EPOXY-RESINS AND EPOXY BLENDS STUDIED BY NEAR-INFRARED SPECTROSCOPY

The cure and the final network of epoxy resins have been investigated by numerous techniques, nevertheless a clear understanding of this net work structure has not yet been achieved. FTIR analysis of polymeric m aterials provides highly precise measurements that are widely interpre table in terms of chemical structure. Yet the high absorption of funda mental bands requires careful sample preparation to reduce the thickne ss of the sample or spacial reflection techniques are needed. Furtherm ore, the occurrence of overlapping bands for epoxy resin (N-H and O-H vibrations in the 3000 cm-l region) renders the quantitative analysis in the region mid IR particularly difficult. However, the overtone and combination bands are 10-100 times weaker than the fundamental ones a nd are observed in near infrared (NIR) region. Longer pathlengths than Mid IR ones can be used allowing transmission analysis of thick sampl es (1-20 mm) without special preparation. NIR absorption bands have di fferent intensities depending on the anharmonicity of vibrations. The strongest absorption bands are due to protons connected to carbon, nit rogen, oxygen. Hydrogen bonding due to inter- and intramolecular inter actions can cause band broadening, peak position shifts and intensity variations. NIR spectroscopy is therefore a useful technique to invest igate polymeric materials and was used to study the cure reactions of various epoxy resins cured with amine hardener. Using different NIR te chniques (reflectance, transmission and microscopy) we will briefly pr esent some results concerning hydrogen bonding between epoxy and amine hardener before curing, epoxy resins, glass/epoxy composites and epox y/PES (polyethersulfone)blends.