Effects Of Steam Heat Treatment On The Main Chemical Components And Their Structure Of Teak Wood

Steam heat treatment is one of effective methods to improve the properties of wood. The modification of heat treated wood properties is, in fact, the changes of the molecular structure and properties of wood’s main components. In this paper, teak(Tectona grandis L. F.) wood was heat treated at temperatures from 120℃ to 220℃ at intervals of 20℃ for 2h in airtight equipment with an atmosphere within comprising less than 2 percent of oxygen content. The influence of steam heat treatment on the content of main components in teak wood was analysed by the method of chemical composition analysis. Fourier transform infrared(FT-IR) spectroscopy revealed the modification in the molecular structure of heat treated wood’s main components. Two dimensional correlation infrared(2D-IR) spectroscopy was employed to analyse the sensitivity of the samples to thermal perturbation, and detected the influence of steam heat treatment on the sensitivity. The purpose of this paper was to uncover the influence mechanism of steam heat treatment on the wood’s properties.Combining with the content above, the results are as follows:(1) The content of cellulose, hemicellulose and lignin in the treated wood has changed. The content of cellulose and hemicellulose decrease with the increasing treatment temperature, and the hemicellulose decreases more. The relative content of lignin increases.(2) Chemical composition analysis shows that, the main components of teak wood occur intense thermal degradation at different temperature. Hemicellulose thermal degradating begins at 140℃, 160~180℃ is the intensest, the degradation ends at about 200℃. The intense thermal degradation of cellulose start at 180℃. Lignin is relatively stable to the heat treatment.(3) FT-IR shows the chemical changes taking place in the structure of wood components during steam heat treatment. The decreasing intensity of the bands assigned to C=O and C-O stretching vibration indicates hemicellulose degradation, the decreasing content of C=O is due to the degradation of the acetyl groups of hemicelluloses through the deacetylation reaction and release of acetic acid. The decreasing band assigned to O-H bending vibration of hygroscopic water in cellulose suggests the loss of hygroscopic water. The changes of O-H association absorption band implies the modification of hydrogen bond content. The increasing band assigned to C=C stretching of aromatic skeletal in lignin indicates the increasing relative content of lignin.(4) 2D-IR spectra reveals the sensitivity of samples to thermal perturbation, it shows taht, the most sensitive group in cellulose and hemicellulose is O-H from hygroscopic water, for lignin is aromatic nucleus, for teakwood is C=O from carbohydrates. The sensitivity of most functional groups present fluctuating decline trend with the increasing treatment temperature.(5) The analysis of benzene-alcohol extractives from wood samples show that, the content of benzene-alcohol extractives decrease with the increasing treatment temperature, relative content of alcohol and ether compounds in the extractives increase, steam heat treatment makes benzene-alcohol extractives less sensitive to the thermal perturbation.