All sorted: Fluorescent markers code all plastic containers for recycling

Materials researchers at Brunel University have developed a new technique using invisible phosphor tags to label plastic packaging that they say could jumpstart a “quantum leap” in UK recycling.

The advance switches up sorting rates by adding phosphors, the luminescent materials that give strip lights their glow, to recyclable plastic packaging.

The researchers have developed a set of invisible phosphor inks that can be coated on labels and detected by UV, the way cashiers spot fake bank notes.

They say that the new technology offers significant advantages over the existing system, which sees plastics sorted automatically on high-speed conveyor belts using infrared radiation to detect the polymer type.

The existing system works extremely well, but has some big deficiencies,” explained Paul Harris, Fellow at Brunel’s Institute of Materials and Manufacturing. “It is fine for transparent plastic but doesn’t work for highly coloured plastic, which makes up a significant fraction of the waste stream.”

Harris also highlighted the inability of conventional sorting systems to identify what a container was used for, making it impossible to separate pesticide containers from food containers, for instance. 

The new, low-cost technique, known as PRISM (Plastic Packaging Recycling using Intelligent Separation Technologies for Materials), coats a transparent phosphor-loaded ink on product labels before use.

Current sorting technology is able to detect luminescence from the phosphors, says the researchers, and, by using PRISM’s coded mix of phosphors, UV readers identify the plastic’s material and its application, even if it is heavily coloured.

Though manufacturers will have to buy the labels, PRISM’s UV source can be attached at low cost to existing near-infrared sorting systems and programmed to read phosphor codes.

Led by recycling consultants, Nextek and Brunel, PRISM is a European consortium. The first full-scale trials by members, Tomra Sorting, showed it collected 98 per cent of labelled plastics with 95 per cent accuracy.

Harris said: “It will mean a larger proportion of waste will be identified and recycled, rather than going to landfill.

“The system is working a treat and we have already had lots of international interest. The next phase is to get the costs down, but the process works, there’s no doubt about it.”