Insights into the chemical composition and thermo-oxidative stability of novel polyethylene copolymers containing ancillary phenolic antioxidant groups as non-migrating polyolefin stabilizer

The chemical composition and thermal characteristics of a series of novel polyethylene based sterically hindered phenolic antioxidant (PE-SHPA) copolymers were investigated using thermal analysis methods. TGA/DTG curves manifest two distinct degradation events, one at about 250 °C while the second observed at a temperature between 450 and 500 °C under oxygen atmosphere. Oxidation induction time evaluation shows a dramatic increment by increasing the first degradation event weight loss percentage. To find out whether the first degradation event stem from the presence of low molecular weight non-bonding antioxidants or not, PE-SHPA copolymers were extracted. The higher OIT values observed after the extraction confirmed the chemical bonding of SHPA moiety to the polyethylene carrier and the absence of free antioxidant groups in the copolymer. Hence, the weight loss at 250 °C was considered as an antioxidant content index in PE-SHPA to find an appropriate model for the thermal stability of copolymers produced at different conditions.