Development of a method for separation of PVC and PET using flame treatment and flotation

Flame treatment can be used to modify the surface of plastics to allow water-based coatings to be attached. The effect of the treatment is to produce hydrophilic species on the surface of the plastic. The process is therefore potentially useful for the separation of plastics by froth flotation, provided that the production of the hydrophilic surface can be achieved selectively. Polyvinyl chloride (PVC) and polyethylene terephthalate (PET) were selected for investigation as they are found as a co-mingled product from the recovery of beverage containers.In this paper we report on the development of a simple, but effective, flame treatment method for flaked plastics. The treatment involves the use of an acceleration chute that delivers the flakes through the flame of an angled burner. In experiments with virgin plastics the PVC was found to be less susceptible to surface modification than PET, as indicated by contact angle measurement. Separation of the treated virgin plastic by froth flotation was found to be possible, using careful control of frother addition.The technique was then considered for the treatment of post-consumer plastic bottles. It was demonstrated that flame treatment was effective in rendering the surface of both plastics hydrophilic, although the process alone was not sufficiently selective. Hydrophobic recovery of the PVC, but not the PET, was achieved by raising the temperature of the material to 140 °C for a period of 10 min. A two-stage flotation process was tested for the separation of the plastics. In the first stage the PET was floated away from the PVC utilising differences in particle thickness and surface contamination. The float product was then subjected to flame treatment and hydrophobic recovery prior to the second stage of flotation. In this stage the PVC reported to the float product leaving a PET-rich sinks fraction.