Cell wall microstructure, pore size distribution and absolute density of hemp shiv

This paper, for the first time, fully characterises 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 visualisation of pore shape and pore connectivity in three dimensions. Mercury intrusion porosimetry showed 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, mercury intrusion porosimetry (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/cm3) consistent with the density of the know...