Concept of secondary heterogeneous structure of long-chain branched polyethylene

The mechanism of formation of surface roughness and extrusion swelling of the extrudate and the steady-shear viscous flow behavior in the region of high shear rate for branched polymers were investigated using two low-density polyethylenes and their sheared samples. These two polyethylenes varied in their degree of branching, molecular weight, and molecular weight distribution but were similar in their melt flow index. The effect of molecular parameters, especially long-chain branching, on viscoelastic properties in the molten state was also considered. Samples of various degree of shearing level were prepared by passing them repeatedly through an extruder. Results of intrinsic viscometry, gel permeation chromatography, and infrared spectroscopy of the original and the sheared samples indicate that no appreciable variation between them takes place in the molecular parameters during the process of extrusion shearing. Both surface roughness and extrusion swelling of the extrudate diminish with increase in the extent of shear. The extrusion shearing affects the surface roughness and extrusion swelling of the extrudate as well as the capillary entrance effect more markedly for the highly branched polymers with considerably higher molecular weight than for the less branched species with bell-type molecular weight distribution. These results demonstrate that heterogeneity becomes more conspicuous with the degree of long-chain branching level, and therefore the role of long-chain branching in the development of the heterogeneity is particularly important. It is suggested that the secondary heterogeneous structure arises through phase separation or from the heterogeneous formation of strongly entangled network at the branching point of the long-chain branching in the manufacturing process of the low-density polyethylene and that its presence causes the distinctive viscoelastic properties of long-chain branched polymer melts.     

Flow properties of molten ethylene–vinyl acetate copolymer and melt fracture

In an investigation of the behavior and formation mechanism of melt fracture the flow properties of molten ethylene–vinyl acetate (EVA) copolymer in the region of high shear rate were measured with a capillary-type rheometer. EVA copolymer differs slightly in flow curve from low-density polyethylene (LDPE); it seems, however, that the difference is due to the difference in molecular weight distribution (MWD) rather than to the materials themselves. The fluidity of molten EVA copolymer having a narrow MWD is equivalent to that of LDPE having a broad MWD and, generally, EVA copolymer has a higher fluidity than LDPE. It is expected that the fluidity increases with incorporation of vinyl acetate at the same MWD and the same M?_w. The critical shear rate increases with melt index and temperature. It cannot be found that the materials themselves and the MWD directly influence the critical point of melt fracture formation when the melt index is taken as a parameter. The critical viscosity (η_c) at which melt fracture forms decreases in an almost straight line with an increase of melt index. It was found from the studies of end correction and behavior of melt fracture formation that melt fracture occurs at the inlet of the die, and it is supposed that the melt fracture formation is caused by the elastic turbulence in the flow pattern due to a failure of recoverable shear strain at the die inlet.     

Determination of diffusion coefficient of oxygen in γ-iron from measurements of internal oxidation in Fe-Al alloys

The internal oxidation of iron alloys containing between 0.069 and 0.274 wt pct aluminum was investigated in the temperature range from 1223 to 1373 K for the purpose of determining the diffusion coefficients in γ-iron as well as in the internal oxidation layer. A parabolic rate law is obeyed in the internal oxidation of the present alloys. The rate constant for penetration of the oxidation front, the oxide formed, and the concentration of aluminum in the oxidation layer were determined. Pronounced enrichment of aluminum in the oxidation layer was observed, resulting from the counterdiffusion of aluminum. The oxygen concentration at the specimen surface was determined by combining the thermodynamic data on the dissociation of FeO and the solution of oxygen in y-iron. The diffusion coefficient of oxygen in the internal oxidation layer,D _o ¹⁰ , was evaluated on the basis of the rate equation for internal oxidation.D _o ¹⁰ increases at a given temperature as the volume fraction of oxide,f ¹⁰, in the oxidation layer increases. The diffusion coefficient of oxygen in γ-iron,D _o, was determined by extrapolation ofD _o ¹⁰ = 0.D _o may be expressed as $$D_o = \left( {1.30\begin{array}{*{20}c} { + 0.80} \\ { - 0.50} \\ \end{array} } \right) \times 10^{ - 4} \exp \left[ { - \frac{{166 \pm 5(kJ \cdot mol^{ - 1} )}}{{RT}}} \right]m^2 \cdot s^{ - 1} .$$ D _o is close to the diffusion coefficients of carbon and nitrogen in γ-iron.     

STM-induced light emission from thin films of perylene derivatives on the HOPG and Au substrates

We have investigated the emission properties of N,N'-diheptyl-3,4,9,10-perylenetetracarboxylic diimide thin films by the tunneling-electron-induced light emission technique. A fluorescence peak with vibronic progressions with large Stokes shifts was observed on both highly ordered pyrolytic graphite (HOPG) and Au substrates, indicating that the emission was derived from the isolated-molecule-like film condition with sufficient π-π interaction of the perylene rings of perylenetetracarboxylic diimide molecules. The upconversion emission mechanism of the tunneling-electron-induced emission was discussed in terms of inelastic tunneling including multiexcitation processes. The wavelength-selective enhanced emission due to a localized tip-induced surface plasmon on the Au substrate was also obtained.     

Female Sex Pheromone Polymorphism in Adzuki Bean Borer, Ostrinia scapulalis, Is Similar to That in European Corn Borer, O. nubilalis

Individual analysis of the female sex pheromone of the adzuki bean borer, Ostrinia scapulalis, has shown that the sex pheromone of this species comprised (E)-11-tetradecenyl acetate (E11–14:OAc) and (Z)-11-tetradecenyl acetate (Z11–14:OAc) at variable blend ratios. The pheromone blend could be tentatively categorized into three types with respect to the proportion of E11–14:OAc: E type (94–100%, median 99.2%), Z type (0–16%, median 3.0%), and intermediate type (I type, 48–85%, median 63.7%). In addition to the identity of components, the blend ratios in the three types were similar to those of the E strain, Z strain, and hybrid of the European corn borer, O. nubilalis, respectively. This finding suggests that two closely related but morphologically distinct species, O. scapulalis and O. nubilalis, share almost the same sex pheromone communication systems. The significance of this similarity in the two sibling species is discussed.     

Host egg kairomones essential for egg-larval parasitoid,Ascogaster reticulatus Watanabe (Hymenoptera: Braconidae)

Several components of an internal kairomone were identified inside eggs of the host,Adoxophyes sp. (Lepidoptere: Tortricidae), that releases egg deposition of the egg-larval parasitoid,Ascogaster reticulatus Watanabe (Hymenoptera: Braconidae). Pupal hemolymph with the same activity as an internal host egg kairomone was used as a convenient test sample. Heat-treated pupal hemolymph was chromatographed on a Sephadex G-25 column. Each fraction was bioassayed and reacted with ninhydrin. The active fractions were ninhydrin-positive. Each fraction was placed onto an araino acid analyzer, which showed that the amino acids were most abundant in active fractions. Among 22 amino acids, alanine, arginine, glycine, histidine, isoleucine, leucine, methionine, proline, serine, tryptophan, and valine were active. The mixture of these active amino acids was as active as the egg-mass homogenate at the same ratio and concentration, suggesting that the most important component as the kairomone in a host egg is the mixture of several amino acids.     

Isolation of enterocin SE-K4-encoding plasmid and a high enterocin SE-K4 producing strain of Enterococcus faecalis K-4

Enterococcus faecalis K-4, which produces a class IIa bacteriocin, enterocin SE-K4, carries two plasmids, pEK4S (approximately 60 kb) and pEK4L (approximately 75 kb). Plasmid-curing experiments showed that pEK4S was involved in the production of and immunity to enterocin SE-K4 in strain K-4. A derivative strain, M6, with pEK4S produced a higher amount of enterocin SE-K4 than the parental strain K-4, although its growth rate was lower than that of parental strain K-4. Phenotypic changes in strain M6 are attributed to an increase in plasmid copy number.     

Effects of grain boundary- and triple junction-character on intergranular fatigue crack nucleation in polycrystalline aluminum

The effects of grain boundary- and triple junction-character on intergranular fatigue crack nucleation were studied in coarse-grained polycrystalline aluminum specimens whose grain boundary microstructures were analyzed by SEM-EBSD/OIM technique. Fatigue crack nucleation occurred mainly along grain boundaries and depended strongly on both the grain boundary character and grain boundary configuration with respect to the persistent slip bands. However, it was little dependent on the geometrical arrangements between the grain boundary plane and the stress axis. Particularly, random boundaries become preferential sites for fatigue crack nucleation. The fatigue cracks were also observed at CSL boundaries when the grain-boundary trace on the specimen surface was parallel to persistent slip bands. On the other hand, no intergranular fatigue cracks were observed at low-angle boundaries. The fatigue cracks were observed at triple junctions as well as grain boundaries. Their nucleation considerably occurred at triple junctions where random boundaries were interconnected. The grain boundary engineering for improvement in fatigue property was discussed on the basis of the results of the structure-dependent intergranular and triple junction fatigue crack nucleation.     

Influence of shearing history on the rheological properties and processability of branched polymers. IV. Capillary flow and die swell of low-density polyethylene

Low-density polyethylene (LDPE) melts show anomalous rheological behavior; their viscoelastic properties vary with their shearing histories although their molecular structural parameters do not change. Capillary flow and die swell behavior were dependent not only on the experimental conditions such as temperature or shear stress but also on the processing index (PI), which was introduced in a preceding article in order to quantify the anomalous rheological behavior of LDPE melts. In addition, it was found that the flow activation energy at constant shear stress also varied with the shearing histories. The experimental findings are discussed in terms of the rheological flow units of LDPE melts.