Polypropylene Pipe Compounds with Varying Post-Consumer Packaging Recyclate Content

Abstract

The high recycling targets set by the European Commission will create an increased availability of polypropylene (PP) post-consumer recyclates (PCRs). However, no regulations mandate the use of recycled PP (rPP), so the industry is challenged to explore possibilities to utilize such 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 pressurized gas and drinking water systems. However, many other pipe and underground applications, such as stormwater systems, open the increased use of PCRs. Additionally, even for less-demanding applications, such as non-pressure sewage systems, highly durable solutions are needed to cover the requested lifetime and request an ambitious property profile to fulfill the application needs that 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 and PP waste were acquired and, together with two predefined virgin PP pipe grades, were blended 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 of the compounds showed good results regarding fatigue crack (FCG) resistance with virgin polymer as the reference. The factors influencing FCG resistance, such as melt flow rate and polyolefin cross-contamination, were thoroughly investigated as the used virgin grades and recyclates cover a broad range of these properties.

Polypropylene Post-Consumer Recyclate Compounds for Thermoforming Packaging Applications

“…For warm drawing or thermoforming, the strain at break (which would relate more to a cold drawing) is also not a critical design parameter. Furthermore, the strain at break value highly depends on the injection molding conditions and MFR or rather orientation due to injection molding [ 13 , 14 ], as well as inclusions within the specimen which lead to premature fracture at lower strains and give an indication of the contamination of the compounds. vPP, rPP-A, and rPP-B, as well as all compounds from these materials, show relatively low strain at break values of between 44% and 71%, as can be seen in Figure 6 c. Only rPP-C (277%) and the compound C55 (176%) achieve much higher strain at break values suggesting fewer unknown inclusions in rPP-C than in rPP-A and rPP-B.…”

“…Another possibility for modifying rPP could be compounding with virgin polymers. While there is research available for other applications [ 13 , 14 , 15 ], no preceding research could be found for creating and assessing thermoforming compounds with post-consumer recyclate content.…”

Simultaneous Modification of Properties Relevant to the Processing and Application of Virgin and Post-Consumer Polypropylene

“…Pipe materials are known for their very low MFR values as it is required by several standards in the pipe industry [ 4 ]. The MFR values of PP pipe grades are usually in the range of 0.25 to 4.5 g/10 min [ 40 ].…”

“…The targeted property adjustment of recyclates by blending with virgin materials opens many areas of application that were previously not possible due to the initial properties of recyclates. Nevertheless, the long-term behavior of recycled materials must not be ignored, as there are still considerable deficits in this area [ 3 , 4 , 5 ]. Depending on the intended property profile and whether the recyclate or the virgin material should be the main component, the right blending ratio must be selected.…”

“…However, no specific products are defined yet for the uptake of polyolefin recyclates as it is already regulated for PET bottles [ 2 ]. Therefore, several applications need to be found where either modified or unmodified recyclates can be used [ 3 , 4 , 5 , 6 , 7 ].…”