Polypropylene (PP) recyclates face limitations in their use due to lower qualities compared with virgin PP, resulting from contaminations and the mixing of different PP grades. In particular, their high melt flow rate (MFR) hinders their suitability for applications requiring low MFR, such as pipes. This study investigates the feasibility of producing low MFR PP recyclates from packaging waste. For this purpose, recyclates were produced exclusively from manually sorted extrusion blow molding grades and compared with a recyclate derived from a conventional PP waste stream. Different washing temperatures and recyclate production processes were used to study their effects on the properties of the recyclates. The main objective was to determine the lowest achievable MFR and the rheological, mechanical, and thermal properties of the recyclates from improved sorting. The results are intended to serve as reference points for the evaluation of future automatic sorting trials. The enhanced sorting resulted in an 80% reduction in the MFR and improved ductility, thereby extending the potential applications of the recyclate. The different washing and production processes did not have a significant effect on the investigated properties, except for a slight decrease in the MFR with hot washing and the omission of the pelletizing step.

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.

The quality of recycled plastics is crucial to make them competitive in more demanding applications and to extend their range of applications. However, there are many influencing factors that can reduce the quality and limit the use of recyclates. One of these factors is degradation, which can occur at different stages of a plastic's life cycle. Degraded material can affect the quality of recyclates. Therefore, it would be beneficial to sort out heavily aged plastics from the recycling stream before further processing. This work investigates the possibility of separating severely degraded polyethylene (PE) from unaged or less degraded PE using near-infrared (NIR) hyperspectral imaging. For this purpose, PE samples were artificially aged using two methods: (i) exposure to UV light, (ii) exposure to aqueous chlorine dioxide solution. The ageing state of the samples was assessed by means of Fourier Transform Infrared (FTIR) spectroscopy and tensile tests and their NIR spectra were recorded on a laboratory NIR sorter. The ability to separate highly degraded from non-/less-degraded samples, which was defined by their mechanical performance, was then analysed using multivariate data analysis and machine learning algorithms applied to the NIR data. These analyses showed promising results for separating highly degraded PE samples, with the classification between degraded and less degraded PE achieving accuracy and F1 scores exceeding 90%.

Driven by global sustainability goals, the use of recycled polymers is increasing, but their inconsistent quality poses a challenge for reliable use in technical applications. In this study, ten batches of an industrially used post‐consumer polypropylene (PP) recyclate were examined over 15 months, all ordered with identical specifications for melt flow rate (MFR = 7–13 g/10 min) and density (0.97 ± 0.03 g/cm ³ ). Despite fulfilling these specifications, considerable differences were found in rheological, thermal and mechanical properties. Filler content varied between 2% and 24%, strongly affecting mechanical performance. While Young's modulus and yield stress varied slightly, elongation at break differed greatly (10%–100%). Particularly large differences were found in the crack resistance. At the same stress level, the number of cycles until failure ranged between 3000 and 6.52 million cycles. These deviations are attributed to variations in molecular structure, filler content and polymeric and non‐polymeric impurities. The findings highlight that, despite fulfilling the target specifications for MFR, considerable compositional differences can significantly affect the material performance. Standard parameters are therefore insufficient to assess the suitability of recycled PP for technical applications. Comprehensive characterization, narrower specification limits and improved sorting are essential for the reliable and sustainable use of recyclates in long‐term applications.