Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Plastics separation by electrostatics

Sorting waste plastics into polymer types is labour intensive and ineffective leading to a recycled product which is costly to produce yet a low value to plastics users. What is needed is effective, automatic separation giving a low cost product which can replace new, pure polymers.

Separation processes based on the different electrostatic properties of different plastics have been tried before but successful laboratory processes have often failed in an industrial environment because of the notorious variability of electrostatic properties. The work carried out for this programme showed that the causes of variation in electrostatic properties, if properly understood and quantified, could be used to advantage. Conditions could then be selected and controlled to maximise the differences between materials and so enhance separation. This would lead to improved separation efficiency for materials already recycled, and discrimination between materials which currently cannot be separated.

A general purpose laboratory separation apparatus was designed to exploit a wide range of electrostatic properties and effects, singly or in combination. Trials have been carried out with a washed, post consumer, mixed polyvinyl chloride (PVC) and polyethylene terephthalate (PET) flake, knowing that the maximum value of these materials cannot yet be realised because of the less than perfect separation achievable. Using the new process, under predicted optimum conditions 100% of the PVC was removed from a 50% mixture of the polymers, falling to only 50% under the predicted worst conditions. Without the careful control essential to the new process, random variation between these extremes of conditions could be expected.

The clear conclusion from this work is that automatic electrostatic separation of polymers can be enhanced by control of those conditions which, when uncontrolled, lead to poor and variable discrimination. Furthermore, laboratory apparatus and procedures are now available for more extensive trials with other mixtures of polymers and polymer grades.


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