Densified cellulose materials and delignified wood reinforced composites

The development of sustainable materials from renewable resources is one of the key challenges in today's materials science. Wood has great potential to play an important role in future materials advancement due to its excellent mechanical properties and high abundance. In this regard, two novel concepts for the development of high-performance wood-based materials in scalable top-down approaches are presented. Both concepts, Densified Cellulose Materials (DCMs) and Delignified Wood Reinforced Polymers (DWRPs), are based on delignification and densification of wood. Matrix free DCMs possess good tensile properties with a stiffness up to 40 GPa and strength up to 250 MPa. The high mechanical properties are obtained by a combination of high fibre volume content (FVC) of up to 80% and stress transfer throughout the cellulose scaffold enabled by mechanically interlocked fibre-fibre interfaces. Matrix infiltrated DWRPs reveal excellent tensile properties with elastic moduli of up to 70 GPa and 600 MPa strength. The epoxy matrix is vacuum infiltrated into the scaffold before densification and curing and provides an additional stiffening effect. The low intrinsic density of cellulose fibres results in attractive specific tensile properties, which are above previously reported values obtained for natural fibre composites such as flax or sisal. By scalable open-mold vacuum processing, DCMs with high tensile properties can be fabricated to partially replace less sustainable materials such as glass fibre reinforced composites in the future.