Pore structure evolution of bamboo fiber and parenchyma cell wall during sequential chemical removal

The pore structure of the cell wall is closely related to biomass recalcitrance. Bamboo fibers and parenchyma cells constitute the main body of bamboo but have significantly different chemical decomposition efficiencies. This study compared the influence of chemical removal on the porosity, pore size distribution, and hygroscopicity of fibers and parenchyma cells in bamboo. The results exhibited that parenchyma cells were more porous and hygroscopic as compared to fibers. However, both cell types exhibited similar changes during sequential chemical removal. The removal of extractives produced many more micropores than mesopores in the cell walls, which were mainly concentrated in the size ranges of 0.4-1.0 nm and 2-10 nm. Delignification reduced both the cell wall porosity and micropore volume, which was attributed to the easy collapse of delignified cell walls in powder samples, as well as the disappearance of micropores in lignin. Several mesopores with a diameter of 2-10 nm were created upon removing hemicellulose after delignification, but almost all micropores disappeared. Changes in the porosity and chemical compositions synergistically affected the water sorption and hysteresis of bamboo. The delignified samples contained more exposed sorption sites, which displayed stronger dynamic water vapor sorption. After removing hemicellulose, the sample exhibited lower water sorption, primarily due to a reduction in the number of sorption sites. The absorption hysteresis of bamboo decreased upon decreasing the cell wall porosity.