## 3 Results and Discussion
### Effect of Thermal Modification and Wax Impregnation on Chemical Changes of Wood  
The FTIR spectra of the control and modified samples, and the chemical compositions of the characteristic peaks, are shown in Figure 5. The peak at 3400 cm\({}^{-1}\) indicates -OH, which influenced the MC of the wood and represents cellulose. The peak of 2900 cm\({}^{-1}\) is the aliphatic C-H vibration peak, and is the characteristic peak of cellulose. The 1700 cm\({}^{-1}\) peak represents the C=O stretching vibration, which is associated with hemicelluloses. The wavelengths of peaks at 1600, 1500, and 1430 cm\({}^{-1}\) are related to the characteristic peak of lignin. Contrasting to the control group, the chemical structures of the TM and TM + WI specimens were modified. The reduction of the intensity of -OH absorption peak at 3400 cm\({}^{-1}\) indicates that TM and TM + WI decreased the relative content of hydroxyl in the wood. Compared with the 150 \({}^{\circ}\)C TM group, the band intensity of 150 \({}^{\circ}\)C TM + WI at 3400 cm\({}^{-1}\) related to -OH stretching increased, indicating that WI influences the hydroxyl group of TM wood. These results can explain why the wood dimensional stability was improved after TM and WI. The peaks at 2917 cm\({}^{-1}\) and 2849 cm\({}^{-1}\) of the 150 \({}^{\circ}\)C TM + WI samples were obviously different from the others, showing typical absorption peaks of a C-H bond, which are the characteristic peaks of saturated alkanes of wax. This indicates that wax was successfully impregnated into the wood.  
In contrast to the control group, the intensity of the TM groups at 1700 cm\({}^{-1}\) peak, which corresponds to C=O increased, indicating thermal degradation of hemicellulose occurred after TM. However, the intensity of the C=O stretching vibration changed little after WI, comparing the 150 \({}^{\circ}\)C TM group with the 150 \({}^{\circ}\)C TM + WI group. The intensity of the stretching vibration of peaks at 1600, 1500, and 1430 cm\({}^{-1}\) of the TM groups increased with temperature, indicating condensation and an oxidation reaction occurred in the process of TM, and more stable compounds with benzene ring groups were formed. For the 150 \({}^{\circ}\)C TM + WI group, the intensity of the stretching vibration of these peaks increased after WI, suggesting that WI could improve the stability of wood structures. Furthermore, the increase in the number of single and double bonds leads to the generation of more electron conjugated systems, which greatly increases the absorption of visible light, decreases the lightness, and deepens the color of wood.  
In addition, the intensity of the stretching vibration of peaks at 1030 cm\({}^{-1}\), which is the characteristics peak of C-O corresponding to cellulose and hemicellulose, decreased after TM and TM + WI. The C-O bonds were selectively activated and produced carbohydrates, such as glucose, glucose  
Figure 5: FTIR spectra of control and modified samples.  
derivatives, xylose, arabinose, etc., which are degraded during the high temperature TM, thus further reducing the capacity for moisture adsorption, and improving wood dimensional stability.