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Superdrawing of polytetrafluoroethylene virgin powder above the static melting temperature
Endo, Ryokei; Kanamoto, Tetsuo
Journal of polymer science. Part B, Polymer physics,
1 September 2001, Letnik:
39, Številka:
17
Journal Article
Recenzirano
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A new two‐stage draw technique was successfully applied to the superdrawing of polytetrafluoroethylene (PTFE) virgin powder. A film, compression‐molded from powder below the melting temperature (Tm = ...
335 °C), was initially solid‐state coextruded to an extrusion draw ratio (EDR) of 6–20 at 325 °C, about 10 °C below the Tm. These extrudates from the first‐stage draw were further drawn by a second‐stage pin draw in the temperature (Td) range of 300–370 °C that covers the static Tm. The maximum achievable total draw ratio was ∼60 at a Td = 300 °C and increased rapidly with increasing Td, reaching a maximum of 100–160 at a temperature window between 340 and 360 °C, depending on the initial EDRs. At yet higher Td's, the ductility was lost as a result of melting. The high ductility of the PTFE extrudates at such high temperatures was ascribed to the improvement of interfacial adhesion and bonding between the deformed powder particles upon the first‐stage extrusion combined with the rapid heating of only a portion of the extrudate followed by the elongation at a high rate. The highly drawn fibers were highly crystalline (χc ≤ 87%) and showed high chain orientation (fc ≤ 0.997) and a large crystallite size along the chain axis (D0015 ≤ 160 nm). The molecular draw ratio, estimated from the entropic shrinkage above the Tm, was close to the macroscopic deformation ratio independently of the initial EDRs. These results indicate that the draw was highly efficient in terms of chain extension, orientation, and crystallization. Thus, the maximum tensile modulus and strength achieved in this work were 102 ± 5 and 1.4 ± 0.2 GPa, respectively, at 24 °C. These tensile properties are among the highest ever reported on oriented PTFE. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1995–2004, 2001
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Uniaxial drawing of polytetrafluoroethylene virgin powder by extrusion plus cold tensile draw
Endo, Ryoukei; Jounai, Kazuhiro; Uehara, Hiroki ...
Journal of polymer science. Part B, Polymer physics,
October 1998, Letnik:
36, Številka:
14
Journal Article
Recenzirano
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
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