Selective separation of PVC from PET/PVC mixture using floatation by tannic acid depressant

Production and consumption of plastic materials have increased in recent decades. The increase in plastic production and consumption has been largely responsible for the increase in plastics waste production. The problem of plastics waste is quite important in terms of environmental sustainability and solid waste management. Plastics recycling requires the separation of materials insofar as being almost pure. To achieve this goal in an economical way, technologies developed in mineral processing are of great help. Each method has certain capabilities and limitations. Instance separation of PET and by gravity techniques is practically not applicable, due to slight differences in density. In this research, separation of PET and PVC by selective floatation was studied. The use of floatation for plastic separation is particularly challenging because of inherent hydrophobic nature of plastics surfaces. To separate PET and PVC, from the mixture of the two, by floatation should make one of them hydrophilic and wettable by water. This can be achieved by several methods among which the addition of a wetting agent that interacts with the surface layer is one of many techniques designed. In this study, tannic acid was employed as the depressant of PET. The results showed that, virgin materials can be separated with 99.62% efficiency. In the case of post-consumer PET and PVC, 88.40% separation efficiency was achieved at optimum conditions. Also, in virgin and postconsumer materials, difference in the contact angles of PET and PVC increased as tannic acid dosage increased. Besides, the results indicated that the pH of the conditioning step is vital with respect to separation efficiency.