Fluorescence characterization of cure and water uptake in polymers and composites

Abstract

This paper summarizes our recent research on using intrinsic fluorescence for cure characterization, and extrinsic and intrinsic fluorescence approaches for monitoring water uptake in epoxy cured with a widely used aromatic diamine curing agent (diaminodiphenyl sulfone, DDS). Intrinsic fluorescence from DDS is used by correlating the red spectral shifts in excitation spectra with the extent of cure. This spectral shift is due to the reaction of DDS amine with epoxide which converts primary amine groups to tertiary amine groups. The technique is applied to neat epoxy cured with DDS as well as composite prepregs reinforced with fibers, using a fiber-optic fluorimeter, and taking into account the effects of temperature on the spectral shift. Use of the fluorescence technique to monitor water uptake is explored, by adding a small amount of extrinsic fluorophore, or by investigating the intrinsic fluorescence near 460 nm in cured epoxy which is probably due to side reaction products. As the water is absorbed, the fluorescence intensity decreases, allowing small amount of water to be detected.