Mix Ratio Identification in Industrially Significant Two-Part Coating Systems Using the Agilent 4300 Handheld FTIR

Significance of the Topic

Two-part coating systems are widely used in industries for protection and aesthetics. Accurate mixing ratios are critical to prevent defects such as reduced durability, discoloration, and adhesion failures.

Objectives and Study Overview

This study evaluates the Agilent 4300 Handheld FTIR for determining the mix ratio of two-part epoxy primer, polyurethane topcoat, and a combined two-coat system under industrially relevant conditions.

Methodology

- Calibration and validation samples prepared with varied resin-to-hardener ratios by weight and volume.
- Coatings applied to steel panels and air-dried overnight.
- Spectra collected at 4 cm–1 resolution over 4000–650 cm–1 using 64 co-added scans (~26 s per measurement).
- Five replicate measurements per mix ratio.
- Partial Least Squares regression with mean centering and multiplicative scatter correction used to build calibration models.

Instrumentation

The Agilent 4300 Handheld FTIR spectrometer was employed with:

• External reflectance interface for metallic substrates.
• Diffuse reflectance interface for non-reflective or filled coatings.

This portable, 2.2 kg system offers rapid scanning, nondestructive analysis, and intuitive software.

Main Results and Discussion

- Calibration models exhibited correlation coefficients (R2) > 0.99 with 5, 6, and 4 PLS factors for polyurethane, epoxy, and two-coat systems.
- Key spectral regions: 2100–2400 cm–1 (aliphatic isocyanate band) for PU; 1650–2200 and 1600–800 cm–1 for epoxy.
- External reflectance interface yielded average prediction errors of 3.24%, 2.24%, and 2.82% on validation samples.
- Diffuse reflectance showed comparable accuracy, with slight variations based on coating composition.
- Interface selection depends on substrate reflectivity and coating formulation.

Benefits and Practical Applications

• On-site, rapid verification of coating mix ratios.
• Ensures compliance with performance specifications.
• Prevents premature failures and material waste.
• User-friendly with real-time results for quality control.

Future Trends and Possibilities

Extending handheld FTIR to monitor degree of cure, support diverse formulations, integrate with IoT for automated QC, and leverage advanced chemometric and machine learning approaches for enhanced predictive maintenance.

Conclusion

The Agilent 4300 Handheld FTIR offers a robust, accurate, and portable solution for assessing mix ratios in two-part and multi-layer coating systems, facilitating improved quality control in both laboratory and field environments.