Effect of Biochar Reinforcement on the Wettability, Mechanical, and Thermal Properties of Extrudable Wood–Sodium Silicate Composites

This original study investigated the effect of biochar (BC) addition, a hydrophobic reinforcing agent, to a thermosetting wood–sodium silicate (W-SS) composite prepared by extrusion for use in additive manufacturing. Commercial BC was blended (10–20% w/w) with W-SS while lowering the SS resin content to form composites. In addition, 50–70% w/w BC-SS composites were also prepared. The flow behavior of the uncured composites was determined by rheometry. The composite mixtures were extruded and cured, and then tested for their flexural, water soak, and thermal properties. Replacing SS content with 10% BC significantly improved the mechanical properties of W-SS while potentially reducing cost and biodegradability; however, 20% w/w BC replacement led to reduced strength. Incorporating BC improved the thermal and dimensional stability of W-SS composites. BC-SS showed improved thermal, hydrophobicity, and flow properties compared to W-SS composites, but lower mechanical properties. It was found that the composite containing 50% W, 10% BC, and 40% SS had an optimum flexural strength of 29 MPa, with thermal property values improving by 29 °C and the dimensional stability improving by 10% compared to 50% W-50% SS (w/w). This implies that BC could help improve the hydrophobicity properties of W-SS while also enhancing mechanical properties, biodegradability, and reducing SS content. 3D printing of the 50% BC-50% SS was demonstrated to showcase the industrial feasibility of printing BC-SS composites. This study demonstrates that BC is an effective additive for enhancing the properties of W-SS composites.