The morphologies of poly(ethylene terephthalate) (PET) films annealed at various temperatures after drawing to various extents were studied by measurements of density and birefringence, wide-angle X-ray analysis, electron microscopy and measurement of the contraction on annealing. It is proposed that a new type of texture with a-axis orientation is formed when the resultant films have negative birefringence. Namely, thin lamellae, in which polymer molecules are folded, are aligned preferentially along the original drawing direction, which means that polymer molecules are oriented preferentially perpendicular to the drawing direction. It is suggested that, on annealing a drawn film with a slight positive birefringence and very low crystallinity, crystallites or a similar conformation of molecules (nuclei) with c-axis orientation may rotate, the extent depending on that of the frozen elongation of the amorphous tie-chains between the crystallites or nuclei, so as to make the tie-chains relax, giving rise to the texture in question.
Посилання на статтю:
Study of a-axis orientation in drawn and annealed poly (ethylene terephthalate) film / Tohru Kawait and Midori Muta // Polymer. – 1992. – Vol 33. – P. 2567-2574.