Strategies for improving product properties of thermoformed multilayer cups with contents of post-consumer polypropylene recyclates

Thermoformed products bear great potential for the application of recycled materials when using multilayer structures for incorporating post-consumer recyclates. For this study, four different commercially available polypropylene recyclates are selected as possible core layers for the processing of multilayer thermoformed products with top layers of virgin polypropylene. Tests are performed on material level as well as on product level. At the material level, recyclates exhibit different mechanical property profiles with lower stiffness but higher toughness values due to polyethylene contamination. At the product level, thermoformed cups with core layers of recyclate material show lower shrinkage than cups made from polypropylene virgin material only. Most cups with recycled content achieve lower top load than the control cup. Based on these results, three strategies for improving product performance are defined and tested. Namely, (i) the use of a higher share of top layers, (ii) the blending of the recyclate core layer with a polypropylene virgin material with higher stiffness, and (iii) the increase in overall film thickness. All the strategies to adjust the film structure achieve better results in terms of shrinkage behavior and top load. However, the strategy that focuses on increasing the overall film thickness is not economically feasible.

Automated summary

Thermoformed products have potential for using recycled materials in multilayer structures. In this study, four commercially available polypropylene recyclates were tested as core layers for thermoformed products with top layers of virgin polypropylene. The recyclates showed lower stiffness but higher toughness due to polyethylene contamination, and cups made with recyclate material had lower shrinkage and top load. Three strategies for improving product performance were tested, all of which achieved better results in terms of shrinkage behavior and top load.