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Determination of Chemical Homogeneity of Fire Retardant Polymeric Nanocomposite Materials by Near-Infrared Multispectral Imaging Microscopy

Polymer nanocomposites containing layered double hydroxide (LDH) additives offer great potential for improving polymer physical properties. Of particular interest is the possibility of improving the fire retardancy and thermal stability of polymers using low loadings of this emerging class of nano-additives. Understanding the relationship between the quality of additive dispersion in the polymer matrix (i.e., chemical homogeneity) and selected flammability properties is a key question for optimizing LDHs for use in fire retardant formulations. We have demonstrated, for the first time, that the near infrared multispectral imaging (NIR-MSI) microscope can be successfully used to characterize the chemical homogeneity of a model system containing a magnesium aluminum hydroxide LDH modified with interlayer undecenoate anions mixed with poly(ethylene). The NIR-MSI is suited for this task because it can simultaneously record spectral and spatial information of a sample with high sensitivity (single pixel resolution) and high spatial resolution (∼0.9 μm/pixel). At 20% added, LDH was found to distributed inhomogeneously in a poly(ethylene) nanocomposite sample on the micron scale.