Determination of the Degree of Cure of a Varnish

Importance of the Topic

Modern varnishes rely on precise curing to achieve optimal mechanical and chemical properties. Quantitative evaluation of cure degree is critical in research and development and in quality control to guarantee performance and longevity of coatings.

Study Objectives and Overview

This application note outlines a rapid and reliable FTIR ATR based method to determine the degree of cure in an acrylic varnish formulated for UV induced polymerization. Two reference states of the varnish are used to establish calibration. The procedure is demonstrated using an ALPHA II FTIR spectrometer with a platinum diamond ATR module.

Methodology and Instrumentation Used

• Instrument: Bruker ALPHA II FTIR spectrometer equipped with a robust platinum diamond ATR accessory
• Measurement range: 4000 to 400 cm-1 with 4 cm-1 resolution
• Acquisition time: approximately 25 seconds per spectrum
• Calibration approach: two point calibration based on the absorption band intensity at 1410 cm-1

Main Results and Discussion

The FTIR spectra of uncured and fully cured varnish display distinct changes in the fingerprint region. Characteristic C=C stretching bands at 1407 cm-1 and 810 cm-1 decrease significantly upon curing, reflecting the conversion of acrylate double bonds to single bonds. A sample with unknown cure state was measured and its absorption at 1410 cm-1 placed it at an 88 percent cure level via the two-point calibration.

Benefits and Practical Applications

• Rapid analysis with minimal or no sample preparation
• High robustness and insensitivity to external disturbances due to diamond ATR design
• Low operating costs and no consumables required
• Suitable for routine quality checks, incoming goods inspection and failure analysis
• User friendly procedure can be performed by non specialized operators

Future Trends and Opportunities

The method can be extended to a wider range of varnish formulations by establishing similar calibrations. Integration into inline or at line monitoring systems could enable real time cure tracking. Advances in ATR materials and miniaturized FTIR instrumentation promise further applications in industrial process control and field analysis.

Conclusion

FTIR ATR spectroscopy using the ALPHA II platform provides a fast, reliable and cost effective solution for quantifying the degree of cure in acrylic varnishes. The simplicity of calibration and sample handling makes it an ideal choice for both R&D and routine quality control environments. It offers significant potential for broader adoption in coating industries and process monitoring.