Study On Dynamic Viscoelasticities Of Heat-treated Wood

In order to look into the dynamic mechanical properties and relaxation changes of heat-treated wood under cyclic loading,to investigate the effect of wood properties, moisture content, heat treatment process and temperature on dynamic viscoelasticity and mechanism of heat treatment,and to provide a theoretical reference for applications and deep processing of heat-treated wood ,the dynamic viscoelasticity of untreated pine (Pinus massoniana), heat-treated pine at 190℃and 210℃were studied by dynamic mechanical thermal analyzer Correlations between air-dried density and dynamic viscoelasticity were investigated .Correlations between modulus of elasticity and dynamic viscoelasticity were studied.Dynamic properties of samples with different moisture content were tested.Dynamic mechanical properties of wood under different heat-treatment process were compared.The temperature spectrum were scanned at different frequency.The mechanism of heat-treatment were studied by X-ray diffractometer, FTIR and TG/DSC comprehensive analysis meter.The results were listed as follows:(1)Both of storage modulus and loss modulus of untreated pine, heat-treated pine at 190℃and heat-treated pine at 210℃had remarkble correlations with modulus of elasticity(MOE) and air-dried density(ρ)respectively.But the loss factor was incorrelate with MOE andρ.(2)As the moisture content increases, E' of the three test materials showed decreasing trend overall, E"and tanδshowed increasing trend,but the range of changes of three test materials were different.The Hygroscopic were decreased by heat-treatment. Equilibrium moisture content was decreased with the heat treatment intensity increasing.(3)At air dried and oven-dried states,comparing with untreated wood, E' of heat-treated wood has increased,E" and tanδhave decreased.The intensitier of heat treatment,the greater E' has increased andt he more E" and tanδhave decreased. Heat-treatment has changed dynamic viscoelasticity of wood.Differences of moisture content between processes have also contributed to the change of dynamic viscoelasticity.(4)E' has gradually decreased with the temperature increasing and untreated wood was more sensitive to the temperature.There are two relaxation peaks in temperature spectrums of E" and tanδof untreated wood. Heat-treatment has decreased the degree of branching of wood, which led to only oneαrelaxation peak in temperature spectrum of heat-treated wood. With the increasing of heat treatment intensity,αrelaxation peak shifted to high temperature. E' has increased with frequencies increasing but E"and tanδhave decreased.(5)The changes of wood chemical structural and physics structural have caused dynamic viscoelastic change.The crystallinity of heat-treated woods were greater than that of untreated wood.The Hydroxyl and Carbonyl have decreased afer wood was heat-treated., the degradation rate of wood is slow when the temperature was below 220℃.When the temperature was above 220℃,there was a apparent degradation of wood. Rapid degradation of wood played an important role in the decline of E'. The temperature should not exceed 220℃for wood Heat treatment. At 271℃, the glass transition of pine has happened.