3D Printing allows the manufacture of complex shapes, and 3D printers have become widely available. However, the resulting parts often lack mechanical strength. Introducing, e.g., glass or carbon fibers into the printed material can help strengthen it, but this approach requires specialized 3D printers and leads to non-recyclable printed parts. Liquid-crystal polymers (LCPs) could solve both of these problems: LCPs self-assemble into ordered, strong structures during the printing process, which can be performed by normal, commercially available 3D printers.

Kunal Masania, Theo A. Tervoort, André R. Studart, and colleagues, ETH Zurich, Switzerland, have developed an approach for the 3D printing of recyclable LCPs using conventional desktop printers. The team used an aromatic random copolyester consisting of the monomers p-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid. The printer was a commercially available model, slightly modified to achieve temperatures up to 400 °C.

When the polymer is extruded through the printing nozzle, the LCP’s domains are aligned in the direction of flow. When the material cools, the flow-aligned arrangement is retained at the surface. Polymer chains within the printed filament cool slower and can reorient themselves. As a result, the printed filaments have a tough core–shell structure. In addition, the printing orientation can be chosen in such a way as to align the filaments along the part’s stress lines, which further improves performance.

The resulting material outperforms state-of-the-art printed polymers and rivals high-performance lightweight materials. In contrast to fiber-strengthened parts, the printed LCP structures can be recycled.

• Three-dimensional printing of hierarchical liquid-crystal-polymer structures,
  Silvan Gantenbein, Kunal Masania, Wilhelm Woigk, Jens P. W. Sesseg, Theo A. Tervoort, André R. Studart,
  Nature 2018, 561, 226–230.
  https://doi.org/10.1038/s41586-018-0474-7