Design and function of thermoresponsive-ultrafast stiffening suspension formulations for 3D printing

An inability to accurately control the rate and extent of solidification of cementitious suspensions is a major impediment to creating geometrically complex structural shapes via 3D printing. In this work, we have developed a thermoresponsive rapid stiffening system that will stiffen suspensions of minerals such as quartz, limestone, portlandite, and Ordinary Portland Cement (OPC) over a wide pH range. When exposed to trigger temperatures between 40 °C and 70 °C, the polymer binder system undergoes a thermally triggered free radical polymerization (FRP) reaction, leading to an ultrafast stiffening of the suspension at an average rate on the order of 1 kPa/s and achieving MPa-level strength in less than a minute. The cured composites exhibit flexural strength and strain capacity far greater than OPC-based composites (${\sigma }_f$ $\sim$ 25 MPa, ${\gamma }_f$ $>$ 1 %). We successfully demonstrated 3D printing using these engineered slurries, showcasing their thermal response, thermal latency, and printability, thereby validating our design approach and its potential for diverse applications. These thermoresponsive slurries facilitate freestyle printing, non-horizontal printing, and the creation of complex geometries with high overhangs. This approach provides a means to surmount the significant limitations of extrusion-based 3D printing using particulate suspensions and open up new possibilities in integrating design and production.