Study on Hygroscopic Hysteresis Properties of HeatTreatedWood by Dynamic Vapor Sorption Method

• Main Authors: Chieh Lien, 廉婕
• Other Authors: 林法勤
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/00758486593370015771

碩士 === 國立臺灣大學 === 森林環境暨資源學研究所 === 104 === The wood dealt with in this work is Swietenia macrophylla, with four groups:untreated (control), heat treated by 170 ºC, 190 ºC and 210 ºC for 1 h. The color changes were determined by the color meter and showed that L*, a* and b* were all decrease when heat-treated at higher temperatures. ΔE is also shown to increase when heat-treated at higher temperatures. Results show that after heat treatment the samples all darken and change to greenish and bluish tints. Analysis using the FTIR (Fourier transform infrared spectroscope) spectra showsthe chemical changes after heat treatment. When treated, there is found a decrease at the 1743 cm-1 mark peak, and an increase at the1513 cm-1 mark peak, meaning there is a degradation of hemicellulose causing the relative content of lignin to increase. The peak areas of 1503 cm-1 and 1106 cm-1 both increase when treated, showing the new formation of cross-link of lignin and causing a decrement of shrinkage and swelling in the treated sample. On the other hand, the ratios of the 1335 cm-1 and 1316 cm-1 peaks represent a degradation in the amorphous region of the treated sample. The DVS (Dynamic vapor sorption) can be used to analyze the sorption properties of water of materials. The results of DVS (Dynamic vapor sorption) show that the EMC (Equilibrium moisture content) and equilibrium time decrease when treated. There is no significant difference in the equilibrium rate when treated. The highest EMC in untreated, treated at 170 ºC, 190 ºC and 210 ºC are 18.85, 18.81, 17.44 and 14.04 %, respectively. Which gives a negative correlation between the heat-treated temperature and the highest EMC. Numerical analysis of the hysteresis loop via the GAB model(Guggenheim-Anderson-de Boer) shows that the volume of adsorbed water of dry wood (untreated – 0.04697, 170 ºC – 0.04864, 190 ºC – 0.04314, 210 ºC – 0.03372 cm3 /g) decreases when treated, as does the monolayer capacity. (untreated –179, 170 ºC – 185, 190 ºC – 164, 210 ºC – 129 m2 /g) In Curve fitting all the experimental data of adsorption and desorption kinetics curves, and plotting the parameters for division into the fast and slow curves by using the PEK (parallel exponential kinetics) model. The results shows that the fast curve, which represents the monolayer of water in the woods internal surface, is higher than the slow curve, which represents the multilayer of water in the woods external surface, in adsorption. It is also shown that the fast curve is much closer to the slow curve for the desorption process.