The crystalline morphology of oriented films of poly(butylene terephthalate) (PBTP) was characterized by wide-angle X-ray diffraction and scanning electron microscopy. The PBTP films were drawn to different draw ratios at various drawing temperatures. Transformation of the lamellar spherulites into a microfibrillar structure occurred in the necking region. The microfibrillar structure appeared at the end of the plateau region. Transformation to perfect microfibrillar structure and the subsequent drawing of this structure were observed in the strain hardening region. The orientation of crystals occurred above the yield point and continued rapidly with draw ratio, while the rate of orientation was decreased by drawing the microfibrillar structure. An optimal drawing temperature of about 423 K (which lies between the glass transition and melting temperatures) was found to provide the highest degree of crystalline orientation. In the glass transition region the strong movement of the non-crystalline chain segments influenced the orientation of crystals. The formation of the microfibrillar structure and the orientation of crystals were also disturbed at the drawing temperature near the melting point. Etching of PBTP films allowed the observation of the stacked lamellae oriented more or less perpendicular to the draw direction as well as the microfibrils existing between the stacked lamellae.
Посилання на статтю:
Morphology of uniaxial oriented films of poly ( butylene terephthalate): 1. Orientation and structural transformation of crystals / Z. Zhou, H. Cackovic, J. D. Schultze and J. Springer // Polymer. – 1993. – Vol 34. – P. 494-500.