Influence of surface-modified nanoclay on the self-organized nanostructure of segmented polyurethane composites

The nanoscale morphology of segmented polyurethane (SPU) nanocomposites containing various proportions of organomodified montmorillonite (MMT) and Laponite (dual modified using ionic amine modification followed by silane modification) was studied. These nanocomposites were prepared by solution casting and characterized using small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), variable-temperature X-ray diffraction (VT-XRD) and modulated differential scanning calorimetry (MDSC). TEM micrographs show uniform dispersion of MMT in SPU nanocomposites, and the dispersion is better than in Laponite-based ones. Nanocrystalline morphology development in annealed samples of the nanocomposites was studied using VT-XRD (140 to 25 degrees C at constant cooling rate), which confirms the formation of near-triclinic unit cell geometry with different planes of reflection depending on temperature, type of clay and modification (aspect ratio, polarity). It is found that clay (MMT) having higher aspect ratios imposes greater restrictions against the formation of crystallographic planes of various inclinations. The overall crystallinity of SPU appears less affected in the presence of Laponite as compared to MMT. This is confirmed by the MDSC results showing variations and multiplicity of the glass transition temperature and entropies. Finally, SAXS studies related to interdomain repeat distances and interfacial roughness give an in-depth understanding regarding the effect of nanoclay on annealing, crystallinity and reinforcement of polymer microstructures. Such reinforcement effect is maximized in the case of dual-modified Laponite-based SPU. (C) 2011 Society of Chemical Industry