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Photoantioxidant versus photodegradant: Action of nanoparticle inorganic fillers in outdoor aging of PP

Owing to the widespread use of polypropylene (PP) nanocomposites, their stability in the environment is becoming increasingly relevant. Accordingly, a systematic study of the relationship between the characteristics of inorganic nanofillers and the environmental aging behavior of PP is necessary to determine the service life of PP nanocomposites in outdoor environments. Therefore, in this study, we systematically investigated the effects of the chemical composition, particle size, crystalline form, and amount of inorganic filler (CaCO3, Al2O3, SiO2, and ZnO) on the outdoor aging behavior of PP. The results of outdoor aging experiments showed that the filler composition affects the aging behavior of PP. It was found that SiO2 and ZnO nanoparticles accelerate and retard the outdoor aging of PP, respectively. In addition, PP composites containing inorganic fillers with relatively large particles or more stable crystalline forms exhibit relatively slow aging. In the case of the fillers other than ZnO nanoparticles, increasing the filler content accelerates the outdoor aging of PP. The evolution of cracks in the exposed surfaces of PP composites during outdoor aging was observed by scanning electron microscopy. The CO2 generated by PP composites during in situ gaseous degradation product detection corresponds well with the results of the outdoor aging experiments. This study elucidates the effects of inorganic fillers on the outdoor aging behavior of PP.