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

Importance of the Topic

Food packaging is a complex multilayer system designed to protect products and extend shelf life. Understanding the composition and thickness of each layer is crucial for ensuring safety, performance, and compliance in the food industry. Raman spectroscopy, especially combined with infrared analysis, offers non‐destructive and sensitive characterization of these materials, enabling both qualitative and quantitative insights into packaging structures.

Goals and Overview of the Study

This study aimed to evaluate the new depth measurement function of the AIRsight infrared Raman microscope spectrometer and compare it to conventional cross‐section analysis. Key objectives included:

• Determining whether depth measurements without sample sectioning yield results comparable to microtome cross‐section data
• Verifying the accuracy of layer thickness determination in a commercial multilayer food packaging sample
• Highlighting the practical advantages of a non‐destructive approach in routine quality control

Methodology and Instrumentation

Instrumentation:

• AIRsight infrared Raman microscope spectrometer combining FTIR and Raman modes
• 785 nm excitation laser, 100× objective, 55 % ND filter (≈140 mW), step width 3 µm

Sample Preparation:

• Cross‐section: Microtome‐cut 10 µm slices of packaging film
• Depth measurement: Intact foil placed directly under the microscope without alteration

Measurement Conditions:

• Five scans per point, 10 s exposure, 5 s bleaching time
• Line scan across cross‐section: 61 measurement points
• Depth mapping: 14 lateral points and 44 depth points

Main Results and Discussion

Cross‐section analysis identified five distinct layers:

1. Outer PET layers, ~12 µm each
2. PET + TiO2 composite layers, ~4 µm each
3. Nylon layers, ~16 µm each
4. Central PP core, ~105 µm

Depth measurements on the intact sample reproduced the same layer sequence and thicknesses within experimental error. Chemical imaging based on Raman purity mapping visually confirmed the spatial distribution of PP, PET, TiO2‐loaded PET, and nylon. The correspondence between cross‐section and depth data validated the non‐destructive approach for multilayer characterization.

Benefits and Practical Applications of the Method

The new Raman depth measurement offers several advantages for industrial and research laboratories:

• Minimal or no sample preparation saves time and reduces risk of artefacts
• Non‐destructive analysis preserves intact samples for further testing
• High spatial resolution (3 µm) enables precise layer thickness determination
• Combined FTIR and Raman capability on one platform provides complementary chemical information
• Ideal for quality control of transparent and translucent polymer films

Future Trends and Potential Applications

Emerging directions for Raman depth profiling in packaging analysis include:

• Integration with automated inline inspection systems for real‐time quality monitoring
• Advanced chemometric and machine learning algorithms to speed up layer identification and classification
• Application to new biodegradable and active packaging materials to assess barrier performance and degradation
• Expansion to contaminant detection within multilayer structures for food safety assurance

Conclusion

The AIRsight infrared Raman microscope’s depth measurement functionality delivers accurate, non‐destructive characterization of multilayer food packaging, matching traditional cross‐section techniques. By eliminating extensive sample preparation and enabling in situ analysis, this method enhances efficiency and reliability in industrial QC and materials research.

Reference

• Aikaterini Karatzia, Shimadzu Europa GmbH. A Comparative Study of Depth and Cross Section Measurement of Food Packaging. Application News No. 05-SCA-110-121-EN, Shimadzu (2025).