ISSN:
0887-6266
Keywords:
polytetrafluoroethylene
;
virgin powder
;
two-stage draw
;
morphology
;
tensile properties
;
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Polytetrafluoroethylene (PTFE) virgin powder was ultradrawn uniaxially by a two-stage draw. A film, compression molded from powder below the melting temperature (Tm), was initially solid-state coextruded to an extrudate draw ratio (EDR) of 6-20 at an established optimum extrusion temperature of 325°C, near the Tm of 335°C. These extrudates from first draw were found to exhibit the highest ductility at 45-100°C for the second-stage tensile draw, depending on the initial EDR and draw rate. The maximum achievable total draw ratio (DRt, max) was 36-48. Such high ductility of PTFE, far below the Tg (125°C) and Tm, is in sharp contrast to other crystalline polymers that generally exhibit the highest ductility above their Tg and near Tm. The unusual draw characteristics of PTFE was ascribed to the existence of the reversible crystal/crystal transitions around room temperature and the low intermolecular force of this polymer, which leads to a rapid decrease in tensile strength with temperature. The structure and tensile properties of drawn products were sensitive to the initial EDR, although this had no significant influence on DRt,max. The most efficient and highest draw was achieved by the second-stage tensile draw of an extrudate with the highest EDR 20 at 100°C, as evaluated by the morphological and tensile properties as a function of DRt. The efficiency of draw for the cold tensile draw at 100°C was a little lower than that for solid-state coextrusion near the Tm. However, significantly higher tensile modulus and strength along the fiber axis at 24°C of 60 ± 2 GPa and 380 ± 20 MPa, respectively, were achieved by the two-stage draw, because the DRt,max was remarkably higher for this technique than for solid-state coextrusion (DRt,max = 48 vs. 25). The increase in the crystallite size along the fiber axis (D0015), determined by X-ray diffraction, is found to be a useful measure for the development of the morphological continuity along the fiber axis of drawn products.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2551-2562, 1998
Additional Material:
13 Ill.
Type of Medium:
Electronic Resource
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