Strong alkaline solutions of sodium hydroxide are able to destroy the hydrophobicity of polyethylene terephthalate (PET) allowing for the flotation separation of PVC (polyvinyl chloride) from PET. Conditioning of the PVC/PET mixture in a low-concentration solution of polymer plasticizer at elevated temperature enhances the hydrophobicity of PVC particles and only slightly affects the surface properties of PET particles. On this basis, enhancement of the flotation separation by conditioning with a polymer plasticizer, and by the use of non-ionic surfactants, has been developed and tested at a laboratory scale. Using this procedure a 93-95% recovery of PET can be obtained while rejecting almost all PVC (98-100%).