Recycling rigid polypropylene from mixed waste: Does the origin affect mechanical recyclate quality?

The increasing demand for plastic and the shortcoming of overall plastic recycling rates underscore the necessary transition towards a circular economy. In Austria, more than half of the generated plastic waste, especially non-packaging waste, is incinerated because of its disposal in mixed wastes. This highlights a vast untapped potential for recycling. While prior research has primarily focused on recycling plastic packaging waste from mixed waste origin, this study addresses a critical gap by exploring the recycling of non-packaging plastics in different concentrations by specifically examining rigid polypropylene (PP) sourced from a mixed waste material recovery facility. The methodology involves mechanical pre-processing of plastics, such as washing and sink-float separation, followed by polymer processing to evaluate the recyclates' tensile (impact), thermal, morphological and rheological properties. Results indicate that the dirt content of rigid PP after sorting is comparable to that of separately collected waste. Furthermore, homogeneous recyclates with minor polyethene impurities were produced, the quality of which is comparable to commercially available recyclates regarding elastic modulus and yield stress. Although further research on odour contamination, substances of concern, long-term applicability and environmental and economic aspects is necessary, this study demonstrates that a substantial amount of PP can be recovered from mixed wastes in Austria. Ultimately, recycling such plastics can considerably contribute to circularity efforts.