A Comparative Study of Depth and Cross Section Measurement of Food Packaging

Importance of the Topic

Food packaging plays a vital role in preserving product quality, safety, and shelf life. Characterizing multilayer films is essential to confirm barrier functions, detect contaminants, and ensure regulatory compliance. Traditional cross-section analysis is accurate but requires sample preparation and may alter sample integrity. Raman depth measurement provides a non-destructive alternative, enabling in-depth chemical profiling without extensive preparation.

Objectives and Study Overview

The aim of this work was to evaluate the performance of the AIRsight infrared Raman microscope for depth measurement of multilayer food packaging films and to compare its results with conventional cross-sectional analysis. By applying both methods to a single sample, the study assesses the accuracy, reliability, and practical advantages of non-destructive depth profiling.

Methodology

• Cross-Section Analysis: Sample sections of 10 µm thickness were prepared using a HistoCore AUTOCUT R microtome (Leica Microsystems). A 100× objective lens with a 785 nm excitation laser and 3 µm step width was employed. Line scans (61 points) were performed to map material distribution and measure layer thickness.
• Depth Measurement: The intact packaging film was directly measured without further preparation using the same spectroscopic parameters. Depth profiling was conducted over 44 points at 3 µm intervals to generate a chemical image of the layered structure.

Instrumentations Used

• Shimadzu AIRsight infrared Raman microscope spectrometer
• HistoCore AUTOCUT R microtome (Leica Microsystems)
• 100× objective lens; 785 nm laser excitation; laser power ~140 mW (55% ND filter)

Main Results and Discussion

The cross-section analysis identified five distinct polymer layers: outer polyethylene terephthalate (PET) layers (~12 µm), PET mixed with TiO2 layers (~4 µm each), nylon layers (~16 µm each), and a central polypropylene (PP) core (~105 µm). Depth profiling produced comparable results, confirming the same layer sequence and thicknesses. Chemical imaging based on spectral purity highlighted PP regions and other materials with high spatial resolution, demonstrating excellent correlation with cross-sectional data.

Benefits and Practical Applications

• Non-destructive analysis eliminates the need for sectioning, preserving valuable or sensitive samples.
• Minimal to no sample preparation reduces analysis time and labor.
• Combined FTIR and Raman capabilities on a single platform allow complementary characterization without instrument changeover.
• Precise layer thickness measurement and material distribution mapping support quality control and failure analysis in packaging manufacturing.

Future Trends and Potential Applications

Advances in Raman depth profiling are expected to integrate automated mapping, artificial intelligence for spectral interpretation, and real-time monitoring of production lines. Extending this approach to other thin-film systems, biomedical samples, and advanced composites could further enhance non-destructive analytical capabilities across industries.

Conclusion

The AIRsight infrared Raman microscope’s depth measurement function offers a reliable, non-destructive alternative to traditional cross-sectional analysis of multilayer food packaging. It accurately replicates cross-section results, simplifies sample handling, and improves workflow efficiency, making it a valuable tool for routine quality control and research in material characterization.

References

• Multilayer Film Analysis Using the AIRsight Infrared Raman Microscope. Application News No. 01-00465, Shimadzu.