The thermal analysis of poly(ethylene terephthalate) by FTIR spectroscopy

Thermal analysis-FTIR spectroscopy, TA-FTIR, has been used to characterize the phase transitions in thin films of poly(ethylene terephthalate) and it has been shown to have distinct advantages over other TA techniques in particular it was not so limited in sensitivity. Since the technique measured property, such as amorphous content or fractional crystallinity directly rather than the rate of change of the properties with time or temperature, it was not so restricted in the time scale over which measurements were made. It also had the advantage of measuring the change in concentration of different functional groups with temperature and determining the temperature range over which chain mobility set in and defining the type of molecular groups involved in the configurational changes.The change in absorbance and shift in peak position with temperature are discussed in terms of the separation of crystalline and amorphous bands as well as defining the cis/trans ratio as a function of temperature.Depending on the change in absorbance or peak position with temperature of the IR bands, they have been characterized as type I or type II behaviour. Measurements on both have been used to characterize the glass transition, crystallization and melting behaviour of PET.

Changes to infra-red spectra of poly(ethylene terephthalate) on heating and cooling.Figure optionsDownload as PowerPoint slideHighlights
► Microgram samples have been analysed to determine glass transition, crystallization and melting behaviour of PET.
► The absorbance of cis/trans bands have been followed with temperature on heating and cooling.
► Fractional crystallinity was determined directly without calibration.
► The IR absorption bands are characterized as type I or type II according to their behaviour with temperature.