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Studies of Processing Chemistry and Stability of High Temperatuare Polyimides Using TG/FTIR/MS. DEPSCOR95

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Final rept. 15 Jul 96-14 Jul 99

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This research project addressed two fundamental aspects of carbon fiber reinforced high temperature polyimide composites, namely the curing chemistry involved for polyimide formation and then, the thermal oxidative stability of the polyimide structure so produced. The latter played a key role in controlling the composite long-term service temperature when the composite was targeted for aircraft and aerospace applications. The TGAFTIR and TGAMS evolved gas analysis provided a convenient means to study these two features by monitoring the off-gas reaction products during cure in the former and following the off-gas degradation products in the latter. TGA served as a curing reactor in the former while FTIR and MS identified the reaction products in real time. Similarly, TGA provided the means of aging a composite in a controlled environment while FTIR and MS were used to detect the degradation products given off, also in real time. According to TGAFTIRMS study, the thermal curing of polyimides including AFR700BT650-35, LARC RP-46IM7 and VCAP-75Glass fiber prepregs proceeded essentially by 1 the elimination of methanol from amic-acid prepolymer formation, 2 the release of water from subsequent imidization, and 3 finally, the thermal crosslinking via a reverse Diels-Alder reaction when a NE end capping monomer was used. Thus, this polyimide curing reaction sequence confirmed the literature findings. However, the FTIRMS data obtained could also accommodate the alternative that the elimination of water from amide-ester formation occurred first, which was followed by the release of methanol from subsequent imidization. In the case of AFR700BT650-35 prepreg, most off-gases were released by 430 deg F 221 deg C, thereby marking this temperature as the time for both vacuum cut-off and application of consolidation during autoclaving to produce low void content parts. Again, this coincided with industrial autoclaving practice.

Subject Categories:

  • Polymer Chemistry
  • Laminates and Composite Materials

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