As we have seen elsewhere in this issue, mixed plastics recycling has been and continues to be a thorny issue in the UK. It’s the most common item in our bins that is still largely thrown away with just 26 per cent being collected from UK households in 2009/10. Partly this has been because the range of different polymers represented in your average mixed plastic bale makes recycling a more difficult process than with plastic bottles, and partly because of the absence of any kind of specialised sorting and reprocessing structure in the UK.

Gradually though, that infrastructure is falling into place. A major step forward – at least as far as the rigid fraction if not the film is concerned – was the opening in March 2011 of a Biffa Polymers facility in Redcar on Teeside that can sort, wash and reprocess rigid mixed plastic material. Jonathan Donohue, Commercial Manager of Biffa Polymers, outlines the main reasons for opening the plant, the first of its kind in the UK: “Plastic bottle recycling is well catered for in the UK either by ourselves or by other contractors. But we also want to capture the pots, tubs and trays fraction, a significant part of that waste stream that previously was either going to landfill, being exported or wasn’t being utilised at all.”

The facility was partly funded by a £1.17 million capital grant from WRAP to Greenstar WES, the original owner of the site before the company was taken over by Biffa last year. The plant is currently processing 15,000 tonnes per annum, a figure that should rise to between 20,000 to 25,000 tonnes when it reaches full capacity next year.

The plant receives mixed plastic material from all over the UK. At present, this means just bales that have already been through Biffa materials recovery facilities (MRFs), although Donohue insists that when it reaches full capacity it will process material from other sources as well. That first part of the process should have already pulled out the plastic bags that all too often get caught up in the material, a technique that is performed by vacuums that pull them off along a conveyor line.

Once the bales arrive at Redcar, the next stage is to remove any lingering contaminants. “Obviously there’s dirt in there”, says Donohue, “as well as a certain amount of paper contamination, broken glass, bits of metal and things like that. So those bales are broken up – overband magnets eject the ferrous metals, it is put through a trommel and then over eddy currents. Then there is optical sortation equipment that picks plastic material off.

“After that we are left with a positive plastic extraction. That is then sent to a granulator that produces plastic flakes. These are then sent through a series of cleaning processes which include separation and a cold wash process with a detergent”, explains Donohue.

The washed plastic flakes that emerge from the process are then put into a centrifuge that separates them into a light and heavy stream, based on whether they float or sink in water. After this, the material goes through a series of nine optical sorters, which separates them into different polymer types and within that a natural colour and mixed colour fraction for each polymer. The facility mainly deals with the five main high-volume polymers – high and low density polyethylene (HDPE and LDPE), polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET).

The material is then bagged up and put out onto the market, in a variety of different forms. “We can either sell it as a washed flake”, says Donohue. “Or for those converters that require pellets, we can put it into our extrusion plant and we can compound it into pellet form with – if required – the addition of additives to either modify or colour the end product.”

Asked if there are any mixed plastic fractions the facility can’t prepare for reprocessing, Donohue explains: “[The plant] is designed to cope with all plastic materials used in packaging applications; therefore all streams at the end have a use. Generally, materials that the plant doesn’t recycle are not introduced. If, for instance, any engineering polymers were included in a bale of feedstock, these would be pulled out before they entered the process.

“Any quantities of no commodity polymers that do get through are recovered into a mixed fraction which is sold as a low-grade polymer for processing or even further sortation.”

The new facility marks an important step on from existing UK plants that deal with just plastic bottles. “It’s completely different”, Donohue insists. “When you’re recycling plastic bottles you’re essentially working with one or two materials – either HDPE or PET. Here, it’s a lot more complex, certainly in terms of sorting it, because there are many more polymer types.” At present, he affirms, there are no plans to add facilities to recycle plastic film, the most difficult of plastic types to reprocess effectively.

The company is, however, in the process of developing the different end markets for the various polymers, according to Donohue. “There are loads of different applications there, it’s how creative and how controlled you can be to meet the requirements of whatever market it is you’re serving.”

Typically, HDPE can be used in a pipe application, a blow-moulded bottle application or as an injection-moulded industrial component. PET can be used in fibre and sheet applications, and PS is increasingly being used as moulding on electrical components.

Meanwhile, PP is used in building products, pipe materials and horticultural materials – a lot of plant pots arerecycled PP. The Redcar plant also extrudes some PP grades into different profiles and sheets for thermoforming. It has also been tested in injection-moulded applications such as caps and pails.

Donohue says that he hopes that the Redcar facility will be the first step in revolutionising mixed plastic recycling in the UK. “I think it’s going to prove that the non-bottle fraction can be commercially viably recycled”, he says confidently. “It’s a huge step in increasing the amount of polymer available on the UK market that comes from recycled sources. And of course hopefully it will also encourage us as consumers to think more about what we do when we put things in the dustbin.”

But with a number of local authorities looking to introduce mixed plastics collections, the UK will probably soon need a larger capacity than the 20,000 tonnes a year that Redcar offers. Will it be the first of many such facilities? “I don’t have the answer to that”, says Donohue. “Obviously though we would like to see a large number more. For the moment this is a look-see for the UK, to prove that it works.”