| Polyurethane-layered silicate nanocomposites with different layered silicates, montmorillonite (MMT) and attapulgite (ATT), were investigated to gain fundamental understanding of the role of nanofillers, the chemistry of the modifiers, and the physics of polymer nanocomposites.;Polyurethane-based nanocomposites with compositions that included soft segments with number average molecular weights of 1000, 2000, and 2900, and organic-modified MMT (including MMT-30B and MMT-I30E) were prepared by in situ polymerization. Transmission electron microscopy (TEM) and wide-angle X-ray diffraction (WAXD) results revealed that both MMT-30B and MMT-I30E were intercalated and partially exfoliated by the PU. Mechanical tests showed that the PU1000 series in soft-segment molecular weight yielded superior tensile properties compared to the PU2000 and PU2900 series. Also, for a given molecular weight of soft segment in PU, the MMT-30B nanocomposites exhibited greater increases in Young's modulus, tensile strength and elongation at break than the MMT-I30E counterpart, and the crystallinity of PU was enhanced by the clays.;In pristine PU and composites containing ATT nano-rods, the effects of functionalization on dispersion and on thermal, physical, and mechanical properties were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and mechanical testing. Functionalization of ATT nano-rods proved beneficial in terms of dispersion, degree of crystallinity, thermal stability, and tensile strength. A higher grafting content of 4,4'-methlenebis(phenyl isocyanate)-modified attapulgite (ATT-MDI) led to more uniform dispersion and enhanced tensile properties of the nanocomposites. However, the grafting content had negligible effects on the thermal behavior of PU/ATT-MDI nanocomposites.;To extend the applications of attapulgite to specific polymer systems and to heterogeneous catalytic reactions, the physicochemical changes resulting from thermal and acid treatments were investigated. TGA analysis of the untreated attapulgite revealed that dehydration and dehydroxylation occurred during heating. The dehydration and dehydroxylation led to changes in attapulgite structure, as demonstrated by FTIR spectra of heat-treated samples. The FTIR spectra also revealed that acid treatment led to hydroxylation of the heat-treated attapulgite. WAXD patterns of heat-treated samples showed a loss of crystal structure of attapulgite. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) images of acid-treated attapulgite nano-rods revealed a rough surface with perforations. |
