Smart design choices provide new applications for recycled polypropylene: The case for tribology

Abstract

Polypropylene (PP) is one of the most used polymers and has a wide scope of application, making it a key target for ambitious new recycling reforms. However, recycled PP is currently rarely used for technical applications. We investigated how reprocessing-induced mechanical and melt property changes restrict the scope of application of PP in open recycling loops, with deterioration of tensile properties and considerable increases in melt mass-flow rate consolidating regranulate use towards injection moulding applications. Remarkably, however, reprocessing had the opposite effect on tribological properties with changes to supramolecular structure reducing wear by up to one order of magnitude. As a proof-of-concept, this demonstrates how smart decisions on material flow during cycling could be a simple, effective, immediately implementable way to increase the scope of application, value and performance of recyclates without radical recycling industry reforms: changing the application of degrading reganulates after each cycle in favour of applications with different design requirements.