落叶松板材常规干燥过程的动态机械吸附特性

Dynamic mechano-sorptive characteristics of larch timber during conventional drying process.

为探索木材常规干燥机械吸附蠕变的动态发展模式,该文在实验室条件下对50 mm厚兴安落叶松板材进行常规干燥,用切片法测定了沿厚度方向的横纹弦向干缩应变、弹性应变、黏弹性应变的一维分布情况与变化趋势,并测定了不同尺寸规格及不同预处理工艺下木材试件的自由干缩变形。根据高聚物流变学理论与木材机械吸附蠕变理论,分析了干燥过程中木材厚度方向不同位置的机械吸附蠕变变形的变化规律及其主要影响因子,概括了木材表层与心层的机械吸附蠕变变形的典型发展模式。结论如下：可以采用线性函数与指数函数来分别描述含水率在低于20%和高于20%阶段的木材自由干缩率曲线,相关性较好;木材干燥机械吸附蠕变现象具有极大变异性,与干燥应力模式及应力发展间存在相互作用;在含水率低于特定温度对应下的纤维饱和点2%~4%时,木材表层的拉伸机械吸附蠕变应变与心层的压缩机械吸附蠕变应变均接近极大值;机械吸附蠕变在一定范围内的增大将有助于干燥应力松弛,机械吸附蠕变数值可作为木材干燥工艺调整的参考因子。

In order to investigate the dynamic developing trend of wood drying mechano-sorptive creep during drying process,larch wood with thickness of 50 mm was dried by conventional experiment under laboratorial conditions.The one dimensional distribution and changes of transverse-tangential strains along wood thickness direction were measured using slicing method（the strains components included shrinkage strain,elastic strain as well as visco-elastic strain）.The free shrinkage ratios of wood were also measured with different specimen dimensions and different preliminary processing techniques.The characteristics of wood transverse-tangential mechano-sorptive strain along thickness direction as well as their main influencing factors were analyzed quantitatively by applying polymer rheology theory and wood mechano-sorptive theory.The following conclusions can be drawn from research data： 1） the relationship between wood free shrinkage ratios and moisture content can be described successfully by linear and exponent functions for moisture content below 20% and above 20%,respectively;2） great variability in wood mechano-sorptive creep during drying process and notable interrelationships between wood mechano-sorptive characteristics and drying stress modes were observed;3） according to experimental data on wood mechano-sorptive creep characteristics during drying process,the typical development modes of mechano-sorptive creep strain at wood surface and center position had been made;4）when wood moisture content was below FSP（for corresponding drying temperatures） 2% to 4%,the wood surface tensile mechano-sorptive creep strain and center compression mechano-sorptive creep strain all approached the maximum.In certain extent,the increase of mechano-sorptive creep is helpful for drying stress relaxation and its value can be a reference for drying technology adjustment.