毛竹材的动态热机械性能分析

采用动态热机械分析(DMTA)测试毛竹材的储能模量(E')和损耗模量(E″),分析在不同初含水率、笔壁径向部位、竹龄及距毛竹基部高度下毛竹材的储能模量和损耗模量及玻璃化转变温度(Tg)。结果表明:①毛竹材储能模量随着温度的升高呈逐渐减小的趋势,损耗模量随着温度的变化出现两个峰,当温度达到玻璃化转变温度时达到第1个峰值。②储能模量和损耗模量受初含水率的影响较大,随着含水率的增加呈相对减小的趋势; 在竹壁径向上,储能模量和损耗模量由内而外依次增大; 在同一温度下,毛竹材的储能模量和损耗模量具有随毛竹高度的增加而降低的趋势; 不同竹龄毛竹材的储能模量和损耗模量略有差别,基本上随竹龄的增大而增大。③毛竹材Tg随含水率的增加而降低,在绝干状态时Tg为217～223 ℃; 含水率为15%到饱水状态时,Tg在113～134 ℃之间; 沿竹壁径向的竹青、竹肉和竹黄的Tg略有差别,30%含水率时的Tg在123～135 ℃之间; 不同竹龄毛竹材的Tg并无较大差异,在120～123 ℃之间; 不同高度的毛竹材Tg也无显著差异,在123～126 ℃之间。研究表明,在毛竹材的实际生产中可通过增加毛竹材周边温度和含水率以增加其塑性,使竹材的竹龄和高度选择更加宽泛。

Dynamic mechanical analysis of moso bamboo timber

In order to provide a theoretical basis for the bamboo softening and flattening, the storage modulus, loss modulus and glass transition temperature(Tg)of moso bamboo were investigated by dynamic mechanical analysis(DMTA)at various initial moisture contents(MC), radial positions, ages and heights. Results showed that the storage modulus decreased with the temperature increasing. The loss modulus increased firstly and then decreased, but when temperature reached a certain extent, loss modulus increased and then decreased again. The moisture content had a great effect on storage modulus and loss modulus, but both moduli decreased with the MC increasing. The storage modulus and loss modulus increased from inner to outer layer in the radial direction and decreased with the height increasing. Besides, the age had a positive but tiny influence on both storage modulus and loss modulus. As MC increasing, Tg decreased from 217-223 ℃at absolute dry to 113-134 ℃ at MC above 15%. The Tg of outer, median and inner layers of bamboo in the radial direction showed slight differences and they were 123-135 ℃ for bamboo at 30% MC, while they were not affected significantly by the age or height,ranginge from 120℃ to123 ℃ and 123℃ to126 ℃ for different ages and heights, respectively. This study showed that the increase of ambient temperature and MC of bamboo could improve the plasticity of bamboo. This provides the wider choice of bamboo timber at its ages and heights, too.