Polyimide-based graphite

Parallel to the fibre axis, the thermal expansion behaviour is controlled only by the thermal expansion of the C fibre, whereas the thermal expansion perpendicular to the fibre axis is dominated mainly by the carbonaceous matrix. In Fig. 14, the thermal expansion and the coefficient of thermal expansion of unidirectionally reinforced C/C composites parallel and perpendicular to the fibre axis is shown versus temperature. In Fig. 14a, curves are plotted of composites with polyimide as the matrix precursor with different final heat treatment temperatures of 1500°C, 2000 C, and 2700°C. Figure 14b illustrates, in comparison with the polyimide-based composites, the expansion behaviour of pitch-based composites reinforced with different types of graphitized C fibres. 

Graphite, boron, Kevlar 49/aromatic-base epoxy, polyimide Graphite, boron, FP-alumina, stainless steel, tungsten/aluminum, copper... 

Polyimide materials can be used as unfilled base polymers or have graphite, PTFE and molybdenum disulphide added to further enhance the low frictional properties and can be used to replace metal and ceramic parts. Material is available as moulded stock shapes, e.g. rod, rings and plate, which can be machined to the final dimensionally accurate product. Some grades can be processed by compression moulding while other grades can be processed to produce a finished product by direct forming. 

A large number of studies have been made on a of polymer matrix composites of epoxy, polyimide and other polymers reinforced with carbon and Kevlar fibers [117-123]. The carbon and graphite fibers are characterized by slightly negative (Xi in their axial directions and very large positive aj in their radial directions [122-124]. The unidirectional and bidirectional composites based on them are found to demonstrate highly anisotropic thermal expansion behavior. In unidirectional composites,... 

The papers read showed that, for application at low temperatures down to 4 K, the most critical properties of nonmetallic materials are their flexibility and resultant mechanical behavior, their coefficients of thermal expansion as compared with that of the inorganic materials with which they are combined, and their thermal conductivity. At present, the leading pol3nneric materials for low-temperature applications are epoxy resins, polypropylene, and polyimide strips and films, and polystyrene and polyurethane based foams. The leading fibers for reinforcement are glass, graphite, boron, and organic polyaramid. 

The lithium ion cells made with DuPont polyimide separators also offer improved power capability when compared to polyolefin-based separators. The improved rate capability can be attributed to lower ionic resistance, which in turn is related with separator thickness and porosity. Higher-porosity, lower-thickness polyimide separators can lead to more than 30% higher capacity at 15C rates, as shown in Fig 11.11. The tests were performed in coin cells with graphitic anode, LiCo02 cathode, and organic electrolyte (IM LiPFe with 30 70 EC/EMC). 

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