Since TPOs are the most sensitive polymers to oxidation phenomena, particularly thermal oxidation, they were chosen for a specific accelerated aging study. Monitoring the aging of TPO formulations enables us to study variations in material properties and antioxidant activity with TPO matrix over time, and to follow the influence of antioxidant type and contents on these properties. Accelerated aging involved keeping the formulations in air at 85 °C for 85 days and carrying periodic analyses. The OITs of the various systems were measured after different aging times as shown in Figure .