Use of a charged coupled device (CCD) camera for evanescent wave optical fiber cure monitoring of liquid composite molding resins

Abstract

An optical fiber evanescent wave fluorescence cure sensor described in a previous paper (1) has been interfaced with a fast detector and computer software to provide real-time monitoring of fast-reacting systems. Advantages to the new system include a reduction in data acquisition time (to 200 ms from 3 min), improved time resolution (to 5 sec from 10 min), and improved signal quality. Isothermal cure monitoring measurements were conducted in both distal and evanescent wave sampling modes for an epoxy-amine system. Following a second order background correction, the results for the two sampling modes were identical. Thus the evanescent wave measurement was unable to detect differences between the chemistry in the bulk and at the fiber-resin interface (if there were any differences to observe).The sensor system was also demonstrated for a fast curing ( < 3 min gel time) polyurethane-isocyanurate system designed for high volume (short cycle time) automotive applications. The system is currently being modified for implementation in a "real world" manufacturing environment.

Process Monitoring of Fiber-Reinforced Polymer Composites

“…Optical-fiberbased evanescent sensors can be constructed using high-index-core optical fibers (the refractive index of the core must be higher than the refractive index of the cured resin) and optical fibers with a thin cladding. [46][47][48][49][50][51][52] Other researchers have also used high-refractiveindex fibers 53,54 and infrared-transmitting chalcogenide fibers [55][56][57][58] as a means to in-crease the refractive-index difference and hence the numerical aperture in the sensing region. When the evanescent sensor is placed in an absorbing medium, the sensing region absorbs some of the transmitted light, due to absorption of specific frequencies by the vibrating molecules in the external medium.…”

Immobilizing a Fluorescent Dye Offers Potential to Investigate the Glass/Resin Interface

“…For example, dimethylaminonitrostilbene (DMANS) was used to measure the glass transition of a cured epoxy resin and to study the physical aging of the resin below the glass transition (5). Fluorescence monitoring has also been used to study water sorption and diffusion in polymers (6,7), polymer reaction kinetics (8,9), and the onset of gelation during cure of thermosetting resins (10,11).…”

“…For example, after doping the resin with trace levels of a fluorescent dye molecule, both distal and evanescent mode fiber optic fluorescence methods have been used to measure the cure of epoxy (11)(12)(13)(14)(15) and polyurethane (11) resins. In one study, the position of the fluorescence maximum from the dye was observed to shift during the resin cure (11). In other work, the intensity changes from a fluorescing dye were monitored, via fiber optics, to follow the curing of an epoxy resin system (15).…”

Interfacial Response of a Fluorescent Dye Grafted to Glass

“…Because the critical area near the surface where the polymer properties are different from the bulk resin is usually less than a micron, the evanescent wave technique does not have true interfacial sensitivity in most cases. Neff et al used evanescent wave fiber-optic fluorescence with a fluorophore dissolved in epoxy resin to monitor the epoxy cure near the fiber surface . No difference in interfacial cure was observed relative to cure of the bulk resin.…”