a method for separating large - sized film - like plastics , such as polypropylene or polyvinyl chloride , which comprises placing the plastics in a separation tank containing an aqueous liquid medium and introducing gas bubbles into the tank thereby to cause the gas bubbles to adhere to the surface of the plastics . the buoyancy of the gas bubbles causes the plastics to rise to the medium surface . addition of a flotation agent and / or a wetting agent further promotes the floating of the plastics .