Investigations on Multilayer Films: Electron Microscopy and Infrared Spectroscopy - Possibilities and Limitations

The study of multilayer films has become an important issue, since every year improved materials are produced. They have to be optimally designed in order to enable the maintenance of aroma, taste and nutritional value of the goods. This is primarily achieved by the use of special laminated films, additives and oxygen barriers. In addition, ecological and economical factors force the industry forwards to create more environmental‐friendly and cheaper films. In this study, two multilayer packaging films differing in the layer and barrier composition are examined with light microscopy (LM), transmission electron microscopy (TEM) and Fourier transformed infrared (FTIR) microspectroscopy: LM gives the number and the thickness of the layers, but there is no information about the chemical composition and the coatings. FTIR and Raman Spectroscopy enable the chemical characterization of the identified layers, but the lateral resolution is restricted in the µm range. TEM visualizes the important characteristics (coatings, filler particles) and enables the detection of inorganic fillers (EELS, EDX), but the organic components cannot be analyzed. Therefore, the use of complementary techniques is crucial in order to achieve a complete analysis of multilayer foils. Special attention was paid on the preparation procedure, since ultrathin sections are an important prerequisite for TEM observation and there is little known about the “perfect” preparation of multilayer films.