratio in radial direction ranges from 28.42 to 70.18 percent, that of air-dry shrinkage ratio in tangential direction ranges from 29.35 to 68.39 percent, that of ovendry shrinkage ratio in radial direction ranges from 17.54 to 57.77 percent, that of ovendry shrinkage ratio in tangential direction ranges from 19.81 to 48.27 percent, that of air-dry swelling ratio in radial direction ranges from 7.25 to 48.4 percent, that of air-dry swelling ratio in tangential direction ranges from 6.83 to 49.3 percent, that of radial swelling ratio in water ranges from 30.85 to 56.58 percent, that of tangential swelling in water ranges from 22.08 to 55.81 percent.(3) All of treating temperature, treating time, and heating rate have effect on the properties of heat treated wood, but the treating temperature is the most sensitive to the properties of treated wood, following by treating time and heating rate among these factors. To physics character, the best factor to fast-growing Chinese fir is as follow: heat treatment temperature is 220℃, heat treatment time is 2 hours, the rate of raising temperature is 15℃/h; Take strength loss into account, the best factor is as follow: heat treatment temperature is 190℃, heat treatment time is 2 hours, the rate of raising temperature is 15℃/h.(4) It is significant that thermo treating is an efficient approach to preventing wood decay. Test result is: The grade of natural decay resistance of Chinese fir wood without any treatment was slightly strong, the weight lose rate to brown rot is 40.33 percent, at temperature 160℃, the weight lose is 33.26 percent. When treatment temperature rises to 190℃,it would be improved nearly to medium level of decay resistance with the weight lose falling to 24.18 percent. Interestingly, it would be improved to the top level of decay resistance with the weight lose reducing to zero when the temperature is up to 220℃, which also indicated that decay resistance were improved.By heat treatment, the dimension stability and natural decay resistance of Chinese fir were improved largely. The heat treatment wood could meet the needs though strength characters have decreased in different degree. In addition, the mechanism of thermo treatment wood is also discussed. With studying FTIR of thermo treated wood, a qualitative analysis for the interior structural change is given, to provide basic data and analytical evidence for future studying. |
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