Background

Of the 3.7 million tonnes of plastic waste generated annually in the UK, only 1.2 million tonnes is recycled. 46% of this is recycled in UK and the rest is exported with a low value of ~£250/tonne. If the latter were recycled into a high quality resin its value would be over £850/tonne for non-food and £1100/tonne for food-grade. This represents a loss of £400m-£550m annually.

Currently the automatic sorting systems for plastics is based on detection of the molecular signature of the plastic by Infra-Red spectroscopy. This system has several drawbacks: it is unable to detect highly pigmented plastic and can not segregate plastic according to its use. It is unable to differentiate between food‑grade, non‑food grade or toxic products. Currently no automated technology exists to overcome these obstacles. Today, this degree of sorting can only be performed manually at slow speeds and high costs.

The ability to detect the type of plastic and its use, as part of an automated high speed recycling process, would greatly increase the sorting of high value plastics. EU food contact regulations require a minimum of 99% food-grade content for the recycling of HDPE and PP and at least 95% for PET.

Technology Overview

This technology makes use of intelligent labels and sleeves for carrying invisible codes for post‑use sorting, as well as for decoration and information sharing. Alternatively the codes can be printed directly onto the articles.

Codes are written using luminescent materials, typically inorganic phosphors, that have a relatively slow decay time. In particular long persistence phosphors are used that decay very slowly and release on stimulation with infra‑red radiation.

At the recycling facility the articles are subject to excitation radiation of a specific wavelength and a few seconds/milliseconds later are subject to infra‑red detection (as currently). This 2‑step process can identify articles according to the codes and sort them as specified.

The process of excitation followed by detection by IR can be easily and cost‑effectively introduced into the existing recycling process with only minimal capital investment. This 2 step process, using specific long persistence phosphors, reduces any issues of signal contamination from other luminescent materials present, for example optical brighteners in paper/polymer labels and in washing powders/liquids. These materials will not be detected by the IR.

After sorting of the articles, the labels are removed, generally by an alkali wash that dissolves the adhesive. This prevents downstream contamination of the recycled plastic with the luminescent material.

The sorted materials can then be recycled into resins for incorporating into the relevant plastics increasing the level of recycling particularly for high value food‑grade plastics.

Demonstration video:

Benefits

• Ability to sort articles by their end use and composition according to pre‑defined labels to increase the value of such plastic
• High accuracy rate as other luminescent materials are not recognised by the IR detector
• Easy and cost‑effective incorporation into existing recycling facilities with limited need for capital investment
• No detrimental effect on speed of recycling
• Does not depend on the integrity of labels (eg: bar or QR codes) during processing (e.g.: objects may be crushed)
• No high dose radiation, if initial blue light excitation implemented, therefore no need for additional protective equipment for workers

Applications

• Separation of post‑consumer waste plastic packaging according to either plastic composition or product uses.
• Separation of hard to identify materials (e.g.: black packaging).
• Separation of composite materials where codes can identify the components and layers.

Opportunity

Brunel are searching for partners to take this technology to the next phase of scale‑up and who may be interested in licensing the technology.

They are particularly interested in brand owners and consumer product manufacturers who are interested in using this technology on their products to improve the sustainability profile and green credentials of their packaging.

They are also interested in sorting and recycling businesses that are interested in adding value to the sorted waste streams.