Investigation of hydrolysis in poly(ethylene terephthalate) by FTIR-ATR

The hydrothermal aging of poly(ethylene terephthalate) (PET) was investigated at 70-95 A degrees C. A new method to investigate the hydrolysis degree of PET by Fourier transform infrared spectroscopy (FTIR) was proposed. The spectra during the hydrothermal aging were measured using attenuated total reflection accessory (ATR). Peak resolving of carbonyl regions was performed, and the ratio of two groups of bands representing carboxylic acids and esters respectively were calculated to show the hydrolysis degree of ester groups in PET. The acid/ester ratio shows exactly the same trend as the average chain scission number per unit mass at various temperatures and thus can be used as a parameter to characterize the hydrolysis and random chain scission of PET. This method related to the hydrolysis mechanism directly, is simple, fast and convenient compared to the traditional methods such as viscometry, end-group titration and size exclusion chromatography (SEC). It may also be useful in hydrolysis characterization of other polyesters.