Structural and textural changes from polyimide Upilex to graphite: Part III

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Abstract
25 μm thick Upilex films (registered UBE trademark) were carbonized, then graphitized at various temperatures up to 2800 °C and studied by optical and electron microscopies. While the graphitizing behavior of Kapton films is similar to that of anthracites, Upilex graphitization is erratic from one film to the other. The thickness of the better graphitizing Upilex films decreases as the anisotropy increases. Their graphitization occurs at a relatively low temperature (2100 °C), because the oxygen is entirely labile (no cross-linking). Non-graphitizing films are obtained when oxygen remains stable as the heat-treatment temperature (HTT) increases. They stay optically isotropic and microporous without flattening, and even show a limited swelling instead of a thinning. This behavior is attributed to the random mobility of the imide part of the molecule when carbonization starts.