Résumé
Since the 90s, bio-based polymers and composites have undergone significant development. For example, the automotive industry is seeking to develop ever lighter structures and increase the bio-based fraction of its composites, which could be achieved by using plant fibres as reinforcements. Beyond the interesting intrinsic properties of plant fibres, the thermo-mechanical properties of biocomposite materials are highly dependent on the fibre / matrix interface. However, most polymer matrices are apolar and hydrophobic, which implies weak interactions, and therefore low interfacial adhesion with plant fibres, and is not easy to overcome. Inspired by natural biological systems that feature hierarchical nanostructured architectures and achieve high strength and toughness [1], the goal of this work is to develop long-scale interphases in polymer biocomposites. Two strategies are explored: (i) a polymer engineering approach based on radiation-induced cross-linked interphases in LDPE-based biocomposites reinforced by aliphatic phosphonic acid modified flax fibres [2], and (ii) a nanotechnology approach based on nanostructured interphases in PP and epoxy-based biocomposites reinforced by Cellulose NanoCrystals (CNC) modified flax fibres [3, 4]. A multi-scale analysis of the resulting interphases is carried out, from the nano & micrometric scale with the characterization of fibre surface topography, work of adhesion and interfacial shear strength (IFSS) between flax fibres and matrices, to the macroscopic scale with the mechanical properties of biocomposites.