Anisotropy of dielectric relaxation in poly(ethylene terephthalate) fibres

Dielectric measurements have been made on poly(ethylene terephthalate) (PET) fibres in the frequency range 0.5–10 kHz in temperature range ?120°?+30° C with the applied electric field parallel and perpendicular to the fibre axis. Considerable directional anisotropy was observed in the β-relaxation process, which was independent of frequency. The observed dielectric anisotropy has been related to the structural parameters thus leading to a value 〈cos²ψ〉 = 0.21, where ψ is the angle between the dipole moment vector responsible for this relaxation and the molecular chain axis. Activation energy for this process in PET fibres (9 kcal/mol) was lower than that reported for PET films and extruded rods.