Recycling WEEE polymers
The UK’s Waste Resources & Action Programme (WRAP) has revealed the results of its research into recycling mixed polymers from waste electrical and electronic equipment (WEEE).
The full force of the UK WEEE Regulations will be felt from 1 July this year. Manufacturers of electrical and electronic goods will be responsible for collecting, recycling and treating household WEEE.
Although the original European WEEE Directive encourages closed loop recycling of waste, one of the barriers to this is removing unwanted additives from some polymers before reuse. Brominated flame retardants (BFRs), in particular, are known to emit harmful dioxins during reprocessing. They are present in about seven per cent of all WEEE plastics.
Commissioned by WRAP, a project was launched in 2004 to separate and remove BFRs from mixed WEEE polymers.
Paul Davidson, Plastics Technology Manager at WRAP, says, ‘EU legislation restricts the sale of polymers containing older BFRs. Therefore, unless those BFRs are extracted, there will be a lack of suitable markets for the recycled products.’
Led by Axion Recycling Ltd, based in Manchester, UK, the team tested two extraction methods – Creasolv and Centrevap.
Researchers at Fraunhofer IVV, in Freising, Germany, invented the Creasolv process. A high boiling point solvent is used to dissolve the shredded feed plastic, which has been pre-sorted into BFR-containing material. Precipitation steps then follow, using proprietary solvents to reduce BFR content to below 0.1%. The resulting polymer gel particles are cooled and pelletised for reuse.
The Waste Resources & Action Programme has adapted the process to enable solvent regeneration – BFRs are recovered from the solvents as slurry through crystallisation.
Trials of the process were conducted in Germany on a polymer mix of 85% high impact polystyrene and 15% ABS from television units. Research has shown that styrenic polymers account for over half of the collectable WEEE polymers and contain the majority of BFRs.
Centrevap, meanwhile, was devised by WRAP and makes use of the differences in solubility between polymers and their additives. The polymer is dissolved into toluene solvent, and the resulting suspension pumped to a decanter centrifuge, followed by a disk-stack centrifuge. The decanter removes undissolved additive particles of 1mm to 50 microns in size, while the disk stack eliminates particles down to 0.3 microns. These residues are then dried and the plastic is pelletised.
Intensive trials show that Creasolv is more successful at removing BFRs, while Centrevap is better at extracting other insoluble impurities from a range of polymer types.
Davidson explains, ‘Centrevap solvents were only able to partially dissolve BFRs. But centrifugal separation accelerates settling force and allows removal of finer impurities, such as fillers, as well as general dirt. Combining the best features of [both methods] has potential.’
He adds that both processes consume less than 20% of the energy used to create virgin material and therefore are more economically and environmentally viable. Further research will focus on improving the techniques to remove residual solvent from recycled polymers, alongside BFR treatment. The Waste Resources & Action Programme hopes the processes will be ready for industrial scale use in the next two to four years.
In a separate two-year study for Defra, Axion Recycling has trialled a range of WEEE polymer separation techniques, including gravity and electrostatic separation. This research could also benefit end of life vehicle recycling.
Axion has established a 40,000sq ft plant in Salford, Manchester, which recycles shredded material from refrigerators and computer casings. The plant also conducts bulk semi-automated separation of polymers by type and those that do and do not contain BFRs. Both WRAP and Axion are investigating various end uses for the recycled product – this includes putting the material back into the electronics industry.