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  • 1990-1994  (13,573)
  • 1920-1924  (688)
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  • 1
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 6-11 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A new class of materials based on a spirodilactam structure has been recently synthesized as part of research into new polymeric materials. Not only is the spirodilactam structure novel, but it was not even the intended product in the synthesis as originally designed. The polymerization process discovered by the reaction of 4-ketopimelic acid or its corresponding spirodilactone with primary amines opened a new field of polysprodilactam chemistry. This paper describes the chemistry leading to the discovery of spirodilactam-based polymers and initial applications in the area of thermoplastics and thermosets. Most recent developments to be covered include aromatic spirodilactams and isomeric spirodilactams.
    Additional Material: 1 Tab.
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  • 2
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 12-16 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Spirodilactam bisallylether is a new high temperature performance monomer. It melts at 154°C, and is thermally inactive in forming a homopolymer. However, it reacts readily with a bismaleimide via “ene” reaction. Therefore, it could be used as a comonomer and an effective toughening modifier for bismaleimide. The properties of the blends of spirodilactam bisallylether and 4,4'-bismaleimidodiphenyl-methane were studied. The cocured resins have high glass transition temperature, 〉 300°C. By adding 30 to 40 mole % of the bisallylether, the compact tension toughness of the bismaleimide was improved to 0.7 MPa-m1/2. Therefore, the resins have a combination of high glass transition temperature and toughness. They also showed good flexural properties. Despite the high water absorption, 5 to 7%, the resins retained high hot/wet flexural properties because of the high glass transition.
    Additional Material: 3 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 59-68 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Four immiscible blend systems, styrene-maleic anhydride/styrene-acrylonitrile (SMA/SAN). styrene-maleic anhydride/acrylonitrile-butadiene-styrene (SMA/ABS), poly(vinylidene fluoride)/SAN (PVF2/SAN), and PVF2/ABS, were investigated. The effect of adding up to about 10 wt% of a third polymer that is miscible with each blend component, poly(methylmethacrylate) (PMMA), was determined. In every case, the addition of PMMA led to the improvement of properties such as tensile strength, tensile elongation, and notched impact strength. Furthermore, the addition of PMMA resulted in finer, more uniform dispersions of the primary blend components. The experimental results are interpreted in terms of interfacial activity of the common phase component, PMMA.
    Additional Material: 13 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 81-85 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Differential scanning calorimetry (DSC) was used to investigate the solid-state cure process of poly(phenylene sulfide)(PPS) resin. Virgin PPS resin in an open sample pan was cured in DSC cell. Either air or oxygen was used as a curing atmosphere. Cure temperatures were in the range of 200 and 250 °C, which are below the melting point of PPS resin. Cure temperature as well as atmospheric condition influenced the cure behavior of PPS in the solid state. Both the rate and the amount of cure increased with increasing cure temperature. On the other hand, the time to reach the maximum cure rate was independent of cure temperature. Changing the atmosphere from air to oxygen increased both the cure rate and the amount of cure. The size effect of PPS particles on the cure reaction was also discussed.
    Additional Material: 9 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 109-115 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Slow crack growth was measured in the perpendicular and parallel directions relative to the extrusion direction of the pipe. For five pipes from different manufacturers, the anisotropy factor, the lifetime to fracture in the perpendicular direction divided by lifetime in the parallel direction, varied from 1.2 to 4.7 for complete fracture and 1.4 to 4.0 for crack initiation. The degree of molecular orientation was determined by measuring the shrinkage that occured when a pipe specimen was heated near its melting point. The amount of shrinkage correlated with the anisotropy factor for slow crack growth. The shape change after shrinkage was related to the flow pattern of the resin during extrusion and the cooling rate after extrusion.
    Additional Material: 9 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 135-140 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The complex Young's modulus, E*(ω), and the complex strain-optical coefficient, O*(ω), of poly(ether sulfone) (PES), polysulfone (PSF), and polyethermide (PEI), were measured over the frequency range 1 to 130 Hz. The data were analyzed with a modified stress-optical rule: The Young's modulus was decomposed into two complex functions, EG*(ω) and ER*(ω); the modified stress-optical coefficient, CR and CG, associated with the rubber (R) and glass (G) components, respectively, were determined. The results for six polymers, including polystyrene, poly(α-methyl styrene), and bisphenol A polycarbonate were compared with each other. One of the coefficients, CR, equivalent to the stress-optical coefficient in melts, mainly depended on the way in which phenyl groups were connected to the chain. The other, CG, was in the range of 20 to 40 Brewsters, and did not strongly depend on the details of polymer structure. The component function, EG*(ω), which was located in the glassy region and originated from the high glassy modulus, was almost the same in shape when plotted against ω with double logarithmic scales. The R component, ER*(ω), located at the long time end of the glass-to-rubber transition zone, was slightly sensitive to the molecular structure of polymers.
    Additional Material: 5 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 159-165 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: While there is abundant evidence that the molecular weight distribution (MWD) of a linear polymer has an influence on the shape of the viscosity function, the ability to convert the viscosity function to an MWD has been questioned. Using strictly numerical techniques, we have shown that the viscosity function can be transformed to the MWD, but always with some distortion. However, distinct bimodality can be qualitatively preserved through both the MWD-viscosity and viscocity-MWD transforms.
    Additional Material: 10 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 169-173 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In microcellular plastics, an unfoamed skin that is integral with the foamed core can be created by allowing the nucleating gas to diffuse from the surfaces of a gas saturated specimen prior to foaming. In this paper, a semi-empirical model is proposed that predicts the skin thickness variation in microcellular foams as a function of gas desorption time. The model shows good agreement with experimental results on the polycarbonate-carbon dioxide system.
    Additional Material: 7 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 174-189 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The present paper proposes “Deformation Characteristics” (DC) as a new deformation measure of screw extrusion processes, based on the Green deformation tensor. In contrast to previous strain measures heuristically proposed by Mohr, et al., Mckelvey, and Pinto and Tadmor, the new DC can naturally incorporate the demixing phenomena and systematically take into account the three-dimensional circulatory flow with the screw flight effect. Therefore, DC can be regarded as an improved strain measure. “Weighted Average Deformation characteristics” (WADC) is also proposed to indicate the overall deformation characteristics as a quantitative measure to the “goodness of mixing” of the extrusion process. The present paper includes discussion on delicate differences between DC and several other strain measures in case of the two-dimensional velocity approximation, and on the application of DC into a general three-dimensional velocity field obtained by a quasi-three-dimensional finite element analysis of extrusion processes. In determining WADC in the three-dimensional application, the residence time distribution function, including the three-dimensional circulatory flow effect, is used.
    Additional Material: 15 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 229-237 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Non-isothermal flow is simulated in the screw and kneading disc elements in a modular co-rotating twin screw extruder. Methods of calculating mean temperature rises for individual elements are discussed and results are presented. The implications of non-isothermal operation for scale-up is discussed. A method is then described for making calculations in a modular co-rotating machine, that contains many different elements. Example calculations are given showing the tendency of larger machines to buildup greater temperatures when viscous heating is included.
    Additional Material: 5 Ill.
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  • 11
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 221-228 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A study of the influence of a compatibilizing agent on phase morphology development in a 75/25 polyethylene/polyamide-6 blend in a modular co-rotating twin screw extruder is presented. The development of phase morphology along the axis of the modular screw was observed by cooling the extruder and removing the polymer from the screw channels. Changes in phase morphology due to the addition of a compatibilizer have been investigated using scanning electron microscopy. Sufficient quantities of compatibilizing agent produce significant increases in the rate of mixing and also reduce the scale of the phase morphology. Much larger quantities (5%) than actually required for interface coverage are needed for rapid mixing. This seems to be due to the high viscosity of the matrix.
    Additional Material: 10 Ill.
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  • 12
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 251-251 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 260-265 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Penrose states that quantum effects can occur even in relatively large systems when energy differences remain small. This is just the situation with polymer materials. A quantum description by Penrose of the formation of quasi-crystals can be rewritten to apply to polymer crystallization. The implications of the need to take account of quantum effects are discussed. Another approach based on the quantization of energy levels in clusters of atoms offers a possible explanation of heat setting in nylon and polyester fibers. Finally some problems of the interpretation of quantum theory are discussed.
    Additional Material: 1 Ill.
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  • 15
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A novel approach to a truly dynamic thermodynamics is proposed in which equilibrium is defined in terms of explicit time, distance, and acceptable error scales. This approach involves reformulating the second law of thermodynamics in terms of an excess energy that vanishes at equilibrium instead of an entropy that assumes some unknown maximum value. Excess energy is defined mathematically as the total Legendre transform of energy with respect to an independent set of extensive variables. Excess energy is effectively the free energy functional of a nonequilibrium system and is a function of the time, distance, and acceptable error scales. Elimination of entropy from thermodynamics requires recognizing temperature as a thermal stress, proportional to the antimetric component of the stress tensor that is neglected when one assumes the validity of Cauchy's second law of motion. The inclusion of temperature as part of the stress-strain couple completes the science of thermomechanics and opens the way for a practical unification of chemistry and physics in strictly mechanical terms.The last sentence of the abstract shows how high the goals that Lindem meyer set for himself were. I personally do not agree with the idea that mechanics is the queen of all sciences, and that given deep enough probing one could achieve “a practical unification of chemistxy and physics in strictly mechanical terms”; for instance, electromagnetism has full citizenship's rights in physics, and it is hard to conceive that it could be reduced to mechanics.
    Type of Medium: Electronic Resource
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  • 16
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The interfacial strength of two paper-polypropylene-paper laminates used for electrical power transmission cable insulation has been measured using a peel test after a variety of conditionings that simulate the service thermal stress conditions. Immersion in dielectric oil at 23°C causes little decrease in peel strength, but heating in the oil at 90°C causes a rapid initial loss followed by a slow loss of strength. Cyclic and static heating show that cyclic fatigue is not a factor as the initial loss of strength occurs in a time comparable to the first two test cycles and further heating causes much less loss of strength. Tensile and compressive stresses resulting from cable winding have no effect on the loss of bond strength during heating in oil. Vacuum drying of the laminate and oil (as in cable manufacture) before heating results in less decrease in peel strength than heating without prior drying. Optical and electron microscopy show minimal wetting of the paper fibrils by the polypropylene with only a few having been either normal to or at a steep angle to the polypropylene surface. That is, the fibrils appear to be parallel to the interface and only partially immersed in the polypropylene. Micrographs show little, if any, differences between the interfaces on the two sides as well as little paper on the polypropylene after delamination and vice versa. It is suggested that the bonding mechanism is a combination of weak mechanical interlocking and secondary bonds. It is also suggested that swelling of the polypropylene relative to the paper by the dielectric oil at 90°C weakens the interfacial bond.
    Additional Material: 7 Ill.
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  • 17
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 290-300 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Variations of stress with temperature for stretched networks of trans-polyisoprene networks in the crystallization region are reported. Such profiles are characteristically U-shaped with the stress at lower temperatures often climbing to high levels. Valley widths of the profiles narrow as annealing temperature increases to about 50°C, then widen at yet higher temperatures. The degree of crystallization at 22°C is 37% and independent of deformation and annealing temperature. The β crystal form is overwhelmingly present with traces of other crystal forms appearing only at high deformations. The theory of stress-induced crystallization provides a good description of experimental results provided the nucleation parameter σ is dependent upon deformation. Therefore, the data provide good qualitative support for the theory in its current form.
    Additional Material: 15 Ill.
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  • 18
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Polyalkylenebenzoxazoles of high molecular weight (inherent viscosity values from 0.76 to 2.95) were prepared from 4,6-diaminoresorcinol dihydrochloride and aliphatic diacids in polyphosphoric acid by heating at 180 to 200°C for 3-5 h. Melting points of the polymers ranged from 148 to 423°C, depending on the length of the alkylene chain. Glass transition temperatures were relatively low, ranging from 50 to 100°C and did not show the pronounced odd/even effect noted for melting points. In all cases, rapid weight loss occurred above 400°C. No evidence for the formation of a molecular composite was observed in an attempt to prepare in situ a rod-like polybenzoxazole in a polyalkylenebenzoxazole.
    Additional Material: 2 Ill.
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  • 19
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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  • 20
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 93-101 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Low levels of oligomer molecules are generally desirable in polymeric materials. It is known that several reactor variables can affect the oligomer distribution, and therefore it is useful to have predictive models for molecular weight distribution. The normal approach of a differential equation-based model is very complex to set up if it is applied rigorously to include all the non-Flory aspects of the step growth polycondensation and in particular the interfacial polycarbonate polymerization. In this paper, simple methods based on the Monte Carlo method and Stockmayer distribution are applied to simulate the effects of mass-transfer, unequal reactivity, and the starting stoichiometry of the polycondensing functional groups on the oligomer distribution. It is shown that these parameters can have a significant effect on the oligomer weight distribution and polydispersity of the final polymer.
    Additional Material: 4 Ill.
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  • 21
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 308-317 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The true crystallite modulus of polyoxymethylene (POM) was evaluated experimentally and thoeretically as a function of temperature. The mechanical deformation mechanism of POM was lattice-dynamically predicted and confirmed by measuring the stress-induced vibrational frequency shifts of the infrared and Raman spectra, which were interpreted on the basis of anharmonic potential field.
    Additional Material: 11 Ill.
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  • 22
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 141-152 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The ultra-high strength/modulus, extended chain polyethylene fiber (Spectra® fiber) composite has shown great potential as a lightweight armor material with its extraordinary capability of absorbing the kinetic energy of projectiles. But the relatively low melting point of this fiber (∼ 145°C) has caused concerns regarding the effect of temperature rise during the impact/penetration process on the performance as armor material. In this article, an analysis of temperature rise in projectile and the fiber composite during the impact/penetration process is described. Combining the simulation of impact deformation by finite element analysis and the simulation of temperature rise by a finite difference approximation of the related dynamic equations, the temperature rise caused by the projectile/composite interaction was estimated. Results show that there is a significant temperature rise at the projectile/composite interface due to the friction but that the short length of time involved in the process and the low thermal conductivity of Spectra fiber composite keep the temperature rise in a very small region (in the order of 0.001 cm) around the interface during the impact/penetration process. Consequently, the volume that is affected by the temperature rise is very small, in the order of total 0.001 cm3 around the projectile, and this is too small to generate any detectable effect on the armor performance. After the projectile is stopped, however, substantial heating of fiber composite can occur under specific conditions as the result of heat flow from the hot projectile embedded in the composite. This heating of fibers, however, is a postmortem effect and hence inconsequential to the ballistic performance of the composite armor.
    Additional Material: 11 Ill.
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  • 23
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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  • 24
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 190-200 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A mathematical model of a polycondensation reactor that can be used in the final stage for poly(ethylene terephthalate) (PET) is established and compared with experimental data obtained from a laboratory scale reactor with film renewal. Detailed side reactions are considered along with the diffusional removal of the small molecules through thin film. Among several kinetic constants, the polycondensation reaction rate constant k1(= k8) and diester group degradation reaction rate constant k7 have an influence over the degree of polymerization. The values of k1(= k8) and k7 for 0.05 wt% Sb2O3 were obtained as curve-fit values: (1) k1(= k8) = 3.4 × 106 exp(- 18.500/RT′) (L/mol-min); (2) k7 = 1.3 × 1011 exp(- 37,800/RT′) (min-1). Effects of the film exposure time, reduced pressure of vacuum, temperature, the initial terephthalic acid (TPA)/ethylene glycol (EG) mole ratio, the initial degree of polymerization, and catalysts were well explained by the model.
    Additional Material: 12 Ill.
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  • 25
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 209-212 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Entrance pressure losses for the creeping flow of a power-law fluid are calculated for an abrupt contraction of ratio 2, 4, 8 and ∞ for both the axisymmetric and planar cases using P2P1 and P+2P1 finite elements. Contrary to some earlier findings in the literature, the entrance pressure loss obtained by using the two different types of finite elements, both of which satisfy the Babus̆ka-Brezzi condition, are found to converge to the same results. The present results also confirm that the variational method of Duda and Vrentas gives excellent upper bounds for both the axisymmetric and planar cases with infinite contraction ratio.
    Additional Material: 8 Ill.
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  • 26
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    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 405-413 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The curing of epoxy-amine polymer has been modeled by the reaction of functional groups, and the mole balance of these is governed by a set of six nonlinear differential equations. In this work, we have first developed a complete analytical solution for isothermal curing. For nonisothermal curing, we have divided the domain of hydroxyl group concentration β into small increments Δβ and adopted our analytical results for this domain. In addition, we solved the energy balance equation analytically and obtained the temperature rise for Δβ. We have compared our results with those obtained from the Runge Kutta numerical solutions. We have shown that our semianalytical technique is about a thousand times more efficient and faster.
    Additional Material: 4 Ill.
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  • 27
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 513-518 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A shear test is proposed as a complement to the tensile test in order to characterize the short time mechanical behavior of thermoplastic polymers. The proposed test geometry makes the test easy to perform and to evaluate and gives relevant information about anisotropy, plastic deformation, crack initiation, and propagation properties. Three different materials have been tested and the results are discussed.
    Additional Material: 5 Ill.
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  • 28
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 500-506 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Material property models for poly(etheretherketone) (PEEK) have been combined with a residual stress model to provide a means for investigating the effect of crystallization process on the residual stress development in semicrystalline materials. The analysis shows that crystallization causes an increase in the residual stress levels. This increase is affected through an increase in the resin modulus values and through the resin modulus build-up at higher temperatures. The shrinkage due to crystallization was found to have no effect on the residual stress development in neat PEEK.
    Additional Material: 13 Ill.
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  • 29
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Temperature sweeps of dynamic viscoelastic properties have shown that phydroxybenzoic acid (PHB)-based liquid crystalline polyesters, specifically in this case those copolymerized with poly(ethylene terephthalate) (PET), can be subjected to considerable supercooling if initial heating curves are compared to subsequent cooling curves, indicating that this type of material can be in quite different states even at the same temperature, depending on thermal history. Utilizing this supercooling behavior, viscoelastic properties of a 60 mol% PHB/40 mol% PET material produced by Unitika were monitored before and, particularly, after large-scale shear deformation to determine how potential structure changes induced by the shear are reflected in viscoelastic properties immediately, and with time. According to dynamic viscoelastic temperature sweep data four quite different initial states were employed including conditions with, as well as largely free of, crystallites. However, in all cases, post-shear monitoring showed decreased G′ and G″ values with almost no evidence of return towards initial values within approximately 25 min. These results, in addition to furthering somewhat the fundamental understanding of the flow and relaxation properties of liquid crystalline polymers, may be useful in polymer processing, where large-scale shear deformations employed in forming processes appear to be capable of changing considerably the subsequent behavior of such materials.
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  • 30
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 507-512 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A thermodynamic model was proposed to correlate the phase behavior of a swelling polymeric gel (vinyl alcohol-sodium acrylate copolymer) and the volume phase transition in alcohol (methanol, ethanol or propanol)-water solutions. The model is based on the Flory-Huggins formula for polymer solution coupled with the osmotic pressure by rubber elasticity proposed by Flory. The volume change behavior and the equilibrium concentrations inside and outside the gel were successfully correlated using the present model.
    Additional Material: 5 Ill.
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  • 31
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 528-531 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Terpolymerization was investigated by dilatometry for zincacrylate (ZnA2), acrylonitrile (AN), and styrene (St), radically initiated by a As2S3-styrene complex (I) in dimethyl sulphoxide (DMSO), at 90 ± 0.1°C for 1 h under inert atmosphere. The system follows non-ideal kinetics, due to primary radical termination as well as a degradative chain transfer reaction. The kinetic expression for the system is Rpα(I)0.27 (St)0.31 (AN) 0.22[ZnA2]0.12. The value for the activation energy and kp2/kt are 55 kJ mol-1 and 1.87 × 10-7 1 mol-1 s-1 respectively. The terpolymer has been characterized by IR and NMR spectroscopy. The thermal stability and solubility of the terpolymer have also been studied.
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  • 32
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 33
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 551-558 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The intermeshing counterrotating twin screw extruder is widely used for compounding, devolatilization, blending, and reactive extrusion. A fluid dynamics analysis package-FIDAP, using the finite element method, was implemented to simulate the 3-D flow patterns in the region of conveying elements and shearing discs of a Leistritz LSM30.34 twin screw extruder. The rheological behavior of the fluid was described by a power law model. The flow fields were characterized in terms of velocity profiles, pressure distributions, shear stresses generated, and a parameter λ quantifying the elongational flow components. The influence of screw rotational speed and axial pressure difference on the flow characteristics was also analyzed. A comparison between the flow characteristics in the shearing discs operated in a corotating or counterrotating mode was also presented.
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  • 34
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 532-540 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A model for the phase distribution and evolution of the heterogeneous (suspension) polymerization of vinyl chloride is presented. Experimental information on pressure, temperature, and conversion has been obtained from a 34 liter bench reactor reproducing reaction conditions and product properties typical of industrial operation. A calculation procedure based on simple plant data is proposed for the description of the phase compositions and their evolution over the entire process. Results based on classical Flory-Huggins theory of solutions are presented and compared with existing data.
    Additional Material: 14 Ill.
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  • 35
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 559-569 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A mathematical model is presented for the computer simulation of multilayer flow of polymer melts in coexitrusion. The proposed model can handle an arbitrary number of layers. The viscosity of each layer is shear-rate and temperature dependent. Given the material properties, die dimensions, and process conditions, the model determines the flow field throughout the die gap. Computer simulations and experimental data are presented for a three-layer polyester/EVA/polyester film coextrusion, with emphasis on the interfacial instability and its effects on optical properties of the film. The rsults are discussed in the context of the critical interfacial shear stress criterion that has been proposed by Schrenk, et al. (1) for the onset of interfacial instability. It appears that elasticity differences between layers contribute to the interfacial instability. It is conjectured that minimizing interfacial shear stress and matching elasticities of adjacent layers is an appropriate criterion in coextrusion analysis.
    Additional Material: 13 Ill.
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  • 36
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 541-550 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A simple unified lubrication approach has been proposed to design a coat-hanger die that can deliver wide and uniform liquid sheets. This approach requires that the wall stress in the manifold be constant. With this constraint, any inelastic non-Newtonian fluid model can be used to describe the liquid motion inside the die. Fluid models that can represent the pseudoplastic or viscoplastic behavior of polymeric liquids have been selected for illustration. A general equation that can be solved to determine the effect of production variations on flow uniformity inside the die has also been derived.
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  • 37
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 570-579 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In this paper we address the aspects associated with shear modification of low density polyethylene by extrusion. By successive passes of the polymer through an extruder it can be shown that both the melt viscosity and melt elasticity are reduced by shear modification. These reversible variations are not accompanied by significant changes in molecular weight distribution. The major effects of extrusion are to decrease the amount of elastically effecitve material. Study of proton relaxation times at 150°C shows that the melt comprises regions of relatively ordered, entangled, and unentangled polymer. Shearing reduces the proportion of more ordered material. The elastically effective anchors that are reduced by shearing are regions with restricted segmental mobility rather than conventional entanglements or intermolecular knots. Successive extrusions produce a relatively small decrease in the number of such constraints to molecular motion. Repeated shearing has a diminishing effect on the proportion of more ordered material in the polyethlene melt. This parallels observations of the effects of repeated shear modification on the properties of polyethylene films and other extrudates.
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  • 38
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 585-597 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper presents the design and analysis of a process control strategy for a reactive extrusion polypropylene degradation process. The primary control objective is to continuously produce polypropylene with desired properties (viscosity) despite variations in the properties of the feed material. The viscosity of the polypropylene, measured using an In-line Wedge Rheometer, is controlled by manipulating the feed concentration of the peroxide which acts as the initiator for the degradation reaction. An empirical model of the reactive degradation process is developed which describes the process dynamics and the characteristic process disturbances. Minimum variance (MV), constrained minimum variance (CMV), and pole placement (PP) controllers are first evaluated and compared in simulation. Then, a pole placement controller is implemented on the actual reactive extrusion process, with results being presented for the response of the controlled process to load disturbances due to feed material changes.
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  • 39
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 40
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 580-584 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A sliding plate rheometer has been developed to measure the normal thrust of a molten plastic in large amplitude oscillatory shear. The normal thrust of a molten plastic in large amplitude oscillatory shear is a significant nonlinear effect that has previously been unobtainable. Normal thrust measurements may now be used to help understand and characterize nonlinear viscoelastic behavior inherent in most molten plastics. The new rhemoeter incorporates a piezoelectric pressure transducer in a very stiff plate that minimizes compliance. Normal thrust measurements with cone and plate rheometers are made by measuring the total force on the plate (or cone) and are subject to error due to edge effects. The new rheometer measures the local pressure in the sample and is therefore unaffected by sample size or edge effects. Normal thrust measurements in large amplitude oscillatory shear are reported for both molten Phillips TR480 high density polyethylene pipe resin which contains 2% by weight of carbon black filler and IUPAC LDPE X. Crosstalk due to shear stress on the active face of the pressure transducer causes signal error which for oscillatory shear is filtered out using a discrete Fourier transform.
    Additional Material: 7 Ill.
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  • 41
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 613-624 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: At 75/25 concentration ratio, bisphenol a polycarbonate (PC)/styreneacry-lonitrile copolymer (SAN) blend has poor impact resistance compared to PC/ABS. A rubber phase methacrylate-butadiene-styrene (MBS) of core/shell type was dispersed in PC/SAN blend. The morphology of the unmodified and modified blend was investigated. The influence of the acrylonitrile ratio in the SAN on the microstructure was studied. It clearly shows that core/shell resides at the interface between PC and SAN. It seems that core/shell particles enhance the adhesion between the different phases. Their presence influences the interface mobility; i.e., the coalescence of the dispersed phase observed in pure PC/SAN is considerably reduced when the MBS particles are added. The impact resistance of the samples was correlated with the morphology.
    Additional Material: 14 Ill.
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  • 42
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    Polymer Engineering and Science 34 (1994), S. 598-612 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper presents the development of a model for free radical initiated polypropylene degradation during reactive extrusion that combines a kinetic model of the polypropylene degradation reaction with a simplified model of the melting mechanism in the extruder. The free radical initiated degradation of polypropylene is characterized by a narrowing of the molecular weight distribution (MWD) and a decrease in the molecular weight averages. A high temperature SEC is used to determine MWD's for three different commercially available polypropylenes degraded at various initiator concentrations in a 1.5 inch single screw extruder (L/D = 24:1). The predictions of the kinetic model alone and the combined kinetic-melting model are compared with the experimentally determined MWD's and molecular weight averages for the degraded polypropylenes. The predictions of a modified kinetic model that includes the possibility of termination by combination are also examined. The kinetic-melting model is found to provide significantly improved predictions of the experimentally determined MWD's and molecular weight averages in comparison to the original kinetic model. A viscosity-molecular weight relationship is also developed, which is then used to determine the gain of the degradation process as a function of the initiator concentration from the molecular weight averages predicted by the kinetic-melting model. Earlier work has shown such prior knowledge of the process gain can be used to significantly improve the performance of process control schemes for the degradation process.
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  • 43
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    Polymer Engineering and Science 34 (1994), S. 625-631 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The curing and vitrification effect during the reaction of ATBN modified epoxy resin was studied through the dynamic differential scanning calorimetry method and a new reaction kinetic equation containing generalized WLF equation was developed to describe the reaction rate at both glassy and rubbery state. An autocatalytic mechanism was found to describe adequately the cure kinetics of the rubber modified epoxy resin and the overall order of reaction was assumed to be 2. The kinetic parameters were determined from the DSC data through the Marquardt's multivariable nonlinear regression method and Runge-Kutta integration technique. The presence of rubber indicated minor effect on the cure kinetics of epoxy resin. The Arrhenius type viscosity function was employed to establish a relationship between viscosity data measured by RMS and chemical conversion calculated from the reaction kinetic equation.
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  • 44
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    Polymer Engineering and Science 34 (1994), S. 642-649 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Polyurethane foam formation involves both polymerization and expansion processes. The dynamics of the water and R-11 blown foams depend on the rates of chemical and physical blowing processes, along with the rate of viscosity increase of the reacting mixture. Experiments were carried out to study the dynamics of free rising, water and R-11 blown rigid polyurethane foams. The density and temperature change during the foam formation were monitored. A theoretical model was developed to predict the density and temperature variation with time. In the model, the physical blowing agent (R-11) evaporation process is assumed to be heat generation-controlled and the carbon dioxide generation process to be controlled by the rate of the water-isocyanate reaction. The kinetic parameters of the reactions of isocyanate with polyol and water were obtained separately and were asssumed to be independent of each other. The water-isocyanate reaction appears to follow first-order kinetics with respect to concentration of water. The theoretical predictions of the model show good agreement with the experimental data for density variation with time. The model predictions for temperature rise also match experimental data, except at the later stages of foaming when it is found to be slower than the experimental measurements. However, this deviation does not affect the dynamics of density change since it occurs after the completion of the expansion process.
    Additional Material: 7 Ill.
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  • 45
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 657-664 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A good extrusion die must distribute the polymer melt in the flow channel such that the material exits from the die with a uniform velocity and temperature. Coathanger dies are commonly used for the extrusion of plastic sheets and films. The die is usually provided with a straining bar allowing a regulation of the flowrate in the case of a poor design. But this, in turn, can affect temperature uniformity. Therefore, the design of coathanger die is a complex task which is mainly accomplished by trial and error in industry. Analyses of the flow in coathanger dies have been reported in the literature. Analytical and numerical approaches are used to solve this problem. The first one involves many simplifying assumptions: the most important ones being the unidirectional and isothermal flow of the polymer. Most numerical methods deal with a 2-D geometry, but only a few of them have considered the non-isothermal flow. A new model has been developed using a modified FAN method (Flow Analysis Network introduced by Tadmor) for the calculation of the 2-D flow, coupled with a finite-difference scheme for the calculation of temperature. The overall model can run on a PC with only a few minutes of calculation. Good agreement was obtained between experimental data and simulations.
    Additional Material: 16 Ill.
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  • 46
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 650-656 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A new finite element model named Corrected Slice Method (CSM) has been developed to cope with three-dimensional vacuum cooling calibrator problems. Such problems appear whenever the cooling channel lay-out comprises transverse channels in the calibrator. The CSM is an extension of the 2D approach (8), which takes into account the axial heat fluxes within the calibrator. The proposed model was validated by comparing the numerical results obtained on a test problem with a rigorous finite element approach. Moreover, a real complex profile-calibrator system was simulated in order to illustrate the full performance of the porposed method.
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  • 47
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 665-670 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The use of bend testers for the determination of critical strains in the study of environmental stress cracking has been assessed. Using the combination of polystyrene in ethanol, various factors affecting the measurement of critical strains were investigated, including the strain applied during the bend testing, the time of immersion in the liquid prior to straining, the surface finish, and the extent of physical aging. It was concluded that the best determination of critical strain is the strain at which a sample just shows signs of crazing, rather than the strain at the outer edge of a band of crazes. The measured value of critical strain increases with increased prior immersion time, decreased surface roughness, and decreased physical aging time. Reasons for these variations are discussed. It is concluded that although the use of bend testers is valuable for qualitative testing, careful testing methodologies need to be adopted for it to be a useful quantitative test.
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  • 48
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 632-641 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The dynamics of R-11 blown polyurethane foam formation depend on the rates of viscosity increase of the reacting mixture and R-11 evaporation, and both are controlled by the polymerization process. Detailed experiments were carried out to study the dynamics of foaming and the measurements made included the cream and rise times, the density change of the expanding foam with time, and the temperature rise during reaction. Dynamic temperature measurements at different points in the foaming mixture were also made to study the spatial variation of the temperature in the foam. The experimental results showed the rate of foaming, the final density, and the maximum temperature decreased with increasing R-11 concentration. The heat losses from the foam were also found to be significant towards the later stages of foaming when density was low. Theoretical models were developed to predict the temperature and density change with time and spatial variation of temperature in the foam due to heat losses, by considering the foaming dynamics to be either heat generation controlled or heat and mass transfer controlled. In the former, the foam was assumed to be a pseudohomogeneous phase and the approach was similar to that of Rojas, et al. (5). New features accounted for in the model were dilution of the reactant concentration due to the presence of liquid blowing agent and heat loss from the foam due to radiation. While excellent agreement between theoretical predictions and experimental results was obtained for temperature variation with time at different locations in the foam, the model gave a much sharper reduction in density with time as compared to the experimental data. In the second model, the rate of foaming was assumed to be controlled by the rate of heat and mass transfer to a single bubble in the foam. Assuming a film model for heat and mass transfer, the theoretical predictions for both temperature and density were found to be in very good agreement with experimental data.
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  • 49
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    Polymer Engineering and Science 34 (1994), S. 821-826 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: When diffusion coefficients are measured with the cup method, the exposed area is often less than the area of the sample. Because of this masking effect the measured diffusion coefficient is overestimated. The present article presents simple formulas based on two-dimensional analytical solutions to correct for this in cylindrical cup samples. Different cases of anisotropical diffusion are dealt with. The error in the analytical solutions is determined by numerical computer simulations.
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  • 50
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    Polymer Engineering and Science 34 (1994), S. 815-820 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A comparative study of warpage, global shrinkage, and residual quench stresses developed in rotational molding is made for a series of thermoplastics including various polythylenes, polypropylene, polyamide-6, polycarbonate, and polystyrene. The influence of rate of quench on uniaxial stress strain and impact behavior of rotomolded parts was also studied. Generally, warpage, global shrinkage, and residual stresses increase with increasing quench rate for all the polymers. Further, the levels of warpage and global shrinkage increases with extent of crystallization, i.e., products from glassy polymers exhibit little warpage and those from highly crystalline polymers are highly warped. Increasing rate of quench tends to increase elongation to break and impact strength.
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  • 51
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 799-803 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Measurements of melt strength and breaking stretching ratio of several blends of thermoplastic polymers with liquid crystalline polymers are presented. The melt strength behavior depends not only on the viscosity of the blends but also on the temperature dependence of the viscosity. In particular, even if the viscosities of the blends are, at the extrusion temperature, lower than that of the thermoplastic matrices, the melt strength can be larger than that of the pure thermoplastics if its viscosity-temperature curve exceeds that of the matrices far from the solidification temperature. This behavior allows one to spin or film blow these blends despite the low viscosity.
    Additional Material: 9 Ill.
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  • 52
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 804-814 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A mathematical model of the high pressure polymerization of ethylene in tubular reactors was tested with experimental data obtained from an industrial size tubular reactor. Series of experiments involving changes in operating conditions were carried out, and process data and polyethylene samples were collected. The collected samples were characterized for their molecular weight distributions and various rheological material functions involving shear and extensional flows. The findings of the model were compared against the generated process data and the molecular weight distributions of the samples. The determined rheological behavior exhibited strong dependence on the primary characteristics of the resins. Overall, this study should introduce a better understanding of the interactions between high pressure reaction conditions and the primary properties of polyethylene, including moments of molecular weight distribution and extent of branching on one hand and the interrelationships between primary properties and the rheological behavior of the high pressure polyethylene product on the other hand.
    Additional Material: 11 Ill.
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  • 53
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 827-834 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The Galerkin finite element method has been applied to study the three-dimensional flow field of power-law fluids inside an extrusion die. Two inlet designs, i.e., center-fed and end-fed, have been considered. The effects of inertial force as represented by the Reynolds number Re, inlet geometry, and the power-law index n on lateral flow uniformity and vortex formation in the entrance region have been examined. A flow visualization technique has been carried out to experimentally verify the theoretical prediction of the three-dimensional flow field inside a die. It has been found that increasing Re or decreasing n will deteriorate flow uniformity. Depending on the direction of the inlet jet stream, the inertial force may create a flow peak in the central region of a center-fed die, or the maximum flow rate will appear close to the end of the die for an end-fed die. For highly shear-thinning fluids, lower flow rates are always observed close to the end of the dies. It is concluded that creating a plug flow in the inlet tube of the extrusion die is advantageous for both center-fed and end-fed designs.
    Additional Material: 13 Ill.
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  • 54
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 835-846 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A two-phase model is presented for simulating the post-filling stage of injection molding of amorphous and semicrystalline materials. A finite-element scheme with quadratic shape function for the pressure is proposed. The melt is considered in terms of Hele-Shaw flow for a non-Newtonian fluid using a modified-Cross model with either an Arrhenius-type or WLF-type functional form to describe the viscosity under nonisothermal conditions; the compressible behavior of the polymer is assumed to obey either a double-domain Tait or single-domain Spencer Gilmore equation of state. The interfacial energy balance equation including the latent-heat effect for semicrystalline materials is coupled with the transient energy equation for the solid and melt phases in order to predict the solidified layer and temperature profile. Two well-characterized materials, namely a commercial-grade PP and PS, were used in the present work. Good agreement is obtained between the present simulation and experimental pressure traces from this study and from previous investigation in the literature. The effects of compressibility, viscosity model, and thermal properties upon the predicted pressure field are also considered.
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  • 55
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 56
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 57
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 1148-1156 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: We have generated microcellular polymeric foam structures using a pressure induced phase separation in concentrated mixtures of supercritical CO2 and poly(methyl methacrylate). The process typically generates a microcellular core structure encased by a nonporous skin, the thickness of which decreases with increasing saturation pressure. This trend can be described by a model for skin formation that is based on the diffusion rate of gas out of the sample. Significant density reductions on the order of 30 to 70% can be achieved by changing the pressure and temperature conditions in the foaming process. There are several ways in which the saturation pressure affects the average cell size, with the net effect that cell size decreases sharply with increasing pressure above 2000 psi, leveling out at higher pressures. Cell size increases with increasing temperature from 40°C to 70°C. A model for cell growth, based on a cell model of Aremanesh and Advani, modified to include the effect of CO2 on model parameters, reproduces these trends.
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  • 58
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 1161-1172 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Multiobjective dynamic optimization has been carried out on a nonvaporizing nylon 6 batch reactor. Three objective functions have been identified, viz., minimization of the concentration of unreacted monomer in the product, minimization of the dimer concentration, and minimization of the reaction time, for producing polymer having a specified value, μn, d, of the number average chain length. Two problems have been studied in this paper, each consisting of two objective functions taken from the above set. Pareto solutions have been generated using an algorithm based on Pontryagin's minimum principle and the method of Lagrangian multipliers. The effects of various physical and computational parameters have been studied, and methods have been developed to overcome the numerical difficulties that arise during the solution. The Pareto sets so generated can be coupled with the surrogate worth trade-off (SWT) method, which facilitates interaction with a decision maker (DM). The optimal temperature histories obtained for the two problems studied are quite different and suggest that one must solve the three-dimensional problem in which the vector objective function incorporates all three objective functions. Results from the present study could be used as starting guesses to converge rapidly on the solution of the three-dimensional problem.
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  • 59
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 1187-1195 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The entrance pressure drop during extrusion cooking of corn grits was measured using a cylindrical die viscometer attached to a single screw extruder and compared with results obtained using low-density polyethylene (LDPE). The cylindrical die viscometer had a length to diameter ratio of 40 with half-entry angles of 30, 37.5, 45 and 90° with the horizontal. The entrance pressure drop at the die was measured as a function of extrusion temperature, product moisture content and the die entry angle. Results indicate that the flow behavior of corn grits and the entrance pressure drop were affected by product moisture content, process temperature and the shear history in the extruder. Entrance pressure drop also increased with wall shear stress for plastic melt, but for food biopolymer, the increase was observed provided shear history effects were minimized. Entrance correction increased with apparent shear rate for LDPE, but the reverse was true for corn meal. Using Cogswell's analysis, corn grits exhibit severe extension thinning behavior in entry flow.
    Additional Material: 13 Ill.
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  • 60
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    Polymer Engineering and Science 34 (1994), S. 1173-1186 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Guidelines are developed for molding large composite parts via structural reaction injection molding using glass preforms and polyisocyanurate resins. These are based on numerical simulations of the simultaneous heat transfer and reaction kinetics of a commercial system during and after mold filling. Premised requirements are that resin does not gel before the mold is filled, yet, reactions are sufficiently vigorous to approach completion. An existing mechanistic kinetic model is used and material parameters found from a chemical kinetics study employing an insulated cup. It is found desirable to use a high mold temperature and a low preform temperature in molding. Nondimensionalization of the governing equations reveals the existence of a Nusselt number (Nu), which describes the relative importance of heat transfer between resin and glass relative to thermal diffusion to the mold wall. With a Nusselt number of about 50 or higher it is possible to use the cooling capacity of the preform to extend gel time. The magnitude of Nu is influenced by part thickness, glass fraction, strand diameter, and flow velocity. Thus, the effect of the preform on extending resin gel time is within control of the molder.
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  • 61
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    Polymer Engineering and Science 34 (1994), S. 1196-1201 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A detailed study of the effect of several extrusion variables was made on the rheological and thermal properties of Delrin II acetal homopolymer and Zytel 42 polyamide 66 materials. A 63.5 mm Davis Standard extruder was used to measure the effect of screw design, screw rpm, die and head pressure, and melt temperature on the rheology of acetal and nylon 66 resins. A single stage metering screw was used to determine the effect of screw geometry and viscous heating on the melt viscosity breakdown and the rate of degradation of each polymer. The melt temperature was measured in the melt stream in the channel and correlations are shown between ideal melt temperature predicted from the rheology data and the actual loss of properties of each polymer due to viscous heating. The paper also discusses how to measure the melt temperature accurately in extrusion, and to use it as a key indicator to optimize the extrusion process, and to control the rheology, thermal stability, and the molecular weight of a polymer during processing.
    Additional Material: 10 Ill.
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  • 62
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    Polymer Engineering and Science 34 (1994), S. 1202-1210 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In this article, we investigate the effect of weld lines on the tensile mechanical properties of unmodified and copolymer modified high density polyethylene (HDPE) and polystyrene (PS) blends. The homopolymers were melt blended in the proportion of 20 wt% HDPE and 80 wt% PS using a twin screw extruder at a temperature of 200°C. The results show that the mechanical properties are generally lower when weld lines are present. The decrease of the mechanical properties is much more pronounced for the blends. The addition of small amounts of a commercial styrene/butadiene copolymer significantly improves the strength and the elongation at break of this blend. An optimum copolymer concentration was observed at 3 wt%. This value coincides with the interphase saturation concentration of the copolymer obtained from the analysis of the DMTA (dynamic mechanical and thermal) properties of the blends. The copolymer was also found to induce important changes in the morphology of the blend. The interdiffusion of the polymer fronts in the weld region was also improved by the presence of the copolymer. It is believed that these two aspects contribute to the enhanced properties obtained with copolymer modified blends in presence of weld lines. An important effect of the injection temperature on the tensile strength and the elongation at break of welded samples with copolymer modified blends was observed. The effect of mold temperature on these properties was less important mainly at low injection temperatures. Only a slight effect of these two parameters was observed for the tensile modulus in the range of mold and injection temperatures considered in this study.
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  • 63
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    Polymer Engineering and Science 34 (1994), S. 1211-1218 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In injection molding of substrates for optical discs, precise transcription of pits and grooves is very important. For high-density optical discs, molding transcription for minute grooves with widths on the sub-micron level is required. In this paper, in order to clarify the relationship between molding conditions and transcription quantitatively, transcription of minute rectangular grooves (width 0.55 μm, depth 70 nm) in injection molding of polycarbonate resin was studied. The relationship between molding conditions and the transcription heights was verified. And, by introducing the equivalent thickness of the vitrified layer concept, a transcription model related to the minute groove width is proposed. This equivalent thickness of the vitrified layer is estimated to be 100 to 150 nm at the point of filling completion under a certain molding condition. Also, using the above description of the equivalent thickness of the vitrified layer, it is possible to estimate the extent of transcription under the various molding conditions.
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  • 64
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 65
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    Polymer Engineering and Science 34 (1994), S. 1224-1230 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The cavity transfer mixer (CTM) was primarily designed as a distributive mixing device to be used as an add-on unit to existing extruders. In determining the CTM overall mixing efficiency as well as its potential use for various applications, the flow patterns/characteristics within this mixer must be well understood. In this work, a fluid dynamics analysis package, FIDAP, based on the finite element method was employed to simulate the flow patterns in a CTM with 6 rows and 4 cavities per row. A 3D, isothermal flow analysis was carried out and the fluid of choice was a flexible polyvinylchloride whose rheological behavior is described by a power-law model fluid. The flow field was characterized in terms of velocity profiles, pressure distributions, shear rates/shear stresses generated and a parameter λ quantifying the elongational flow components. The results of the flow simulations were compared with experimental data. The CTM potential use for dispersive mixing was discussed.
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  • 66
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    Polymer Engineering and Science 34 (1994), S. 929-936 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Moldability diagrams for the filling and curing stages of a dicyclopentadiene (DCPD) based reaction injection molding (RIM) system were established based on a simplified engineering approach. Initial monomer temperature and filling time are the critical parameters for the filling stage whereas in the curing stage, mold wall temperature and demold time proved to be the main processing variables. The physical and thermal properties of the molded samples were examined and the results indicate that such simplified moldability diagrams are sufficiently accurate to establish the processing conditions for the system under investigation.
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  • 67
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    Polymer Engineering and Science 34 (1994), S. 913-920 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Anisotropy and molecular orientation are well known phenomena in the field of thermoplastics, but only a few studies have described anisotropy in rubber materials. It has been shown that injection molding gives rise to a higher degree of anisotropy than compression molding. The anisotropy in the rubber material was strengthened by carbon black and is presumably due to molecular orientation. This paper describes the anisotropy of injection-molded ethylene-propylene-diene rubbers. The two polymers had different molecular weight distributions and thus different rheological properties. The compounds were injected into center-gated 4mm thick disks. The disks were subsequently split into three layers using a water-jet cutting technique. Measurement of mechanical and swelling properties in the different layers and directions showed that the anisotropy varied through the thickness of the disk. By X-ray scattering it was shown that rubber molecules had a preferred direction and thus, that the anisotropy was probably predominantly due to molecular orientation created during the mold filling.
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  • 68
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    Polymer Engineering and Science 34 (1994), S. 958-964 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Measurements are reported for air drag on fine filaments whose axes are oriented at oblique and normal angles to the air velocity. In terms of the drag coefficient CDN the data are fit well by the following relation: CDN = 6.96(ReDN)-0.440(d/d0)0.404, where ReDN is the Reynolds number based on flow normal to the fiber axis, and d/d0 is a dimensionless fiber diameter. A wide range of conditions were tested: filament diameters ranged from 13 to 390 microns, gas velocities ranged from 22 to 83 m/s, and fiber Reynolds numbers ranged from 29 to 2120.
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  • 69
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    Polymer Engineering and Science 34 (1994), S. 981-985 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Compounds based on poly(vinyl chloride) (PVC), and containing CaCO3 filler and trifunctional acrylic crosslinking agent have been crosslinked by exposure to γ-rays at dosages to 70 kGy. The crosslinking agent was found to be essential for crosslinking to proceed, only minor sensitivity to the irradiation having been found in compounds omitting the chemical. The presence of filler somewhat inhibits crosslink effectiveness, as measured by solvent uptake data. Elastic moduli and elongations at rupture respond to crosslinking processes, the latter being particularly sensitive to the effects of irradiation. The presence of filler was found to raise modulus, while ductilities of compounds were greater than expected, owing to adhesion at polymer/filler interfaces. Favorable acid/base interaction forces appear responsible for the effect. The reduced sensitivity of filled PVC compounds to γ-ray exposure is attributed to polymer immobilization, the consequence of strong interfacial bonding with the filler.
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  • 70
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    Polymer Engineering and Science 34 (1994), S. 975-980 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The relationship between spinnability and composition of poly(vinyl alcohol)/polyacrylonitrile block copolymer emulsions prepared by an ultrasonic technique is presented. Theoretical analysis and experimental investigation by multiple techniques show that the micellar structure characteristics of the block copolymer emulsions and the behavior of emulsion in shear flowing and coagulating in spinning process are the key factors affecting the spinnability. The mechanical properties of the final fibers are related to the composition, molecular weight, spinnability of the copolymers, and the processability of the as-spun fibers.
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  • 71
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    Polymer Engineering and Science 34 (1994), S. 986-994 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The flow analysis network (FAN) method was modified to analyze the flow of poly(methyl methacrylate) (PMMA) in a model counter-rotating nonintermeshing screw extruder. The numerical prediction of the pressure profiles was compared with the experimental results. Flow patterns in the screw elements of the model counter-rotating nonintermeshing twin screw extruder were also predicted. A new flow path method was developed to calculate the residence time distribution. This result will be applied to analyze the flow during the reaction in the model twin screw extruder.
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  • 72
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    Polymer Engineering and Science 34 (1994), S. 1005-1010 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Brittle isotactic polystyrene has been toughened by the presence of emulsified rubber particles. Semicrystalline diblock copolymers of isotactic polystyrene and polybutadiene functioned successfully as emulsifying agents, as revealed by the results of scanning and transmission electron microscopy. Semiquantitative measures of the toughness of the various materials were obtained via a home-built micromechanical testing device. The minimum amount of copolymer required to achieve emulsified morphologies and significant toughness depended on the thermal history of the material being tested.
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  • 73
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    Polymer Engineering and Science 34 (1994), S. 1319-1326 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Stress-relaxation behavior is studied in polypropylene samples subjected to different cyclic preloadings and to simple tension. The relaxation tests are performed under different sets of strain amplitude, number of cycles, and strain rate, using a closed-loop, electrohydraulic, servocontrolled testing machine. The calculated stress-strain curves are determined from a constitutive equation based on an overstress theory in which an equilibrium stress and a viscosity function are treated. The calculated results agree well with the experimental ones. It is concluded that the overstress theory explains the nonlinear viscoelastic-plastic behavior of polypropylene.
    Additional Material: 14 Ill.
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  • 74
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In this work we report the effects of single stage zone drawing on the properties of NEW-TPI thermoplastic polyimide homopolymer, and its blends with Amoco's Xydar liquid crystalline polymer. Zone drawing was performed first on homopolymer NEW-TPI films to determine the effect of load weight, heater speed, and drawing temperature on the attainable draw ratio. Degree of crystallinity and chain orientation increase as the draw ratio increases for NEW-TPI. Blends of NEW-TPI/Xydar compositions 90/10 and 70/30 were studied next. In blends, the Xydar component is not molecularly dispersed, and is initially preferentially oriented along the machine direction during the film processing stage. Xydar acts as a nucleation site and lowers the temperature for crystallization of the NEW-TPI from the rubbery amorphous state. Zone drawing was performed either parallel or perpendicular to Xydar's initial preferred orientation direction. Blends with lower Xydar fraction could be zone-drawn to higher ratios. Zone drawing perpendicular to Xydar's initial orientation direction also resulted in increased draw ratio. Dynamic mechanical properties of the zone drawn materials were studied. In homopolymer NEW-TPI, dynamic modulus increased by a factor of two to 4.0 GPa in zone drawn films, largely as a result of the formation of oriented crystallites. In the blends, the modulus parallel to Xydar's initial orientation direction was greater than that in the transverse direction. Depending upon composition and test direction, zone drawing increased the dynamic moduli of the blends from 1.5 up to 2.7 times, in the temperature range from 150°C to 300°C.
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  • 75
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    Polymer Engineering and Science 34 (1994), S. 1327-1335 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The molecular orientation and disclination defects in injection molded bulk samples of liquid crystal polymers have been revealed by transmission electron microscopy (TEM). Using a recently optimized lamellar decoration and etch technique for use with poly(benzoate-co-naphthoate), we have studied in detail the skin-core morphology produced by realistic injection molding processing. In the skin, the director is observed to be highly aligned along the flow direction, and the defect density is very low (10 cm-2). In the core, however, the defect density is six orders of magnitude greater, and the director lies predominantly in the plane defined by the flow and neutral directions. The flow during processing is turbulent, giving rise to distinct morphological features and disclination clusters. When the material is filled at 20% volume fraction with long glass fibers, the molecular and filler orientations are nearly parallel. Dimensional precision also correlates with the morphology and improves with increasing core fraction.
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  • 76
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 1305-1313 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Comb-shaped graft polymers were synthesized and complexed with a LiCF3SO3 salt to form a new class of polymer electrolytes. The polymers based on an acrylonitrile-butadiene copolymer (NBR) have pendant, short-chain poly(ethylene oxide) (PEO) grafted onto a butadiene unit. The characteristics of these polymer electrolytes were investigated in terms of number of pendant EO groups and grafting degree in the graft copolymer. The maximum conductivity was observed at the optimum side PEO chain length, and the PEO chain length for the maximum conductivity decreased with an increase in the grafting degree. And a solid 7Li NMR relaxation technique was used to study the local environments and dynamics of the ions in the polymer electrolytes. The maximum conductivity value obtained from our study was three orders of magnitude higher than that of classical PEO-based electrolytes at ambient temperature. These improved low temperature conducting polymers with higher relative mechanical strength are expected to be suitable for practical applications, such as in rechargeable lithium batteries or electrochromic devices.
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  • 77
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 1336-1345 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Injection molded samples of binary blends of Vectra (LCP) and the three amorphous polymers polyethersulfone (PES), polycarbonate (PC), and aromatic poly(ester carbonate) (APEC) have been subjected to morphological and rheological characterization, and coefficients of linear thermal expansion and Young's moduli have been determined. The Young's modulus of the PES/LCP blends exhibited a near lower-bound behavior that could be predicted by the one-adjustable-parameter equations of Halpin-Tsai (ζ = 0.18) and Takayanaga (b = 0.23), whereas the coefficients of linear thermal expansion followed the Takayanaga equation with a value of b = 0.50. The chain orientation of the LCP component was essentially constant in all PES/LCP blends with a Herman's orientation parameter of 0.39 ± 0.03. Transesterification reactions led to randomization of the constituents of the PC/LCP and APEC/LCP blends. The effect was more pronounced in the PC/LCP blends. The introduction of the LCP into the PC/LCP blends led to no reduction in melt viscosity and no self-reinforcement. APEC/LCP exhibited self-reinforcement in blends with a content greater than 27 vol% LCP, and especially the blend with 67 vol% LCP. The self-reinforcement was caused by the presence of an oriented LCP phase, confirmed by X-ray diffraction, and by improved interfacial bonding, presumably resulting from the transesterification reactions occurring at the phase boundaries.
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  • 78
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    Journal of Morphology 221 (1994), S. 309-320 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Gastrocnemius tendons of 10 White Leghorn chickens at 6, 8, and 12 weeks of age were divided into proximal, middle, and distal portions to assess regional variability in composition and growth. Body weight increases ∼ 150% during the period examined, whereas the lateral gastrocnemius muscle and tendon increase ∼ 193% and 227%, respectively. No significant changes in cellularity (DNA concentration) or hydroxypyridinium (OHP) crosslinks occur with increasing age. Hydroxyproline (HYP) concentration increases by 12 weeks of age, as hexuronate, glucosamine, and galactosamine decrease. Composition shows some regional variation: the distal region of the tendon has a lower HYP concentration, and increased GAGs and OHP crosslinks compared to either the proximal or middle regions, which do not differ from each other. The mean collagen fibril diameter increases with age, but the oldest tendons also contain more small diameter fibrils (〈40 nm). There is a unimodal fibril distribution at all three ages, although this has broadened by 12 weeks. The data from this study suggest that rapid tendon growth occurs throughout the time period examined and that changes characteristic of mature tendon, such as increased OHP crosslink concentration, have not yet developed in hatchlings because of the large amount of new tissue being produced. Whereas all three regions of the tendon are similar in size, composition of the distal region differs from that of the proximal and middle regions, suggesting that this portion of the tendon should be avoided when sampling a tendon. © 1994 Wiley-Liss, Inc.
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  • 79
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    Journal of Morphology 222 (1994), S. 33-48 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The integument of Pycnogonida (Arthropoda) consists of an epicuticle decorated with tubercles and a filamentous coat, an exocuticle with a small number of ill-defined layers, and an endocuticle whose numerous layers are composed of conspicuously cross-banded fibrils. This cuticular periodicity, attributable to cross-linked chitin, has been observed previously in uncalcified and untanned cuticle of many lower crustaceans, especially branchiopods and copepods, and in scattered examples of thin respiratory or excretory cuticles of other arthropods. It is uniformly present in all representatives of all nine pycnogonid families examined to date. Stomodeal, proctodeal, and arthrodial cuticles are devoid of the endocuticular periodicity. The cuticle is decorated with sensory filaments and setae, but is more noteworthy for a dense coverage by glands, up to 1,400/mm2. Myocuticular junctions have desmosomal fine structure previously found only in chelicerates. Muscle fine structure is that of slow fibers with long sarcomeres and a high actin to myosin filament ratio, except for cardiac muscle, which has short sarcomeres. Among the arthropods, only merostomates resemble the pycnogonids in the lack of fast somatic muscle fibers. Pycnogonids display a hybrid array of fine structural features that variously serve to relate them to some arthropod subphyla and distance them from others. © 1994 Wiley-Liss, Inc.
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  • 80
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    Journal of Morphology 222 (1994), S. 111-111 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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  • 81
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    Journal of Morphology 222 (1994), S. 73-89 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The chimaeroid holocephalian fishes are distinguished among extant chondrichthyans by the possession of three pairs of tooth plates, evergrowing and partially hypermineralized, that are not shed and replaced like the teeth of living elasmobranchs. Although derivation of the chimaeroid tooth plate from the fusion of members of a plesiomorphic chondrichthyan tooth family has been proposed, evidence for this hypothesis has been lacking. A new analysis of the development and structure of the tooth plates in Callorhinchus milii (Holocephali, Chimaeriformes) reveals the compound nature of the tooth plates in a chimaeroid fish. Each tooth plate consists of an oral and aboral territory that form independently in the embryo and maintain separate growth surfaces through life. The descending lamina on the aboral surface of the tooth plate demarcates the growth surface of the aboral territory. Comparison with the tooth plates of Chimaera monstrosa indicates that compound tooth plates may be a feature of all chimaeroids in which a descending lamina is present. The tooth plates in these fishes represent the fusion of two members of a reduced tooth family. The condition of the tooth plates in C. milii is plesiomorphic for chimaeroids and is of evolutionary significance in that it provides further evidence to support a lyodont dentition in chimaeroid fishes similar to that found in other chondrichthyans. © 1994 Wiley-Liss, Inc.
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  • 82
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    Journal of Morphology 219 (1994), S. 1-6 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The process of morphological and functional regeneration was followed on a tilapid fish, a cross of Oreochromis aureus × Oreochromis niloticus, by observations on movements and the use of X-rays. A four-year-old adult fish that lost its tail as post larva, including ten vertebrae, was able to reconstruct a novel and shorter central skeleton, including a specially modified urostyle. The enlarged and strengthened pterygiophores and their junctions with the dorsal and anal spine formed a fast-holding base for the fins, the posterior part of which largely performed the functions of the missing caudal fin. Although the fish was much shorter than usual, this male behaved and functioned normally. © 1994 Wiley-Liss, Inc.
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  • 83
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    Journal of Morphology 219 (1994), S. 7-13 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A study of the ultrastructure and function of the paraphysis in Bufo bufo larvae was carried out. The structure is a tubular-ramified gland made up of numerous tubules with monolayered epithelial walls surrounded by connective tissue and sinusoids. The epithelial cells secrete glycoprotein to contribute to production of the cephalorachidian fluid. The role of the paraphysis in the transport of fluids and electrolytes from the blood to the cephalorachidian fluid in regulation of ionic and osmotic homeostasis is discussed. © 1994 Wiley-Liss, Inc.
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  • 84
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    Journal of Morphology 219 (1994), S. 15-20 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Spermatozoa from representatives of the five insect orders in superorder Neuropteroidea were examined by electron microscopy following a new fixation method that includes tannic acid in the primary fixative but has uranyl acetate rather than osmium tetroxide as the secondary fixative. The sperm axoneme was found to be similar in the four orders Megaloptera, Raphidioptera, Neuroptera, and Coleoptera, and is characterized above all by its so-called intertubular material being divided into two portions, one located outside, but in contact with the doublet, and the other projecting from the accessory tubule and having a beak-like shape. These features have not been seen in insects from other orders and may be a synapomorphy for these neuropteroid orders. The accessory tubules in these four orders have 16 protofilaments. The shape of the accessory bodies adjacent to the mitochondrial derivatives is nearly the same in insects from the more primitive neuropteroid orders and in Coleoptera. The sperm tail of the examined strepsipteran deviates in several respects from that of other neuropteroids: the particle row in the wall of accessory tubules is incomplete, an intertubular material is missing, and the mitochondria contain no crystal. © 1994 Wiley-Liss, Inc.
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  • 85
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    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: In the embryo of Haliotis tuberculata spiral cleavage induces size differences between the quadrants in the 4-cell embryo. These size differences, together with the formation of compact cell configurations, induce asymmetrical positions of equivalent cells in the 8- and 16-cell embryo. The asymmetries in size and position influence the final specification of the dorsoventral asymmetry in the 32-cell embryo, as well as formation of the mesentoblast. © 1994 Wiley-Liss, Inc.
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  • 86
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    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The anatomy and histology of the abdominal eversible vesicles and the male reproductive tract of the spoonwing lacewing Palmipenna (Neuroptera: Nemopteridae) have been examined. The eversible vesicles open as a pair of large bulbous sacs between tergites five and six, each folding into halves during retraction. They consist of highly pleated cuticle, beneath which are typical gland cells, each having a circular or oval end apparatus surrounded by closely packed microvilli. These communicate to the surface via cuticularized channels. In spite of considerable behavioral observations, male Palmipenna were never noted with everted vesicles. Even during mating trials, where females were presented to males in the field, the vesicles were never everted during the attempted copulation that ensued. Our observations indicate that mate attraction is mediated by the release of a female pheromone. The function of the eversible vesicles and their associated gland cells remains unknown, and their structure appears to be unique to the Nemopteridae. The reproductive tract is similar to that of other Neuroptera, consisting of a pair of five-lobed testes, a medium-to-large pair of seminal vesicles, and three pairs of accessory glands. The major accessory glands are surrounded by circular and longitudinal muscle, and are lined by an epithelium, the cells of which presumably secrete the amorphous rods of material always present in this pair of glands. The sperm in the seminal vesicles are elongate, with a pointed head and a 9 + 9 + 2 configuration in the flagellum. A single spermatophore, similar in shape to that described for other Neuroptera, was found occluding the bursa copulatrix of a teneral female. © 1994 Wiley-Liss, Inc.
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  • 87
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    Journal of Morphology 219 (1994), S. 35-46 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Embryos of viviparous goodeid fishes undergo a 10 to 150 × increase in dry weight during gestation. Maternal nutrients are transferred across a trophotaenial placenta comprised of the ovarian lumenal epithelium and the trophotaeniae of the embryo. Trophotaeniae are externalized projections of the embryonic hindgut. Epithelial cells of the ribbon trophotaenia (Ameca splendens) resemble intestinal absorptive cells of suckling mammals and endocytose macromolecules. They possess an apical brush border, endocytotic complex, endosomal-lysosomal system, and apical and basal clusters of mitochondria. Cells of the rosette trophotaenia (Goodea atripinnis) lack an endocytotic apparatus, have small lysosomes, two mitochondrial clusters, and transport small molecules. Organelle-specific fluorescent probes were employed to characterize the functional organization of the two types of trophotaenial cells. In A. splendens, Lucifer Yellow, a membrane-impermeable tracer of vesicular transport, first appears in peripheral vesicles (15-45 sec), then passes into elongated tubular endosomes (1-3 min) and later appears in large central vacuoles (10-15 min). These vacuoles accumulate Acridine Orange, a classical probe for lysosomes, and have been shown to contain lysosomal enzymes. Endosomelysosome fusion was observed. In both A. splendens and G. atripinnis, Rhodamine 123 fluorescence was localized in two clusters of fine spots that corresponded to mitochondria. 4′,6-diaminido-2-phenyl-indole (DAPI) staining of nuclei established the positional relationships of cell organelles with respect to the nuclei. 3,3′-dihexyloxacarbo-cyanine iodide (DiOC6) revealed the perinuclear distribution of the endoplasmic reticulum. In order to compare in vivo fluorescence of Lucifer Yellow with previous ultrastructural observations, we employed fluorescence photoconversion and electron microscopy. © 1994 Wiley-Liss, Inc.
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  • 88
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    Journal of Morphology 219 (1994), S. 59-71 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The ontogenesis and structural characteristics of the seminal vesicles in Clarias gariepinus (sharptooth catfish) were studied by light and electron microscopy and are described in detail. The seminal vesicles, beginning as simple protrusions from the vas efferentia, becomes more complex with age. Their distal ends become fingerlike and the bases form palm-like extensions. Juvenile male organs do not reveal any signs of seminal vesicles although spermatogenic tissue is already well delineated. The developing gonads contain clusters of large cells, close to the sperm duct and cysts of the testis, from which seminal vesicles are formed. Secretory epithelium lines the tubules of the seminal vesicles and becomes columnar as the tissue matures. Electron micro-graphs of these epithelial cells reveal two types of cells: opaque cells and cells with very vacuolized cytoplasm. Dense pinocytotic vesicles are present between the membranes of neighbouring seminal tubules and apical cell membranes facing the lumen. Maturation and onset of secretion by the secretory cells is accompanied by morphological changes. Protruding cylindrical cells become shortened, modified to cuboidal, rounded cells that send tubular extensions into the lumen. In the final stage of differentiation, only connective tissue membranes supporting the tubule walls remain intact. At the points of contact between the testis, seminal vesicles, and sperm duct, the epithelia of these organs often become confluent. The distal parts of the seminal vesicles, rarely contain sperm; during spawning sperm accumulated in the proximal tubules of the vesicles. © 1994 Wiley-Liss, Inc.
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  • 89
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    Journal of Morphology 219 (1994) 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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  • 90
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    Journal of Morphology 222 (1994), S. 11-18 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The long (49-93 mm) antennae of two species of Australian gryllacridids have high total numbers of sensilla consisting of five sensillar types. Ametrus sp. 7 has 22,300 (♀) and 26,250 (♂) sensilla; although the antennae of males are 33% longer than those of females, their sensillar density was 11% less. Bothriogryllacris pinguipes has 26,700 (♂) and 31,900 (♀) sensilla; antennae of females are 55% longer than those of males but sensillar density is 23% less. Aporous sensilla chaetica form 94.5 to 99.5% of all sensilla; they are presumably mechanoreceptors. Uniporous trichoid contact chemoreceptors range from 75-900 in number. Olfactory, multiporous, basiconic sensilla range from 22-440 and olfactory, coeloconic sensilla from 16-235. Two to five multiporous lenticular organs occur on all but female A. sp. 7. Differences in sensillar abundance between males and females are discussed as well as are the relationships between sensillar diversity on gryllacridid mouthparts and antennae. © 1994 Wiley-Liss, Inc.
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  • 91
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    Journal of Morphology 222 (1994), S. 19-32 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Homozygous recessive cardiac mutant gene c in the axolotl, Ambystoma mexicanum, results in a failure of the embryonic heart to initiate beating. Previous studies show that mutant axolotl hearts fail to form sarcomeric myofibrils even though hearts from their normal siblings exhibit organized myofibrils beginning at stage 34-35. In the present study, the proteins titin and myosin are studied using normal (+/+) axolotl embryonic hearts at stages 26-35. Additionally, titin is examined in normal (+/c) and cardiac mutant (c/c) embryonic axolotl hearts using immunofluorescent microscopy at stages 35-42. At tailbud stage-26, the ventromedially migrating sheets of precardiac mesoderm appear as two-cell-layers. Myosin shows periodic staining at the cell peripheries of the presumptive heart cells at this stage, whereas titin is not yet detectable by immunofluorescent microscopy. At preheartbeat stages 32-33, a myocardial tube begins to form around the endocardial tube. In some areas, periodic myosin staining is found to be separated from the titin staining; other areas in the heart at this stage show a co-localization of the two proteins. Both titin and myosin begin to incorporate into myofibrils at stage 35, when normal hearts initiate beating. Additionally, areas with amorphous staining for both proteins are observed at this stage. These observations indicate that titin and myosin accumulate independently at very early premyofibril stages; the two proteins then appear to associate closely just before assembly into myofibrils. Staining for titin in freshly frozen and paraffin-embedded tissues of normal embryonic hearts at stages 35, 39, and 41 reveals an increased organization of the protein into sarcomeres as development progresses. The mutant siblings, however, first show titin staining only limited to the peripheries of yolk platelets. Although substantial quantities of titin accumulate in mutant hearts at later stages of development (39 and 41), it does not become organized into myofibrils as in normal cells at these stages. © 1994 Wiley-Liss, Inc.
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  • 92
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    Journal of Morphology 222 (1994) 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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  • 93
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    Journal of Morphology 222 (1994), S. 113-131 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Based on a detailed description of hatchling skeletons of the precocial buttonquail (Turnix suscitator) and the altricial budgerigar (Melopsittacus undulatus), this report presents the hypothesis that the rate of avian posthatching growth is limited by the quantitative design (i.e., relative volumes of cartilage, bone, and marrow) of the hatchling skeletons. A Jarge portion of bone in the skeletal elements and fast growth are hypothesized to be mutually exclusive. This hypothesis is tested by morphometric techniques and by statistical comparison of morphometric and growth data. All predictions are met by the data, and the design of hatchling skeletons is described as determined by a tradeoff between tissue composition of skeletal elements and maximum rates of posthatching growth. The precocial design shows large bony areas that supposedly resist mechanical stress of locomotion; however, the relatively small cartilaginous areas exclude high growth rates. The altricial design shows the reverse relationship with small bony areas and a lack of locomotion on the one side but large cartilaginous areas and fast posthatching growth on the other side. © 1994 Wiley-Liss, Inc.
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  • 94
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    Journal of Morphology 222 (1994), S. 175-190 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Jaw protrusion is an important component of prey capture in fishes, although the mechanics of protrusion have thus far been studied largely in teleosts. Elasmobranchs are also able to protrude their jaws (Tricas and McCosker [1984] Proc. Cal. Acad. Sci. 43: 221-238; Tricas [1985] Mem. S. Calif. Acad. Sci. 8:81-91.; Frazzetta and Prange [1987] Copeia 4:979-993). Several related features of the feeding apparatus contribute to jaw protrusion in sharks. Labial cartilages form an extendible series attached dorsally to the anterolateral face of the palatoquadrate and ventrally to the anteroventral surface of Meckel's cartilage. The labial cartilage chain swings anterolaterally as the lower jaw is depressed, thrusting the labial margins forward to form a circular oral opening and displacing the jaw apparatus towards the food; this pattern is analogous to halecomorph and primitive actinopterygian fishes in which the maxilla swings forward (Lauder [1979] J. Zool. Lond. 187:543-578). The palatoquadrate and Meckel's cartilage also project anteriorly and represent the major contribution to protrusion. These movements occur simultaneously with enlargement of the oral cavity to generate suction. The wobbegong sharks (Orectolobidae) are specialized for jaw protrusion. The spotted wobbegong protrudes its jaw by 33% of its chondrocranial length using two different mechanical systems. In the first mechanism of jaw protrusion, the intermandibularis and interhyoideus muscles medially compress the lower jaw and hyomandibulae. Compression of the lower jaw results in a more acute symphyseal angle so that the anteroposterior alignment of the lower jaw increases due to the rotation of each lower jaw towards a saggital orientation. Distal compression of the hyomandibulae at their attachments to the jaws swings the jaws forward. The second mechanism involves rotation of the ceratohyal around a posterior process of the lower jaw, pushing the hyomandibulae anteroventrally, thereby pushing the jaw articulation ventrally and anteriorly to protrude the jaws. © 1994 Wiley-Liss, Inc.
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  • 95
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    Journal of Morphology 222 (1994), S. 203-213 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Gap junctions in mammalian heart function to provide low-resistance channels between adjacent cells for passage of ions and small molecules. It is clear that the almost unrestricted passage of ions between cells, ionic coupling, is required for coordinate and synchronous contraction. This knowledge of gap junction function has made it important to study their properties in normal and abnormal tissues. In the present study, we analyzed gap junction distribution in normal and cardiomyopathic heart tissue utilizing immunofluorescent and electron microscopy techniques. Frozen, unfixed sections of age-matched normal and cardiomyopathic cardiac tissues were immunofiuorescently stained using an antibody directed against a specific peptide sequence of the connexin-43 gap junction protein. These studies revealed a characteristic punctate staining pattern for the intercalated discs in normal tissues. Some of the intercalated discs in cardiomyopathic hearts appeared to stain normally; however, others stained diffusely. The pixel intensity distribution of the confocal images demonstrated a marked difference of up to 90% increase in the number of pixels in cardiomyopathic myocardium (CM), yet the pixel intensity of gap junctions had a decrease of approximately 60%. This suggests the possibility that connexin-43 is present in CM cells in significant quantity; however, it does not become localized on the membranes as in normal cells. Electron-microscopic findings corroborate these observations on CM cells by showing an irregular distribution of intercalated discs relatively smaller in size with abnormal orientation and distribution. © 1994 Wiley-Liss, Inc.
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  • 96
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    Journal of Morphology 222 (1994) 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
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  • 97
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 222 (1994), S. 223-230 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We describe some significant structures of the adult ovary in a Japanese penicillate diplopod, Eudigraphis nigricans, with respect to phylogenetic implications. The ovary is a long, saclike organ lying between the alimentary canal and the ventral nerve cord from the fourth through the ninth body segment. The ovarian wall consists of a thin ovarian epithelium and a sparse muscle covering. There are two types of oogenetic sites: a single, mound-shaped germarium sitting on the center of the ventral ovarian epithelium, and ∼ 10 pairs of patchlike vitellarial areas metamerically arranged anterior and posterior to the germarium. The germarium consists of oogonia, early previtellogenic oocytes, and some somatic interstitial cells. In contrast, the vitellarial areas are composed of more advanced oocytes, follicle cells surrounding the oocytes, and some interstitial cells, but no oogonia. A few larger previtellogenic oocytes rise up from each vitellarial area into the ovarian lumen. Each of these oocytes is still connected with its own vitellarial area by a partial extension of its follicle. Vitellogenesis takes place in these oocytes rising in the ovarian lumen. The ripe primary oocytes leave their follicles to be transported forward into the oviducts. Some phylogenetic implications of the basic characteristics in ovarian structure and oogenesis of E. nigricans are discussed. © 1994 Wiley-Liss, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 98
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 222 (1994), S. 103-110 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The morphology of eggshells from hatched eggs of captive Chinese alligators (Alligator sinensis) was compared with that of shells from eggs with early embryonic death and with the morphology of eggshells from the American alligator (Alligator mississipiensisis). Pieces of shells were examined in the scanning electron microscope. Parameters examined included: numbers of open pores on the outer surfaces, total shell thickness, and thickness of the outer densely calcified and inner mammillary layers. Results indicate that shells from Chinese and American alligator eggs with early embryonic death have a thicker outer densely calcified layer than do shells from hatched eggs or full-term embryos. Also, eggshells from Chinese alligator eggs with dead embryos have fewer open pores on the outer surface than do shells from hatched eggs, as has been reported earlier for the American alligator (Wink et al., '90). © 1994 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 99
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 222 (1994), S. 149-173 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Development of craniofacial muscles of Monodelphis domestica (Marsupialia, Didelphidae) is described. In a period of 4-6 days all craniofacial muscles in M. domestica progress from myoblast condensation, to striated myofibers that are aligned in the direction of adult muscles and possess multiple, lateral nuclei. This process begins 1 to 2 days before birth and continues during the first few days after birth. Compared to other aspects of cranial development, muscle development in M. domestica is rapid. This rapid and more or less simultaneous emergence of craniofacial muscles differs from the previously described pattern of development of the cranial skeleton in marsupials, which displays a mosaic of acceleration and deceleration of regions and individual elements. Unlike the skeletal system, craniofacial muscles show no evidence of regional specialization during development. M. domestica resembles eutherian mammals in the relatively rapid and more or less simultaneous differentiation of all craniofacial muscles. It differs from eutherian taxa in that most stages of myogenesis occur postnatally, following the onset of function. The timing of the development of muscular and skeletal structures is compared and it is concluded that the relatively early development of muscle is not reflected by any particular acceleration of the differentiation or growth of skeletal structures. Finally, the difficulties in accounting for complex internal arrangements of muscles such as the tongue, given current models of myogenesis are summarized. © 1994 Wiley-Liss, Inc.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 100
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 222 (1994), S. 191-201 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Study of the epithelial morphology of a stingless bee ileum from the pyloric valve to the last portion of high absorptive cells shows that although the bee ileum is an anatomically undifferentiated tube, four types of epithelial cells along the tube (in addition to the valve cells) indicate physiological differentiation. The anterior end seems to be less active in reabsorption, while the posterior region contains cells with typical morphology of an ion pump and permits conclusions about the mechanisms of absorption in the posterior end of the intestine. © 1994 Wiley-Liss, Inc.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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