Optimizing Wood–Hemp–Sodium Silicate Composites for Strength, Extrudability, and Cost in Additive Manufacturing Applications

Utilizing forestry and agricultural byproducts like wood and hemp residues advance sustainable additive manufacturing (AM), while reducing material costs. This study investigated the development and characterization of wood-sodium silicate composites incorporating hemp hurd and hemp fibers for AM applications. Formulations varied by wood fiber type (unsifted, 40 mesh, and pellet), sodium silicate concentration (50-60 wt%), and hemp hurd content (0-15 wt%). Properties evaluated include particle size and bulk density of the constituent materials, rheological behavior, extrusion performance, composite bulk density, and flexural and compressive strengths. Rheology and extrusion were largely influenced by the liquid content. Mixtures with low liquid content (50 wt% sodium silicate) had high motor power and low viscosity. As liquid content increased, motor power decreased, while viscosity increased up to 55 wt% and then decreased at 60 wt%. Mechanical properties correlated with particle size, where finer particles enhanced strength. A cost analysis was conducted using raw material prices to determine the economic feasibility of each formulation. Finally, the formulations were evaluated based on strength-to-cost ratios, extrudability and processability. The formulation with pellet wood fibers, 55 wt% sodium silicate, and 10 wt% hemp hurd achieved a high ratio of 73.0 MPa/$ while maintaining low motor power. This formulation offered additional benefits which are discussed qualitatively.