An FT-IR study of the effect of hydrolytic degradation on the structure of thin PET films

Thin (∼100 nm) PET films were treated in pure water and 1% KOH solution and changes in the chemistry and morphology were followed using FTIR–RAIRS. Degradation was monitored using the intensity of the alcohol and acid ν(OH) bands. Dramatic changes in intensity of the ν(C–H) band were noted as a function of degradation for both samples treated in pure water and KOH solution. This was interpreted as resulting from a change in the environment of the aliphatic methyl groups and subsequent extensive hydrogen bonding, due to an increase in the numbers of hydrophilic end groups. Differences in the ν(OH) and ν(CO) bandshapes were noted between the two systems suggesting different hydrogen bonded species. The autocatalytic nature of the hydrolysis in pure water was confirmed and evidence of the so-called ‘chemicrystallisation' effect, with crystallinity increasing with degradation, was observed. The thin nature of the films allowed a spectroscopic insight into the morphology of the degrading films as a function of treatment time.