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Processing of Nascent Polymer Powders to High Performance Fibers pp. 295-316 $100.00
Authors:  (Naoyuki Morooka, Daisuke Sawai, Toshio Ohama, Akira Sano, Kazuo Matsuura, Tetsuo Kanamoto)
Abstract:
Superdrawing of nascent reactor powders of ultrahigh-molecular-weight
polyethylene (UHMWPE) and polytetrafluoroethylene (PTFE) is discussed. In Part 1,
UHMWPEs were synthesized under various conditions by using a highly active Ziegler
catalyst system, and the effects of polymerization variables on the ductility of nascent
powders of UHMWPE were studied. These variables include polymerization temperature
(Tpoly), ethylene pressure (Ppoly), and polymerization rate (Rpoly). At a given Tpoly, the Rpoly
increased rapidly and the ductility of nascent powders decreased slowly with increasing
Ppoly. At the lowest Ppoly of 1 atm, the ductility increased with increasing Tpoly. At higher
Ppolys of 6 and 11 atm, however, the ductility decreased with increasing Tpoly.. These
results combined with previous reports indicate that the effect of each of the
polymerization variables on the ductility depend on the characteristics of the catalyst
used.
In Part 2, superdrawing of nascent PTFE powder is discussed. A film of nascent
powder of PTFE, compacted below the ambient melting temperature (Tm = 335 C), was
drawn by using a two-stage draw technique which consisted of first-stage solid-state
coextrusion to low extrusion draw ratios of 6-20 followed by second-stage PIN draw at
elevated temperatures. Although the extruded tapes showed low ductility below their
static Tms, they were ultradrawable to total draw ratios (DRts) of 300-500 by PIN draw
at draw temperatures (Tds) of 350-430 C, 15-95 C above the static Tm, reflecting the
specific morphology of the nascent PTFE powder. Superdrawn samples showed a nearly
perfect crystalline chain orientation ( fc < 0.997), a remarkably large crystallite size in the
chain direction (D0015 = 150 nm), and high crystallinity (χc  88 wt%). The drawn
products exhibited ductile failure at room temperature due to chain slippage in the
crystalline phases and interfibrillar slippage, which were enhanced by the crystalline
chain motion activated at around room temperature. In the PIN draw above the Tm, partial
melting of the extrudates occurred upon contact with a hot heater kept at a Td
significantly above the Tm. The melting introduced some chain entanglements that acted
as a bottleneck and also improved bonding between fibrils, and suppressed chain as well
as the interfibrillar slippage. Therefore, in contrast to the modulus, the maximum strength
achieved at a given Td increased with the Td. Thus, the maximum tensile modulus and
strength of superdrawn PTFE tapes achieved by PIN draw above the Tm were 120  5 and
0.73  0.3 GPa at 24 C, respectively. The former was comparable to that previously
achieved by solid-state coextrusion of nascent PTFE powder, but the latter was 1.5 times
higher. 


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Processing of Nascent Polymer Powders to High Performance Fibers pp. 295-316