ANOMALOUS DIFFUSION IN POLY-ETHER-ETHER-KETONE

Poly-ether-ether-ketone (PEEK) is a thermoplastic tough polymer used a s a matrix for advanced composite materials in aeronautic applications . The investigation of its resistance to humid environment and to expo sure to organic and chlorinated solvents is extremely important. A ser ies of integral sorption experiments were performed on PEEK with three different kinds of penetrant, namely water, methylene chloride and me thylene chloride-n-heptane mixtures. Coupled diffusion and relaxation phenomena were observed to occur in most of the adopted experimental c onditions. Moreover, for the case of methylene chloride sorption at me dium and high activities a solvent-induced crystallization phenomenon was also detected. The sorption behavior was found to range from ideal Fickian diffusion (where the molecular mobility is not affected by th e penetrant concentration) to so-called anomalous diffusion. In the la tter case the penetrant mobility is a complex function of penetrant co ncentration, time and temperature. An overview of theoretical models r eported in the literature to describe such phenomena is also presented with the aim of interpreting the experimental results obtained.