The need for renewable bio-based materials that could replace well-established synthetic composite materials is rapidly growing. For example, bio-based materials are increasingly used in applications where a lightweight design should be combined with sustainability and recyclability. However, it is often very challenging to directly transfer the excellent properties of biological materials to a product in a scalable and cost-efficient manner. In this study, we combined delignified wood layers (veneers) and a starch-based glue into bio-based high-performance composites. First, we investigated the ideal amount of starch-based glue between the layers to prevent delamination in the final composite. Then, we produced laminates in unidirectional, cross-ply, and quasi-isotropic configurations using wet processing. Laminates with tensile properties up to 40 GPa and 200 MPa in tensile stiffness and strength, respectively, were fabricated with a very high fiber volume content of up to 80%. The high fiber volume contents led to mechanical interlocks between neighboring fibers and made the need for an additional matrix unnecessary. The water-based laminate process is cost-efficient and scalable and additionally allows one to make full use of delignified wood’s formability by producing shaped parts for various applications.@en

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

Wood is increasingly considered in sustainable structural materials development due to its hierarchical structure, including an oriented reinforcing cellulose phase combined with carbon capturing and renewability. Top-down manufacturing techniques can provide direct access to this hierarchical cellulose scaffold for use in new functional materials. For high-performance load-bearing wood-based materials, the volume content of the reinforcing phase needs to be increased to much higher fiber volume contents (FVCs). This has been achieved by structure-retaining delignification followed by densification. The obtained matrix-free materials possess high tensile stiffness due to preservation of hierarchical fiber alignment; however, they demonstrate low mechanical properties in bending and cannot be used in moist conditions due to their propensity for water absorption. In order to address these two challenges, an interpenetrating wood polymer phase composite is developed using a delignified wood scaffold as a continuous reinforcing phase and epoxy resin as the interconnected matrix phase. We utilize the continuous flow channels in delignified wood for vacuum-assisted matrix infiltration in a condition of open continuous porosity in the wood scaffold. Prior to matrix curing, the material is densified in order to increase the FVC, decrease porosity, and reduce density variations in the wood scaffold. Due to the compressibility of delignified cellulose fibers, interpenetrating phase composites (IPCs) with very high FVCs of up to 80% could be produced, leading to exceptionally high tensile stiffness and strength of up to 70 GPa and 600 MPa. The obtained stiffness values far exceed the upper limit of the rule of mixtures due to an enhanced stress transfer through mechanically interlocked fiber-fiber interfaces combined with the stiffness providing matrix phase that further aids stress transfer between neighboring wood cells via their pits. This new approach paves the way for an efficient production of high-performance sustainable materials that can be used as alternative for glass fiber reinforced composites or natural fiber composites.@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

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

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