Markedly improved photo-oxidation stability of α form isotactic polypropylene with nodular morphology

Photo-oxidation degradation behaviors of isotactic polypropylene (iPP) films with different crystalline morphology were investigated by artificially accelerated aging test. The alpha form iPP with nodular morphology was obtained by quenching the melt and subsequent annealing process, and its photo-oxidation degradation behavior was compared with that of the melt-crystallized alpha form iPP sample. Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), X-ray scattering, dynamic mechanical analysis (DMA) and atomic force microscopy (AFM) were utilized to characterize the microstructural variations of these two kinds of iPP films during photo-oxidation degradation process. The results showed that iPP film of nodular morphology exhibits improved photo-oxidation stability compared with that of lamellar and spherulitic structure. UV-Vis spectra and O-2 diffusivity test of unexposed and aged samples demonstrated that the iPP film of nodular morphology has higher transparency and lower O-2 diffusivity than that of lamellar morphology. Combining the microstructural analysis and surface morphology observation, the improved photo-oxidation stability of nodular iPP was correlated with its higher UV light transparency, lower O-2 diffusion coefficient as well as the slower segmental mobility in the amorphous phase. (C) 2021 Published by Elsevier Ltd.

Automated summary

Based on accelerated aging tests, isotactic polypropylene (iPP) films with nodular morphology exhibited superior photo-oxidation stability compared to films with lamellar and spherulitic structures. The improved stability of nodular iPP was attributed to its higher UV transparency, lower O-2 diffusion coefficient, and slower segmental mobility in the amorphous phase.