title: Attenuated total internal reflection infrared microscopy of multilayer plastic packaging foils.
abstract: Multilayer plastic foils are important packaging materials that are used to extend the shelf life of food products and drinks. Fourier transform infrared (FT-IR) spectroscopic imaging using attenuated total internal reflection (ATR) can be used for the identification and localization of different layers in multilayer foils. A new type of ATR crystal was used in combination with a linear array detector through which large sample areas (400 x 400 microm(2)) could be imaged with a pixel size of 1.6 microm. The method was tested on laminated plastic packing materials containing 5 to 12 layers. The results of the identification of the different materials using ATR-FT-IR were compared with differential scanning calorimetry (DSC) and the layer thickness of the individual layers measured by ATR-FT-IR was compared with polarized light microscopy (LM) and scanning electron microscopy (SEM). It has been demonstrated that individual layers with a thickness of about 3 microm could be identified in multilayer foils with a total thickness ranging from 100 to 150 microm. The results show a spatial resolution of about 4 microm (measured at wavenumbers ranging from 1000 to 1730 cm(-1)), which is about a factor of two better than can be obtained using transmission FT-IR imaging. An additional advantage of ATR is the ease of sample preparation. A good correspondence was found between visible and FT-IR images. The results of ATR-FT-IR imaging were in agreement with those obtained by LM, SEM, and DSC. ATR-FT-IR is superior to the combination of these techniques because it delivers both spatial and chemical information.
authors.affiliation: Advanced Measurement and Imaging, Unilever Research and Development, Olivier van Noortlaan 120, 3133 AT Vlaardingen, The Netherlands. Gerard-van.Dalen@unilever.com
authors.forename: Gerard
authors.initials: G
authors.lastname: van Dalen
authors.forename: Patricia C M
authors.initials: PC
authors.lastname: Heussen
authors.forename: Ruud
authors.initials: R
authors.lastname: den Adel
authors.forename: Robert B J
authors.initials: RB
authors.lastname: Hoeve
mesh_terms: D018857:Food Packaging / Q000145:classification*; D008422:Materials Testing / Q000379:methods*; D008853:Microscopy / Q000379:methods*; D010969:Plastics / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*
chemical_list: D010969:Plastics