Cellulose, lignin or hemicelluloses: What provides strength to plant biomass when grinding

Almost all plant biomass refining technologies involve grinding, and the wrong choice of the type and mode of mechanical action can dramatically reduce the economic efficiency of the process. In this study, we assessed the contribution of polymers forming the supramolecular structure of the cell wall (cellulose, hemicelluloses, and lignin) to compare grindability of plant biomass when using standard equipment with two types of mechanical action, the impact-shear mode in a planetary ball mill and the shear mode in an attritor. Individually, these types of grinding equipment are well upscaled to the industrial level, while their hypothetical combination with different ratios between individual “impact/shear” actions describes the micromechanics for most other grinding setups. Assessment of energy consumption and grinding productivity demonstrates that grinding in the impact–shear mode is more efficient compared to the shear one. Chemical removal of any polymeric component of the plant cell wall increases energy efficiency of grinding in the impact–shear mode up to ninefold. In the case of shear-type loads, each polymeric component of the cell wall contributes to grindability of the plant biomass. Partial hydrolysis of hemicelluloses has the strongest positive effect on subsequent grinding. In contrast, oxidation and partial dissolution of lignin reduces grindability, probably because of the redistribution of oxidation products over the cell surface.