UB scientists invent ‘transient thermal barcodes’ to improve plastic recycling

BUFFALO, N.Y. — Barcode readers excel at quickly identifying groceries and other products. Could a similar idea work at industrial recycling facilities to make sorting different plastics quicker and more cost-effective?

The answer, according to a University at Buffalo research team, is yes.

Unlike traditional barcode scanners, which rely on optical sensors, the team is developing a system that creates “three-dimensional transient thermal barcodes” that could rapidly identify plastics moving on conveyor belts.

The work is described in a Nature Communications Engineering study posted according to the journal’s early access policy.

“Our goal was to develop a cost-effective, scalable and industrially relevant plastics sorting technique that addresses the key prevailing scientific gaps restricting the recycling of plastics,” says corresponding author Amit Goyal, PhD, SUNY Distinguished Professor and SUNY Empire Innovation Professor in the UB Department of Chemical and Biological Engineering.

Goyal directs the UB Initiative on Plastics Recycling and Innovation, which is designated as a New York State Center for Plastics Recycling Research and Innovation by the New York State Department of Environmental Conservation (DEC).

The system, he says, aims to “improve the quality of sorted plastics by reducing contamination and, hence, increasing the recycling of these materials to help enable a circular economy.” He adds that it “is estimated that one ton of recycled plastic saves 5.7 megawatts of electricity, 685 gallons of oil, and 30 cubic yards of landfill space.”

Plastic waste generated by households and businesses are sent to material recovery facilities where plastic is separated from other wastes. This is often done by hand, which can result in false identification and poor quality of sorted bales.

Plastics are then separated into different types. Presently, there is a lack of cost-competitive and accurate techniques that can effectively identify plastic types by their resin codes.

Developing techniques – including near-infrared spectroscopy, Raman spectroscopy, laser-induced breakdown spectroscopy – suffer from one or more issues. These include poor sensitivity; subpar selectivity; slow speeds; inability to detect black plastics; or they cannot be operated in standoff mode (identifying plastics from a distance) that’s often required in material recovery facilities.

These limitations explain, in part, why plastic recycling rates remain relatively low worldwide.

To overcome these challenges, the UB team sought to invent a technology that quickly captures the molecular signature of waste plastics from a distance. It also must have the potential to be easily retrofitted into existing sorting machinery.

The researchers started with a range of mid-infrared wavelengths, which they shine onto plastic items. (Mid-infrared is known as the “molecular fingerprint regime” because of the unique spectral peaks for all plastic types that exist in this part of the electromagnetic spectrum.)

As the plastic absorbs the light, molecular bonds within the plastic vibrate, generating temporary heat patterns that are measured by a thermal camera. These heat patterns, which reflect the unique molecular structure of each plastic, are essentially a “three-dimensional transient thermal barcode.”

Researchers used six mid-infrared wavelengths identify all six common types (PET, PP, PS, HDPE, LDPE, PVC) of plastic waste. Moreover, the technique can also identify black plastics (all black plastics are based on one of the six types of plastics but with significant carbon derivatives added).

At this point, the system is not ready for industrial deployment. The research team is working on advancements – faster hardware to sort plastics on high-speed conveyor belts; cost-effective light sources that project multiple mid-infrared wavelengths simultaneously; and artificial intelligence-based software – to improve the technology.

Still, the study shows that the transient thermal barcode technique fundamentally works and provides early promise to improve plastics recycling efficiency. It could eventually help divert more plastic waste from landfills and the environment, where plastics break down and cause health problems among animals, plants and humans.

The study was led by the New York State Center for Plastics Recycling Research and Innovation at UB. Lead author Kunal Singh, PhD,  is a postdoctoral fellow mentored by Goyal and co-corresponding author Thomas Thundat, PhD, a SUNY Distinguished Professor at UB. All three authors are affiliated with the Department of Chemical and Biological Engineering in the School of Engineering and Applied Sciences at UB.

Singh’s work has been central to this invention and study, Thundat and Goyal say. They note he has “not only done outstanding scientific research but has also developed advanced, custom instrumentation” and that his “rigorous and meticulous work identified key shortcomings in our initial approach and provided elegant technical solutions.”

Singh says: "We hope to further develop the technique so that it can be transferred to industry.”

The New York State Center for Plastics Recycling Research and Innovation at UB provided funding for the research. The center is supported by a grant from New York State Environmental Protection Fund, which is administered by the DEC.