Analysis of Resin Using FTIR and Thermal Analysis - "Silent Change" -

Importance of the topic

The unapproved substitution of resin materials in precision parts such as motor gears, known as "silent change," poses serious risks for product performance and safety. Detecting such material changes early is essential for quality assurance, preventing failures, and maintaining trust in supply chains.

Objectives and overview

This study examines two polyacetal (POM) gears—one that performed correctly and one that failed prematurely—to identify differences in resin composition and thermal properties. The goal is to demonstrate a combined spectroscopic and thermal analysis approach for pinpointing material substitutions that compromise mechanical strength.

Used methodology and instrumentation

A two-step analytical workflow was applied:

• Fourier Transform Infrared Spectroscopy (FTIR) to determine resin type and assess subtle spectral differences.
• Simultaneous Thermogravimetric Analysis and Differential Thermal Analysis (TG/DTA), complemented by Differential Scanning Calorimetry (DSC), to compare melting behavior, crystallinity, and thermal stability.

Main results and discussion

FTIR spectra of both gears showed characteristic C–O–C stretching bands at 1100–800 cm⁻¹, confirming polyacetal composition with no obvious differences in functional groups. TG/DTA analysis and DSC uncovered key variations:

• The proper gear exhibited a higher melting point (172.3 °C) than the failed gear (166.9 °C), indicating greater crystallinity and mechanical robustness.
• The failed gear began thermal decomposition at a higher temperature, suggesting a copolymer formulation with enhanced thermal resistance but reduced structural strength.

These findings reveal that the failed component was produced from a POM copolymer rather than a homopolymer, leading to accelerated wear under mechanical load.

Benefits and practical applications

This combined FTIR and thermal analysis strategy provides a rapid, reliable route for:

• Verifying resin identity and crystallinity in production parts.
• Detecting unauthorized material substitutions before they lead to component failure.
• Supporting failure investigations in quality control and product safety assessments.

Future trends and potential applications

Advances in polymer characterization are likely to focus on higher-resolution spectroscopic imaging, automated thermal profiling, and integration of chemometric analytics. Such developments will enable real-time material verification on production lines and more sensitive detection of compositional variations in advanced polymer systems.

Conclusion

The study demonstrates that while FTIR effectively identifies resin type, detailed thermal analysis (TG/DTA and DSC) is essential to distinguish homopolymer POM from copolymer variants. Identifying such silent changes allows manufacturers to prevent premature gear wear and ensure consistent mechanical performance.

Instrumentation used

• FTIR spectrophotometer (IRTracer-100 with DuraScope, resolution 4 cm⁻¹, integration 40 scans)
• Simultaneous Thermogravimetric Analyzer (TG/DTA)
• Differential Scanning Calorimeter (DSC)

Reference

• Handbook of Polymer Analysis, pp. 481–482
• Handbook of Polymer Analysis, p. 903