University of Manchester researchers develop technique to determine recycled contents of plastic products; method tags raw HDPE plastic materials with fluorescent BBS molecules for light detection, does not affect materials' appearance, quality

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MANCHESTER, United Kingdom , November 22, 2022 (press release) –

Materials researchers have developed a new technique to successfully determine the recycled contents of plastic products.

To encourage more recycling, some countries are taxing single-use plastic products containing less than 30% recycled plastic material. But aside from a manufacturer’s word, there isn’t an easy way to verify this.

Now, researchers reporting in ACS Sustainable Chemistry & Engineering have developed a simple, fraud-resistant technique to evaluate the recycled content of new plastic products. They added a fluorescent tag to plastic resins, successfully tracking the recycled content in products made with a variety of plastics and colours.

After reducing and reusing, recycling is the last line of defence for keeping plastic out of landfills or the environment. To encourage plastic recycling, some countries have shifted the responsibility to producers for incorporating these “post-consumer materials” in new products, such as single-use items and packaging. Whereas the U.K. is taxing plastic products with little recycled content, other countries, such as Italy and Spain, plan to impose taxes soon on products that contain no recycled content.

However, approaches to verify these amounts aren’t always accurate, potentially leading to fraud and public mistrust. One solution could be to tag recycled plastics with the fluorescent molecule 4,4,-bis(2-benzoxazolyl)stilbene (BBS), and then track the tagged recycled feedstocks into their resulting products. BBS’s fluorescence intensity and colour vary when different levels are present, and it’s inexpensive and approved for food contact applications. So, Michael Shaver and colleagues wanted to see how BBS could be used to measure the recycled content of single-use plastic products.

In tests, the method could identify the recycled content in other real-world plastics, including recycled milk bottles with additives, coloured HDPE, polypropylene and poly(ethylene terephthalate). The BBS strategy could be applied to a variety of single-use plastic products without impacting their appearance or quality.

Michael Shaver, Professor of Polymer Science

The researchers mixed small amounts of BBS into melted high-density polyethylene (HDPE) and then mixed that with virgin HDPE resin, simulating 0 to 100% recycled content materials. As the amount of BBS tagged-HDPE rose in the samples, the fluorescence intensity shifted toward a greener hue of blue under a UV light.

The marked plastic had a unique fluorescence behaviour, which the researchers suggest would be hard for someone with fraudulent intentions to replicate. Next, the team developed a simple digital image analysis technique that converted the material’s fluorescence into the percentage of recycled content.

“In tests, the method could identify the recycled content in other real-world plastics, including recycled milk bottles with additives, coloured HDPE, polypropylene and poly(ethylene terephthalate). The BBS strategy could be applied to a variety of single-use plastic products without impacting their appearance or quality,” says Professor Michael Shaver.

The authors acknowledge support from the Henry Royce Institute for Advanced Materials, the Sustainable Materials Innovation Hub and the Manchester Institute of Biotechnology.

The authors have filed a patent on this technology in the U.K.

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