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Multilayer films have been utilized in packaging food and drink for many years as they satisfy multiple requirements in barrier properties, mechanical integrity, and functional properties. In recent years, in addition to conventional approaches such as coextrusion and lamination, nanotechnology is used to prepare composite multilayer films with enhanced characteristics.
Traditionally IR spectroscopy (FTIR) has been used to chemically analyze cross-sectioned samples of multilayer material. More recently, more advanced IR techniques (AFM-IR and O-PTIR) have been used to overcome the diffraction limit of FTIR, which cannot analyze component layers that are thinner than ~ 5 µm. O-PTIR provides a spatial resolution of ~ 0.5 µm, which provides more versatility, but it also falls short of required spatial resolution for more advanced packaging materials that incorporate nanoparticles or ultrathin layers . While AFM-IR (PTIR type) provides better spatial resolution, sample preparation is more cumbersome in that thin microtomed cross-sectional samples need to be put on an IR transparent substrate for analysis .
In this application note, IR PiFM is utilized to analyze the cross-section of a packaging material utilized in microwave-compatible ready-to-eat rice products. The packaging material was cut and embedded in UV-curable resin, which was then microtomed to prepare a flat cross-section for analysis. Figure 1 shows the optical image of the embedded material, which appears to be ~125 µm in thickness. Since the maximum range of the scanner is 120 µm, two measurements were needed to cover the full width of the material. For this discussion, we will focus on the results acquired in the larger area (region 1, 116 µm × 20 µm).
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