IN-SITU NEAR-IR CURE MONITORING OF A MODEL EPOXY MATRIX COMPOSITE

To improve the performance of composites it is imperative that the int erphase region between the inorganic reinforcement and the polymer mat rix be more completely understood. It is in this region that the stres s transfer between the matrix and the reinforcement occurs. To this en d, the curing of epoxy adjacent to an embedded silica optical fiber ha s been monitored in situ by evanescent wave spectroscopy. The epoxy st udied is partially fluorinated and has a lower refractive index than t he silica optical fiber. This combination of epoxy/silica served as a model composite system. The lower refractive index of the partially fl uorinated epoxy allowed the silica optical fiber to be used as a waveg uide for the internal reflection of near-infrared light, The epoxy cur ing was determined as a function of time and temperature by analysis o f the near-infrared spectrum from the epoxy adjacent to the fiber obta ined by the interaction of the evanescent wave that occurs at each int ernal reflection with the low-refractive-index epoxy. The results obta ined from the examination of the near-infrared spectrum, particularly the disappearance of the NH2 stretching/bending combination band at si milar to 4925 cm(-1) and the concomitant increase of the C-N overtone band at similar to 4725 cm(-1), showed that epoxy ring-opening and cro ss-linking reactions could be followed in real time. Finally, treatmen t of the fiber with a silane coupling agent had no observable effect o n the curing reaction of the epoxy.