Study On The Properties And Moisture Absorption Of Heat-treated Softwood

Wood is a high quality renewable biomass material,the appropriate modificationmethod can improve its utilization.As an environmentally modification method,heat-treat technology can improve the dimensional stability of wood,corrosionresistance,arthroscopic and other properties.It has great significance to ease thetimber market supply and demand contradiction.The paper is research heat-treatedtemperature on 180 ℃,200 ℃ and 220 ℃ to test the propertiesand moisture absorption characteristics of Pseudotsuga menziesii and picea abies,and use NMR technology test the water sorption diameter distributions and gets following results:The heat-treated technology has increased MOE and decreased MOR of softwood.When the heat-treated temperature up to 220 ℃,the MOE of two kinds of softwood has increased 10204 Mpa to 12525 Mpa,the other has increased 9965 Mpa to 12743 Mpa,the rate of MOE is 22.75% and 27.88%.The MOR of two softwoood has decreased77.47 Mpa to 59.36 Mpa,the other has increased 68.05 Mpa to 58.43 Mpa the rate of MOE is 23.38% and 14.14%.Using the NMR cryoporometry to shielded the free water signal of heat-treated wood by the experimental method of freezing phase change.The result shows that FSP of Pseudotsuga menziesii and its control is 39.71%、33.59%、25.13%、22.01%,picea abies and its control is 2.72%、37.08%、29.10%、23.11%.Heat-treated technology can effectively reduce the FSP of the wood,and the result is consistent with the wood theory.Test the pore distribution of the cell wall in two kinds of wood by the relationship between the freezing point and the equivalent capillary diameter determined under the Gibbs-Thomson equation.The result shows that pore size distribution of the cell wall is related to heat-treated technology.When the temperature up to 220℃,The rate of diameter distributions more than 4.56 nm is 12.69% and 13.83%and less than 1.26 nm is 49.35% and 41.01%.The equilibrium moisture content of the heat-treated wood was fitted by Hailwood-Horrobin isothermal adsorption curve,and the result shows that,heattreated technology can effectively reduce the moisture content of the wood.The single layer water molecules decreased10%、20% and 40%,multilayer water molecular has decreased 20%、40% and 50% compared with control.The Hailwood-Horrobin model can describethe isothermal adsorption of water during the heat treatment process.when the temperature up to 220℃,the maximum single layer water is 2.41% and 3.54%and the maximum multilayer water molecular is 6.59% and 8.61%,the rate compare the control decrease 50%.Using the nuclear magnetic resonance technology to test top time of under different relative humidity.The result shows that change interval of top time onPseudotsuga menziesii 0.215-0.883 ms 0.168-0.738 ms,0.164-0.684 ms,0.149-0.679ms(180℃、200℃、220℃)and picea abies is 0.236-0.839ms(control),0.183-0.733 ms,0.162-0.720 ms,0.147-0.616ms(180℃、200℃、220℃);Based on the water adsorption model of Hailwood-Horrobin model,test the relaxation intervals of single layer water molecules and multi-layer water molecules.The result shows that nuclear magnetic resonance technology is reasonable and convenient both in principle and in practice,and can be further used for wood modification studies compare with thetraditional method.