UV Aging Behavior of Functionalized Mullite Nanofiber-Reinforced Polypropylene

In this study, the effect of accelerated ultraviolet (UV) aging on the properties of polypropylene (PP) as well as its blend with PP-graft-maleic anhydride (PP-g-MA) and composite with amine-functionalized mullite nanofibers (AMNF) was compared. Solid-state NMR exhibited some changes in the macromolecular chain structure after aging, whereas the formation of degradation products was confirmed through Fourier transform infrared (FTIR) spectroscopy. The aged composite was observed to exhibit the least increment in the crystallinity from X-ray and differential scanning calorimetry (DSC) analyses (0.3 and 0.5%, compared to 9.7 and 10.4%, respectively, for PP) owing to the stability of its amorphous phase against degradation. Similar resistance toward degradation was also confirmed by thermogravimetric analysis (TGA). The surface morphology of the materials also exhibited the lowest extent of surface embrittlement as well as a small number of shallow cracks in the case of a-PP/PP-g-MA/AMNF composite. The aged composite had a much higher impact strength of 14.9 kJ m^-2 compared to 2.5 kJ m^-2 for aged PP, thus exhibiting its stability against degradation owing to a synergistic combination of the filler and compatibilizer. The optimal performance of the composite was further confirmed through the least extent of reduction in the tensile strength and elongation at break. These findings demonstrate the superior performance of AMNF-reinforced PP composite over PP for outdoor applications.