Agricultural and forestry plant residues are available sources of carbon, but require fragmentation/ separation operations to extract ultrafine powders with targeted properties. This plant-based dry biorefinery is a promising alternative to oil, particularly for energy and materials applications. IATE laboratory hosts the INRAE national plant fractionation platform and is developing, in collaboration with LMGC laboratory, unique numerical models for granular materials composed of breakable particles. A major challenge is to understand how the microstructure and interactions in plant tissues influence the size, composition and shapes of the fragments. In this thesis, we will associate a massively parallel peridynamic model for the propagation of the fracture across the histological structures of plants (μm scale), and a Discrete Element approach for grain fragmentation (process scale). The ultimate goal is to elucidate the deconstruction mechanisms and develop bottom-up models accounting for both mechanical and physicochemical interactions.