STRUCTURAL-CHANGES FROM POLYIMIDE FILMS TO GRAPHITE .4. NOVAX AND PPT

Various polyimide films (Kapton, Upilex, Novax, and PPT) were carboniz ed and graphitized up to 3000 degrees C. They were studied by optical and electron microscopies. All films retaining oxygen as a cross linke r over 1000 degrees C, i.e., Kapton, Upilex, and Novax, graphitize as anthracites (high rank coals) do. They get a long range statistical or ientation parallel to the film plane with a nanotexture of flattened p ores. Graphitization is both sudden and perfect above 2100 degrees C w hen the pore walls break. Since oxygen is released at 1000 degrees C, the film PPT behaves as a compact nonporous graphitizing carbon (orien tation parallel to the film plane). Thermal graphitization is progress ive and begins at a higher temperature.