AbstractThe viscoelastic properties of the amorphous and semicrystalline PEEK and of a PEEK‐based composite (APC2) have been analyzed as a function of the aging time and related free volume relaxation, at temperatures close to the glass transition temperature. The effect of thermal treatments (physical aging) on the polymer amorphous phase of the three systems is presented. Creep tests approaching the “zero stress” were performed on samples subjected to different thermal histories. The presence of a second phase, namely crystallites and fibers, determines a loss of the mobility of the polymeric amorphous chains and consequently a decrease of the rate of free volume relax
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