Degradation of post-consumer polypropylene materials exposed to simulated recycling—mechanical properties

Abstract

Two post-consumer polypropylene (PP) materials have been examined and compared using a simulated recycling test procedure consisting of repeated cycles of alternating extrusion and accelerated thermo-oxidative ageing. The materials were also subjected to repeated extrusion and thermo-oxidative ageing separately. The materials were characterized by mechanical and chemical properties, such as elongation-at-break, oxidative induction temperature, carbonyl index and changes in molecular weight distributions. The different batches of recycled PP differed substantially in terms of durability and recycling potential. This illustrates one of the problems involved in handling recycled materials i.e. different batches and material streams may differ quite a lot. Interestingly, the elongation-at-break was significantly different for samples taken after ageing and extrusion, respectively. The elongation decreased upon each ageing step, and increased as a result of the subsequent extrusion. Furthermore, the combination of extrusion and ageing tended to degrade the materials faster compared to ageing or repeated extrusion performed separately.