Summary: The effectiveness of some thermoplastic elastomers grafted with maleic anhydride (MA) or with glycidyl methacrylate (GMA) as compatibilizer precursors (CPs) for blends of low density polyethylene (LDPE) with polyamide‐6 (PA) has been studied. The CPs were produced by grafting different amounts of MA or GMA onto a styrene‐block‐(ethylene‐co‐1‐butene)‐block‐styrene copolymer (SEBS) (KRATON G 1652), either in the melt or in solution. A commercially available SEBS‐g‐MA copolymer with 1.7 wt.‐% MA (KRATON FG 1901X) was also used. The effect of the MA concentration and of other characteristics of the SEBS‐g‐MA CPs was also studied. The specific interactions between the CPs and the blends components were investigated through characterizations of the binary LDPE/CP and PA/CP blends, in the whole composition range. It was demonstrated that the SEBS‐g‐GMA copolymers display poor compatibilizing effectiveness due to cross‐linking resulting from reactions of the epoxy rings of these CPs with both the amine and the carboxyl end groups of PA. On the contrary, the compatibilizing efficiency of the MA‐grafted elastomers, as revealed by the thermal properties and the morphology of the compatibilized blends, was shown to be excellent. The results of this study confirm that the anhydride functional groups possess considerably higher efficiency, for the reactive compatibilization of LDPE/PA blends, than those of the ethylene‐acrylic acid and ethylene‐glycidyl methacrylate copolymers investigated in previous works.
Constraint-based modeling is largely used in computational studies of metabolism. We propose here a novel approach that aims to identify ensembles of flux distributions that comply with one or more target phenotype(s). The methodology has been tested on a small-scale model of yeast energy metabolism. The target phenotypes describe the differential pattern of ethanol production and O2 consumption observed in “Crabtree-positive” and “Crabtree-negative” yeasts in changing environment (i.e., when the upper limit of glucose uptake is varied). The ensembles were obtained either by selection among sampled flux distributions or by means of a search heuristic (genetic algorithm). The former approach provided indication about the probability to observe a given phenotype, but the resulting ensembles could not be unambiguously partitioned into “Crabtree-positive” and “Crabtree-negative” clusters. On the contrary well-separated clusters were obtained with the latter method. The cluster analysis further allowed identification of distinct groups within each target phenotype. The method may thus prove useful in characterizing the design principles underlying metabolic plasticity arising from evolving physio-pathological or developmental constraints. 相似文献
Pheromone components for many lepidopteran species are produced by the use of unique chain-shortening and 9, 10, and 11 desaturase systems. Correlations in the Tortricidae indicate that the pheromone components derived from 9 and 01 desaturases are found in the more primitive species (those possessing morphological plesiomorphies). The precise blend ofZ andE acetates in a number of species is regulated in the final reduction sequence from acyl intermediates. Preliminary research has been conducted on the characterization of the various desaturase enzymes used and on the important blend regulating sequence. Initial purification work on the 11 desaturase enzyme found in the cabbage looper moth is reported. 相似文献
Performance data are presented for methane oxidation on alumina-supported Pd, Pt, and Rh catalysts under both fuel-rich and fuel-lean conditions. Catalyst activity was measured in a micro-scale isothermal reactor at temperatures between 300 and 800 °C. Non-isothermal (near adiabatic) temperature and reaction data were obtained in a full-length (non-differential) sub-scale reactor operating at high pressure (0.9 MPa) and constant inlet temperature, simulating actual reactor operation in catalytic combustion applications.
Under fuel-lean conditions, Pd catalyst was the most active, although deactivation occurred above 650 °C, with reactivation upon cooling. Rh catalyst also deactivated above 750 °C, but did not reactivate. Pt catalyst was active above 600 °C. Fuel-lean reaction products were CO2 and H2O for all three catalysts.
The same catalysts tested under fuel-rich conditions demonstrated much higher activity. In addition, a ‘lightoff’ temperature was found (between 450 and 600 °C), where a stepwise increase in reaction rate was observed. Following ‘lightoff’ partial oxidation products (CO, H2) appeared in the mixture, and their concentration increased with increasing temperature. All three catalysts exhibited this behavior.
High-pressure (0.9 MPa) sub-scale reactor and combustor data are shown, demonstrating the benefits of fuel-rich operation over the catalyst for ultra-low emissions combustion. 相似文献
8-Hydroxyquinoline-5-sulphonate/Al(III) aqueous solutions were studied both by potentiometric titrations and voltammetric measurements, in order to obtain the number, the stoichiometry and the stability constants of the complexes formed at equilibrium, and to evaluate the redox and (electro)kinetic properties of the free ligand and of the metal/ligand complexes. The complexes formed in 0.2 m (Na)Cl aqueous solution (stability log beta values ± standard deviation) are AlL+ (8.95 ± 0.05), AlL2− (17.43 ± 0.03) and AlL33− (24.58 ± 0.05), where “L” denotes the free ligand in the completely deprotonated form (L2−, pKa1 = 3.910 ± 0.008, pKa2 = 8.319 ± 0.004). AlL33− is the predominant Al(III) species in a very wide range of pH, metal and ligand concentrations and metal-to-ligand ratios. The free ligand shows an oxidation wave at 0.62 V versus SCE. The proposed oxidation mechanism includes a first reversible one-electron oxidation of the ligand, followed by a coupling reaction and by a second reversible one-electron oxidation, and finally by a decomposition reaction. The addition of Al(III) lowers the intensity of the oxidation wave due to the formation of the redox-inactive complex AlL33−. A residual low signal was attributed to the free ligand produced by the complex dissociation, AlL33− = AlL2− + L2−. All the kinetic parameters involved in the ligand oxidation and in the complex disruption were calculated on the basis of the agreement between experimental and simulated linear sweep and cyclic voltammetries. Correctness of the mechanisms proposed was further confirmed “a posteriori” by the agreement between potentiometric and linear sweep voltammetric results. The low residual signal observed in the presence of fully formed complex was attributed to the free ligand produced by the complex dissociation, having a kinetic constant estimated 0.2 s−1. 相似文献
The glass transition temperatures (Tg's) of several polystyrenes and styrene–alkyl methacrylate copolymers and terpolymers were measured using thermomechanical analysis (TMA) and differential scanning calorimetry (DSC). The polymers studied had number-average molecular weights from 3000 to 250,000 g/mole. The results indicate that the composition dependence of the Tg's for the copolymers and terpolymers can be satisfactorily described by a general Fox equation. In general, the measured Tg's of the copolymer and terpolymer samples depend more on the steric effects of the constituent pendent groups than on their molecular weights. The chain flexibility rather than the size of the pendent group is the determining factor in the glass transition properties of the styrene polymers. 相似文献
The alarm pheromone system ofLeptoglossus zonatus (Dallas) adults was shown to be composed of hexyl acetate, hexanol, hexanal, and hexanoic acid. Single components tested in the field elicited dispersive behavior of over 70% of adults. 2-(E)-Hexenal, found in the secretion of nymphs, but not in the exudates of adults, was also active against adults. In addition, first-instar nymphs responded to the four components of the alarm pheromone of adults as well as to 2-(E)-hexenal, a component of their own alarm pheromone system. Adults and nymphs possess different alarm pheromone systems, which are not specific to their own life stage. That hemipteran alarm pheromone systems are not species-specific was supported by the fact that both adult and nymphL. zonatus responded to butanoic acid, an alarm pheromone of Alydidae, which was not found in this Coreidae species. 相似文献
The potentials of X-ray absorption spectroscopy (XAS) (quantitative phase composition and average valence together with a short-range order structure analysis) combined with a time-resolution in the second range make time-resolved (TR-) XAS a powerful tool for investigating the reactivity of solids in catalysis and solid-state chemistry. General aspects of TR-XAS investigations are discussed (i.e., instrumentation, data analysis). In addition, some experiments illustrate how the kinetics of solid-state reactions in heterogeneous catalysis can be elucidated from TR-XAS studies. 相似文献