• Be resistant to vibration and shocks
• Have software that is intuitive and provides answers
• Have a user interface and ergonomics that reflect the environment in which the analyzer will be used
• Have sampling technology that is easy to use, readily interchangeable, and designed to meet the measurement objectives
• Have limited maintenance needs, use as few consumables as possible, and be highly reliable
• Allow use in a lab for methods development and data analysis.
Because of these special attributes, it is neces- sary to design and engineer the FTIR system with the end-goal in mind—for application in more diverse environments when compared to lab- only instruments (Figure 1).
Handheld FTIR for the analysis of polymers, composites, coatings, and contaminants
Composites In 2008, A2 Technologies, now Agilent Technologies (Danbury, CT), developed the first handheld FTIR spectrometer targeted at materials applications in the aerospace indus- try. The first application to be studied was a nondestructive method for analyzing thermally induced stresses in epoxy–carbon composites. This led to the development of the Exoscan FTIR spectrometer, which over the past several years has evolved into a complete system for the analysis of materials. The Agilent 4100 ExoScan FTIR system has five interchangeable sampling interfaces that can analyze infrared reflective, nonreflective, scattering, and absorbing ma- terials. It is equally usable for both in-lab and out-of-lab material analysis applications.
In the analysis of aircraft composites, the diffuse reflectance interface is used for both unsanded and sanded composite surfaces. Sanded surfac- es result from the process of repairing composite in which a damaged area is sequentially re- moved by sanding in preparation for patching and bonding. Unsanded composite surfaces have a higher polymer-to-carbon fiber ratio as compared to the sanded material, and produce
a stronger infrared signal than the sanded sur- face. It is straightforward to track the effect of thermal exposure on large areas of unsanded composite surfaces by measuring the carbonyl band intensity as a function of position (Figure 2). The carbonyl moiety is indicative of oxidation of the epoxy polymer, which results from excess thermal exposure. This oxidation potentially leads to microcracks, delaminations, and weak- ening of the exposed area. Sanding the exposed
composite reveals the inner material, which has a far higher carbon fiber-to-polymer ratio and is more absorbing of infrared radiation. For this measurement, the diffuse reflectance sampling technology can be employed with the handheld FTIR to track the change in polymer composition as a function of location during the sequential sanding process. The goal of the sanding process is to remove thermally overexposed composite to reveal pristine material. The handheld FTIR
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AMERICAN LABORATORY • 17 • JUNE/JULY 2013
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