Impact Of Different Heat Treatment Temperatures On The Properties Of Chinese Fir Wood

As an effctive method to elevate the properties of plantation wood,thermal modification is controllable,inexpensive,environmental-friendly and can significantly improve the dimensional stability and durability of wood.Temperature has obvious effects on both physical and mechanical properties of wood and has been assumed as the key parameter during thermal modification.In this thesis,the effects discipline as well as mechanism of temperature on thermally modified wood were discussed from the aspects of chemical constituents,micro-and ultra-structure of wood.Sapwood of Chinese-fir(Cunninghamia lanceolata(Lamb.)Hook.)were heat-treated at 140 °C,155 °C,170 °C,185 °C,200 °C,215 °C,230 °C and 245 °C using atmospheric pressure steam as media.The heating duration were 2h respectively.Basic physical and mechanical properties of Chinese fir were studied along the elevation of temperature.Wet chemical analysis,pyrolysis gas chromatography-mass spectrometer(Py-GC-MS),Fourier transform infrared(FTIR)spectroscopy and two-dimensional correlation infrared(2D-IR)spectroscopy were employed to track the chemical changes aroused by steam-heat treatment.Scaning electron microscope,BET N2 adsorption analysis and X-ray diffraction were carried out to study the anatomy characterization,pore structure,size and crystalization of cellulose.The main results are as follows:(1)In the range of 140 to 170 °C:Thermal modification started to impact on the properties of Chinese fir.Only the content of hemicellulose was affected.Due to the thermal degradation of hemicellulose and hydrophilic group,the loss of mass,oven-dry density and equilibrium moisture content(EMC)of Chinese fir were within 10 percent.(2)In the range of 170 to 200 °C:Hemicellulose was heavily degraded.The loss rates of mass,density and EMC were increased.With the presence of acetic acid,content of primary degradation products-furanose increased significantly which deepened the surface color of Chinese fir.Crystalization if cellulose increased slightly.This offset the strength loss arosed by thermal degradation of hemi-cellulose.(3)In the range of 200 to 245 °C:Mass,density and EMC decreased sharply.By 245 °C,52.97% of hemicellulose has degraded,furanose disappeared as the content of furfural(degradation product)increased.Contents of Klason lignin and phenolic substances increased significantly.The structure of lignin was affected as the methyl and ethyl side chain increased.The strength of cell wall decreased significantly.A large number of micro-and mesopores appeared.The crystalisation of cellulose decreased due to high temperature.Hence the modulus of rupture of Chinese fir rapidly decresed by 19.51%.(4)Thermal susceptibility of specific peaks of Chinese fir derived by 2D-IR:Functional groups of hemicellulose are highly sensitive to temperature,followed by lignin,guaiacyl unit and cellulose.