Closed-loop recycling of polypropylene: A case study on mechanical recycling of separately collected yogurt cups in Austria

Abstract

Yogurt cups with their recognizable design are made from plastics that are approved for food contact. The materials used have an interesting property profile. Therefore, these products represent a promising waste fraction for plastics recycling. In this study, yogurt cups were pre-sorted by consumers and further hand-sorted. A 2:1 ratio of polypropylene (PP) cups to polystyrene cups was found. In terms of decorations, cups with printing inks dominated. Two thirds of the PP cups were produced by thermoforming and one third by injection molding. Compositional analysis of the recycled PP showed no significant contamination other than residual dyes. Material characterization exhibited that both processing and application-oriented properties can compete with virgin material. To demonstrate a closed-loop, the recycled PP was used to produce thermoformed cups with exceptional properties. This study shows the positive effect of closed-loop recycling and points out potential waste fractions that can be used in the future.