Restabilization of Post‐Consumer Recycled Polypropylene With Natural Antioxidants From Spent Coffee Residue

ABSTRACT The efficiency of natural compounds as stabilizers against thermo‐mechanical degradation during the reprocessing of a post‐consumer recycled polypropylene (PCR‐PP) is herein investigated. For this purpose, natural active ingredients are extracted from spent coffee residue (SCR). Different methods of extraction are tested and all extracts are subjected to characterization methods in order to identify the most promising extract in terms of antioxidant properties, which is then reproduced on larger scale and added to a PCR‐PP at a content of 1.0 wt%. The stabilized compound undergoes five cycles of extrusion, after which it is compared to a nonstabilized PCR‐PP and a PCR‐PP stabilized with a commercial synthetic primary antioxidant, which have both undergone the same reprocessing. Consequently, the reprocessing of the nonstabilized PCR‐PP resulted in degradation and extrudates of higher melt flow rate (MFR) and lower thermal stability, that is, reduced oxidative induction time (OIT) and onset temperature (OOT). Contrariwise, with the natural compounds embodiment, the degradation was found to be suppressed, resulting in stable MFRs and higher OITs and OOTs, imitating the behavior of the PCR‐PP with the typical synthetic antioxidant. In conclusion, natural compounds from SCR may sufficiently serve as high value‐added antioxidants for the recycling of a PCR‐PP via remelting‐restabilization.