Attenuated total internal reflection infrared microscopy of multilayer plastic packaging foils

Area of Science:

• Materials Science
• Analytical Chemistry
• Spectroscopy

Background:

• Multilayer plastic foils are crucial for extending food and drink shelf life.
• Accurate identification and localization of individual layers within these foils are essential for quality control and material analysis.
• Existing methods may lack the resolution or integrated chemical information required for comprehensive foil analysis.

Purpose of the Study:

• To evaluate the efficacy of a novel Attenuated Total Internal Reflection Fourier Transform Infrared (ATR-FT-IR) spectroscopic imaging method for analyzing multilayer plastic foils.
• To determine the capability of ATR-FT-IR imaging in identifying and localizing individual layers and measuring their thickness.
• To compare the performance of ATR-FT-IR imaging with established techniques like Differential Scanning Calorimetry (DSC), Polarized Light Microscopy (LM), and Scanning Electron Microscopy (SEM).

Main Methods:

• Utilized a new ATR crystal combined with a linear array detector for large-area imaging (400 x 400 µm²) with a 1.6 µm pixel size.
• Applied ATR-FT-IR spectroscopic imaging to laminated plastic packaging materials with 5 to 12 layers.
• Validated material identification against DSC and layer thickness measurements against LM and SEM.

Main Results:

• Successfully identified and localized individual layers as thin as approximately 3 µm in multilayer foils (100-150 µm total thickness).
• Achieved a spatial resolution of about 4 µm, outperforming transmission FT-IR imaging by a factor of two.
• Demonstrated excellent agreement between ATR-FT-IR imaging results and those obtained from LM, SEM, and DSC.

Conclusions:

• ATR-FT-IR spectroscopic imaging is a powerful, non-destructive technique for the detailed analysis of multilayer plastic foils.
• The method provides both spatial and chemical information, surpassing the combined capabilities of traditional analytical techniques.
• Ease of sample preparation and high spatial resolution make ATR-FT-IR imaging a superior choice for multilayer foil characterization.