Structure and properties of poly(ethylene terephthalate) crystallized by annealing in the highly oriented state. 3. Dynamic‐ and static‐mechanical properties

Commercial undrawn and cold drawn (5 × ) poly(ethylene terephthalate) (PETP) fibers and bristles have been annealed with fixed ends for 6 h in vacuum at different temperatures between 60 and 260°C. With these samples static‐ and dynamicmechanical measurements have been carried out. It has been found that the α‐and β‐processes as well as the moduli depend on the annealing temperature (T a ) in different way, for undrawn and drawn material. The temperature position of the β‐peak evaluated from tg δ and loss modulus as well as the step height of α‐ and β‐processes are unsensitive to the T a for the undrawn material in contrast to the drawn one for which maxima are observed. The appearance of these maxima is explained by the dominating role at the corresponding crystallization temperature of one of the two concurrent processes ‐ crystallization and disorientation, reflected in the change of the effective density of amorphous regions. The dynamic and static measured moduli as well as the stress at break for drawn PETP decrease with the increase of annealing temperature as generally observed. The predominating significance of orientation and the state of amorphous phase in comparison with crystallinity is demonstrated. An extremely high deformation ability at room temperature (up to 200%) of previously drawn and annealed at 255 or 260°C bristles is observed. This originates from the solid state postcondensation and premelting phenomena taking place during annealing in vacuum.