Theoretical framework and experimental validation for monitoring the glass transition temperature of thermosets using a low-cost Fresnel reflection sensor

The first part of this paper reports on the theoretical basis for using an optical fibre-based Fresnel reflection sensor for monitoring the cross-linking reactions, and subsequently, the evolution of the glass transition temperature. The Fresnel reflection sensor is produced by cleaving an optical fibre to obtain an end-face that is perpendicular. The device is simple to manufacture, interrogate and it is relatively straightforward to integrate into analytical and industrial equipment. The second part of the paper describes the integration of the low-cost Fresnel reflection sensor within a differential scanning calorimeter to track the cross-linking reactions in real-time. The same sensor was used subsequently to detect the glass transition temperature. As predicted by the theoretical study, a distinct change in the slope of the Fresnel reflection sensor data were observed as the cross-linked resin was heated past the glass transition temperature. An excellent correlation was observed between the outputs from the Fresnel reflection sensor and the differential scanning calorimeter with regard to the cross-linking kinetics and the glass transition temperature.