Oxidative Stability and Rheological Features in Recycled Composites Based on Postconsumer Polypropylene and Antioxidant‐Loaded Silicas

ABSTRACT Plastic recycling efforts are hindered by the reduction of material properties in recyclates stemming from oxidative degradation of their polymeric chains. Recent efforts to ameliorate this focus on incorporation of carrier particles functionalized with antioxidants in conjunction with mixing of virgin resin to the recyclates. However, further work is needed to understand how these formulations influence oxidative stability, melt rheology, and crystallization behavior. In the present work, a postconsumer polypropylene (PP) recyclate was blended with approximately 30% by mass virgin PP in conjunction with an antioxidant‐loaded nanosized or mesoporous silica. While both silicas prove to be effective antioxidant carriers based on oxidative induction time measurements, the nano‐silica shows a clear advantage at the lowest level of particle addition. Small‐amplitude rheological measurements show modest enhancements in moduli for the mesoporous composites, indicating good dispersion of these particles, but significant enhancements in moduli are observed at low frequency for the nano‐silica materials for concentrations exceeding 2% by mass, indicating sparse network formation. The particles are shown to be also effective nucleating agents for PP, particularly in the presence of flow, but less so for the polyethylene (PE) that is present as a contaminant. Such measurements should prove valuable in optimization of the recycled formulations across the myriad performance and processing parameter space.