Light scattering studies on the crystalline morphology of stretched poly(ethylene 2,6-naphthalate) film

The crystalline morphology of poly(ethylene 2,6-naphthalate) (PEN) film obtained by uniaxial stretching at 145 °C (Tg + 25 °C) was investigated by use of a light scattering photometer equipped with a CCD camera system. The Hv scattering showed a symmetric, circular pattern at a low stretch ratio of λ < 3. The intensity profile became sharper with an increase in λ, suggesting that anisotropic crystal rods are randomly assembled and that the length of the rods increases with λ. At a high stretch ratio of λ ≥ 3, a double-cross-type pattern consisting of a broad rod-like pattern and sharp cross streaks was observed. The rod-like pattern became smaller and the streaks became sharper with an increase in λ. By the model calculation of the scattering pattern, the double-cross-type pattern is explained by the stacking of anisotropic crystal rods oriented in the stretch direction. As λ increases, the thickness of the rods and the number per stack increase, and the stacks and rods are slightly oriented in the stretch direction. The change in the wide angle X-ray diffraction pattern suggested that the ordering of the molecular chain in the crystal rods increases with increasing λ.