Osmotic tension, plasticization and viscoelastic response of amorphous poly-ether-ether-ketone (PEEK) equilibrated in humid environments

Abstract

Dynamic-mechanical analysis (DMA), Differential scanning Calorimetry (DSC) and water moisture sorption-desorption kinetics and equilibria have been parallely investigated to monitoring the environmental and thermal sensitivity of amorphous thermoplastic Poly-Ether-Ether-Ketone (PEEK). Morphological modification occurring in PEEK during the calorimetric and thermo-mechanical characterizations and the hygrothermal stability are presented. An interpretation based on the free energy of mixing of a polymer chains with penetrant molecules and pseudo-equilibrium Flory-Huggins interaction parameter and related osmotic tension is proposed. The correlation between dynamic mechanical measurements and water saturation is discussed in terms of different levels of osmotic tension generated in the amorphous PEEK. From the analysis of the water diffusion coefficients in amorphous PEEK equilibrated at low and high activity environments, it has been found that even samples with very low water contents may undergo bulk matrix relaxation above 40°C.