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Hybrid polyimide (PI)-polytetrafluoroethylene (PTFE)/Nomex fabric composites and Nomex-PTFE/Nomex fabric composites were prepared with benzoxazine (BOZ) as the resin binder. The tribological properties and wear mechanisms of the two composites at different temperatures were investigated using a ball-on-disk wear tester. Before sliding wear tests, a thermo-aging test, thermogravimetric analysis and dynamic mechanical analysis of PI and Nomex fibers were performed to evaluate the thermal properties of the two reinforcing fibers. After each wear test, scanning electron microscopy was employed to analyze the morphologies of the worn surfaces of the composite. The results of sliding wear tests show that the difference between the tribological properties of the two composites is small at room temperature. However, the hybrid PI-PTFE/Nomex fabric composite achieves better tribological properties at high temperatures compared with the hybrid Nomex-PTFE/Nomex fabric composite, which suffered wear failure at 240℃. It is proposed that the excellent thermal mechanical property and thermal stability of PI fibers is the main factor that endows the PI-PTFE/Nomex/BOZ composite with a more favorable tribological property at high temperatures. Moreover, the influence of the increasing temperature on the tribological properties of the two composites was also investigated. [ABSTRACT FROM AUTHOR]

1,1,3,5-tetraphenoxy-3,5-bis(4-aminoanilino)cyclotriphosphazene, 1,1,3,5-tetraphenoxy-3,5-bis[4-(4-aminophenysulfone)anilino)]cyclotriphosphazene, and 1,1,3,5-tetraphenoxy-3,5-bis( N, N′-ethanediamine)cyclotriphosphazene were synthesized in two steps from the p-Phenylenediamine, 4,4′-diaminodiphenylsulfone, and ethylenediamine via nucleophilic substitution and catalytic reduction with hexachlorocyclotriphosphazene. Three novel aromatic polyamides such as poly(cyclotriphosphazene-p-phenylene amide), poly(cyclotriphosphazene-p-sulfuryl amide), and poly(cyclotriphosphazene-ethyl amide) were synthesized from these diamines by direct polycondensation reaction with terephthaloyl chloride and pyridine in N-methyl pyrrolidone, respectively. The chemical structures of the diamine monomers and three novel poly(cyclotriphosphazene-aryl amide)s were characterized by Fourier Transform Infrared, (1H and 31P) Nuclear Magnetic Resonance, and Elemental Analysis. The thermal properties of the polyamides were determined by Differential Scanning Calorimetry and Thermogravimetric Analysis (TGA). The crystallization behaviors of the polyamides were studied by Wide-ray X-ray diffraction, and the morphology of the pyrolysis residues were observed by Scanning Electron Microscope. The three poly(cyclotriphosphazene-aryl amide)s with amorphous structure would exhibit an enhanced solubility in polar aprotic solvents and a superior thermal stability with initial decomposition temperature being at about 198-259°C. TGA curves of the poly(cyclotriphosphazene-aryl amide)s exhibit mainly three thermal decomposition steps, and the poly(cyclotriphosphazene-p-phenylene amide) presents the highest solid residue rate 62.6% heated to 600°C. In the morphology analysis of the poly(cyclotriphosphazene-aryl amide) solid residues, organophosphorus gelatum forms in the surface layer were observed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

Carbon–carbon reinforced aluminum composites with different content of pyrolytic carbon and carbon fibers were manufactured. Porous carbon–carbon preforms in sandwich structure are composed of unidirectional T300 carbon fibers and carbon felt encapsulated and connected by Cpy sheaths. The characterizations of C–C/A1 composites were investigated. The obtained thermal conductivity (κ) reaches 128 W/m K and CTE of samples varies in a wide range. Mechanical properties are analyzed through three-point bending. The effects of graphitization are investigated. Graphitization of carbon–carbon preforms strengthens bonding between carbon fibers and Cpy sheaths so that the characterizations of composites are changed. [Copyright &y& Elsevier]