Axion Consulting has seen a major breakthrough in sorting technologies which could increase the recycling of an estimated 180,000 tonnes of waste polypropylene (PP) pots, tubs and trays every year in the UK.
Its research focuses on developing an automatic process, which uses diffraction gratings to identify and separate PP that has been in contact with food from that which has not.
Under European food packaging regulations only PP that has been in prior contact with food can be recycled into new food grade PP.
Diffraction grating concept
Richard McKinlay, chemical engineer, Axion Consulting, who helped to build a demonstration unit for the project in partnership with WRAP environmental association, said it was the first time the diffraction grating concept had been used in this type of sorting application.
The process involves marking food contact PP packaging material with lines (a diffraction grating) that can be scanned by a laser to reflect a specific pattern.
The pattern is then captured by a camera connected to a computerized image recognition system which is able to identify the marked food contact PP packaging.
Food contact plastic recycling
“This represents an innovative application of existing technology that could revolutionize any food contact plastic recycling in offering a commercially-viable automated product,” he said.
“Manual sorting is simply too expensive. Diffraction is when one beam of light is split into several, so we are utilizing this to detect a particular type of plastic packaging.”
This technique is potentially applicable to other polymer types, particularly high density polyethylene (HDPE) and polyethylene terephthalate (PET) packaging.
The diffraction grating can be used on packaging labels, stamped on a mold or directly onto a packaging item.
Payback in four years
Axion estimates the total capital cost for a single diffraction grating sorting unit, including conveyors and ancillary equipment, at £500,000 ($808.743) with a potential payback within four years.
Its report states that this payback period ‘should represent a good investment for a Plastics Recovery Facility (PRF) operator or a potential food grade reprocessor processing bales of sorted PP packaging’.
Acknowledging that further work is still needed, Liz Morrish, senior consultant, Axion, said its research had helped to move the development of technology a step closer.
“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 optimize the identification and subsequent recycling of these waste streams,” she said.
“Although we focused 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 commercialized.”