Superstructure and mechanical properties of poly(ethylene terephthalate) fibers zone‐drawn under critical necking tension

The superstructure and mechanical properties of poly(ethylene terephthalate) fibers zone‐drawn under a critical necking tension (σ c ) were studied. σ c was defined as the minimum tension needed to generate a neck at a given drawing temperature (T d ) and was measured over a temperature range of 70–120°C. The σ c value increased rapidly with decreasing T d in the temperature range below 85°C, but the temperature dependence of σ c was small above 85°C. The neck profile relied on T d , becoming more shapely with decreasing T d . A neck with a gradual decrease in diameter was observed in the fibers drawn at 100°C and above. The draw ratio increased significantly with increasing T d above 90°C, but birefringence decreased. Density decreased gradually with increasing T d , and fiber drawn at 120°C had a density of 1.347 g/cc. Wide‐angle X‐ray diffraction photographs of the fibers drawn at 100°C and below showed reflections due to crystallites, but a photograph of the fiber obtained at 120°C showed a ring‐like amorphous halo. The storage modulus (E′) at 25°C increased progressively with decreasing T d , and the fiber drawn at 70°C had the maximum E′ value among the fibers drawn at a series of T d 's. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 179–185, 2002