Analyse de la dégradation thermique du Poly(éther éther cétone)

Abstract

The thermal degradation of PEEK has been studied in rubbery state in wide ranges of temperature (between 180 and 320 °C) and oxygen partial pressure (between 0.21 and 50 bars). First of all, the thermal ageing mechanisms have been analysed and elucidated by FTIR spectroscopy and by differential scanning calorimetry (DSC) on sufficiently thin PEEK films (between 10 and 60 μm thickness) to be totally free of the effects of oxygen diffusion. Oxidation occurs on aromatic rings causing the growth of five new IR absorption bands centered at 3650, 3525, 1780, 1740 and 1718 cm -1 and attributed to the stretching vibrations of the O-H bonds of phenol and benzoïc acid, and the C-O bonds of benzoïc anhydride, phenyl benzoate and fluorenone respectively. In addition, oxidation leads to a large predominance of crosslinking over chain scissions (increase in T g ) preventing the annealing of PEEK, in particular when the temperature of exposure is higher than the onset of the melting endotherm. Finally, the consequences of oxidation on the elastic properties have been analysed and elucidated by micro-indentation on preliminarily polished cross-sections of PEEK plates of 3 mm thickness. The changes in Young's modulus and crystallinity ratio correlate perfectly, thus checking the Tobolsky's relationship.