T5% and Tdeg values are reported in Table . The results show a positive impact of antioxidants on the thermal stability under air of the TPO, with only small variations between the different antioxidants tested. This behavior is in line with results previously reported in the literature on the addition of lignin-based antioxidants on polyolefins . The significant temperature shift (ca. 103 °C) of the main mass loss observed for the different formulations therefore indicates the efficiency of the antioxidants to capture free radicals delaying the thermo-oxidative degradation. The antioxidant activity of these materials was particularly characterized by the OIT test. The results are shown in Figure . The aim of this test is to observe the impact of the addition of an antioxidant on the polymer oxidation. The role of the antioxidant is to delay the oxidation of the material in which it is incorporated. Thus, the higher the OIT, the more effective the antioxidant is.