Photo-Induced Method Helps Plastic to Self-repair

Engineers at the University of New South Wales (UNSW) have demonstrated a photoinduced, dual-wavelength approach to help 3D-printed plastic heal itself at room temperature and without prior deoxygenation. The team from the UNSW School of Chemical Engineering showed that the addition of a powder to the liquid resin used in the printing process can assist with quick and easy repairs should the material break. The repair mechanism involves shining standard LED lights on the printed plastic for around one hour, which causes a chemical reaction and fusion of the two broken pieces.

According to the team, the entire process makes the repaired plastic stronger than it was before it was damaged.

The powdered additive the team used is a trithiocarbonate, known as a reversible addition fragmentation chain transfer (RAFT) agent that was originally developed by the Commonwealth Scientific and Industrial Research Organisation, Australia’s national science agency.

The team applied RAFT polymerization to visible light-induced 3D printing taking place at 405 nm, to produce high-resolution objects. The RAFT agent enables rearrangement of the nanoscopic network of elements that make up the material and allows the broken pieces to be fused.

Researchers at UNSW have shown how 3D-printed items treated with a trithiocarbonate, such as this violin, can self-heal when placed under UV light. Courtesy of UNSW.

This occurs within 30 minutes when UV lights are directed onto the broken plastic; the self-healing process is based on the reactivation of the RAFT agent embedded in the 3D-printed thermosets under the UV light, at 365 nm. Full healing then takes place after approximately 30 more minutes.

The team performed tests on instruments and devices including a 3D-printed violin.

“There are other processes that do this, but they rely on thermal chemistry to repair the material and typically it takes around 24 hours and multiple heating cycles to achieve the same type of result,” said Nathaniel Corrigan, a member of the team that introduced the method. “Another restriction is that you need an oven that is heated to high temperature, and you obviously cannot repair the plastic material in situ — you would need to disassemble it from the component first, which adds a level of complexity and delay. With our system, you can leave the broken plastic in place and shine the light on the entire component. Only the additives at the surface of the material are affected, so it’s easier and also speeds up the entire process.”

Wearable sensors and shoe manufacturing are among the applications that the method supports, the engineers said.

Further, the team hopes further development and commercialization of the technique will help reduce chemical waste; vat photopolymerization-based 3D printing techniques have been widely used to produce high-resolution 3D thermosetting materials — though the lack of repairability of these thermosets leads to the production of waste, the team said. This is because broken plastic parts would not need to be discarded, or even recycled, and could be mended even when remaining embedded in a component including many other materials.

The research was published in Angewandte Chemie (www.doi.org/10.1002/anie.202114111).