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.

OCVD polymerization of PEDOT: effect of pre‐treatment steps on PEDOT‐coated conductive fibers and a morphological study of PEDOT distribution on textile yarns

“…It is a powerful technique to find out the spatial distribution of chemical identities within a sample, because we can get full spectral information at each pixel of the obtained IR images. In other words, we can get spatial and chemical information at the same time …”

“…All the reaction steps, after the oxidant enrichment, were performed as we did in our previous article. [21] For evaluating the effects of drying time and drying temperature, the viscose fibers were first soaked with oxidant (FeCl 3 ) solution and then dried at different temperature (30,40,50, and 60 0 C) for variable times (3, 5, 7, and 10 min). The oxidant concentration, dipping time, and polymerization time were kept constant followed by the other polymerization process as discussed before.…”

“…In other words, we can get spatial and chemical information at the same time. [28][29][30] We acquired the ATR-FT-IR image across the cross section of pure viscose yarns, shown in Fig. 12 (left), where we can see the IR images of some monofilaments of viscose yarn in particular pixel size.…”

Waste Electrical and Electronic Equipment: A Review on the Identification Methods for Polymeric Materials

“…FTIR mapping allows transient effects to be studied in real-time, and the main disadvantage of this technique is the expense of the equipment. ATR mapping can be used to observe the microstructures of mixed polymers and has been used for multilayer packaging films and polymer blends and it has good potential as a technique for studying coarse phase structure in recycled polymer blends [97][98][99].…”

“…For example, in a study Arnold J.C. and co-workers used FTIR to investigate some virgin blended and recycled polymers (ABS, HIPS, and PC). The method was compared to optical microscopy and it was reported that the optical microscopy showed up phase separation on a scale of tens of microns, while the FTIR mapping allowed compositional details to be investigated [98]. In another study, FTIR was used to examine plastic plaque samples of television (black plastics) and computer (grey plastics).…”