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Samples of an aerospace structural epoxy composite (8552/IM7) were subject to long-term (% 1 year) thermal aging at temperatures of 708, 1208, 1708, and 2008C (in air). The changes to the chemical and physicochemical structure of the composite were analyzed by a range of different techniques, including gravimetric analysis, Fourier transform infrared (FTIR), and dynamic mechanical analysis (DMA) to compare the effects of different severities of degradation treatment. The results highlighted the large differences in chemical effects between the surface and the interior of the composite with very minor changes in the latter even at quite high aging temperatures and long aging times. The oxidative changes at the surface, however, varied from highly selective molecular changes for particular chemical groups at the lower aging temperatures (708 and 1208C), to quite general and extensive oxidative degradation at the higher aging temperatures (1708 and 2008C). The results indicated that the mechanical changes in an aged composite of this type will vary greatly with the material thickness and surface protection as well as the aging temperature the composite is exposed to.

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