A method for preparing contaminated plastics ground into flakes, such as RPET or such polymers, having at least decontamination and SSP treatment steps, with at least one reactor, with heating to the process temperature taking place essentially outside the reactor. Also, a device for carrying out the method, and having at least one decontamination reactor and at least one SSP reactor, a device for heating plastic flakes to the process temperature being arranged upstream of the decontamination reactor. Also an SSP reactor having at least two individual reactors, and preferably between 3 and 7 individual reactors.