Resource recovery specialist Axion Consulting has claimed that automatic sorting systems designed to ‘revolutionise’ the recycled content of plastic food packaging could be available ‘within a few years’.

The claim follows technical research undertaken by Axion for the Waste and Resources Action Programme (WRAP), culminating in WRAP’s ‘Diffraction gratings for food contact packaging identification’ report.

According to Axion, ‘major’ breakthroughs in sorting technologies could increase the recycling of an estimated 180,000 tonnes of waste polypropylene (PP) pots, tubs and trays arising annually in the UK.

More than 60 per cent of this PP packaging comprises food contact packaging, while the remaining 40 per cent consists of non-food applications, such as cleaning products or cosmetics.

The process

Axion has centred its research on an automatic process, which involves marking food contact PP packaging with lines (a diffraction grating) that can be scanned by a laser to reflect a specific pattern (see demo unit pictured).

The pattern is then captured by a camera connected to a computerised image recognition system, which is able to identify and separate PP that has been in contact with food from that which has not. Under European regulations only PP that has been in contact with food can be recycled into new food grade PP.

Axion claims that this technique has the potential to be applied to other polymer types, for instance high-density polyethylene (HDPE) and polyethylene terephthalate (PET) packaging.

The diffraction grating can be used on packaging labels, stamped on a mould or directly onto a packaging item.

‘An innovative application of existing technology’

Speaking of the project, Axion Chemical Engineer, Richard McKinlay, said it was the ‘first’ time the diffraction concept had been used in this type of sorting application.

He said: “This represents an innovative application of existing technology that could revolutionise any food contact plastic recycling in offering a commercially-viable automated solution. Manual sorting is simply too expensive.

“Diffraction is when one beam of light is split into several, so we are utilising this phenomena to detect a particular type of plastic packaging”, he went on to explain.

Axion estimates the total capital cost for a single diffraction grating sorting unit at £500,000, with ‘a potential payback within four years’. Its report states that this payback period ‘should represent a good investment opportunity for a Plastics Recovery Facility (PRF) operator or a potential food grade reprocessor processing bales of sorted PP packaging’.

‘Challenges remain’

Acknowledging that further work is still needed, Axion Senior Consultant, Liz Morrish, said: “Challenges remain, including the need to widen applications and markets for this technology. It is also crucial for retailers, manufacturers and machinery suppliers to adopt agreed industry-wide methods that would optimise the identification and subsequent recycling of these waste streams.

“Although we focussed heavily on PP for this project, using this technology initially to sort HDPE milk bottles could be advantageous. Once it has been shown to work on this material, it may give the industry more confidence to invest further to allow the technology to be used on PP.

“Overall it appears that diffraction gratings can potentially be used to identify food contact packaging effectively and economically; however, they are not yet ready for use commercially until a full industry-wide solution has been developed and commercialised.”

Read WRAP’s diffraction grating report.