In situcure monitoring of epoxy resins using optical fibre sensors

Abstract

This paper describes a comparative study of in situ cure monitoring by three methods: (i) evanescent wave spectroscopy; (ii) refractive index change; and (iii) near-infrared spectroscopy.The cure characteristics of an epoxy/amine reaction were followed in real-time during the crosslinking reaction via the above-mentioned techniques. The evanescent wave spectroscopy technique was based on monitoring the characteristic infrared absorption bands of the resin system to compute the concentration of the amine hardener as a function of cure time. Good correlation was obtained between the evanescent wave spectroscopy data and a conventional method of studying cure reactions, i.e. infrared spectroscopy.During the cure reaction, the refractive index of the resin system increases as a function of the crosslink density. This increase in the refractive index was monitored using two optical fibre techniques. In the first case, a declad region of the optical fibre was immersed in the resin system and in the second method an optical fibre reflectometer was used to track the changes in the refractive index. Once again, good correlation was obtained between the optical fibre techniques and infrared spectroscopy cure data. The results obtained from the optical fibre sensor experiments were used to model the cure kinetics of the resin system. The cure kinetic models were found to predict the cure reaction up to approximately 60% of the reaction.

Thermal energy harvesting for large-scale applications using MWCNT-grafted glass fibers and polycarbonate-MWCNT nanocomposites

“…Glass fiber reinforced polymer composites (GFRPs) offer a flexible design approach for structural materials with significantly enhanced specific properties such as strength and stiffness [5]. Composite materials are exposed in several cases to environments where there exists a temperature difference, i.e composite parts of airplanes, cars, etc.…”

Quantitative control of RTM6 epoxy resin polymerisation by optical index determination

“…They require to measure the light transmitted along a fibre sensor connected to the mould through two optical access ports. Detailed optical analysis of the process has been proposed by Crosby [5]: the optical spectrum evolution during the curing process can be obtained from the evanescent wave spectroscopy. The resin refractive index depends on the physical and/or chemical changes of the macromolecules.…”

Characterisation of the cross-linking process in an E-glass fibre/epoxy composite using evanescent wave spectroscopy

“…In the optically rarer medium, a non-propagating electric field occurs and this is known as the evanescent field. The magnitude of the evanescent field decays exponentially with increasing distance from the interface [3].…”

“…Therefore, this phenomenon can be used to obtain an absorption spectrum of the matrix by measuring the fibre's optical output as a function of input wavelength. The penetration depth, d, of the evanescent field into cladding medium can be expressed as [3,4]: where k is the wavelength of light, n core and n clad are refractive indices of the core and the cladding and h is the angle of incidence at the core/cladding interface. The surface chemistry of the reinforcing fibres plays a key role in determining the wettability of the fibre surface and the nature of the bonding with the matrix or resin system.…”

“…Crosby et al [3] and Powell et al [4] used optical fibres where the refractive index of the core was 1.62 to study the cure kinetics of an epoxy/amine resin system. Crosby et al found a good correlation between cure kinetic data obtained via conventional FTIR spectroscopy and a refractive index-based sensor system [3]. Powell et al reported a good correlation for the cross-linking kinetics between transmission FTIR and refractive index sensor designs [4].…”