Analysis of Contaminations on a Plastic Part using the FT-IR Microscope LUMOS II

Significance of the Topic

Polymers and plastic components are susceptible to microscopic contaminations that can impair performance and quality. Identifying the chemical nature of surface defects is essential in industries like electronics, automotive, and pharmaceuticals to ensure product reliability and trace contamination sources.

Objectives and Study Overview

This application note demonstrates an FT-IR microscopy approach for characterizing black streak contaminations on a polycarbonate part. It aims to determine whether the contaminant resides on the surface or is embedded, and to identify its chemical composition.

Methodology and Instrumentation

The analysis employed the LUMOS II FT-IR microscope, which integrates an infrared spectrometer and motorized stage into a compact stand-alone system. Key features include:

• An 8× Germanium ATR objective for ATR, transmission, and reflection measurements
• Motorized attenuated total reflectance crystal enabling fully automated background and sample spectra acquisition
• High working distance and unobstructed sample access for easy positioning
• Large field of view (1.5×1.2 mm) and deep focus for comfortable sample inspection
• OPUS Video-wizard software guiding users through measurement steps

Six ATR spectra were collected across contaminated and clean regions at 17 s acquisition time and 4 cm⁻¹ resolution. A difference spectrum was generated by subtracting the polycarbonate reference from the contaminated spot spectrum.

Key Results and Discussion

The IR spectra of the black streaks differed significantly from the polycarbonate matrix. Subtraction highlighted characteristic absorption bands of a black ink. A library search identified the contaminant as black marker ink (marker ink black 6558). This confirms the streaks were superficial inks rather than embedded material, facilitating traceability to the contamination source.

Practical Benefits and Applications

• Rapid, non-destructive identification of organic and inorganic contaminants
• High lateral resolution—four times better in ATR mode compared to transmission/reflection
• No sample preparation or microtome sectioning required
• User-friendly interface suitable for QC laboratories with limited spectroscopy expertise
• Built-in library search accelerates unknown compound identification

Future Trends and Opportunities

As FT-IR microscopy evolves, integration with automated workflows and advanced data analytics (e.g., machine learning for spectral classification) will enhance defect screening throughput. Expanding spectral libraries and coupling with imaging modalities could further improve contamination detection in polymers, electronics, and pharmaceutical packaging.

Conclusion

The LUMOS II FT-IR microscope provides a turnkey solution for high-resolution, automated contaminant analysis on plastic parts. Its ATR capability, ease of use, and rapid library-based identification make it an ideal tool for quality control environments tackling diverse surface defects.