Changes in superstructure and mechanical properties of poly(ethylene‐2,6‐naphthalate) fibers with critical necking tension

Abstract

Poly(ethylene-2,6-naphthalate) fibers were zone-drawn under a critical necking tension (σc) defined as the minimum tension needed to generate a necking at a given drawing temperature (Td). In the zone drawing under σc, the neck was observed from 110 to 160 °C. The superstructure in a neck zone induced at each Td was studied. The σc value decreased exponentially with increasing Td and dropped to a low level at a higher Td. The draw ratio increased rapidly with Td increasing above 90 °C, but the birefringence and degree of crystallinity decreased gradually. To study the molecular orientation in the neck zone, we measured a dichroic ratio (A‖/A⟂) of a CO band at 1256 cm−1 along a drawing direction in the neck zone with a Fourier transform infrared microscope. A‖/A⟂ at Td = 110 °C increased rapidly in the narrow neck zone, and that at Td = 140 °C increased in the edge of the wide neck zone. Wide-angle X-ray diffraction patterns of the fibers obtained at Td = 130 °C and lower showed three reflections due to an α form, but those at Td = 140 and 150 °C had reflections due to the α form and a β form. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1629–1637, 2001