Analysis of the aging and stabilization processes in cyclic polyolefins containing various natural or synthetic stabilizers.

The aim of this research was to perform a new evaluation of stabilizers dedicated to ethylene-norbornene copolymer (EN). The aging and stabilization processes of the EN polymer filled with natural (xanthone, naringenin) or synthetic (Rianox 626, Rianox 1726, Rianox 3114) antioxidants with different chemical structure were thoroughly analyzed and the suitability of the methods described in the literature to study these processes was assessed. EN is successfully used in optics, electronics or packaging sectors, but like any other organic material, it will degrade under the influence of environmental factors. The EN films were subjected to thermo- and photooxidation for 150, 300, 450, and 600 h. We observed that all composites exhibited an excellent resistance to thermo-oxidation, but as expected, much greater differences were noted after exposure to ultraviolet radiation. The performed tests: thermal analysis, FTIR spectroscopy, contact angles determination, color change measurements, static and dynamical mechanical tests proved the high effectiveness of the used antioxidants for the EN stabilization. However, in the case of the EN-xanthone sample, during the FTIR analysis, a higher value of the carbonyl index in comparison with the reference EN was obtained, and a greater change in the glass transition temperature (T g) compared to the other used stabilizers was observed. These changes could be caused by xanthone oxidation on the polymer surface and its plasticization because of aging, as evidenced by the increased T g value. In addition, we also discussed possible stabilization mechanisms of EN through the use of selected antioxidants. Interestingly, based on the obtained results, Rianox 626 containing phosphite groups in its structure turned out to be the most effective stabilizer for the ethylene-norbornene copolymer, even though it is a secondary antioxidant. It can therefore be suggested that the propagation stage plays a leading role in the degradation of this polymer, in which antioxidants decompose hydroperoxides. In the case of Rianox 626, phosphite groups reacted with hydroperoxides, thus creating the phosphate form of this stabilizer and alcohols, which are more stable and non-radical products. [Display omitted] • Polymer products based on ethylene-norbornene copolymer show high thermal resistance. • Natural stabilizers of plant origin can be a green alternative to synthetic antioxidants. • Chemical structure of antioxidant can affect the aging process of the polymer. • Rianox 626 is a highly effective stabilizer dedicated to EN polymer (Topas E−140). [ABSTRACT FROM AUTHOR]