Creep Behavior in Amorphous and Semicrystalline PEN

Poly(ethylene-2,6-naphthalate), PEN, is a suitable candidate to replace poly (ethylene terephthalate), PET, in some applications. PEN can be produced in either the amorphous or semi-crystalline states, depending on the processing conditions. Here, we report on results from uniaxial tension experiments in creep conditions in which we probed the viscoelastic and physical aging responses for both amorphous and semi-crystalline forms of PEN. The data show the existence of overlapping β and a relaxations in the experimental creep time range studied. The β process is stronger in the amorphous than in the semi-crystalline material and, in both cases, shows different aging time and temperature dependencies. A model in which the a process is treated as a stretched exponential process and the β process as a Cole-Cole process is developed and its validity examined for both the amorphous and semi-crystalline PEN materials.