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Peculiarity of the Mechanism of Early Stages of Photo-Oxidative Degradation of Linear Low-Density Polyethylene Films in the Presence of Ferric Stearate
Summary
This study investigated how ferric stearate (an iron-based additive used in oxo-degradable plastics) accelerates the early stages of polyethylene photo-oxidation, finding that it acts not merely as a catalyst but actively generates radicals that fragment the polymer chain from the outset. While framed as a materials science study, the findings are relevant to the microplastics debate: oxo-degradable plastics marketed as environmentally friendly may in fact fragment more rapidly into persistent microplastic particles rather than fully mineralizing.
Ferric stearate (FeSt3) is very efficient in accelerating polyethylene (PE) degradation, but there is a lack of exploration of its role in accelerating the early stages of polyethylene photo-oxidative degradation. This study aimed to investigate the effect of FeSt3 on the photo-oxidative degradation of PE films, especially in the early stages of photo-oxidative degradation. The results show that FeSt3 not only promotes the oxidative degradation of PE but also contributes significantly to the early behavior of photo-oxidative degradation. Moreover, the results of the density functional theory (DFT) calculations proved that the C-H in the FeSt3 ligand was more easily dissociated compared with the PE matrix. The generated H radicals participate in the coupling reaction of the primary alkyl macro radicals leading to the molecular weight reduction, thus significantly increasing the initial rate of molecular weight reduction of PE. Meanwhile, the transfer reaction of the dissociation-generated C-centered radicals induced the PE matrix to produce more secondary alkyl macroradicals, which shortened the time to enter the oxidative degradation stage. This finding reveals the mechanism by which FeSt3 promotes the degradation of PE at the early stage of photo-oxidative degradation. It provides guiding significance for the in-depth study of the early degradation behavior in photo-oxidative degradation on polyolefin/FeSt3 films.