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Cure monitoring of aerospace epoxy resins and prepregs by Fourier transform infrared emission spectroscopy
Author(s) -
George G. A.,
Cash G. A.,
Rintoul L.
Publication year - 1996
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/(sici)1097-0126(199610)41:2<169::aid-pi606>3.0.co;2-2
Subject(s) - fourier transform infrared spectroscopy , materials science , epoxy , curing (chemistry) , infrared spectroscopy , analytical chemistry (journal) , boron trifluoride , composite material , infrared , amine gas treating , catalysis , polymer chemistry , chemical engineering , chemistry , organic chemistry , optics , engineering , physics
Spectral analysis of the infrared radiation emitted from thin films of resin transferred from the surface of high performance aerospace carbon fibreepoxy composite prepregs and heated to the cure temperature allows the cure chemistry and kinetics to be monitored in real time. Quantitative spectra with excellent signal‐to‐noise ratio are obtained by heating a thin resin film on a platinum hotplate fitted to the external optics of a Fourier transform infrared (FTIR) spectrometer and referencing the resulting emission (with the platinum emission subtracted) to a graphite black body at the same temperature. The resulting spectra are identical to absorption spectra and the quantitative features of the analysis are demonstrated by the appearance of isosbestic points during the curing reactions, so indicating that concentration profiles of the reacting species may be obtained. From the initial rate of amine and epoxy consumption, activation energies of 75kJ mol −1 were obtained for both functional groups in the uncatalysed resin 4,4′‐tetraglycidyl diamino diphenyl methane (TGDDM) with 27% 4,4′‐diaminodiphenylsulfone (DDS), while values of 74 and 89kJ mol −1 were obtained for amine and epoxy consumption from the TGDDM/DDS prepreg catalysed with boron trifluoride monoethylamine (Hercules 3501–6), consistent with homopolymerization occurring in the prepreg as well as amine–epoxy addition. Analysis of the FTIR emission at 177°C of resin from prepreg aged up to 90h at 23°C and 55% relative humidity shows a lowering of epoxy and amine concentration and a higher rate of cure, consistent with the formation of catalytic species. This technique may be used to monitor changes in surface properties such as tack and resin transfer, in addition to changes in the cure profile of the aged epoxy propreg.