TG-MS analysis of nitrile butadiene rubber blends (NBR/PVC)

Blends of nitrile butadiene rubber (NBR) with polyvinyl chloride (PVC) are widely used in products such as hoses and seals. As part of a project that uses NBR/PVC blends for manufacturing forest fire hoses, blends of NBR/PVC with various inorganic fillers, such as Mg(OH)₂, china clay (organic modified kaolin) and nano clay (organic modified bentonite) were studied by TG-MS. No significant changes were observed to the type of the polymers’ decomposition products, compared to that of NBR/PVC blend without additives. The most remarkable change was the absence of HCl from decomposition products in the presence of the Mg(OH)₂ additive.     

Relation of lattice ion solution composition to octacalcium phosphate dissolution kinetics

The kinetics of dissolution of octacalcium phosphate (OCP) has been investigated under conditions of constant relative undersaturation with respect to OCP, σ_OCP=−0.57, at pH 4.500, and ionic strength (I), 0.15 mol l⁻¹. The molar calcium/phosphate ratio (R) in the solutions was varied from 0.1 to 10. The dissolution rate decreased by 160% as R increased from 0.1 to 10. The ζ-potential of the OCP surfaces was measured in solutions equilibrated with respect to OCP at pH values ranging from 5.0 to 11. Under stoichiometric conditions (R=1.33), OCP was positively charged at pH values from 5.0 to 10. As the solution calcium concentration was increased, ζ became more positive over the entire pH range studied. At R=0.1, two isoelectric points were apparent at pH values of about 6.3 and pH 9.5. This behavior may be related to the solubility product (K_sp) of OCP. The relationship between surface characteristics and dissolution rate are discussed in terms of kink density and the kinetic ionic ratio model developed previously (J. Zhang, G.H. Nancollas, J. Colloid Interf. Sci., 200 (1998) 131.     

Simultaneous multielement‐specific detection of a novel glutathione–arsenic–selenium ion [(GS)2AsSe]− by ICP AES after micellar size‐ exclusion chromatography

In order to confirm the solution structure of [(GS)₂AsSe]⁻ (GS = glutathione), we have investigated the retention behaviour of a [(GS)₂AsSe]⁻/oxidized glutathione (GSSG) mixture on a Sephadex G‐25 (SF) column with Tris buffers (0.1 mol dm⁻³, pH 8.0) containing ­various surfactants at concentrations above the critical micellar concentration (CMC): hexadecyltrimethlammonium bromide (HDTAB; 30, 40 and 50 mmol dm⁻³); dodecyltrimethylammonium bromide (DDTAB; 50 mmol dm⁻³); and sodium lauryl sulfate (SLS; 50 mmol dm⁻³). ­An inductively coupled plasma atomic emission spectrometer (ICP AES) provided simultaneous on‐line detection of arsenic, selenium and ­sulfur in the column effluent. The chromatographic retention behaviour was used to investigate the association of both compounds with the positively charged micelles (HDTAB and DDTAB mobile phases). The relative strength of association with the micelles provided insight into the effective negative charge on [(GS)₂AsSe]⁻ and GSSG. The chromatograms obtained with 50 mmol dm⁻³ HDTAB indicated that two glutathione molecules are associated with the elution of an arsenic–selenium compound. Combined, these chromatographic data strongly support the spectroscopically derived solution structure of [(GS)₂AsSe]⁻. Copyright ­© 2000 John Wiley & Sons, Ltd.     

An experimental verification of statistical discrimination between the terminal and penultimate copolymerization models

In this article, the modified Buzzi–Ferraris model discrimination method was used to design experiments to discriminate between the terminal and penultimate models for styrene methyl methacrylate (STY/MMA) copolymerization. The measured variables were ¹³C-NMR peak areas. The peak area assignments of Aerdts⁸ were used. After nine experiments, the terminal model was picked over the penultimate model at 99.99% confidence. More importantly, the experimental data showed that computer simulated data used in previous studies were realistic, and the conclusions drawn from the simulation studies were valid. This experimental verification continues to show that the use of statistical model discrimination techniques can improve our ability to discriminate between competing copolymerization models. © 1996 John Wiley & Sons, Inc.     

In search of the plastic enzyme

Photozymes are novel polyelectrolytes made from mixtures of hydrophobic and hydrophilic comonomers. They often contain a relatively high concentration of bound chromophores as photon harvesting or antenna groups, which transport excitation energy to organic substrates located in the interior of the macromolecular coil in aqueous solution. Previous studies have shown that the photocatalytic behavior of these polymers has many similarities to natural enzymes which carry out thermal reactions in biological systems. Mechanistic studies of four photozyme reactions are discussed: (1) the oxidation of perylene to perylenequinones; (2) the dehalogenation of hexachloro- and pentachlorobenzene; (3) the high-yield synthesis of Vitamin D; and (4) the selective photolysis of aliphatic and aromatic ketones.