Jiang Y, Lawrence M, Ansell M P, Hussain A
BRE Centre for Innovative Construction Materials, Department of Architecture and Civil Engineering, University of Bath, Bath BA2 7AY, UK.
R Soc Open Sci. 2018 Apr 4;5(4):171945. doi: 10.1098/rsos.171945. eCollection 2018 Apr.
This paper, for the first time, fully characterizes the intrinsic physical parameters of hemp shiv including cell wall microstructure, pore size distribution and absolute density. Scanning electron microscopy revealed microstructural features similar to hardwoods. Confocal microscopy revealed three major layers in the cell wall: middle lamella, primary cell wall and secondary cell wall. Computed tomography improved the visualization of pore shape and pore connectivity in three dimensions. Mercury intrusion porosimetry (MIP) showed that the average accessible porosity was 76.67 ± 2.03% and pore size classes could be distinguished into micropores (3-10 nm) and macropores (0.1-1 µm and 20-80 µm). The absolute density was evaluated by helium pycnometry, MIP and Archimedes' methods. The results show that these methods can lead to misinterpretation of absolute density. The MIP method showed a realistic absolute density (1.45 g cm) consistent with the density of the known constituents, including lignin, cellulose and hemi-cellulose. However, helium pycnometry and Archimedes' methods gave falsely low values owing to 10% of the volume being inaccessible pores, which require sample pretreatment in order to be filled by liquid or gas. This indicates that the determination of the cell wall density is strongly dependent on sample geometry and preparation.
本文首次全面表征了麻屑的固有物理参数，包括细胞壁微观结构、孔径分布和绝对密度。扫描电子显微镜揭示了与硬木相似的微观结构特征。共聚焦显微镜揭示了细胞壁中的三个主要层：中层、初生细胞壁和次生细胞壁。计算机断层扫描改善了三维孔隙形状和孔隙连通性的可视化。压汞法（MIP）表明，平均可及孔隙率为76.67±2.03%，孔径类别可分为微孔（3-10纳米）和大孔（0.1-1微米和20-80微米）。通过氦比重瓶法、MIP法和阿基米德法评估绝对密度。结果表明，这些方法可能导致对绝对密度的错误解读。MIP法显示的实际绝对密度（1.45克/立方厘米）与已知成分（包括木质素、纤维素和半纤维素）的密度一致。然而，由于10%的体积是不可及孔隙，氦比重瓶法和阿基米德法给出的值过低，为了使液体或气体填充这些孔隙，需要对样品进行预处理。这表明细胞壁密度的测定强烈依赖于样品的几何形状和制备方法。
