Combination of sink–float separation and flotation technique for purification of shredded PET-bottle from PE or PP flakes

Abstract

In this contribution, the separation of polyethylene terephthalate (PET)–polyethylene (PE) and polyethylene terephthalate (PET)–polypropylene (PP) mixtures was studied in order to improve the grade of the raw input used in PET bottle recycling. First, PET bottles and their caps (made of PE or PP) were shredded and the floatability of each polymer was tested. Even with the addition of the wetting reagents dodecylamine acetate (DAA) or polyvinyl alcohol (PVA), the results did not suggest that the required 99.995% purity of PET plastic could not be achieved by floatation. Second, the mixtures were separated with a sink–float process using a drum separator. Finally, as the required purity of PET could not be obtained by either technique alone, a system utilising a combination of the two processes was developed. This system easily achieved the desired PET grade. At last, some sink–float experiments were performed with a medium of magnesium sulphate (dense medium separation).