Application of a dual depressant system and microwave irradiation for flotation-based Separation of Polyethylene Terephthalate, Polyvinyl Chloride, and Polystyrene Plastics

Abstract

The absence of an effective technique for the individual separation of plastics within a plastic mixture remains a paramount concern in the domain of plastic waste management. Recently introduced, the floatation technique has emerged as a method for segregating specific plastics, such as polystyrene (PS), polyethylene terephthalate (PET), and polyvinyl chloride (PVC), from mixed waste streams. This separation process involves the utilization of traditional dual depressants (chemical agents). The study investigated the impact of pre-microwave irradiation of plastic surfaces at varying microwave output powers (20-100%) on the floatation behavior of each plastic. Additionally, the influence of depressant concentration (200-1600 mg/L) on plastic floatation was examined. The results revealed that pre-microwave irradiation at different output powers and varying depressant concentrations significantly affected the sink-float behavior of the studied plastics, with the exception of PET. It was observed that the microwave irradiation altered the number and type of active sites on the plastics' surfaces. Notably, there was no discernible regular trend in the flotation of plastic with an increase in microwave output power. The outcomes were substantiated by conventional identification techniques, including contact angle (θ) measurement, scanning electron microscopy (SEM) images, and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) spectra analysis. Equations derived through the use of the design of experiment software (Design-Expert®) demonstrated a commendable alignment between the predicted and actual values of plastic flotation. This underscores the efficacy of the applied methodology in forecasting and validating the outcomes of the floatation process.