Chemical Analysis for Flexible Packaging
Evaluating Properties of Films and Polymers
21 April 2020
Flexible packaging made up of films and polymers, is used in a variety of industries such as: medical devices, pharmaceutical, food/drink, cosmetics and industrial sectors. Using these materials can present challenges, such as qualifying alternative suppliers, dealing with recycled raw material streams, changing regulatory climate and managing manufacturing and customer demands. A combination of standardized testing and custom approaches can help balance these priorities.
Testing performed on flexible packaging must consider film properties and chemistry. Evaluation of permeations properties, for example, helps understand the steady state and kinetic permeation properties in single layer or engineered multilayer films using a variety of probe gases, chemicals and water. These evaluations look at: oxygen transmission, water vapor transmission, probe gases and liquid/vapor permeation and migration. Correlating these properties to the chemical make-up and film structure help tailor the packaging solution for the end-use.
Film composition analysis methods can determine bulk composition, multilayer chemical and thickness analysis, surface treatment and chemistry and polymer molecular weight. Cross-section and Raman mapping allow for the evaluation of multi-layer film. Fourier-transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) can determine polymer type and glass transition temperature (Tg) or melt properties. To evaluate surface chemistry or treatment, x-ray photoelectron spectroscopy (XPS) can be utilized. Gel permeation chromatography (GPC) is useful when evaluating alternative raw materials or recycled material as well as for identifying polymer exemption classification under laws like the US Toxic Substances Control Act (TSCA). In addition to bulk composition, trace components such as volatile organic chemicals (VOC) can release with processing, thereby, potentially creating a worker safety issue from monomers, solvents or other additives. Techniques such as thermal desorption gas chromatography with mass spectrometry (TD-GCMS) can both identify and quantify these species as input for an industrial hygiene assessment.
Failure analysis, involving a suite of tests, can evaluate heat seal adhesion failure, compatibility and failure in-use. FTIR and XPS for trace compound detection on sealing surfaces and FTIR microscopy and confocal Raman to identify particle and gel impurities. DSC, Raman and scanning electron microscope-energy dispersive x-ray spectroscopy (SEM-EDS) identify causes of opacity or localized discoloration and GPC can be used to assess mechanical degradation through molecular weight changes.
Assessing chemical migration properties provides input for food contact or packaging compatibility studies. It uses techniques such as Raman mapping, liquid chromatography–mass spectrometry (LC/LCMS), gas chromatography–mass spectrometry (GC/GCMS) and inductively coupled plasma mass spectrometry (ICP-MS) to evaluate compatibility of additives or contaminants when exposed to a food or cosmetic product.