Preferred orientation of crystallites in uniaxially deformed polytetrafluoroethylene

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Abstract
X‐ray methods have been used to determine the preferred orientation of crystallites in PTFE sheets stretched varying amounts in the trigonal phase at room temperature. Spherical harmonic analysis of the x‐ray data was carried out to obtain inverse pole figures. At high elongations results show preferential alignment of the c axis (chain direction) with the extension axis. At lower elongations there is also a tendency for (h0h̄l) poles to be aligned with the extension axis. The results at low extension are interpreted as being caused by slip occurring on {1120} planes along the tangent to the helix formed by the PTFE molecule. Experiments carried out in the hexagonal phase above 30°C, and in the triclinic phase below 19°C support these conclusions.