New Polylactide/Layered Silicate Nanocomposites, 6

The measurement of rheological properties of any polymeric material under molten state is crucial to gain fundamental understanding of the processability of that material. In the case of polymer/layered silicate nanocomposites, the measurements of rheological properties are not only important to understand the knowledge of the processability of these materials, but is also helpful to find out the strength of polymer‐layered silicate interactions and the structure‐property relationship in nanocomposites. This is because rheological behaviors are strongly influenced by their nanoscale structure and interfacial characteristics. In order to get this knowledge in the case of polylactide/montmorillonite nanocomposites, we have studied melt rheological properties of these materials in detail. On the basis of rheological data, we have conducted foam processing of pure polylactide and one representative nanocomposite by a newly developed pressure cell technique using carbon dioxide as a physical‐blowing agent.

The time variation of the elongational viscosity of one of the intercalated polylactide/montmorillonite nanocomposites.     

Intercalation of Diphenyl Sulfide into Nanogalleries and Preparation of Poly(p‐phenylenesulfide)‐Based Nanocomposites

Summary: For the reference system of PPS‐based nanocomposites, we investigated the intercalation behavior of DFS molecules into nano galleries based on OMLFs consisting of different types of intercalants and nanofillers with different surface charge densities. The smaller initial interlayer opening led to the larger interlayer expansion, regardless of the miscibility between the intercalant and DFS. We examined the preparation of PPS‐based nanocomposites with and/or without shear processing at 300 °C. The finer dispersion of OMLFs in the nanocomposite was observed when using OMLF having small initial interlayer opening. The delamination of the stacked nanofillers was governed by the initial interlayer opening, whereas the uniform dispersion of the nanofillers was affected by the shear.

Plot of initial interlayer opening versus Δ opening for various OMLFs intercalated with DFS.     

The effect of crystallization on the structure and morphology of polypropylene/clay nanocomposites

The effect of crystallization on the structure and morphology of maleic anhydride grafted polypropylene (PP‐MA)/clay (montmorillonite) nanocomposites (PPCNs) is presented. Wide‐angle X‐ray diffraction (WAXD) measurements of PPCNs crystallized at different temperatures show that the extent of intercalation increases with the crystallization temperature. The enhancement of intercalation occurs with lower clay content PPCNs, and maximum intercalation takes place for 4 wt% clay content. The mechanism of intercalation has been proposed through crystallization. Excess γ‐form of the crystallite of PP‐MA appears in presence of clay, possibly because of the confinement of the polymer chain between the clay particles. WAXD data also reveals that d‐spacing increases gradually with clay content. The decrease of spherulitic size is observed with increasing clay content, which indicates that clay particles act as nucleating agents. Lamellar textures have been explored by using small angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM), which exhibit that both the lamellar thickness and long period of the PPCNs are higher than those of PP‐MA.     

E.s.r. study of γ-irradiated isotactic and atactic polypropylene

An e.s.r. study of γ-irradiated isotactic (i-) and atactic (a-) polypropylene (PP) was carried out. Both the 17 line (or 9 line) spectrum for i-PP and the 6 line spectrum for a-PP are attributed to the tertiary carbon radical, CH₂C(CH₃)CH₂. The difference in the hyperfine structure between the spectrum of i-PP and that of a-PP can be explained by different radical conformations owing to the stereoregularity. Hyperfine coupling and the radical conformation for the tertiary carbon radical in i- and a-PP were determined from the cos² ? rule. It is shown that the δ methylene proton as well as the β methylene proton contribute to the slight anisotropy in the stretched sample. The spectral change from 9 lines to 17 lines with elevation of temperature, observed at low temperature in i-PP, could be explained by the hindered oscillation of the β methylene proton.     

Studies on the radical polymerization of vinyl acetate in benzene,chlorobenzene and ethyl acetate by 1H NMR spectroscopy

Summary Polymerizations of vinyl acetate were carried out with AIBN in benzene, chlorobenzene and ethyl acetate, and the resultant polymers were analyzed for terminal group by using ¹H NMR technique. The results revealed that a part of the polymer molecules prepared in aromatic solvent contained one solvent fragment at the chain end, indicating the incorporation of aromatic molecule through the chain transfer reaction and not by the copolymerization. It was found that there existed at least 0.7 branching per a molecule in the polymer prepared in ethyl acetate, whereas almost no branching in the polymer prepared in aromatic solvents.     

EXAFS and XANES studies of americium dioxide with fluorite structure

EXAFS and XANES analyses were applied in a study of americium dioxide (AmO₂) with fluorite structure. EXAFS result for Am-L_III absorption edge of AmO₂ was in good agreement with the long-ranged structural data from X-ray diffraction analysis. In order to characterize XANES in aspect of the electronic structure, the theoretical assignment for the AmO₂ was performed with the relativistic DV-Xα molecular orbital method. The calculated XANES spectrum well reproduced the experimental spectrum. From this theoretical assignment, it was found that the peaks of the XANES spectrum were created due to the specific hybridization of orbital components.     

The diffusivity of oxygen in liquid copper-lead alloys

The oxygen diffusivity in liquid copper-lead alloys at 1403 K (1130‡C) was measured us-ing the electrochemical cell: Ni-NiOJZrO₂(+CaO)/O in liquid Cu-Pb alloy(I)/ZrO₂(+CaO)/O in liquid Cu-Pb alloy(II). Oxygen in liquid Cu-Pb alloy(I) was transferred to the right by applying a preselected voltage between the two liquid Cu-Pb alloys. The oxygen diffusivity in liquid Cu-Pb alloy(I) was calculated from the emf change with time between the Ni-NiO and liquid Cu-Pb alloy (I) electrodes. The results were: D_o (in pure Cu) = 8.14 (^+0.70 _-0.43) × 10⁵ cm²/s, D_o (in Cu-25 at. pct Pb) = 11.4(^+0.4 _-0.6) × 10^-5 cm²/s, D_o (in Cu-50 at. pct Pb) = 12.9(^+1.9 _-1.5) × 10^-5 cm²/s, D_o (in Cu-75 at. pct Pb) = 11.0(^+2.4 _-1.2) x 10^-5 cm²/s, D_o (in pure Pb) = 26.3(^+4.8 _-3.7) × 10^-5 cm²/s. It was found that the oxygen diffusivity in liquid copper-lead alloys did not change dras-tically over the entire composition range, in contrast with that reported by other investi-gators for liquid copper-nickel alloys. The oxygen diffusivity in pure liquid lead agreed with the results of our previous work using an FeO-Fe₃O₄ mixture as a sink for oxygen.     

Preparation and characterization of rapidly quenched glasses in the systems R2O—WO3 (R=Li,Na, K)

In the systems R₂O-WO₃ (R=Li, Na, K), the glass-forming region was extended by use of the rapid quenching technique combining a thermal-image furnace with a twin roller. The infra-red spectra revealed that the Li₂WO₄ glass contains no condensed macro-anions but only discrete ions of Li⁺ and WO ₄ ^2– . The glass transition temperature (T _g) and the crystallization temperature (T _c) were determined.T _g is affected very slightly by the type of alkali cations, whereas it is decreased with increase in the alkali oxide content. More than oneT _g was observed in Li₂O-WO₃ glasses, which is due to the formation of metastable phases. The conductivity of glasses containing the same amount of alkali oxide (of different types) increased with decrease in the radius of the alkali cation. Electrochromism was observed in the glasses with R=Li, Na; the electric field required for colouration is lower than that in WO₃ films. The electro-colouration is due to H_xWO₃ formed in the glass matrix by the double injection of protons and electrons.