Natural sunlight ageing of control and sterilized poly(ethylene terephthalate): Two‐dimensional infrared correlation spectroscopic investigation

ABSTRACT Attenuated total reflection Fourier transform infrared (ATR‐FTIR) and two‐dimensional correlation (2D‐COS) spectroscopies were utilized to probe the structural changes occurring upon sunlight ageing up to 6 months in air atmosphere of both control and sterilized poly(ethylene terephthalate), (PET) bottles.Two dominant reactions were found; namely oxidation of the carbonyl groups and trans to gauche transformation of the ethylene glycole units. Oxidation manifested itself by the progressive development of a distinct band at 1690 cm −1 assigned to the antisymmetric stretching of the carbonyl band in an aromatic carboxylic acid. Sterilizing the bottles by E‐beam or Gamma rays prior to ageing reduced the correlation intensity of the band at 1690 cm −1 , and led to the presence of higher molecular weight compounds such as terephthalic acid in stored water. The infrared spectroscopy combined with 2D‐COS provides a powerful tool to investigate chemical and stero‐chemical modification of polymers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44736.