Detecting, characterising and assessing PEEK’s and CF-PEEK’s thermal degradation in rapid high-temperature processing

In this study, a methodology is proposed that can identify and characterise the extent of thermal degradation that takes place in rapid high-temperature processing of PEEK and CF-PEEK. Initially, their decomposition mechanisms are examined in air with thermogravimetric analysis (TGA). Then, PEEK and CF-PEEK samples are heated in static air conditions up to temperatures that are close to and above the onset of thermal degradation with heating rates up to 100 °C/min. The samples are then examined with attenuated total reflection - Fourier transform infrared (ATR-FTIR) spectroscopy and a new fluorenone peak is detected at 1711 cm-1 that is directly linked with the progress of degradation. A correlation between its intensity and the resulting thermal degradation takes place and it is shown that the 1711 cm-1 peak can be safely used as a tool for characterising the extent of thermal degradation at the examined heating conditions. Finally, an investigation with differential scanning calorimetry (DSC) is conducted to identify the extent of thermal degradation that would not induce a severe thermal damage on the two materials. In both PEEK and CF-PEEK, faster heating rates are found to have a reduced effect on their crystallinity content and a degradation around 1% of their PEEK matrix content is found tolerable.