Determining the PE fraction in recycled PP

The presence of a polyethylene (PE) fraction in recycled polypropylene (PP) will influence the processing as well as mechanical and thermal properties of recycled polypropylene. The objective of this work has been to compare methods used to determine the fraction of PE in recycled PP, establishing calibration curves for each method. Plastics waste will be a mix of different grades – homopolymers and copolymers. It has therefore been tested how specific material grades affect the results. Characterization methods used were differential scanning calorimetry (DSC), FT-IR spectroscopy, NMR, and gel content measurement after peroxide extrusion. We have applied the derived calibration curves for two different post-consumer, recycled PP (rPP) in addition to a known 50/50 blend of PE and PP. DSC, NMR, FT-IR and gel content give quite consistent estimates of the PE content.