Delignified densified wood is a new promising and sustainable material that possesses the potential to replace synthetic materials, such as glass fiber reinforced composites, due to its excellent mechanical properties. Delignified wood, however, is rather fragile in a wet state, which makes handling and shaping challenging. Here we present two fabrication processes, closed-mold densification and vacuum densification, to produce high-performance cellulose composites based on delignified wood, including an assessment of their advantages and limitations. Further, we suggest strategies for how the composites can be re-used or decomposed at the end-of-life cycle. Closed-mold densification has the advantage that no elaborate lab equipment is needed. Simple screw clamps or a press can be used for densification. We recommend this method for small parts with simple geometries and large radii of curvature. Vacuum densification in an open-mold process is suitable for larger objects and complex geometries, including small radii of curvature. Compared to the closed-mold process, the open-mold vacuum approach only needs the manufacture of a single mold cavity.@en

Elegant design principles in biological materials such as stiffness gradients or sophisticated interfaces provide ingenious solutions for an efficient improvement of their mechanical properties. When materials such as wood are directly used in high-performance applications, it is not possible to entirely profit from these optimizations because stiffness alterations and fiber alignment of the natural material are not designed for the desired application. In this work, wood is turned into a versatile engineering material by incorporating mechanical gradients and by locally adapting the fiber alignment, using a shaping mechanism enabled by reversible interlocks between wood cells. Delignification of the renewable resource wood, a subsequent topographic stacking of the cellulosic scaffolds, and a final densification allow fabrication of desired 3D shapes with tunable fiber architecture. Additionally, prior functionalization of the cellulose scaffolds allows for obtaining tunable functionality combined with mechanical gradients. Locally controllable elastic moduli between 5 and 35 GPa are obtained, inspired by the ability of trees to tailor their macro- and micro-structure. The versatility of this approach has significant relevance in the emerging field of high-performance materials from renewable resources.@en

Elegant design principles in biological materials such as stiffness gradients or sophisticated interfaces provide ingenious solutions for an efficient improvement of their mechanical properties. When materials such as wood are directly used in high-performance applications, it is not possible to entirely profit from these optimizations because stiffness alterations and fiber alignment of the natural material are not designed for the desired application. In this work, wood is turned into a versatile engineering material by incorporating mechanical gradients and by locally adapting the fiber alignment, using a shaping mechanism enabled by reversible interlocks between wood cells. Delignification of the renewable resource wood, a subsequent topographic stacking of the cellulosic scaffolds, and a final densification allow fabrication of desired 3D shapes with tunable fiber architecture. Additionally, prior functionalization of the cellulose scaffolds allows for obtaining tunable functionality combined with mechanical gradients. Locally controllable elastic moduli between 5 and 35 GPa are obtained, inspired by the ability of trees to tailor their macro- and micro-structure. The versatility of this approach has significant relevance in the emerging field of high-performance materials from renewable resources.@en

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.@en

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.@en