Additive manufacturing of functional wood materials with integrated mechanical robustness and thermal energy storage

• Optimized printing and drying processes yield cellulose composites stronger than natural wood. • Extrusion-aligned fibers and unidirectional printing yield high flexural strength. • Phase change material integration enables thermal energy storage and load-bearing strength. • Unveil a potential way to upcycle wood waste for high-value building materials. Wood is a widely used structural material, valued for its mechanical strength and natural renewability. Conventional wood manufacturing relies on subtractive processes that generate significant waste. Meanwhile, emerging additive manufacturing techniques offer a sustainable alternative to upcycle wood waste with functionalities including thermal energy storage (TES). One key challenge in developing TES-enabled wood-based composites lies in integrating phase change materials (PCMs) without compromising mechanical properties. Here, a cellulose fiber-based composite with PCM additives is fabricated via direct ink writing. The fiber alignment from ink extrusion and densification during drying yield high flexural strength of 11.2–90.7 MPa, especially when printed unidirectionally. The composites also show a latent heat of 37.6–112.6 J/g for TES, while exhibiting outstanding durability with minimal loss in energy density after isothermal aging and repeated thermal cycling. This work demonstrates a feasible approach for manufacturing mechanically robust and thermally efficient composites from recycled wood.