Polypropylene (PP), a widely used recyclable plastic in packaging and engineering applications, is prone to thermo-oxidative degradation during reprocessing and molding at high temperatures. Antioxidants (AOs) are essential for stabilizing PP in both its virgin and recycled states. The quantity of AO added is critical: insufficient amounts can lead to poor stabilization, while excessive amounts can cause safety concerns due to build-up. This study presents a modified approach to measure the Oxidation Induction Temperature (OIT) using Differential Scanning Calorimetry (DSC), particularly for recycled PP from waste that contains unpredictable contaminations. This modified approach ensures the safety of the calorimetry cell by limiting the oxidation reaction and preventing the release of volatile compounds during measurements. By performing DSC measurements in inert environments, we obtain the OIT, which can be correlated to residual intact AO levels. This approach to monitoring AO levels is demonstrated in both open- and closed-loop recycling of rigid PP. Although the presence of contamination is known to catalyze thermo-oxidative degradation in PP, our results indicate that recycled PP from open-loop collection still contains sufficient residual AO that allows it to withstand limited thermal reprocessing. However, this tendency of AO retention leads to significant build-up during closed-loop recycling when AOs are added to each cycle, where the PP grade remains fairly homogeneous and the dispersity (Đ) does not significantly increase over multiple recycling loops.

Adding recycled content is paramount for achieving circular packaging. However, packaging films produced from postindustry or postconsumer recycled polyethylene (PCR PE) have been reported to have various visual and mechanical issues related to impurities and degradation, which affect their performance. This paper studies the gel presence and seal characteristics of packaging films produced from 100% monolayer PCR PE with the addition of antioxidants and compatibilizers. It additionally evaluates the performance of commercially produced multilayer PE films that contain 30% and 50% PCR PE in the core layers and virgin sealant and top layers, checking the quality variations that arise from the difference in PCR PE batches. In the research, the presence and surface area ratio of gels related to recycled content are analyzed using FTIR, microscopy and a newly introduced image analysis method; seal performance is measured via hot‐tack and cold‐tack tests, and material performance is evaluated via tensile testing. According FTIR findings, some spherical and fibre like impurities coming from PCR PE were found to be polyamide or cellulose based, respectively. In nonfood contact commercial films with PCR PE content, the quality varied largely from batch to batch as well as the hot and cold seal strength. In 100% PCR PE films produced in laboratory settings, adding antioxidants during film production did not significantly influence the gel presence while one of the maleic anhydride‐based (MAH) compatibilizers used in the research reduced both the gel number (from 432 to 375 pcs/9 cm ² ) and gel area ratio (from 0.81% to 0.67%). On the other hand, both types of additives delayed the breakage failure providing a larger operation window in hot‐tack tests. During the cold‐tack test, stronger attachment at the seal interphase is observed at 100°C sealing temperature in samples with added compatibilizer. Finally, according to tensile test results, the Young's modulus and the elongation at break only showed slight changes with the addition of antioxidants and compatibilizers. The results can be used for guidelines for design from recycling working with PE films.