Design and development of a hyphenated technique for monitoring the cure of epoxy-amine resin systems

The main focus of the current study was to design, construct and evaluate a common platform to enable the integration of multiple sensing systems for cure monitoring. An Abbe refractometer was selected to house a custom-made cell which accommodated the following optical sensors: (i) Fresnel reflection sensor; (ii) near-infrared transmission sensor; (iii) evanescent wave sensor; and (iv) fibre Bragg grating sensor. The cell was designed such that it was also possible to simultaneously acquire conventional refractive index data during the cross-linking process. Thus, the cross-correlation of data on refractive index, cross-linking kinetics, strain and temperature was facilitated. It was found that the trends observed in the qualitative (intensity-based refractive index monitoring via the Fresnel reflection sensor) and quantitative (optical fibre-based transmission FTIR spectroscopy) approaches were similar during the cure of common thermosetting resin systems. Furthermore, for the first time, S-2 glass® fibres were used to obtain evanescent wave spectra during cross-linking, and excellent correlation was observed with the transmission FTIR spectral data. Fibre Bragg grating sensors were used to infer the magnitude of the residual fabrication strain. Excellent correlation was observed between the refractive index data generated using the Abbe refractometer and Fresnel reflection sensor.