Quantification of Release Agent on a Carbon-Fiber-Reinforced Polymer using a Hand-Held FTIR

Significance of the topic

Release agents facilitate demolding of carbon-fiber-reinforced polymer (CFRP) components but residual films compromise subsequent bonding or coating quality. Rapid, nondestructive quantification of leftover release agent is therefore critical in aerospace and industrial composite manufacturing.

Objectives and study overview

This study, part of the EU ENCOMB project, aimed to demonstrate a handheld FTIR method for in-situ measurement of residual Frekote 700NC release agent on a T700/M21 CFRP system. Four contamination severity levels were evaluated and compared against established bond strength metrics.

Methodology and Instrumentation

• Sample preparation: Six-layer unidirectional T700/M21 CFRP coupons treated with Henkel Frekote 700NC release agent (1–3% PDMS in hydrocarbons) at four severity levels.
• Bond strength: Mode-I critical strain-energy release rate (GIc) measured by MTS Universal Testing Machine per ISO 15024/25217.
• FTIR analysis: Agilent 4100 ExoScan handheld spectrometer with diffuse reflectance, 128 coadded interferograms at 8 cm–1 resolution, 71 spectra per coupon.
• Data processing: Multivariate analysis via partial least squares (PLS) regression calibrated with 55 spectra and validated with 16, referenced to XPS-determined surface silicon content.

Main Results and Discussion

Bond strength (GIc) decreased sharply as residual PDMS increased from 2.2% to 10.5% silicon, falling from ~1,036 J/m2 to ~40 J/m2. FTIR spectra resolved the four contamination levels, and the PLS model achieved R2=0.96, predicting silicon content within 1–2% of XPS values. Severity classification was implemented in a color-coded pass/fail format.

Benefits and Practical Applications

• Rapid, nondestructive assessment completed in under one minute without sample preparation.
• Operable by users with minimal training for on-line quality control.
• Ensures optimal surface condition prior to bonding or coating in aerospace, automotive, and composites manufacturing.

Future Trends and Opportunities

Expansion of handheld FTIR applications to detect moisture uptake, acidic contaminants, and thermal damage in composites; integration with the upgraded Agilent 4300 model for enhanced sensitivity; development of automated inspection systems and broader multivariate models for diverse polymer and surface treatments.

Conclusion

The handheld FTIR approach enables accurate, fast, and nondestructive quantification of residual release agent on CFRP surfaces, correlating strongly with XPS references. It offers a valuable tool for manufacturing quality assurance and improves reliability of bonded and coated composite parts.

References

1. ENCOMB Project. www.encomb.eu
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4. Markatos D. N., Tserpes K. I., Chamos A., Pantelakis S. In Proceedings ICEAF III, 2013.
5. Henkel Frekote 700NC Safety Data Sheet. mymsds.henkel.com
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