Ammonia modification for flotation separation of polycarbonate and polystyrene waste plastics.

•Ammonia modification was developed for flotation separation of waste plastics.•Ammonia modification changes selectively the wettability of PC surface.•Mechanism of ammonia modification was studied by FT-IR and XPS analysis.•Plastic mixtures with different particle sizes were separated effectively.•A process combined with flotation and ammonia modification was proposed.