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Mechanism of Epoxy Moisture Effects
Final rept. 1 Jan 1976-1 Apr 1977
MCDONNELL DOUGLAS RESEARCH LABS ST LOUIS MO
Pagination or Media Count:
The loss of mechanical properties of resin matrix composites at elevated temperatures which occur following absorption of atmospheric moisture is considered a reversible phenomenon caused by the plasticizing effect of the absorbed water. At the molecular level, these losses could be attributed to the disruption of interchain hydrogen bonding by water molecules. Based on mechanochemical considerations, the possibility for occurrence of irreversible stress-induced chemical changes in epoxy polymers exposed to humid environments is the main objective of this study. Internal reflectance Fourier transform infrared FT-IR spectra of tetraglycidyl diaminodiphenyl methane TGDDM cured with diaminodiphenyl sulfone DDS obtained before and after exposure to the combined effect of stress, elevated temperature, and moisture STM, elevated temperature and moisture TM or stress and elevated temperature ST environments were used to obtain comparative evidence for irreversible chemical changes. The results of eight different experiment series provide spectroscopic evidence indicating that exposure of epoxy specimens to STM and TM environments which greatly exceed anticipated service conditions leads to detectable rupture of chemical bonds in the polymer network. Internal swelling stresses are believed responsible for the observed bond cleavages. Spectral evidence indicates that, as expected, post-cure reactions are the most prominent chemical changes induced by exposure of epoxy specimens to the ST, SM, M and T environments. The infrared intensities of the bands attributed to the sulfone group are sensitive to chemical changes which suggests their potential use as molecular monitors within the epoxy network.
APPROVED FOR PUBLIC RELEASE