Polyimide/graphite composites

Aerosol spray delivery, 23 196 Aerosol sprays, 7 773-774 Aerospace applications aluminum alloys, 2 340 artificial graphite in, 72 740-741 for high performance fibers, 13 397-398 of liquid-crystal polymers, 20 85 metal-matrix composites in, 16 191 polyimide matrix composites in, 20 284 Aerospace bearings, corrosion resistance of, 74 452... 

Aromatic nitriles may be trimerized at moderate temperature and pressure with p-toluenesulfonic acid as catalyst. Studies were conducted to establish the effect of the reaction temperature, pressure, time, and catalyst concentration on yield of the trimerized product. Trimerization studies were also conducted to establish the effect of substituting electron donating or withdrawing groups on benzonitrile. Preliminary results of using the catalytic trimerization approach to prepare s-triazine cross-linked polyimide/graphite fiber composites are presented. 

The irradiation of some composite materials such as epoxy/graphite, polyimide/graphite, and polysulfone/graph-ite fibers have shown that the effects for irradiation up to 5 X 10" kGy for electrrMi radiation and up to 3,500 kGy for 7-radiation are negligible provided the irradiation is carried out in the absence of oxygen [196,197]. 

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. 

W. B. Alston, "Characterization of PMR-15 Polyimide Resin Composition in Thermooxidatively Exposed Graphite Fiser Composites", NASA TM-81565, 1980 and Proc. of 12th SAMPE National Technical Conference, October, 1980. 

Various other soft materials without the layer—lattice stmcture are used as soHd lubricants (58), eg, basic white lead or lead carbonate [598-63-0] used in thread compounds, lime [1305-78-8] as a carrier in wire drawing, talc [14807-96-6] and bentonite [1302-78-9] as fillers for grease for cable pulling, and zinc oxide [1314-13-2] in high load capacity greases. Graphite fluoride is effective as a thin-film lubricant up to 400°C and is especially useful with a suitable binder such as polyimide varnish (59). Boric acid has been shown to have promise as a self-replenishing soHd composite (60). 

Experimental results are presented that show that high doses of electron radiation combined with thermal cycling can significantly change the mechanical and physical properties of graphite fiber-reinforced polymer-matrix composites. Polymeric materials examined have included 121 °C and 177°C cure epoxies, polyimide, amorphous thermoplastic, and semicrystalline thermoplastics. Composite panels fabricated and tested included four-ply unidirectional, four-ply [0,90, 90,0] and eight-ply quasi-isotropic [0/ 45/90]s. Test specimens with fiber orientations of [10] and [45] were cut from the unidirectional panels to determine shear properties. Mechanical and physical property tests were conducted at cold (-157°C), room (24°C) and elevated (121°C) temperatures. 

Tests of a graphite-reinforced polyimide composite (C6000/PMR15) did not show any effect of radiation exposure (1 MEV electrons 6x109 rad total dose) on the thermal expansion behavior (14). DMA curves for unirradiated and irradiated composites were essentially identical over the temperature range of the thermal expansion measurements. 

Chen, E.J.H. and Croman R.B. (1993). Microdebonding investigation on the effects of thermal residual stress on the bond strength of a graphite/polyimide composites. Composites Sci. Technol. 48, 173-179. 

Systems that employed HREELS for interfacial-composition determinations included poly(ethylene oxide)-polystyrene diblock copolymer on Si wafers formaldehyde poly(oxymethylene) films on Cu(lOO) and Lang-muir-Blodgett films of 4,4 -oxydianiline-pyromellitic dianhydride polyimide on Au and on highly ordered pyrolytic graphite. ... 

Sliney, H.E. and Jacobson, T.P., Graphite-Fiber-Reinforced Polyimide Liners of Various Compositions in Plain Spherical Bearings, Proc. 2nd ASLE Inti. Conf. on Solid Lubrication, Denver, Colorado, (15-18 Aug. 1978) ASLE SP-6, p. 258. 

Graphite Fiber Reinforced TSTR Polyimide Composites (3). 

The flexural strengths (three-point method) of these two unidirectional HMS graphite fiber reinforced TSTR polyimide composites with or without post curing were measured with a universal Instron machine at room temperature and at 316°C. These results are shown in Table II. 

Figure 5. Bunsen burner burning test of graphite fiber reinforced polyimide composites. Key a, TSTR-XL-PI/GrF specimen before test b, TSTR-XL-PI/GrF specimen after test and c, PMR-15-PI/GrF specimen after test.

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