The effect of adding virgin material or extra stabilizer on the recyclability of polypropylene as studied by multi-cell imaging chemiluminescence and microcalorimetry

It has been shown that upgrading recycled PP with virgin material was not effective. Adding 80% virgin material did not increase the lifetime more than adding 20% virgin material. This indicates that a small amount of recycled material can induce degradation by contamination. Adding extra stabilizers instead of virgin material was much more effective. Of all techniques used the OIT as determined with CL showed a clear difference in residual stability of differently treated materials and seems to be the most valuable analytical method to determine the recyclability of PP. A comparison between CL and MC shows that MC is sensitive enough for measuring the solid-state oxidation of stabilized PP. Slightly lower OITs were detected by MC probably associated with the static atmosphere used during the measurements. The TLI method is not suitable to determine the degradation state of to be recycled material.