The effect of moisture on the dielectric relaxations in wood
The effect of moisture on the dielectric relaxations in wood
复制标题
水分对木材介电弛豫的影响
DOI：
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发表时间：
1982
期刊：
影响因子：
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通讯作者：
T. Kanamoto
中科院分区：
文献类型：
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作者：
T. Handa;M. Fukuoka;S. Yoshizawa;T. Kanamoto
在-196至0°C的温度范围内，在30 Hz至1 MHz的频率范围内，在宽范围的含水量（MC）（0-40 wt%）内测量潮湿木材的介电常数ε′和损耗因子ε″。根据MC和频率，观察到三种松弛。在-103 °C（30 Hz）的烘干木材中，第一个“α”峰是由于无定形区域的羟甲基旋转。在-110 ° C至-40 °C（30 Hz）时，MC > 0.6wt%时出现的一个新的“π”峰（第二个峰），取决于MC，被归因于木材系统中水分和极性基团之间的复合物的局部模式运动;由于水分的进一步吸附，初始氢键网络的整体松散被延长的水化促进，因此它被增强。这些弛豫的峰值温度和活化能的变化复杂地依赖于MC。在MC > 10wt%时，在-40 °C（30 Hz）附近公开了一个新的“π”峰（第三峰），作为离子传导的肩部。这个新的峰可以归因于冻结在木材中的水的基础上的峰值温度，松弛强度与MC，活化能，和的事实，即峰没有观察到的各种极性有机溶剂的吸附。这表明，木材吸收的一些水分可能在低温下以冻结状态存在，即使在MC远低于通常接受的纤维饱和点。
The dielectric constant ϵ′ and the loss factor ϵ″ of moistened wood were measured over a wide range of moisture content (MC), 0–40 wt% in the temperature range −196 to 0°C, and in the frequency range 30 Hz to 1 M Hz. Three relaxations were observed depending on the MC and frequency. The first ϵ″ peak at −103°C (30 Hz) in oven-dried wood is known to be due to the methylol rotation in the amorphous regions. A new ϵ″ peak (second peak), which appeared for MC >0.6 wt% at −110 to −40°C (30Hz) depending on the MC, is assigned to the local mode motions of the complexes between moisture and polar groups in the wood system; it is enhanced as the overall loosening of the initial hydrogen bond network is promoted by the extended hydration due to further sorption of moisture. The peak temperatures and the activation energies for these relaxations changed complexly depending on the MC. At MC > 10 wt%, a novel ϵ″ peak (third peak) was disclosed around −40°C (30 Hz) as a shoulder of the ionic conduction. This novel peak may be attributed to the water frozen in wood on the basis of the peak temperature, relaxation strength vs. MC, the activation energy, and the fact that the peak is not observed for the sorption of various polar organic solvents. This suggests that some of the moisture sorbed by wood may probably exist in a frozen state at low temperatures, even at a MC well below the commonly accepted fiber saturation point.