A method to convert commonly discarded plastic into a resin used in 3D printing could make better use of plastic waste.
Researchers have developed a simple and effective way to convert polylactic acid (PLA), a bio-based plastic used in products such as filament, plastic silverware and food packaging, into a high-quality resin.
“We found a way to immediately turn that into something stronger and better, and hopefully that will inspire people to recycle those things instead of just throwing them away,” says Yu-Chung Chang, a postdoctoral researcher in the State of Washington. University School of Mechanical and Materials Engineering and corresponding co-author of the study, published in Green chemistry. “We made stronger materials directly from waste. We think this could be a great opportunity.
About 300,000 tons of PLA are produced each year and its use is increasing dramatically.
Although it is of biological origin, PLA, which is classified as one of the seven plastics, does not break down easily. It can float in fresh or salt water for a year without degrading. It is also rarely recycled because, like many plastics, when melted and reformed it does not perform as well as the original version and loses its value.
“It’s biodegradable and compostable, but once you examine it, it turns out it can take up to 100 years for it to break down in a landfill,” Chang says. “In reality, it still creates a lot of pollution. We want to make sure that when we start producing PLA at million-ton scale, we know how to deal with it.
In the study, lead author Jinwen Zhang, a professor in the School of Mechanical and Materials Engineering, and colleagues developed a rapid, catalyst-free method to recycle PLA, breaking down the long chain of molecules into simple monomers – the building blocks of many plastics. The whole chemical process can be done at mild temperatures in about two days. The chemical they used to break down the PLA, aminoethanol, is also inexpensive.
“If you want to rebuild a Lego castle in a car, you have to break it down brick by brick,” says Chang. ” That’s what we did. Aminoethanol precisely cut the PLA into a monomer, and once it becomes a monomer again, the sky is the limit because you can repolymerize it into something stronger.
After the PLA was broken down into its basic building blocks, the researchers reconstructed the plastic and created a type of photocurable liquid resin that is commonly used as printing “ink” for 3D printers. When used in a 3D printer and cured into plastic pieces, the product showed equal or better mechanical and thermal properties than commercially available resins.
While the researchers focused on PLA for the study, they hope to apply their work to polyethylene terephthalate (PET), which is more common than PLA, has a similar chemical structure and has a greater waste problem.
The researchers have filed a provisional patent and are working to further optimize the process. They are also investigating other applications for the upcycling method.
Source: Washington State University