In‐situ cure monitoring of diamine cured epoxy by fiberoptic fluorimetry using extrinsic reactive fluorophore

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Abstract
This paper describes the application of a molecular sensor for in‐situ monitoring of epoxy‐diamine cure via remote sensing fiberoptic probes. A custom‐built, fiberoptic fluorimeter allows on‐line recording of fluorescence spectra directly from the cure environment. Cure reactions in epoxy‐diamine network, such as diglycidyl ether of bisphenol A‐diaminodiphenyl sulfone (DGEBA‐DDS) or diglycidyl ether of butanediol‐diaminodiphenyl sulfone (DGEB‐DDS), have been monitored by a reactive molecular sensor, diamino azobenzene (DAA). DAA exhibits sensitive changes in UV‐visible and fluorescence spectra due to the conversion of its primary amine groups to secondary and tertiary amine groups. Fluorescence intensities are correlated with extent of reaction in epoxy network and processing parameters, such as cure temperatures and time. The use of an internal reference dye for normalization of fluorescence intensities is necessary for the quantitative correlation of spectral signals with the network structure. Variables affecting the fluorescence intensity such as excitation volume, probe location, excitation intensity fluctuation, temperature, and background intensities from optical fiber can be calibrated by normalizing the signal intensities against the internal reference. Sulforhodamine 101 was found to be a satisfactory reference dye which provides stable, readable signals over temperatures up to 200°C.