Synthesis and characterization of polyurethane‐urea clay nanocomposites using montmorillonite modified by oxyethylene–oxypropylene copolymer

Clay organifier with propylene oxide‐capped polyethylene glycol (PEG) with amine end group (jeffamines ED_600–2003) was synthesized through an ion exchange process between sodium cations in montmorillonite (MMT) and ? NH groups in ED_600–2003. The d‐spacing of organoclay was found to be 1.697–1.734 nm compared to 0.96 nm of pristine MMT. Transmission electron microscopy (TEM) was used to determine the molecular dispersion of the clay within ED₆₀₀. Polyurethane‐urea/montmorillonite (PUU‐MMT) nanocomposites were prepared via in situ polymerization from polyethylene glycol (PEG 400) or 1,4 butane diol (1,4 BD), toluene diisocyanate (TDI), jeffamines ED_600–2003, and 1–12 wt% of organoclay. Intercalation of PUU into modified clays was confirmed by X‐ray diffraction (XRD), scanning electron microscopy, and TEM. The barrier properties were significantly reduced; however, the thermal stability was increased in the nanocomposites as compared to the pristine polymer. Nanocomposites exhibited optical clarity and solvent resistance. The mechanical properties and the glass transition temperature of PUU were improved with the addition of organoclay. The incorporation of silicate layers gave rise to a considerable increase in the storage modulus (stiffness), demonstrating the reinforcing effect of clay on the PUU matrix. Copyright © 2009 John Wiley & Sons, Ltd.     

Study of the parameters in electrical discharge machining through response surface methodology approach

Whereas the efficiency of traditional cutting processes is limited by the mechanical properties of the processed material and the complexity of the workpiece geometry, electrical discharge machining (EDM) being a thermal erosion process, is subject to no such constraints. The lack of correlations between the cutting rate, the surface finish and the physical material parameters of this process made it difficult to use. This paper highlights the development of a comprehensive mathematical model for correlating the interactive and higher order influences of various electrical discharge machining parameters through response surface methodology (RSM), utilizing relevant experimental data as obtained through experimentation. The adequacy of the above the proposed models have been tested through the analysis of variance (ANOVA). Optimal combination of these parameters was obtained for achieving controlled EDM of the workpieces.     

Biodegradation of γ-sterilised biomedical polyolefins under composting and fungal culture environments

Polyolefin-based commodities are widely used as biomedical devices and food packaging after γ-sterilisation. The aim of the present work was to study the effect of γ-sterilisation on the biodegradation of polyolefins. Films of isotactic polypropylene, high-density polyethylene and ethylene-propylene (EP) copolymers were sterilised under γ-radiation with doses of 10 and 25 kGy. Neat and sterilised samples were incubated in compost and fungal culture environments. The changes in functional groups, surface morphology and chain scission in polymer chains were characterized by FTIR spectroscopy, SEM and viscometric measurements, respectively. A gradual decrease in intrinsic viscosity [η] and increase in carbonyl and hydroxyl regions in FTIR spectra were found for the γ-sterilised samples as a function of increasing dose. Polypropylene was found to be more susceptible to both radio-oxidation and biodegradation. It was observed that in case of ethylene-propylene copolymers, extent of γ-sterilisation and/or biodegradation depends on the composition and distribution of comonomers. Important surface erosion was detected by SEM, for higher sterilisation doses, after composting.     

Molecular modeling study of the aggregation behavior of nickel(II), cobalt(II), lead(II) and zinc(II) bis(2-ethylhexyl) phosphate complexes

The physiochemical nature of the metal-extractant species in organic solvent has been a matter of debate over liquid-liquid extraction of transition metals by bis(2-ethylhexyl) phosphate. The aggregation behavior of nickel(II), cobalt(II), lead(II), and zinc(II) bis(2-ethylhexyl) phosphate have been investigated using molecular modeling. The recently confirmed "open" water channels rodlike reversed micelles which is in contact with the nonaqueous solvent rather than in an inner core (or "closed" water channel) of the nickel-extractant species by Ibrahim and Neuman appears to be a unique structure for such species. Lead-, cobalt- and zinc-extractant species behave in a different manner. The cobalt-extractant species form rodlike reversed micelles, but does not show the formation of any open water channel. The zinc- and lead-extractant species form ellipsoidal (or deformed spherical) reversed micelles with fewer water molecules located at the core of the micelles which is in accord with the conventional view of reversed micelles. The structural variations of the reversed micelles for the metal extracted species are in accord with the known extraction behavior of such metals when using HDEHP.     

Limit distributions of generalized order statistics in a stationary Gaussian sequence

In this paper we study the limit distributions of extreme, intermediate and central m-generalized order statistics, as well as m-dual generalized order statistics, of a stationary Gaussian sequence under equi-correlated set up. Moreover, the result of extremes is extended to a wide subclass of generalized order statistics, as well as dual generalized order statistics, when the parameters γ_1,n, γ_2,n,?…?, γ_n,n are assumed to be pairwise different.     

Raman microscopy for the chemometric analysis of tumor cells

Raman spectroscopy is recognized as a tool for chemometric analysis of biological materials due to the high information content relating to specific physical and chemical qualities of the sample. Thirty cells belonging to two different prostatic cell lines, PNT1A (immortalized normal prostate cell line) and LNCaP (malignant cell line derived from prostate metastases), were mapped using Raman microscopy. A range of spectral preprocessing methods (partial least-squares discriminant analyses (PLSDAs), principal component analyses (PCAs), and adjacent band ratios (ABRs)) were compared for input into linear discriminant analysis to model and classify the two cell lines. PLSDA and ABR were able to correctly classify 100% of cells into benign and malignant groups, while PLSDA correctly classified a greater proportion of individual spectra. PCA was used to image the distribution of various biochemicals inside each cell and confirm differences in composition/distribution between benign and malignant cell lines. This study has demonstrated that PLSDAs and ABRs of Raman data can identify subtle differences between benign and malignant prostatic cells in vitro.     

Cyclohexene Reactivity Using Catalysts Containing Pt,Re and PtRe Supported on Na‐ and H‐Mordenite

The reactivity of cyclohexene (CHE) over catalysts containing 0.3 wt% Pt, 0.3 wt% Re or 0.3 wt% Pt + 0.3 wt% Re supported on Na‐ and H‐mordenite has been studied in an atmospheric flow‐type reactor at a temperature range of 100–400 °C, using a flow of hydrogen (20 cm³/min). The catalysts were characterized for acid sites strength‐distribution, using desorption of ammonia in DSC. The acidity of H‐mordenite (HM) is attributed to strong acid sites, whereas the acidity of Na‐mordenite (NaM) is due to weak acid sites which are not involved in the catalytic reaction under study. The catalysts containing HM enhance the reactivity of CHE for isomorization reactions. However, the reactivity of CHE on NaM catalysts enhances only the hydrogenation and dehydrogenation reactions. Pt/HM is the most selective catalyst for isomerization of CHE, whereas Pt/NaM and PtRe/NaM catalysts are the most selective for hydrogenation and dehydrogenation reactions, respectively. The hydroisomorization of CHE seems to depend only on the acidity of the catalysts, whereas both hydrogenation and dehydrogenation reactions were controlled by metallic function of the catalysts.     

Polarographic Determination of the Formation Constants of the Mixed Ligand Complexes of Cd(II) and Pb(II) with Thiosulphate and Halide Ions

The mixed ligand complexes of Cd(II) and Pb(II) with thiosulphate as a primary ligand and chloride, bromide of iodide (individually) as a secondary ligand have been polarographically, investigated at 30°C and at a constant ionic strength of μ = 1.0 M (NaClO₄). Two mixed ligand complexes were formed with the Cd(II) ion: log β₁₂ = 4.77, 5.30 and 6.78 for the chloride, bromide and iodide ions, respectively; and log β₂₁ = 5.36, 5.04 and 6.22 for the same ions. For the Pb(II)-Ts-Cl system, only one mixed ligand complex was formed with a log stability constant log β₂₁ =4.35. For the Pb(II)-Ts-Br system, three mixed ligand complexes are obtained with log β₁₁ = 3.63, log β₁₂ = 4.51 and log β₂₁ = 4.85.