Page 277 - Academic Press Encyclopedia of Physical Science and Technology 3rd Polymer

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Encyclopedia of Physical Science and Technology En012c-604 July 26, 2001 16:2

786 Polymers, Thermally Stable

FIGURE 7 Tensile strength of polyethersulfones as a function of temperature. A is Udel P1700, B is Astrel 360, and
C is Polyethersulfone 200P. [Reprinted with permission from Critchley, J. P., Knight, G. J., and Wright, W. W. (1983).
“Heat Resistant Polymers—Technologically Useful Materials,” Plenum, New York. Copyright 1983 Plenum Press.]

For PEEK itself, a large proportion of reporting has con- during the fabrication of PEEK composites. To minimize
centrated on polymer morphology relating, for example, deleterious thermal effects, it has been shown that PEEK
the time and temperature of heating with the crystallinity composites are best fabricated under nonoxidative condi-
◦
of the microstructure. A study of PEEK/carbon fiber com- tions at temperatures less than 400 C. Reheating the com-
posites revealed that PEEK in combination with carbon posite (e.g., in repair or readjustment of lay-up) results in
fiber has a higher nucleation density than neat PEEK resin. significantmorphologicalchangesunlesstheseprocessing
Strong bonding at the resin–fiber interface is suggested to conditions are retained.
be caused by crystallization on the fiber surface. Morphol- Binary blends of PEEK and sulfonated PEEK (SPEEK)
ogy and consequential physical properties of the resin are are miscible over the entire composition range with Torlon
greatly influenced by the processing conditions applied 4000 T (amide-imide) and Ultem 1000 (ether-imide). It
has been suggested that electron donor-accepter com-
plexes involving the phenylene rings of PEEK/SPEEK
TABLE IV Retention of Room Temperature Mechanical and N-phenylene units of the polyimides are responsible
Properties of an Aromatic Poly(Ethersulfone) Carbon Fiber for this miscibility. A single, sharp T g for each composi-
Composite (200P/AS) at Elevated Temperature a tion has been observed. The increase of T g over that of
Retention of initial PEEK for some of these compositions has suggested that
Temperature room temperature blending may be a technique for improving the mechanical
Property ( C) value (%) properties and increasing the heat distortion point for these
◦
thermoplastic materials. A further method for improv-
Tensile strength 175 90
ing the thermal and mechanical properties of the PEEKs
Tensile modulus 175 100
has involved polymer chain interaction/cross-linking via
Compressive strength 175 73
pendant or terminal maleimide, styryl, ethynyl, or nitrile
Compressive modulus 175 100
groups.
Flexural strength 160 58
Unreinforced PEEK is used in a number of applications,
Flexural strength 145 73
including high-temperature bearings and seals, wire and
Flexural modulus 160 100
cable coatings, and in electronics. But the main growth
Interlaminar shear strength 160 51
area has been in advanced structural composites based
Interlaminar shear strength 145 61
on a carbon fiber reinforced PEEK(APC-2) developed
a Data from Hoggatt, J. T. (1975). Nat. SAMPE Symp. Exhib. 20, 606. by Imperial Chemical Industries (ICI) as one of their