Morphological Study by TEM on Uniaxially Oriented Thin Films of PET, PEN and Their Blends
Taiyo Yoshioka, Masaki Tsuji, Yutaka Kawahara, Shinzo Kohjiya
Institute for Chemical Research, Kyoto university
Japan

Keywords: TEM, morphology, stacked-lamella

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Uniaxially oriented thin films of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) and their blends (weight percentage compositions: PET/PEN = 80/20, 50/50 and 20/80) were prepared: A thin molten film of homopolymer or blend which was sandwiched between the two glass slides heated at a predetermined temperature was sheared/crystallized by displacing one of the glass slides quickly (~1 km/h) by hand. The resulting films were studied by transmission electron microscopy (TEM). The selected-area electron diffraction (SAED) pattern obtained from each of the uniaxially oriented thin films of PET, PEN and their blends shows a well-defined fiber pattern. In particular, the SAED pattern obtained from the PEN film consists of the reflections assigned to both alpha- and beta-modifications.
In the dark-field image of the uniaxially oriented thin PEN film, stacked-lamellar structures are frequently observed together with many narrow domains in which the crystallites (10-30 nm in size) were aligned along the shearing direction over about 500nm. The average long period of such stacked-lamellar structures is about 27nm which contains a crystalline region about 15nm thick and an amorphous one about 12nm thick. On the other hand, in the dark-field images obtained from the uniaxially oriented thin PET film, the crystallites (10-30 nm in size) are observed to align themselves along the shearing direction over about 500nm, but stacked-lamellar structures are rarely observed. In the case of the PET/PEN blends, the morphologies observed in the respective dark-field images have changed from a PET-type to a PEN-type with increasing content of PEN. Thus it is concluded that PEN is more likely to crystallize in a lamellar form than PET.