Wood fiber - sodium silicate mixtures for additive manufacturing of composite materials

A composite mixture of wood fiber and sodium silicate (SS) binder has been explored as a viable material for use in additive manufacture of wood based composite materials. Mixtures of 50–60% wood fiber and 50 − 40% SS were explored. The curing behavior of these formulations were examined by differential scanning calorimetry (DSC) and dynamic rheometry. An exothermic curing peak of 83 °C was observed for SS and increased to 153 and 163 °C with the addition of wood fiber. Rheology flow curves showed higher viscosity values for 50/50 blends and lower values for SS. A custom extrusion system was fabricated and 50/50 wet blends were extruded, cured at different temperatures, and characterized for flame retardancy, mechanical, thermal, and water absorption properties. Surface chemistry changes before and after curing were determined by Fourier Transform Infrared (FTIR) spectroscopy. Mechanical properties, determined by three-point bend testing, improved with the addition of the wood fiber but varied with different curing temperatures and thermal stability of the composites increased with curing temperature. This extruded wood-SS composite shows promise for use in additive manufacturing.