竹材内耗和介电的研究

Investigation on Internal Friction of Bamboo

用葛氏倒扭摆仪测量了竹材样品在153K到523K温度范围内的低频下的内耗(IF)行为,在173K2、28K3、23K和489K观察到4个内耗峰,对323K内耗峰的机理进行了较为详细地研究,利用多功能摆研究了其对频率的依赖性,发现该峰峰温不随测量频率变化,而峰高与测量频率及升温速率有关,呈现相变内耗峰的特征.介电测量表明:在323K附近同样存在一介电损耗峰.为了探讨该峰的机理,进一步研究了竹材含水量对该损耗峰的影响.实验结果表明该峰与水在竹材中的某种转变有关.

In order to investigate the mechanic property of bamboo, an inverted torsion pendulum was used to measure the internal friction (IF) of bamboo from 150 K to 520 K at low frequency range. Four IF peaks were observed at 173 K, 228 K, 323 K and 489 K, respectively. The IF peak appearing at 323 K was investigated intensively. The dependence of this IF peak on frequency was measured by multifunction torsion pendulum. It was found that this IF peak was associated with a phase transition, because the peak position was independent of frequency, but the peak height was affected by the frequency and heating rate. The dielectric properties of the same bamboo samples were measured by HP4194A. A peak of dielectric loss was also observed near 323 K. Similar to the results of IF measurements, the position of the peak did not change with the frequency, but the peak height decreased with increasing frequency. The results of dielectrics loss further confirmed that the peak was not a relaxation peak but associated with phase transition. To find the origin of IF peak at 323 K in bamboo, the dependence of the loss peak on the content of water was thoroughly investigated. It was found that the lager water content, the higher the peak height and peak temperature and no IF peak was observed in the absolutely dried bamboo specimen. It is suggested that the internal friction peak should be associated with the water content inside bamboo. The measurement of the dielectrics loss of cellulose and lignin was performed. No peak was found at the vicinity of 323 K in both cellulose and lignis. The measurement of the dielectrics loss of molecule bolt samples which have similar porous structure with bamboo was performed. The behavior of the dielectric peak in molecule bolt is similar to that in bamboo. It is suggested that the peak at 323 K in bamboo may be attributed to one kind of transition of water in bamboo.