Fatigue Crack Growth Resistance of Polypropylene Pipe Compounds Containing Post-Consumer Packaging Recyclates

The European Commission set demandingly high recycling targets which will, when followed, eventually create an increased supply of polypropylene (PP) post-consumer recyclates (PCRs). No regulations currently mandate the use of recycled PP (rPP), so the industry is challenged to explore possibilities to utilize these materials. One option, as suggested by the European Commission, is the introduction of rPP in pipe applications. According to existing standards, the use of recyclate is not allowed in pressured gas & drinking water pipe systems. However, many other pipe and underground applications such as stormwater systems opens the increased use of PCRs. Also, even for less-demanding applications like non-pressure sewage pipe systems high durable solutions are needed to cover the requested life-time and request an ambitious property profile to fulfill the application needs which cannot be met by PP packaging materials and even less by PCRs thereof. Hence, this work explores the possible use of commercially available PCRs out of polypropylene from packaging applications in compounds together with virgin PP pipe grades to meet the demands for less-demanding applications. Two different commercially available rPPs and one commercially available recycled polyolefin (rPO), from mixed polyethylene (PE) and PP waste, were acquired and blended together with two predefined virgin PP pipe grades to compounds in the range of 10 m%, 20 m% and 30 m% recyclate content. The compounds and three virgin PP pipe grades, acting as benchmarks, were tested in terms of short- and long-term mechanical performance as well as for many other physical properties. All compounds showed good results in the fatigue crack growth (FCG) resistance with virgin polymer as the reference. Factors influencing FCG resistance, such as melt flow rate and PE cross-contamination, were also investigated.