The influence of thermal history on the dynamic mechanical and dielectric studies of polyetheretherketone exposed to water and brine

Abstract

The effects of thermal history on the absorption of distilled water and brine and their influence on the dynamic mechanical and dielectric properties of semi-crystalline polyetheretherketone (PEEK) are reported. Changes in the physical properties of the samples were monitored as a function of time of exposure using gravimetric measurement, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC) and dielectric spectroscopy. The water and brine sorption behaviour follows a Fickian Case I process with a maximum solubility of 0.5 w/w% at 75°C. The observed sorption behaviour was independent of the salinity of the water to which the polymer was exposed. The water uptake proved to have an effect on the degree of crystallinity. It is observed that the crystallite distribution generated in the formation of the sample has a profound effect on the nature of the water uptake process and also its reversibility. During the initial stages of water uptake smaller crystallites are destroyed and these do not reform when the samples are dried. Low frequency dielectric spectroscopy exhibits a very close correlation with the gravimetric measurements and indicate that this method provides a useful non-destructive evaluation technique for the assessment of water content in filler free thermoplastics.