Flotation separation of hazardous polyvinyl chloride from waste plastics based on green plasma modification

Abstract

Flotation has a great potential in the separation of complicated poly-mixtures to obtain qualified resins for recycling, but it remains a technological challenge for selective wetting between components. This study provided a combined flotation process with the prepositive plasma modification, separating hazardous polyvinyl chloride (PVC) from recyclable high-density polyethylene (HDPE) and polyethylene terephthalate (PET). The plasma process was characterized by surface morphology, molecular weight, contact angle, surface free energy and spectrum. The results suggested that amorphous low molecular weight oxidic substances can be selectively introduced on these polymers through the hydrogen extraction and Norrish І type radical pathways in plasma zone, leading to a desired surface wetting. Under the optimal unit activating energy of 12.0 kJ/m2 (PVC-HDPE) and 15.0 kJ/m2 (PVC-PET), separated PVC can reach above 93% of both recovery and purity. Benefiting from the green and mild operation in plasma unit, this study paves a new way to effectively separate waste plastics as an alternative to traditional surface modification with chemical reagents.