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The absence of an effective technique for separation of an individual plastic from a mixture of plastics, is one of the most important concern in plastics waste management. The recently introduced floatation technique used to separate the selected engineering plastics including, polystyrene (PS), polyethylene terephthalate (PET), and polyvinylchloride (PVC) from each other. The floatation was assisted by using the traditional depressants (chemical agents). The effects of plastics surface pre-microwave irradiation at different microwave output powers, 20–100% studied on the floatation of each plastic. Also, the effect of depressant concentration, 400–2000 mg/L on the plastics floatation was evaluated. The results showed the pre-microwave irradiation of the plastics surface at different microwave output powers and depressant concentrations had important influence on the sink-float behavior of the studied plastics with the exception of PET. It seemed, the number and type of the active sites on the plastics surface changed after microwave irradiation. There was not any regular trend for the floatability of a plastic with increasing the microwave output power. The results reinforced by the traditional identification techniques including contact angle (θ) measurement, scanning electron microscope (SEM) images, and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) spectra analysis. The driven equations by a design of experiment software (Design-Expert ®) showed suitable conformity between the predicted and actual plastics flotation values.