Natural antioxidants for polypropylene stabilization

A study on the efficiency of bio-based compounds as stabilizers for polypropylene (PP) is reported. A water extract from French maritime pine bark (Pycnogenol®), a by-product containing polyphenols obtained from wine production, and a carotenoid-containing oleoresin from processing of tomatoes were used. Their stabilizing activity was compared with that of a commercial phenolic antioxidant. Thermogravimetric analysis and Oxidative Induction Time measurements performed on unaged samples, as well as infrared spectroscopy on samples aged at 70 °C, provided evidence for the effectiveness of the natural stabilizers. Mechanical characterization was carried out on aged films and injection moulded samples. Experimental results indicated that particularly grape extract could provide long-term stabilization to PP under conditions of oxidative degradation. Therefore, it could be used as efficient and high value-added additive for polypropylene. Pycnogenol® also showed antioxidant activity, however the achievement of a more homogeneous dispersion in the polymer matrix could improve the mechanical performance of aged samples.