Aging and Degradation of LDPE by Compact NMR

Morphological and structural changes of commercial-brand low-density polyethylene induced by thermal aging for different times at different temperatures are studied by compact H-1 NMR relaxation, FTIR spectroscopy, and SEC including the impact of wax content. Two regimes were observed. The changes in phase composition and relaxation time suggest that thermally induced crystallization is predominant during aging and oxidation of LDPE below 100 degrees C while, after 28 d aging at 100 degrees C, oxidative degradation is predominant. This is in good agreement with carbonyl index and molecular weight variations evaluated by FTIR and SEC, respectively, which indicate multi-stage oxidation during aging.