Compounding is the process of melting a polymer and mixing it with additives, fillers, colour or other polymers to produce granules with defined properties. It is normally done on a twin-screw extruder, which mixes more intensively than a simple recycling extruder.
For recycled plastics, compounding is how variable waste becomes a specified grade. Blending different recycled lots evens out melt flow, while impact modifiers, stabilisers or mineral fillers tune stiffness, toughness and heat resistance. This is essential for demanding uses such as automotive parts, where rPP compounds must meet a precise specification batch after batch.
