In-situ monitoring of cross-linking reactions using E-glass fibres and evanescent wave spectroscopy

E-glass fibres are used in products such as printed circuit boards, wind turbine blades, pipes, marine vehicles and pressure vessels. With reference to the production of fibre reinforced composites, the reinforcement (E-glass) is impregnated with a resin system, consolidated and generally processed by the application of heat. This results in the resin system being converted from a liquid or semi-solid to a highly cross-linked and infusible solid. There is significant interest in monitoring the progression of these cross-linking or chemical reactions and a number of optical and electrical, ultrasonic-based techniques have been developed and demonstrated. The current paper reports on the use of the reinforcing E-glass fibres to track the cross-linking of commercially available epoxy/amine resin systems. The mode of interrogation was based on using the E-glass fibres as evanescent wave sensors thus enabling Fourier transform infrared spectroscopy to be conducted. This enabled the cross-linking reactions at the glass/resin interface to be monitored. Conventional transmission Fourier transform infrared spectroscopy experiments were also conducted. The cross-linking kinetic data from the two methods were modelled and compared. A good correlation was obtained between the experimental and predicted data using a single rate constant.