Carbon fibers are being increasingly used in composites for aircraft. They are bound together with a binder, often an epoxy. There are many grades of binders, and many different types of composites sold on the market. They are expensive. We have some donated materials of unknown type, and would like to be able to be cost-effective and use them without incurring a large cost to analyze the materials using laboratory methods. Visual inspection is not normally sufficiently accurate to be able to tell one composite from another. Optical methods that involve a broader spectrum have commonly been used to discriminate organic materials. A five-band spectral reflectometer is used to measure reflectivity of the surfaces, and is a simple way of extracting data into the infrared bands. The instrument used in these tests is less resolved than a narrow band spectrometer, but is easier to deploy because it is a hand-held device that only requires a flat surface of approximately 3 cm diameter.
Reflectivity of many different composite materials, including a bismaleimide, several thermoset epoxies, and some low temperature epoxies from various manufacturers is measured. Other materials are also included to demonstrate that non-composites can be rejected by the methods. Analysis shows that the reflectometer measurements are capable of discriminating some materials, but have difficulty with discriminating others. The raw reflectivity data are likely to be helpful for future radiation modeling of composite surfaces.
