Spectroscopic evidence for mechanochemical effects of moisture in epoxy resins

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Abstract
Internal reflectance Fourier transform infrared (FT‐IR) spectra of tetraglycidyl diaminodiphenylmethane (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 search for evidence of irreversible chemical changes in epoxy resins. These changes were compared with the infrared changes observed during the late stages of curing. The infrared intensities of the bands attributed to the sulfone group are sensitive to chemical changes and moisture content, which suggests their potential use as molecular monitors within the epoxy network. The results of eight experimental series provide spectroscopic evidence indicating that exposure of epoxy specimens to STM and TM environments that greatly exceed anticipated service conditions results in detectable rupture of chemical bonds in the polymer network. The extent of bond rupture is independent of the applied stress in the 0–90 kg/cm2 range. Internal swelling stresses are therefore believed responsible for the observed bond cleavages. Spectral evidence indicates that postcure reactions are the most prominent chemical changes induced by exposure of epoxy specimens to the ST, SM, M, and T environments.
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