Dual-Wavelength Method Helps Plastic Repair Itself | Dec 2021

SYDNEY, December 29, 2021 – Engineers from the University of New South Wales (UNSW) have demonstrated a photo-induced dual-wavelength approach that helps 3D-printed plastics self-heal at room temperature without prior deoxygenation. The UNSW School of Chemical Engineering team showed that adding a powder to the liquid resin used in the printing process can help with quick and easy repairs in the event the material breaks. The repair mechanism consists of shining standard LED lights on the printed plastic for about an hour, which causes a chemical reaction and fusion of the two fragments.

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

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

The team applied RAFT polymerization to visible light induced 3D printing at 405 nm to create high resolution objects. The RAFT agent enables the reorganization of the nanoscopic network of elements that make up the material and allows the fragments to be fused together.

UNSW researchers have shown how 3D printed objects that have been treated with a trithiocarbonate, such as this violin, can heal themselves when placed under UV light. With the kind permission of UNSW. It does this within 30 minutes if UV light is shone on the broken plastic; The self-healing process is based on the reactivation of the RAFT active ingredient embedded in the 3D-printed thermoset under UV light at 365 nm. Complete healing then takes place after another 30 minutes.

The team ran tests on instruments and equipment, including a 3D printed violin.

“There are other methods that do this, but they rely on thermal chemistry to repair the material and it typically takes about 24 hours and multiple heating cycles to achieve the same result,” said Nathaniel Corrigan, a member of the Teams that introduce the method. “Another limitation is that you need an oven that is heated to high temperatures and of course you cannot repair the plastic material on site – you would have to disassemble it from the component first, which adds complexity and delay. With our system, you can leave the broken plastic in place and illuminate the entire component with light. Only the additives on the surface of the material are affected, this is easier and also speeds up the entire process. ”

Wearable sensors and shoe manufacturing are among the applications that the process supports, according to the engineers.

In addition, the team hopes that further development and commercialization of the technology will help reduce chemical waste; Vat photopolymerization-based 3D printing techniques are widely used to make high-resolution 3D thermosets – although the lack of reparability of these thermosets leads to waste production, the team said. Broken plastic parts do not have to be disposed of or even recycled and can be repaired even if they remain embedded in a component with many other materials.

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