handbook of carbon, graphite, diamond and fullerenes

204 Carbon, Graphite, Diamond, and Fullerenes
Table 9.2. Maximum-Use Temperature of Polymer Matrices! 2 '
Maximum-Use
Polymer Temperature, °C
Epoxies up to 150
Bismaleimides-epoxies (BMI) 205 - 245
Polyimides (PI) 260-315
Polybenzimidazoles (PBI) 315 - 370
Thermoplastic Polymers. Thermoplastic polymers do not require a
cure cycle but need only to be melted during processing (usually injection
molding). The most common are nylon, polypropylene, and polyethylene
which are usually molded with 10-25 vol.% discrete (chopped) carbon
fibers. The addition of fibers substantially increases the modulus and, to a
lesser degree, the strength. Electrical conductivity is also considerably
increased and many applications of these composites are found in electromagnetic-interference
(EMI) shielding.
The major drawback of carbon-fiber thermoplastic composites is their
low-temperature resistance.! 7 '! 8 ] However, recently developed thermoplastic
polymers have much higher temperature resistance and are being
considered as matrices for continuous-fiber composites. These polymers
include polyethersulfone (PES), polyetheretherketone (PEEK) and
polyphenyl sulfide (PPS) .!*' PEEK in particular has excellent potential since
it is less brittle than the epoxies and provides a tougher composite (see
Table 9.5 below).
The various fabrication techniques for carbon-fiber composites include
filament winding, injection and compression molding, pultrusion, and
wet layup. They are described in Ref. 9.
3.2 Surface Treatment of Carbon Fibers
The surface of a carbon fiber (or of diamond, graphite, and any other
crystalline solid) has been described as an extreme case of lattice defect.! 10 '
The regular configuration of carbon atoms ends abruptly and the surface
atoms have a different coordination with dangling bonds which are able to
react with any atom or molecule present on the surface. The result is the
formation of compounds such as basic or acidic surface oxides, CO2, and