Analysis of different polypropylene waste bales: Evaluation of the source material for PP recycling

The use of the polypropylene (PP) recyclates in certain processing methods and applications is still limited by their quality. The high melt flow rate (MFR) and the inconsistent properties of recyclates are common obstacles to their use. Therefore, this work aims to identify possible reasons for the low and inconsistent quality of PP recyclates depending on the source material in PP waste bales. The levels of polymeric and non-polymeric contaminants were assessed. As mixing of different PP grades is an issue for the MFR, the proportions of the different processing grades were also investigated and the potential of sorting by processing method to produce lower MFR recyclates was assessed. The analysis showed that the waste bales, although pre-sorted, still contained high amounts of contaminants. Injection moulding was found to be the predominant processing method in the bales, explaining the high MFR of PP recyclates. However, a sufficiently high amount of low MFR products was found in the bales, which seems promising for the production of low MFR recyclates. Seasonal variations in the composition of the waste bales were identified as one of the reasons for the inconsistent qualities of recyclates. These results highlight the importance of proper sorting and treatment of PP waste bales prior to reprocessing in order to obtain high-quality recycled products.