Creep behavior in amorphous and semicrystalline PEN

Poly(ethylene-2,6-naphthalate), PEN, is a suitable candidate to replace pol y (ethylene terephthalate), PET, in some applications. PEN can be produced in either the amorphous or semi-crystalline states, depending on the proces sing conditions. Here, we report on results from uniaxial tension experimen ts in creep conditions:in which we probed the visco elastic and physical ag ing responses for both amorphous and semi-crystalline forms of-PEN. The dat a show the existence of overlapping beta and alpha relaxations in the exper imental creep time: range studied. The beta process is stronger in the amor phous than in the semi-crystalline material and, in both cases, shows diffe rent aging time and temperature dependencies. A model in which the alpha pr ocess is treated as a stretched exponential process and the beta process as a Cole-Cole process is developed and its validity examined for both the am orphous and semi-crystalline PEN materials.