Oriented crystallization induced by uniaxial drawing from poly(tetrafluoroethylene) melt

The melt-drawing behavior of poly(tetrafluoroethylene) (PTFE) with ultrahigh molecular weight (UHMW) was analyzed using in situ measurements composed of stress-strain curves and wide-angle X-ray diffraction with synchrotron radiation. The stress-strain behavior of the melt-drawing of UHMW-PTFE was quite different front that of the solid drawing. In particular, the former exhibited a plateau stress region, followed by a rapid increase in stress with strain. No crystalline reflection appeared in the plateau stress region. However, oriented crystallization was observed in the later strain-hardening region. Correspondingly, the resultant mechanical properties and transparency of the melt-drawn films are much better than those of the solid-drawn films. Optimizing the melt-drawing conditions elongated the plateau stress region, which successfully achieved further property development. The effects of sample MW on melt-drawing behavior and resultant properties were also discussed. The lower MW film produced a longer plateau region. Subsequent oriented crystallization in the strain-hardening region also exhibited a rapid increase of the crystalline reflection intensity, compared to that for the higher MW film. However, the resultant properties were lower than those for the higher MW film, due to the higher content of the chain ends, even if a higher resultant crystallinity was achieved.