Postprint Thermal Bonding of Clay–Polyester Pastes

We demonstrate the three-dimensional (3D) printing of clay-based pastes, extrudates of which are thermally strengthened after printing. The technique involves mixing the clay paste with polymer particles: the clay contributes plasticity, and the polymer provides strength through its ability to melt upon heating and harden upon cooling, thereby bonding the printed material despite negligible geometrical alterations. Paste extrusion tests reveal a decreasing force with increasing polymer content (PCv) and water content (w). The flexural strength of bonded extrudates increases with PCv, with a notable inflection at PCv ≈ 30%, beyond which the material appears to be furnished with an interconnected polymeric scaffolding. Extrudates with PCv ≤ 18% crumble upon wetting, whereas those with PCv ≥ 30% absorb water to levels that meet construction standards and exhibit flexural strengths comparable to concrete counterparts. Extrudates with PCv ≥ 30% exhibit a slight strength reduction after wetting; reheating significantly recovers or enhances their original strength, highlighting the potential for thermal repair through polymer remelting. Preliminary test results reveal that bonded extrudates exhibit self-extinguishing after direct torch exposure, indicating a promising degree of fire tolerance.