【作者】 唐荣强；

【导师】 鲍滨福； 李延军；

【作者基本信息】 浙江农林大学 ， 木材科学与技术， 2011， 硕士

【摘要】 为了深入了解高温热处理木材在动态交变载荷作用下的力学性能及松弛转变,探讨材性、含水率、热处理工艺、温度等对木材动态粘弹性的影响规律和木材高温热处理机理,为高温热处理木材的深加工及设计应用提供理论参考,本文主要采用未处理马尾松、190℃热处理马尾松和210℃热处理马尾松作为试材,利用动态热机械分析仪研究了气干密度和抗弯弹性模量与动态粘弹性的相关性,测试了不同含水率试样的动态力学性能,比较了不同工艺下木材动态力学性能的差异,在不同频率下进行温度谱扫描,并运用X射线衍射仪、傅立叶红外光谱仪、TG/DSC综合热分析仪等辅助设备,研究了木材高温热处理机理。研究结果表明:(1)未处理材、190℃热处理材和210℃热处理材的储能模量(E’)、损耗模量(E")均与气干密度、抗弯弹性模量存在显著的正相关关系,而损耗因子(tanδ)无明显相关性。(2)随着含水率的增大,三种试材的E’总体呈减小趋势,E"和tanδ均呈增大趋势,但三种试材变化幅度有差异;热处理降低了木材的吸湿性,平衡含水率随热处理强度的增大而减小。(3)在绝干和气干状态下,与未处理材相比,热处理材E’均增大,E"和tanδ均减小,且随热处理强度的增大,E’增幅越大,E"和tanδ降低越多;热处理本身使木材动态粘弹性发生变化,不同工艺间含水率差异也是造成木材性能差异的原因。(4)E’随着温度的升高而逐渐减小,未处理材对温度的敏感性更大;未处理材E"温度谱和tanδ温度谱均出现两个松弛峰,热处理使木材支化程度下降导致热处理材只有一个α松弛峰;随热处理强度的增大,α松弛峰向高温方向移动;随频率的增大,E’增大,E"和tanδ减小。(5)木材化学、物理结构的改变是造成动态粘弹性变化的原因。190℃和210℃热处理材结晶度大于未处理材,热处理后羟基和羰基数目减少,吸湿性降低,220℃以下,降解速度缓慢,在220℃以上木材发生明显的降解,构成木材E’下降的重要因素,热处理不宜超过220℃。在271℃附近,马尾松发生玻璃化转变。更多还原

【Abstract】 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.更多还原