With the use of high-resolution transmission electron microscopy the structure and morphology of
montmorillonite (MMT), a material of current interest for use in polymer nanocomposites, was characterized.
Using both imaging theory and experiment, the procedures needed to generate lattice images from MMT
were established. These procedures involve careful control of the microscope's objective lens defocus to
maximize contrast from features of a certain size, as well as limiting the total dose of electrons received by
the sample. Direct images of the MMT lattice were obtained from neat Na+ MMT, organically modified
MMT, and organically modified MMT/epoxy nanocomposites. The degree of crystallinity and turbostratic
disorder were characterized using electron diffraction and high-resolution electron microscopy (HREM). Also,
the extent of the MMT sheets to bend when processed into an epoxy matrix was directly visualized. A minimum
radius of curvature tolerable for a single MMT sheet during bending deformation was estimated to be 15 nm,
and from this value a critical failure strain of 0.033 was calculated. HREM can be used to improve the
understanding of the structure of polymer nanocomposites at the nanometer-length scale.
In the current study, we present the synthesis of novel low cost bio‐polyurethane compositions with variable mechanical properties based on castor oil and glycerol for biomedical applications. A detailed investigation of the physicochemical properties of the polymer was carried out by using mechanical testing, ATR‐FTIR, and X‐ray photoelectron spectroscopy (XPS). Polymers were also tested in short term in‐vitro cell culture with human mesenchymal stem cells to evaluate their biocompatibility for potential applications as biomaterial. FTIR analysis confirmed the synthesis of castor oil and glycerol based PU polymers. FTIR also showed that the addition of glycerol as co‐polyol increases crosslinking within the polymer backbone hence enhancing the bulk mechanical properties of the polymer. XPS data showed that glycerol incorporation leads to an enrichment of oxidized organic species on the surface of the polymers. Preliminary investigation into in vitro biocompatibility showed that serum protein adsorption can be controlled by varying the glycerol content with polymer backbone. An alamar blue assay looking at the metabolic activity of the cells indicated that castor oil based PU and its variants containing glycerol are non‐toxic to the cells. This study opens an avenue for using low cost bio‐polyurethane based on castor oil and glycerol for biomedical applications.
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