a method for recycling polymeric materials , including a mechanical separation step , a first density separation step , an intensive cleaning step , and a second density separation step is described . additional separation steps , such as a third density separation step , and optionally a fourth density separation step . further less essential steps such as wetting , grinding , air flow separation , drying , electrostatic sorting and optional sorting steps may also be carried out to achieve optimized and refined separation . polymeric materials from refuse or crushed motor vehicles may thus be separated , and polyethylene , polypropylene , polystyrene and acrylonitrile - butadiene - styrene resins may be recycled .]