Abstract
The top-cover of a conventional differential scanning calorimeter (DSC) was modified to accommodate two custom-made fibre-optic probes. The function of the probes was to illuminate the sample and reference compartments of the DSC and to return the reflected light from the DSC pans to a fibre-coupled Fourier transform near-infrared (FTIR) spectrometer. The cross-linking kinetics of a commercially available epoxy/amine resin system were studied using the conventional and modified DSC along with conventional transmission FTIR spectroscopy. The cross-linking kinetics and the activation energies for the epoxy/amine resin system obtained via the conventional DSC and simultaneous DSC/FTIR were similar (60.22–60.97 kJ mol−1). However, the activation energy obtained for the cuvette-based conventional transmission FTIR experiments was found to be lower (54.66 kJ mol−1). This may be attributed to the temperature-control attained within the cuvette holder. The feasibility of using a simple fibre-optic probe to link the DSC to the FTIR spectrometer was demonstrated.
Highlights
Analytical techniques such as differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy are used extensively to characterise the cross-linking of thermosetting resins [1]
The extent of the reaction for the conventional differential scanning calorimeter (DSC) is seen to be lower than that observed for the simultaneous DSC/FTIR combination and conventional transmission FTIR spectroscopy; the observed discrepancies were lower at the higher isothermal temperature
All the conversion data obtained from the simultaneous DSC/FTIR fall within the autocatalytic conversion range, whose error bars were 5% of their value. This indicates that the cross-linking kinetic data obtained using the simultaneous DSC/FTIR technique can be described by the autocatalytic model
Summary
Analytical techniques such as differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy are used extensively to characterise the cross-linking of thermosetting resins [1]. DeBakker et al [10] employed near-infrared spectroscopy to study the cross-linking of a commercially available epoxy/amine resin system They used glass pans to contain the mixed resin system and an external light source was used to illuminate the specimen. The intensity of the reflected light from the sample compartment of the DSC was acquired simultaneously with the thermal analyser These authors reported a discrepancy of 1 ◦C with regard to the melting point of pure indium when the experiments were carried out on the modified DSC. Harju et al [16] removed the chamber of a power-compensated DSC and secured it in the sample compartment of a FT-Raman spectrometer They demonstrated that simultaneous Raman and DSC data could be obtained to study the phase transitions in ammonium nitrate between 300 and 425 K. The resin system was characterised using conventional transmission FTIR spectroscopy where a 1 mm path-length cuvette was used in conjunction with a temperaturecontrolled cuvette holder
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