Monitoring of Adhesive Curing using Time Course Measurement with FTIR Spectroscopy

Significance of the Topic

Monitoring the curing process of reactive adhesives is critical in industrial bonding applications to ensure proper adhesion strength and consistency. Fourier transform infrared spectroscopy equipped with time-course measurement offers a non-destructive way to observe molecular changes during polymerization in real time.

Objectives and Study Overview

The study aimed to track the curing kinetics of a commercial cyanoacrylate adhesive by capturing spectral changes at regular intervals. Using time-course software, the research sought to quantify reaction rate and correlate absorbance variations at key wavenumbers with the progress of polymerization.

Methodology and Instrumentation

• Sample Preparation: A thin layer of cyanoacrylate adhesive was spread on a disposable silicon ATR slide.
• Instrumentation: IRXross FTIR spectrophotometer with KRS-5 window, QATR 10 ATR accessory, Specac Arrow silicon slide accessory and a DLATGS detector.
• Measurement Conditions:
  
  • Wavenumber range 4000 to 650 cm⁻¹
  • Resolution 4 cm⁻¹
  • Accumulations 10 scans per spectrum
  • Apodization function Square Triangle
  • Time-course acquisition every 30 seconds for 3600 seconds

Main Results and Discussion

A three-dimensional time-course spectrum revealed significant changes between 650 and 2000 cm⁻¹. Comparison of spectra at the start and end points showed:

• Decrease of peaks at ~1288 cm⁻¹ (conjugated C–O–C stretching) and ~804 cm⁻¹ (C=C vibration), indicating consumption of unsaturated bonds.
• Increase of the 1252 cm⁻¹ band (saturated C–O–C stretching), reflecting formation of methylene linkages.

Selected Absorption Curves (SAC) for the 1252 and 1288 cm⁻¹ bands were plotted as absorbance versus time. The curing reaction rate was calculated by normalizing absorbance changes from initial to final values and expressed in percentage. The resulting kinetic curve demonstrated a rapid initial polymerization followed by a slower approach to completion.

Benefits and Practical Applications

• Time-course FTIR provides quantitative insight into reaction kinetics, aiding formulation optimization.
• Disposable silicon ATR slides eliminate cross-contamination and protect expensive crystal prisms from adhesive residues.
• Rapid, non-destructive analysis supports quality control workflows in adhesive manufacturing and assembly processes.

Future Trends and Potential Applications

• Integration of chemometric models to predict curing endpoints and mechanical properties in real time.
• Development of miniaturized, portable FTIR systems for on-site adhesive monitoring in manufacturing lines.
• Extension to multi-component and hybrid adhesive systems, enabling simultaneous tracking of multiple reaction pathways.

Conclusion

Time-course FTIR using disposable ATR slides offers an effective approach to monitor cyanoacrylate adhesive curing. This technique delivers reliable kinetic data while simplifying sample handling and minimizing instrument maintenance.

Reference

• Kwon Y and Kennedy JP 2007 Polymerizability Copolymerizability and Properties of Cyanoacrylate Polym Adv Technol 18 808-813