Additive manufacturing of thermosetting bio-composites by temperature-controlled paste extrusion: application to honeycomb sandwich panels

Abstract A temperature-controlled paste-extrusion process was developed to enable additive manufacturing of otherwise unprintable thermosetting bio-composites. Bioepoxy was combined with lignin-containing cellulose particles to form a high-viscosity paste. Ambient partial curing raised the apparent viscosity to approximately 10⁵ mPa·s at 1 s⁻¹, after which the premix was cooled to 5–10 °C to retard further crosslinking during loading and deposition. The resulting formulations exhibited pronounced shear-thinning behaviour, were cost-effective, and contained a high bio-based fraction (58–71%). Systematic printability trials demonstrated that direct extrusion of the uncooled paste produced failed specimens, whereas the delayed-deposition route yielded stable, geometrically accurate honeycomb cores. Printed objects displayed good machinability under computer numerical control. As a representative application, hexagonal honeycomb cores were fabricated and bonded between plywood face sheets to produce bio-based sandwich panels. Tensile characterisation of the core material and three-point bending tests of the completed panels confirmed that the printed bio-composite provides adequate stiffness and load-bearing capacity for lightweight structural use. Overall, the process offers a practical route for valorising lignocellulosic fillers in thermosetting matrices and for achieving on-demand solidification in layer-wise fabrication of sustainable cellular structures.