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 χ 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.
Highlights
The use of high performance engineering thermoplastics for advanced composites and application need a more deep understanding of the physical phenomena induced in the polymer during their lifespan operations in aggressive environments
The effect of the plasticizing penetrant molecules should be researched in the modification of the interaction between polymer-polymer chains that are substituted by the penetrant molecules polymer chains interactions
Small molecules sorption could induce different levels of plasticization and swelling according to the amount of penetrant and to the intensity of the osmotic tensions generated by the penetrant-polymer pair (Sarti and Apicella 1980)
Summary
The use of high performance engineering thermoplastics for advanced composites and application need a more deep understanding of the physical phenomena induced in the polymer during their lifespan operations in aggressive environments. The loss factor (lower curve in Fig. 2), which represents the ratio between the elastic and viscous mechanical response of the material at the different temperatures, is about 0.025 up to 150°C (namely, the sample is still glassy and it is essentially behaving elastically) and it starts to increase to values that reach 0.3 at 250°C.
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