A team of researchers at ETH Zürich in Switzerland has developed an approach to 3D print recyclable materials using cheap desktop printers that outperform state-of-the-art printed polymers and rival the highest performance lightweight materials.

Fiber-reinforced polymer structures are often used when stiff lightweight materials are required, such as in aircraft, vehicles and biomedical implants.

Despite their very high stiffness and strength, such lightweight materials require energy- and labor-intensive fabrication processes, exhibit typically brittle fracture and are difficult to shape and recycle.

This is in stark contrast to lightweight biological materials such as bone, silk and wood, which form by directed self-assembly into complex, hierarchically structured shapes with outstanding mechanical properties and are circularly integrated into the environment.

ETH Zürich researcher Silvan Gantenbein and co-authors were able to print objects from a single recyclable material with mechanical properties that surpass all other available printable polymers and can compete even with fiber-reinforced composites.

“We were inspired by two natural materials: spider silk and wood,” they explained.

“Spider silk gets its unrivalled mechanical properties from the high degree of molecular alignment of the silk proteins along the fiber directions.”

“First, it was possible to reproduce this high alignment during the extrusion from a fused deposition modeling (FDM) nozzle by using a liquid-crystal polymer (LCP) as an FDM feedstock material, resulting in unprecedented mechanical properties in the deposition direction.”

“Second, the anisotropic fiber properties were utilized by tailoring the local orientation of the print path according to the specific loading conditions imposed by the environment. This design principle is inspired by the ability of living tissue like wood to arrange fibers along the stress lines developed throughout the loaded structure as it grows and adapts to its environment.”

The 3D-printed LCP structures are much stronger than the state-of-the-art 3D printed polymers and do not require the labor- and energy-intensive steps involved in current composite manufacturing technologies.

“The freedom in design that comes with using a 3D printer can be used to create more complicated geometries with complex print line architectures,” the researchers said.

“Combined with the fact that these printed structures can be recycled, it should finally be possible to create FDM structures that can be used in industry as lightweight structural parts.”

The team’s work is published in the journal Nature.

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Silvan Gantenbein et al. 2018. Three-dimensional printing of hierarchical liquid-crystal-polymer structures. Nature 561: 226-230; doi: 10.1038/s41586-018-0474-7