Analysis of Discoloration and Coloration Using FTIR and EDX

Importance of the Topic

The precise identification of discoloration and coloration in materials such as paper and resin is critical for quality control, failure analysis, and materials research in manufacturing. Non-destructive, direct-measurement methods accelerate troubleshooting, minimize sample handling, and provide rapid insights into root causes.

Objectives and Overview

This study illustrates the combined use of Fourier transform infrared spectrophotometry (FTIR) and energy-dispersive X-ray fluorescence spectrometry (EDX) to identify both organic and inorganic agents responsible for discoloration in paper and coloration in resin samples. Examples include minor staining from lubricating oils, metal contaminant fragments, and colored pigment additives.

Applied Methodology and Instrumentation

Measurements were performed directly on samples without prior extraction or pretreatment.

• FTIR: Single-reflection ATR on IRTracer-100 with MIRacle 10 diamond prism; 4 cm⁻¹ resolution; 40-scan accumulation; Happ–Genzel apodization; DLATGS detector.
• EDX: EDX-8000 with Rh target X-ray tube; vacuum atmosphere; 15 kV for light elements (C–Sc, S); 50 kV for heavier elements (Al–U, Zn–Pb); measurement diameters 1–10 mm; integration times 60–100 s; blank-corrected qualitative/quantitative profiling.

Main Results and Discussion

• Paper Discoloration: FTIR difference spectrum (discolored vs. normal) revealed a carbonyl stretch around 1750 cm⁻¹, indicating a colored additive in paraffin oil. EDX on a resin product identified Al (99.8 %) and Fe (0.2 %) exclusively in the discolored area, implicating aluminum alloy fragments as the contamination source.
• Resin Coloration: FTIR confirmed polyethylene as the base polymer for both white and green resins. EDX detected Si, P, Al, and S in both samples (from functional additives) and Cl and Cu only in the green resin. Elemental ratios matched those of phthalocyanine green pigment, explaining the green coloration.

Practical Benefits and Applications

The FTIR/EDX combination provides a fast, non-destructive workflow that distinguishes between organic and inorganic discoloration sources. This approach supports quality assurance, failure investigations, and forensic analyses without the need for extraction or extensive sample preparation.

Future Trends and Potential Uses

Emerging developments may include integrated chemometric libraries for automated spectral matching, multimodal imaging for spatially resolved chemical maps, and portable FTIR-EDX systems for on-site diagnostics in manufacturing and conservation fields.

Conclusion

By leveraging FTIR for organic additive detection and EDX for elemental identification, this combined analytical strategy effectively uncovers the causes of discoloration and coloration in diverse materials, enhancing efficiency and reliability in material investigations.

Reference

1) Shimadzu Application News No. X255