Completely biodegradable composites of poly(propylene carbonate) and short,lignocellulose fiber Hildegardia populifolia

The composites of biodegradable poly(propylene carbonate) (PPC) reinforced with short Hildegardia populifolia natural fiber were prepared by melt mixing followed by compression molding. The mechanical properties, thermal properties, and morphologies of the composites were studied via static and dynamic mechanical measurements, thermogravimetric analysis, and scanning electron microscopy (SEM) techniques, respectively. Static tensile tests showed that the stiffness and tensile strength of the composites increased with an increasing fiber content. However, the elongation at break and the energy to break decreased dramatically with the addition of short fiber. The relationship between the experimental results and the compatibility or interaction between the PPC matrix and fiber was correlated. SEM observations indicated good interfacial contact between the short fiber and PPC matrix. Thermogravimetric analysis revealed that the introduction of short Hildegardia populifolia fiber led to a slightly improved thermooxidative stability of PPC. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 666–675, 2004     

Synthesis and characterization of polyaniline/graphite conducting nanocomposites

A new method for the synthesis of exfoliated graphite and polyaniline (PANI)/graphite nanocomposites was developed. Exfoliated graphite nanosheets were prepared through the microwave irradiation and sonication of synthesized expandable graphite. The nanocomposites were fabricated via the in situ polymerization of the monomer at the presence of graphite nanosheets. The as-synthesized graphite nanosheets and PANI/graphite nanocomposite materials were characterized with Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis (TGA). The conductivity of the PANI/graphite nanocomposites was dramatically increased over that of pure PANI. TGA indicated that the incorporation of graphite greatly improved the thermal stability of PANI. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1972–1978, 2004     

Physical properties of glycosaminoglycan hydrogels

The chemical composition of glycosaminoglycan (GAG) hydrogels was found to have a profound effect on the physical properties of gels. Hyaluronan (HA) and chondroitin sulfate (CS) were each modified with adipic dihydrazide (ADH) with carbodiimide chemistry. The resulting polymer was crosslinked with various concentrations of poly(ethylene glycol) dialdehyde (PEG‐diald) to produce a series of hydrogels. The physical properties of these GAG hydrogels varied in a concentration‐dependent fashion. Maximal crosslinking was observed at a theoretical crosslinking of 50% for the HA‐ADH‐PEG‐diald hydrogels and 75% for the CS‐ADH‐PEG‐diald hydrogels. Adding PEG‐diald beyond the optimum for crosslinking prolonged the in vitro enzymatic degradation time of the hydrogels. The swelling of the crosslinked GAG hydrogels was correlated with the amount of PEG‐diald used rather than with the crosslinking density. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4344–4356, 2004     

Permeability of N2, Ar,He, O2, and CO2 through as‐extruded amorphous and biaxially oriented polyester films: Dependence on chain mobility

For as‐extruded amorphous and biaxially orientated polyester films based on poly(ethylene terephthalate), poly(ethylene naphthalate), and copolymers containing poly(ethylene terephthalate) and poly(ethylene naphthalate) moieties, permeability, diffusion, and solubility coefficients are interpreted in terms of chain mobility. The influence of polymer morphology is determined by comparison of the data for as‐extruded amorphous sheets and materials produced with different biaxial draw ratios. The crystallinities of the samples were assessed using differential scanning calorimetry and density measurements. Changes in mobility at a molecular level were investigated using dielectric spectroscopy and dynamic mechanical thermal analysis. The study, in conjunction with our earlier work, leads to the conclusion that the key to understanding differences in gas transport is the difference in local chain motions rather than in free volume. This was illustrated by the permeability results for He, Ar, N₂, and O₂ in the range of polyesters. However, the permeability of CO₂ was found to require alternative explanations because of polymer–penetrant interactions. For biaxially oriented samples, the differences in diffusivity are not only due to differences in local chain motions, but also additional constraints resulting from the increased crystallinity and chain rigidity—which also act to hinder segmental mobility. The effectiveness of the reduction in permeability in the biaxially oriented films is consequently determined by the ability of the polymer chains to effectively align and form crystalline structures. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2916–2929, 2004     

Differential pulse anodic stripping voltammetric determination of traces of copper with a tobramycin-Nafion modified electrode.

A Nafion-modified glassy carbon electrode incorporated with tobramycin for the voltammetric stripping determination of Cu2+ has been explored. The electrode was fabricated by tobramycin containing Nafion on the glassy carbon electrode surface. The modified electrode exhibited a significantly increased sensitivity and selectivity for Cu2+ compared with a bare glassy carbon electrode and the Nafion modified electrode. Cu2+ was accumulated in HAc-NaAc buffer (pH 4.6) at a potential of -0.6 V (vs. SCE) for 300 s and then determined by differential pulse anodic stripping voltammetry. The effects of various parameters, such as the mass of Nafion, the concentration of tobramycin, the pH of the medium, the accumulation potential, the accumulation time and the scan rate, were investigated. Under the optimum conditions, a linear calibration graph was obtained in the concentration range of 1.0 x 10(-9) to 5.0 x 10(-7) mol l(-1) with a correlation coefficient of 0.9971. The relative standard deviations for eight successive determinations were 4.3 and 2.9% for 1.0 x 10(-8) and 2.0 x 10(-7) mol l(-1) Cu2+, respectively. The detection limit (three times signal to noise) was 5.0 x 10(-10) mol l(-1). A study of interfering substances was also performed, and the method was applied to the direct determination of copper in water samples, and also in analytical reagent-grade salts with satisfactory results.     

Determination of polymeric aluminum in soil extracted with a modified anion-exchange resin as a solid-phase adsorbent by ICP-AES.

In the present work, a new method was established by applying solid-phase extraction (SPE) to preconcentrate and separate polymeric aluminum (Al) and using ICP-AES to determine the polymeric Al, the total monomeric Al, and the total Al in soil extracts, respectively. A modified resin was prepared with impregnated 8-hydroxyquinoline-5-sulfoxinate (HQS) on the anion-exchange resin. It has good recognition ability for Al fractions, compared to the commonly used cation ion-exchange resin, which has a better ability to adsorb cations and a weak ability to recognize detailed Al species. The optimum conditions for Al fractionation sorption, elution and separation and the interference of foreign ions were studied with the prepared resin by continuous column and batch procedures. Monomeric Al was bound to Pyrocathecol Violet (PCV) at pH 6.2, whereas the polymeric Al species did not react with PCV for at least 15 min. Because a stable complex of Al-PCV was not absorbed on the HQS modified resin, the polymeric Al could be preconcentrated on-line by the HQS-modified resin. The adsorbed polymeric Al was eluted with 3 mL of 3 mol L(-1) of HCl, and then detected by ICP-AES. The method has been applied to directly determine polymeric Al in soil extracts with high selectivity as well as a high preconcentration factor. It gives a limit of detection of 0.6 ng mL(-1) with a relative standard deviation of less than 5.7% (n = 5, 0.24 microg mL(-1) Al).     

Structure and properties of the mesophase of syndiotactic polystyrene—III. Selective sorption of the mesophase of syndiotactic polystyrene

Syndiotactic polystyrene (sPS) has various crystalline forms such as α, β, γ, and δ forms, and a mesophase depending on the preparation method. In this study, we focused on the mesophase with the molecular cavity of sPS, which is obtained by step‐wise extraction of the guest molecules from the sPS δ form. To prepare the mesophase containing different shapes and sizes of the cavity, two kinds of the sPS δ form membrane cast from either toluene or chloroform solution were first prepared and then the guest molecules were removed by a step‐wise extraction method using acetone and methanol. We could succeed in the preparation of two kinds of mesophase with different shapes and sizes of the molecular cavity. Either toluene or chloroform vapor sorption to the sPS mesophase membranes was examined at 25 °C. Sorption analysis indicates that the mesophase with large molecular cavities can mainly sorb large molecules; on the other hand, the mesophase with small cavities can sorb only the small molecules, and is unable to sorb a large amount of large molecule because the cavity was too small to sorb the large molecules. Therefore, the sPS mesophase membrane has sorption selectivity based on the size of the molecular cavity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 238–245, 2004     

Extractive spectrophotometric determination of Cobalt(II) in synthetic and pharmaceutical samples using Cyanex 923.

Cyanex 923 has been proposed as a sensitive analytical reagent for the direct extractive spectrophotometric determination of cobalt(II). Cobalt(II) forms a blue-colored complex with Cyanex 923 in the organic phase. The maximum absorbance of the complex is measured at 635 nm. Beer's law was obeyed in the range 58.9 - 589.0 microg of cobalt. The molar absorptivitiy and Sandell's sensitivity of the complex was calculated to be 6.79 x 10920 l mol(-1) cm(-1) and 0.088 microg cm(-2), respectively. The nature of the extracted species was found to be Co(SCN)2 x 2S. An excellent linearity with a correlation coefficient value of 0.999 was obtained for the Co(II)-Cyanex 923 complex. Stability and regeneration of the reagent (Cyanex 923) for reuse is the main advantage of the present method. The method was successfully applied to the determination of cobalt in synthetic mixtures and pharmaceutical samples was found to give values close to the actual ones. Standard alloy samples, such as high-speed tool BCS 484 and 485, have been tested for the determination of cobalt for the purpose of validating the present method. The results of the proposed method are comparable with atomic absorption spectrometry and were found to be in good agreement.     

Preparation and characterization of finely dispersed drugs. 5. Ethyl 3,5-di(acetylamino)-2,4,6-triiodobenzoate

Controlled precipitation of the diagnostic imaging agent ethyl 3,5-di(acetylamino)-2,4,6-triiodobenzoate has been used to produce fine particles of various sizes, morphologies, and degrees of crystallinity, which depended on experimental conditions. In addition, two distinct polymorphic forms of the drug have been fully characterized by single crystal X-ray diffraction studies, and evidence for a third polymorph was also observed. Some of the so prepared dry particles were coated with a thin layer of silica.     

Fold‐2‐covering triangular embeddings

For a graph G and a positive integer m, G_(m) is the graph obtained from G by replacing every vertex by an independent set of size m and every edge by m² edges joining all possible new pairs of ends. If G triangulates a surface, then it is easy to see from Euler's formula that G_(m) can, in principle, triangulate a surface. For m prime and at least 7, it has previously been shown that in fact G_(m) does triangulate a surface, and in fact does so as a “covering with folds” of the original triangulation. For m = 5, this would be a consequence of Tutte's 5‐Flow Conjecture. In this work, we investigate the case m = 2 and describe simple classes of triangulations G for which G₍₂₎ does have a triangulation that covers G “with folds,” as well as providing a simple infinite class of triangulations G of the sphere for which G₍₂₎ does not triangulate any surface. © 2003 Wiley Periodicals, Inc. J Graph Theory 43: 79–92, 2003