The recycling of plastics is an important challenge for modern industrialized countries. For a modern recycling cycle a 100% mono-fraction sorting of plastic waste is needed. Non perfect sorting results produces low-grade plastics granulate which can only be used downgraded products. THz systems offer the possibility for a spectroscopy analysis of shredded plastics. Full spectroscopy systems which cover large area of the THz region are under a more economic view to expensive. Test measurements and publications in the last year's show the possibility to separate plastics with electronic THz systems. The limitations in bandwidth are compensated by external height sensors and sophisticated mathematic methods.