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Circular economy 'unlikely' for the bulk of plastic waste

Achieving high waste plastic recycling rates is fraught with difficulties because of several factors ranging from the variety of the plastic materials to their colours. Focusing on designing packaging for reuse or shifting to biodegrading packaging could be a better way to move in the direction of a low carbon, circular economy, says Bob Pringle, former waste reduction and recycling lecturer at Edinburgh University.

Plastic packaging ranges from tough plastic bottles to flimsy film bags used in retail help-yourself displays. Non-films are marked with triangles, with a number ranging from one to seven, denoting the plastic polymer used. Each polymer has a melt temperature and characteristic unique to it, and will not usually bond with other polymers. This requires each polymer to be dealt with separately, commonly resulting in only PET and HDPE bottles being collected for recycling.

To make the situation worse, colour causes further problems. Different colours must either be separated, or a costly pigment added to the melted plastic mix to hide the different colours.

In the high wage UK, high labour costs make separation costly; this is why so much waste plastic packaging goes overseas to China, where it is separated, cleaned, shredded and reformed into new feedstock. New automated high tech clean MRFs are being built in the UK to keep labour costs to a minimum. However, the Near Infrared Reflectance (NIR) scanners used cannot “see” through black poly propylene trays and are confused with PET fizzy drinks bottles with an outer, coloured PVC sleeve.

To “solve” the mixed polymer, mixed colour problem, this relatively worthless polymer mix is heated and extruded into moulds to make materials used in park benches and tables. These have to be thick to compensate for the polymers not bonding together. This is down-cycling not recycling, converting a high value material into a low value wood alternative.

Closed loop recycling and the circular economy is unlikely to be achieved for the bulk of plastic waste. Retailers would like to continue business-as-usual, using attractive packaging to sell their products, while leaving councils to collect waste plastic packing, and remove plastic waste from ditches, roadsides and beaches. Burning waste plastics is an option, but energy from waste plants are never popular with the public, especially when dioxin producing PVC plastics can be in the mix. Minimising the number of polymers used in packaging would make recycling easier, but this has faced opposition from retailers.

Light-weighting of plastics is of questionable benefit as light flimsy plastics are more difficult to separate than stiff, heavier ones. Requiring food plastic packaging to be biodegradable makes a lot of sense, as the adhering yoghurt, ice cream or blood, helps gets the bacteria and fungi off to a good start in in-vessel composters or AD plants.

Biodegrading packaging avoids the long recycling journey that conventional plastics require. The solution is to design packaging for reuse if possible, or failing that for disposal through recycling or composting. Only then will a low carbon, circular economy free from plastic litter be achieved.

Bob Pringle, former waste reduction and recycling lecturer


Bob Pringle CV

Bob Pringle is a Chartered Engineer, with a BSc in Mechanical Engineering, a MSc in Agricultural Engineering and member of the CIWM and the IAgrE. He was with VSO for one year in Nigeria followed by 35 years with the Scottish Agricultural College as a consultant, researcher and teacher working in crop storage, mechanisation, energy studies and wastes management.

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