Different methods are used to separate sleeves from cups.
One key step is the sink-float process – if the sleeve and cup have different densities, the flakes can easily be separated from each other (PP and PE flakes float to the top, PS and PET flakes sink to the bottom).
Another important step is wind sifting, where a jet of air separates the lighter sleeve flakes from the heavier cup flakes.
After these steps have been followed, if parts of the sleeve are still present in the PP recycling stream, a PO sleeve will not contaminate the material stream to a significant extent (when compared with other sleeve materials).