an apparatus for pre - processing and subsequent plastification or agglomeration of synthetic plastic materials , in particular thermoplastic waste plastics for recycling purposes , has a receptacle in which at least one comminuting tool circulates . the housing of a screw is connected to the receptacle . the diameter of the receptacle has the following relationship to the screw diameter : d = 10 . }, wherein d is the inner diameter of the receptacle in mm , d is the screw diameter in mm and k is a dimension - less constant which amounts to at least 190 . thereby the dwell times of the synthetic plastic material within the receptacle are kept at optimal values .