Impact of reprocessing cycles and chain extender on recycled polypropylene properties

The main aim of this work was to study the influence of recycled Polypropylene (rPP) incorporation into a polypropylene (PP) base material and the effect of chain extender addition on the mechanical performance of injected parts. The impact of multiple processing cycles (up to five) was also evaluated. Formulations with rPP contents up to 50 wt% were produced by twin-screw extrusion, pelletized, and then injected. For the most critical case (50 wt% rPP), a chain extender (1–3 wt%) was added to assess its effect on flexural properties and melt flow index (MFI). Differential scanning calorimetry (DSC) was performed to examine potential changes in thermal transitions. Results showed that rPP incorporation caused only a slight decrease in flexural strength, while the modulus and thermal behaviour remained stable. The addition of 1 wt% chain extender partially recovered flexural strength and improved stiffness, whereas higher contents offered no benefit. Reprocessing cycles led to small reductions in strength, but the chain extender mitigated these. Finally, a school chair was successfully injected using 50 wt% rPP with 1 wt% chain extender, confirming the feasibility of high rPP integration without changes to processing parameters.