An overview of structural-functional-integrated composites based on the hierarchical microstructures of plant fibers

Plant fiber-reinforced composites have raised great attention among materials scientists and engineers during the past decade. Most of the efforts were put on the interfacial modifications to improve the mechanical properties of the composites so that they could partly replace the currently largely used glass fiber-reinforced composites. The modifications were mainly focused on the surface treatment of plant fibers so that mechanical or chemical bonding between plant fibers and polymeric matrices could be set up. However, the unique hierarchical microstructures of plant fibers make the building up of multiscale interfaces possible so that more forces or energies would be needed to fracture the plant fiber-reinforced composites. The additional hollow structures could also bring benefits for sound absorption and damping properties. Therefore, this article reviewed R&D efforts to develop structural and functional-integrated plant fiber-reinforced composites by fully taking advantage of the hierarchical microstructures of plant fibers. Firstly, the unique hierarchical structures of plant fibers were revealed and hierarchical theoretical models for mechanical properties were discussed. Then, the modification, characterization, and evaluation of plant fibers in terms of their interfacial properties with polymeric matrices, especially by nanotechnologies with the consideration of their unique hierarchical microstructures, were reviewed. Finally, the design and manufacture of quasi-structures and structural-damping components using technologies that have been fully adapted to state-of-the-art industrial processes for use in critical applications, such as aircraft interiors, rail transportation vehicles, and constructions, were also introduced.