A TEM Study on Poly(tetrafluoroethylene) Heat-treated on Alkali Halides

Granules of poly(tetrafluoroethylene) [PTFE] wax were heat-treated near/above the melting point on NaC1 or KI, and their morphologies were studied by transmission electron microscopy. In the granule, fibrils of 70-120nm inwidth were observed, exhibiting a pattern of parallel crosses: the fibrils oriented in the <110> directions ofthe alkali halides. Long fibrils came out of the granule along <110> of the alkali halides, and the cross-sectional shape of the fibrils appeared to be trianglar (or trapezoidal). Electron diffraction patterns from a bandle of the fibrils • revealed that the PTFE chain stems in such a fibril are set perpendicular to the fibril axis, and also that the (100) plane of PTFE hexagonal crystal lattice is in contact with the (001) face of the alkali halides. The degree of fibril orientation was better on KI than on NaCl. Some flat-on platelets of PTFE single crystal were identified inthe granules heat-treated on KI, not on NaCI. Lattice images of such a platelet were obtained, and their optical diffractograms clearly showed a hexgonal pattern consisting ofthree sets of the 100 reflection. KEY WORDS: Transmission electron microscopy/PTFE/Epitaxy/Electron diffraction/Orientation/Annealing/Sintering/Morphology