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  • 2010-2014
  • 1985-1989  (6,639)
  • 1970-1974  (2,295)
  • Chemical Engineering  (5,336)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989) 
    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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  • 2
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1-1 
    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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  • 3
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 29-35 
    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 recently developed analytical technique, modulus profiling, conveniently allows the mechanical properties of elastomers to be mapped with spatial resclutions approaching 0.05 mm. Thus, spatial heterogeneities in modulus caused by processing and aging phenomena can be easily monitored. This paper describes some typical results from polymer aging studies, which Indicate the insights available from this technique. These include application of modulus profiling to understanding (1) mechanical property deterioration of Viton in an elevated temperature, gamma-radiation environment, (2) recent continuous stress-relaxation results, and (3) the role of ozone for non mechanically-stressed materials in high energy radiation environments.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 4
    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: Thermal and mechanical studies on many linear polyesters have revealed their behavior in crystalline, liquid crystalline, and amorphous phases. Their phase behavior in binary compositions has also been studied by a range of additional techniques and in combinations including the polycarbonate of bisphenol-A. Regions of amorphous compatibility and incompatibility have been identified and measures made of transition temperature changes with composition. The conditions for transreaction have also been determined and the properties measured for the resultant new copolymers.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989) 
    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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  • 6
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 100-106 
    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 describes the evaluation of nonlinear thermally induced residual stresses in the cooling of polymer melt during injection molding of plastic components. The computational methodology adopted is based on the transfinite element approach, which is a hybrid scheme as it combines transform methods and classical Galerkin schemes with finite element formulations to preserve the modeling versatility. The applicability of the proposed formulations for understanding the physics and the nature of the nonlinear thermally induced stresses in the solidifying process of a sample amorphous polystyrene specimen demonstrates the basic capabilities and potential of the methodology. Results obtained agree qualitatively well with earlier research studies and experimental findings relevant to thermally induced residual stresses in the injection molding of plastic components.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 127-133 
    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 method to obtain microscopic and macroscopic coatings with improved resistance to debonding is described. The procedure, based on polymer-metal complexes, involved the adsorption on inorganic substrates of a poly(vinyl alcohol)-copper II chelate that is also able to catalyze the polymerization of monomers or prepolymers with grafting. The molecular structure of the complex, its adsorption on inorganic surfaces, and the mechanism of the polymerization induced by the supported catalyst are summarized. Much emphasis is placed on application of this technology to the realization of encapsulated filler and pigment and of coatings with improved adherence and solvent resistance. In the field of composite materials, it is demonstrated from several examples that the encapsulation of the filler can be a way to block chemical interactions between filler and matrix, to promote filler dispersion, and to improve mechanical properties.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 334-338 
    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: As a result of increased interest from industry in using dielectric cure monitoring, a need has arisen for simplifying frequency, cure, and temperature dependent data so that control decisions can be readily made. Techniques utilizing data covering several decades of frequency now exist for separating ionic conduction levels from dipole and electrode polarization responses. Ionic conduction levels are particularly useful since they can be correlated to both viscosity and extent of cure. In addition to being a function of extent of cure, dielectric properties are also influenced by temperature. This dependence often makes the dielectric response more difficult to interpret. This paper investigates two methods for overcoming the temperature dependence of the dielectric response during nonisothermal cure. The first method utilizes recent WLF modeling techniques and extends them with the end result of extracting Tg in real time during cure. The second technique involves measuring the temperature dependence of uncured and cured material. Utilizing the correlation between log ionic conductivity and extent of cure, which has been noted by previous researchers, the normalized conductivity can be converted to a cure index. Several examples including epoxy, polyurethane, and a UV cured photoresist are presented, showing data before normalization and after both Tg and cure index determination.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 359-365 
    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: Poly(ethylene terephthalate) (PET) and bisphenol-a-polycarbonate (PC) are known to form a miscible blend whereas ternary blends of PET, PC, and polypropylene (PP) form two phases. This is based on the considerations of various chemical events which may occur in these systems. The role of ester-carbonate interchange reactions during melt mixing and fabricating is found to be unimportant. Differential scanning calorimetric analysis of the ternary blends shows that there appears to occur an exothermic transition in the heating mode of the instrument. This exothermic event was found to be suppressed considerably by incorporating suitable additives into the system. Degradation reactions studied by thermogravimetric analysis and a dilute solution viscometric technique reveal that there exists some kind of interaction among the components even with the immiscible PP component.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 397-404 
    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: Interpenetrating polymer networks of polyurethane and unsaturated polyester were prepared by reaction injection molding (RIM) and transfer molding. The structures of the molded samples were analyzed by electron microscopy and dynamic mechanical analysis. It was found that polymer morphology and dynamic mechanical properties depend strongly on the molding temperature, reaction rate and reaction sequence. Simplified structure models based on Takayanagi's model and sample morphology can predict the storage modulus reasonably well but not the tanδ.
    Additional Material: 14 Ill.
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  • 11
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 432-432 
    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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  • 12
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 448-455 
    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 plasticating or melting behavior of polymer pellets sliding on a hot metal surface was investigated. An analytical model was developed for predicting the melting rate and the shear stress of an incompletely compacted solid bed of pellets in terms of the rheological and thermodynamic properties of the polymer, the pellet size, the degree of compaction, and the operating conditions. This investigation extends the results of the previous investigators obtained for a fully compacted solid bed of polymers to an incompletely compacted solid bed of polymers, closely representing the initial stage of the plasticating mechanism inside a screw extruder. Experimental verification of the analytical model developed here was made by testing six different commercial polymers.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 456-462 
    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: Vitrification occurs during the reaction injection molding (RIM) of epoxy resin, and the curing reaction rate is reduced as the Tg of the reacting mixture exceeds or approaches the local reaction temperature inside the mold cavity. The effect will be manifested in the distribution of the glass transition temperature across the thickness direction of the molded product. The reaction kinetic equation which includes the vitrification term in the form of the WLF equation is used in the computer simulation of the epoxy RIM process and the effect of the vitrification is shown by comparing with models with no vitrification considerations.
    Additional Material: 8 Ill.
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  • 14
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 479-487 
    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 performance of screws of advanced design in injection molding has been investigated with respect to four different objectives: (1) improvement of distributive mixing; (2) improvement of dispersive mixing; (3) increase of plasticating capacity; and (4) reduction of inhomogeneity of melt temperature.The screws used are three zone screws with different compression ratios, screws with pineapple or Maddock/Egan mixing elements, with one or two channel barrier sections, with static mixers mounted in the valve or in the nozzle, or with combinations of these different elements. The best mixing quality is obtained with multi-channel Maddock sections. The highest plasticating capacity and, consequently, the shortest cycle times are achieved with the barrier screws. Temperature measurements show that these screws improve melt homogeneity considerably with a relatively small loss of plasticating time. In all cases, increasing the back pressure gives inferior results compared with improvement of the screw design.
    Additional Material: 14 Ill.
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  • 15
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 505-512 
    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: The impact fracture energy (Gc) for a polypropylene homopolymer and a copolymer with and without calcium carbonate fillers was measured over a range of temperatures between -40°C and 40°C using fracture mechanics principles. The fillers studied were Omyacarb (∼2.7 μm) and Winnofil (∼75 nm) and 10% by weight was added to the matrix material. These fillers did not have any appreciable effect on Gc of the copolymer-based composites. However, the Omyacarb fillers improved Gc of the homopolymer at low temperatures (≤20°C) due to enhanced microplastic flow as observed on the fracture surfaces. The fillers increased the stiffness of both the homopolymer and copolymer. It would appear that up to 10% of cheap calcium carbonate fillers could be added to the more expensive polypropylene to reduce the production cost without any significant loss of impact fracture energy.
    Additional Material: 15 Ill.
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  • 16
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 499-504 
    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 sliding plate rheometer has been developed that is suitable for use with molten plastics, concentrated polymer solutions, raw elastomers, and other viscoelastic or thixotropic materials. It can generate steady shear rates from 0.05 to 500 s-1 and can also be used to measure linear viscoelastic properties. In addition, it can be used to measure a broad spectrum of nonlinear viscoelastic properties such as the nonlinear relaxation modulus and the shear stress growth coefficient. In order to measure these nonlinear properties it is necessary to generate large, uniform, transient deformations Involving high strain rates. Rotational and capillary melt rheometers are not capable of generating this type of deformation, and until now it was not convenient to use sliding plate rheometers for this type of application. However, the recent development of a reliable and robust shear stress transducer makes it very convenient to use the sliding plate geometry to carry out all of these tests. The new rheometer is described, and examples of the types of data it can generate are shown.
    Additional Material: 8 Ill.
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  • 17
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 308-314 
    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: During the sheet molding compound (SMC) compression molding process, a premeasured polymer charge is placed between the heated halves of a mold which are then brought together to squeeze the polymer and fill the mold, after which pressure is maintained while the part cures. The cure stage constitutes the larger part of the molding cycle and thus affords the largest potential for cycle time reduction. In general, cure times in SMC processing are set longer than necessary, since the inherent material and process variation make it difficult to predict cure times with more than 10 to 20% accuracy. Accurate methods to detect the end of cure would be very beneficial and would permit opening the mold as soon as the material has cured, avoiding unnecessary waste of time. In this paper, several techniques that show promise for monitoring the state of cure are reviewed and experimental results given. Their relative advantages and accuracies are compared. In particular, the use of linear variable displacement transducers, pressure transducers, and thermocouples is discussed. We also show how the measurements compare to theoretical predictions of the state of cure.
    Additional Material: 15 Ill.
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  • 18
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 339-346 
    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 parallel-plate test fixture on a Rheometrics viscometer was electrically isolated so that the rheological and dielectric properties of a thermoset polymer system could be simultaneously measured. This enabled the relationship between the dielectric properties and the rheological properties to be directly examined. A close relationship was established between the dielectric properties (dipole relaxation time and specific conductivity) and the pre-gelation bulk viscosity. This relationship suggested that models similar in form to those used to describe the change in viscosity might be used to describe the changing dielectric properties. The limitations and advantages of two such models, which attempt to describe the time-temperature behavior of the dielectric properties, were then tested for use with a typical aerospace epoxy resin system.
    Additional Material: 8 Ill.
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  • 19
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989) 
    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 29 (1989), S. 586-592 
    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 investigated the miscibility of polybutadienes with butadiene-styrene copolymers of varying styrene content. The methods of optical microscopy, differential scanning calorimetry, and small angle light scattering (SALS) were used. All polymers/copolymers used in this study have equivalent butadiene microstructures. Copolymers with high styrene levels are immiscible with polybutadiene. The tendency to miscibility increases with decreasing styrene content. An upper critical solution temperature is observed with the 23 percent styrene copolymer.
    Additional Material: 12 Ill.
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  • 21
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 405-414 
    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: Poly(ether-ether-ketone) (PEEK) is a newly developed engineering thermoplastic with potentially vast application in advanced composites due to its exceptional performance. It is thus desired to understand the relationship between physical processing, microstructure and fracture in this semicrystalline polymer. Both oriented and unoriented PEEK were mechanically characterized using static test of three-point bend specimens. The molecular chain orientation was imposed using a rolltrusion technique. The effects of thickness, strain rate, Initial crack length ratio, and orientation on fracture toughness (Kc) are investigated. The crystallinity is also examined by density measurement. The degree of orientation is determined qualitatively by wide-angle X-ray scattering diffraction patterns and quantitatively by further measurement using an image analysis system. Fractographic analysis, using scanning electron microscopy, provides precise information about the mode of fracture, Results indicate that both the modulus and the fracture toughness are remarkedly increased in the direction of drawing (T-type) as opposed to the transverse direction (L-type).
    Additional Material: 15 Ill.
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  • 22
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 420-425 
    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: Herein is more detail to microscopic aspects of electron transport through a conductor-filled polymer than has yet been considered in the literature (irrespective of quantum mechanical tunneling and thermal expansion). Some of these details only clarify earlier theories, but others lead to new discoveries such as the cubic conduction path coordination number z = 18 (contrasted with the classical geometric coordination number of z = 6). New also are simplified derivations of the high and low fill asymptotes of the master equation for conductance as a function of fill fraction in the effective medium theory of conductor-filled polymers.
    Additional Material: 6 Ill.
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  • 23
    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: Several recent calculations of the stress field around crazes in glassy polymers have been based on experimentally obtained craze opening displacements. Although various techniques for performing these calculations have been presented (i.e., Fourier transform, boundary integral, and finite element methods), all are based on the solution of the same ill-conditioned boundary value problem. Specific boundary conditions required to calculate the stresses around a craze lead to a large change in the stress field with small changes in the craze profile which are within the reported experimental tolerance.
    Additional Material: 5 Ill.
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  • 24
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 433-440 
    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 of Newtonian and non-Newtonian fluids which obeys a power law relationship between shear stress and shear rate has been modeled in the melt conveying section of a self-wiping co-rotating twin-screw extruder using a finite element analysis of an unwound channel section. Predictions of throughput against pressure gradient are compared with experimentally obtained results for maize grits which is represented as a power law material. Rheological data applicable to extrusion simulation were obtained from capillary rheometry. Comparisons are reasonable with predicted characteristic showing similar behavior.
    Additional Material: 6 Ill.
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  • 25
    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 emulsifying activity of a poly(hydrogenated butadiene-b-methyl methacrylate) (HPB-b-PMMA) copolymer is investigated in incompatible blends of a low density polyethylene and poly(styrene-co-acrylonitrile) resins (mainly ABS) prepared in the melt state on a two-roll mill. Optical and scanning electron microscopy observations clearly demonstrate that a moderate amount of copolymer (5 wt %) very significantly decreases the particle size and enhances interfacial adhesion. The block copolymer is also responsible for a strong improvement in both the ductility and Charpy impact resistance of PE/ABS blends.
    Additional Material: 7 Ill.
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  • 26
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 564-572 
    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: To improve the powder processing behavior of ultrahigh-molecular-weight polyethylene, a conductive iron filler was distributed within the polymer in a segregated network. The filler level was kept at a minimum of 10 volume percent, which was sufficient to coat completely all the polymer particle surfaces. This filler level was low enough to avoid modifying the resin properties to a significant extent. Compaction of these filled samples showed a slower densification, under pressure, similar level of final densification at 80% densification parameter, and a doubling of plateau pressure value to 200 MPa in comparison with the unfilled polymer. The filler was found to reduce drastically the postcompaction relaxation time from 24 h to 6 h. The magnitude of the axial (compaction direction) relaxation was unchanged, but the radial relaxation was one quarter of that for the unfilled polymer. Sintering behavior showed improved densification because of lower dimensional changes during sintering resulting in 80% relative sintered density, higher than the 75% percent value for the unfilled polymer, but yielded a 20% lower sintered strength, An alternative process of rapid sintering by induction heating was explored, its feasibility demonstrated, and a recommendation is made to make powder processing of this polymer commercially attractive.
    Additional Material: 9 Ill.
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  • 27
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 874-877 
    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 application of X-Ray lithography in mass production of devices is only economically viable if resist materials of highest sensitivity can be provided. Chemical amplification is the key concept to achieve such performance. It is outlined for a highly sensitive three component positive tone X-Ray resist, consisting of a Novolak binder matrix, a starter compound, which - on X-Ray exposure - yields an acid, which catalytically decomposes a dissolution inhibitor. Resist performance is discussed in terms of reaction kinetics and their implications on resist response, simulation, and handling procedures.
    Additional Material: 4 Ill.
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  • 28
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989) 
    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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  • 29
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 898-901 
    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: Many styrylpyridinium compounds (SPC), which are very stable in the dark, were prepared and evaluated as photobleachable dyes for contrast enhanced lithography (CEL). The photobleaching characteristics of water-soluble contrast enhancing materials composed of SPC and water-soluble polymer depend on the structure of the SPC and the kind of polymers used. The technique using SPC-based CEL proved to be very effective for the resist pattern profiles.
    Additional Material: 7 Ill.
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  • 30
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 916-919 
    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: Dissolution inhibition mechanisms of naphthoquinone diazides in novolak based positive photoresists were investigated from three different aspects: • Dipolar interaction.• Interfacial chemical reactions.• Chemical structures of naphthoquinone diazides.The results suggest that there exists a hydrogen bonding interaction between the compounds with the matrix novolak resin and that naphthoquinone diazides would crosslink the resin in contact with an alkaline developer, both of which contribute to dissolution inhibition mechanisms. However, there seems to exist another dissolution inhibition mechanism; namely, 1,2-naphthoquinone diazide does not inhibit dissolution of the matrix novolak resin at all while a clear dissolution inhibition effect Is observed for its derivatives containing sulfonyl groups. In the present paper, three dissolution inhibition mechanisms of naphthoquinone diazides will be proposed.
    Additional Material: 4 Ill.
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  • 31
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), 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: A commercial liquid crystalline polymer (LCP) sample was characterized both in shear and in nonisothermal elongational flow over a wide range of temperatures (240-350°C). The LCP sample employed was a copolyesteramide of 2,6 hydroxynaphthoic acid, terephthalic acid, and aminophenol manufactured by Celanese and commercially known as Vectra B950. The viscosity decreases dramatically at temperatures above the crystal-nematic transition of the polymer. At lower temperatures, the extrusion of the sample is mainly due to plastic flow. Die-swell values are very small and contraction of the extrudate is also revealed, but the sample shows high elasticity. The polymer is not spinnable at very low temperatures, and the melt strength rapidly decreases with increasing temperature.
    Additional Material: 12 Ill.
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  • 32
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 639-644 
    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: Calculation of gas permeation in food packaging structures can be done using a steady-state analysis employing the permeability coefficient. While this approach is adequate for some applications, for many others a time-dependent transport analysis must be considered to make quantitative predictions of shelf life. The limitation of the simple permeability analysis for multilayer structures is illustrated for Saran-coated polycarbonate and poly(ethylene terephthalate) soda cans. These more detailed calculations on package structures can be done using standard computer library routines to include both the effect of gas sorption and diffusion.
    Additional Material: 7 Ill.
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  • 33
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1097-1102 
    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: Nonisothermal differential scanning calorimetry (DSC) measurements were used to estimate the kinetic parameters for the curing reaction of a commercial unsaturated polyester resin. The reaction rate expression was derived from a mechanistic kinetic model based on the concept of free radical polymerization, accounting also for the diffusion controlled reaction. The total heat of reaction was evaluated in experiments run at very low scan speeds and using high amount of initiator. The kinetic parameters were found to show no dependency on the heating rate nor on the initiator concentration. Dynamic DSC measurements provide reliable kinetic data over a broad range of temperatures that is mostly significant for process simulations.
    Additional Material: 5 Ill.
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  • 34
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1103-1106 
    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 solid state hydrolysis of a copolyester based on a mixture of 1,4-cyclohexanedimethanol and ethylene glycol condensed with terephthalic acid was studied at 100°C and 57 to 96 kPa water vapor partial pressure (55% to 95% relative humidity). The equilibrium water sorption in weight percent (C∞) was found to be \documentclass{article}\pagestyle{empty}\begin{document}$$ C_\infty = 1.45 \times \,10^{ - 5} (P_{H_2 O} )^{1.2} $$\end{document} where PH2O is the water vapor partial pressure in kPa. For specimens 0.32-cm thick, it took about 24 h to reach 0.9C∞. The intrinsic viscosity (IV) was measured and used to calculate the relative change in molecular weight (M̄w) from the relationship IV ∝ (M̄w)0.7. The decrease in molecular weight was linear with time, and the rate of decrease was found to be proportional to C∞; the empirical correlation is \documentclass{article}\pagestyle{empty}\begin{document}$$ k = 0.026 \times C_\infty $$\end{document} where the rate constant, k, is in day-1. A decrease of 50% in M̄w was observed after 22 days at 95% relative humidity.
    Additional Material: 5 Ill.
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  • 35
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989) 
    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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  • 36
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 887-890 
    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 positive-working photosensitive system of silicon polymer, containing silylether groups in the main chain and a photo-induced acid precursor was investigated. The silicon polymer is hydrolized by a photogenerated acid and degraded to low molecular weight compounds. Thus the effect of solubility inhibition of the polymer is diminished. The higher photosensitivity of this system as compared with 1,2-quinone diazide compounds is due to the catalytic reaction of the acid on the hydrolysis of the silicon polymer. The chemical structure around silylether groups in the polymer, in particular more hydrophilic and less steric structures, affects the rate of hydrolysis and thus the photosensitivity. Among various types of photo-induced acid precursors examined, e.g., s-triazine and 1,3,4-oxadiazole compounds substituted by trihalomethyl groups were effective.
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  • 37
    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 finite element technique has been developed for coupled reaction and heat transfer analysis in which mass diffusion is negligible. The temperature unknowns are located at nodal points, while the reaction variables (species concentrations, reaction rates) are at the Gauss points in each element. With a mechanistic kinetic model, the SMC (sheet molding compound) cure in 2-D and 3-D geometries was analyzed. The results for plate-and-rib configurations show the progression of cure and heat transfer and the influence of geometry on the progression. The analysis for a flat sheet of SMC in a mold with localized heating using bubblers indicates the thermal interaction between the mold and the curing SMC. Temperature and reaction profiles are given for each case.
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  • 38
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1309-1309 
    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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  • 39
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1340-1367 
    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: Studies of strength development at polymer-polymer interfaces are examined and applications to welding of similar and dissimilar polymers are considered. The fracture properties of the weld, namely, fracture stress, σ, fracture energy, GIc, fatigue crack propagation rate da/dN, and microscopic aspects of the deformation process are determined using compact tension, wedge cleavage, and double cantilever beam healing experiments. The mechanical properties are related to the structure of the interface via microscopic deformation mechanisms involving disentanglement and bond rupture. The time dependent structure of the welding interface is determined in terms of the molecular dynamics of the polymer chains, the chemical compatibility, and the fractal nature of diffuse interfaces. Several experimental methods are used to probe the weld structure and compare with theoretical scaling laws, Results are given for symmetric amorphous welds, incompatible and compatible asymmetric amorphous welds, incompatible semicrystalline and polymer-metal welds. The relevance of interface healing studies to thermal, friction, solvent and ultrasonic welds is discussed.
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  • 40
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1387-1395 
    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 integrity of a pipeline system is determined by its weakest links. Joints may be such places. Heat fusion is the most common joining method for distribution gas piping. There are procedural, thermal, and mechanical aspects of making fusion joints. Procedural aspects, such as heater calibration and cleanliness, can be assured only by rigorous training and certification of the operators. Thermal and mechanical aspects consist of specifying joining conditions such as the heater temperature, heating time, and joining pressure. In the absence of procedural errors, the strength of a fusion joint should depend on the pipe material, pipe dimensions, and the thermal and mechanical joining conditions.The measured parameters that are measures of strength are impact energy and location of failure in the tensile impact test. A parameter, termed the joining parameter, was found to characterize the joining conditions. This parameter is a function of bead volume, melt volume at the end of the heating phase, and pipe wall thickness. Of the mechanical test parameters, the impact energy was found to correlate best with the joining parameter.
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  • 41
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1413-1418 
    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 variety of thermoplastic fully imidized poly(imide siloxane) segmented copolymers with useful thermal and mechanical properties have been prepared. Other interesting properties described are the materials' hydrophobic character, surface domination, UV stability, and atomic oxygen plasma resistance.
    Additional Material: 7 Ill.
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  • 42
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    Polymer Engineering and Science 29 (1989), S. 1446-1455 
    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 study deals with the cold compaction of polyether-etherketone (PEEK) and nickel powder blends. Four different types of PEEK powders which are commercially available from Imperial Chemical Industries (ICI) were utilized for this investigation. These PEEK powders included fine and coarse size powders of a low viscosity grade (150PF and 150P) and similar powders of a high viscosity grade (450PF and 450P). Each of the four different PEEK powders were blended with about 10 vol-% nickel powder (Novamet) using a dry mixing technique. These PEEK/nickel powder blends were then successfully compacted at room temperature. Green strengths as high as 39.5 MPa and 26.3 MPa were measured on nickel filled 150 grade and 450 grade compacts, respectively. The higher strength values of the nickel filled compacts compared to their respective unfilled ones were attributed to a higher degree of mechanical interlocking and plastic deformation, which was induced in the polymer particles during compaction by the hard nickel filler. These composites also exhibited lower viscoelastic recoveries than their respective unfilled compacts. Electrical resistivities as low as 0.06 ohm-cm were achieved by compacting 150P/nickel powder blends. This resistivity value agreed well with the calculated value predicted from the literature.
    Additional Material: 15 Ill.
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  • 43
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1456-1465 
    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 study deals with the characterization and cold compaction of polyetheretherketone (PEEK) powders. Four different types of PEEK powders which are commercially available from Imperial Chemical Industries (ICI) were characterized for density, crystallinity, particle size, particle size distribution, and particle morphology. Fine and coarse size powders of a low viscosity grade (150PF and 150P) and similar powders of a high viscosity grade (450PF and 450P) were processed. Compaction was successful at room temperature using the 150 grade powders but not with the 450 grade powders. Compressibility curves were obtained at room temperature for the 150 grade powders and their post-compaction viscoelastic recoveries were measured. The coarse and fine size 150 grade powders reached relative plateau densities of 95.8% and 95.1%, respectively, when compacted at pressures exceeding 300 MPa. These high densification values at room temperature were associated with minimal post-compaction viscoelastic recoveries and as-compacted strengths as high as 8.9 MPa. A modified densification parameter (DP*) was developed based on the plastic deformation of the crystalline regions alone. This new dimensionless parameter, DP*, demonstrated a better fit of all the compaction data. The transverse rupture strength and the green density data are presented and explained in terms of this DP*.
    Additional Material: 12 Ill.
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  • 44
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989) 
    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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  • 45
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1528-1533 
    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 was conducted of blends of poly(vinyl chloride) (PVC) with a poly(methyl methacrylate co imide). The latter polymer was found to be miscible in PVC and to raise the glass transition temperature of the blend. Blends of all compositions could be oriented, but the processing temperature increased in proportion with Tg. For a given blend composition, orientation increased with increasing stretch ratio and strain rate and with decreasing stretch temperature. Increasing copolyimide content and increasing orientation generally lead to improved mechanical properties, though the blends containing high levels of copolyimide exhibited low ductilities.
    Additional Material: 14 Ill.
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  • 46
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    Polymer Engineering and Science 29 (1989), S. 1574-1578 
    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 optical properties of polyetherimide resin as described by the complex index of refraction, N = n - ik, are derived by Kramers-Kronig analysis of experimental absorption and reflectance data obtained in the range 40 μm ≥ λ ≥105 nm. Potential uses of this polymer as a printed circuit board material and as a packaging medium for microelectronic circuitry and the relevance of optical data in laser-assisted processing schemes used in these and other applications are briefly discussed.
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  • 47
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    Polymer Engineering and Science 29 (1989), S. 214-226 
    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: Shear modification treatment represents a special shearing history affecting mainly the elastic behavior of polymer melts. This process has been attributed to reversible physical changes in the entanglement structure of the polymer chain network. Shear modification studies were performed for two well-characterized low-density polyethylene (LDPE) grades differing in molecular weight distribution and degree of long chain branching. The shear working of the material was carried out using a specially designed shearing unit producing definable amounts of pure shear in a continuous process. Measurements of the dynamic storage modulus, G′, steady-state shear compliance; Je, extrudate swell, melt flow index, and the extensional behavior (Rheotens test) indicate that primarily properties associated with the elasticity of the melt are reduced in value. The observed reduction is found to correlate with the mean specific energy dissipated during sample preparation. Comparing the two LDPE grades showed that higher degrees of modification can be obtained at lower energy input levels for the more highly branched grade. Reversibility tests were performed and complete recovery of the initial material behavior was observed. Comparison of measurement results for samples prepared using the shearing unit presented here and a Brabender Plasticorder indicates that the degree of modification depends not only on the molecular structure of the polymer but also on the manner in which the shearing history is imposed upon the material.
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  • 48
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989) 
    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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  • 49
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1637-1637 
    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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  • 50
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1628-1635 
    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 compressive and tensile properties of polyester mortar were studied under various curing conditions, temperature, and strain rate. The curing temperature was varied from room temperature to 80°C. The behavior of polyester mortar was studied using a uniform sand with strain rate and temperature varied between 0.01 to 6 percent strain per minute and 22°C and 120°C, respectively. The strength, failure strain, modulus and stress-strain relationships of polyester mortar are influenced by the curing method, testing temperature, and strain rate to varying degrees. The influence of test variables on the mechanical properties of polyester mortar are quantified. Pretreating the aggregates with a silane coupling agent further enhances the compressive and tensile strength of the mortar. The compressive modulus and splitting tensile strength of polyester mortar are related to the compressive strength. A constitutive model is used to predict the compressive stress-strain behavior of polyester mortar.
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  • 51
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    Polymer Engineering and Science 29 (1989), S. 1667-1676 
    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: Under the right conditions, high strengths are shown to be achievable in vibration welded polycarbonate to polyetherimide Joints. While welding of thermoplastic interfaces of the same material can be understood in terms of interchain diffusion at elevated temperatures, this mechanism is severely limited in the case of dissimilar materials. Scanning electron microscopy is used to show that part of the bond strength in such dissimilar materials results from mechanical interlocking of the two polymers, which is caused by viscous mixing. The effects of the weld parameters on the weld morphology are considered in detail.
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  • 52
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    Polymer Engineering and Science 29 (1989), S. 1689-1698 
    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: Ultrasonic welding is one of the most popular techniques for joining thermoplastics because it is fast, economical, and easily automated. In near-field ultrasonic welding, the distance between the horn and the joint interface is 6 mm or less. This study investigated the near-field ultrasonic welding of amorphous (acrylonitrile-butadiene-styrene and polystyrene) and semicrystalline (polyethylene and polypropylene) polymers. High frequency ultrasonic wave propagation and attenuation measurements were made in order to estimate the dynamic mechanical moduli of the polymers. The estimated moduli were entered into a lumped parameter model in order to predict heating rates and energy dissipation. Experimental results showed that variations in the welding pressure had little effect on energy dissipation or joint strength; Increasing the amplitude of vibration increased the energy dissipation and the weld strength. For the semicrystalline polymers, increasing the weld time improved strength up to weld times greater than 1.5 s, where strength leveled off. For the amorphous polymers, the weld strength increased with Increasing weld time up to times of 0.8 s; for longer weld times, the power required was too high, causing overloading of the welder. Monitoring of the energy dissipation and static displacement or collapse provided valuable information on weld quality.
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  • 53
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    Polymer Engineering and Science 29 (1989), S. 1733-1737 
    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 hydrolytic stability of a new commercial polycarbonate (Calibre 300, Dow Chemical USA) was investigated and compared with that of other commercial polycarbonates. The tests were conducted between 56% and 95% relative humidity (R. H.) at 100°C. Also performed were water immersion tests at 80 and 100°C. The water diffusivity was found to be 8.7 × 10-7 cm2/s at 100°C with an activation energy of 7.9 kcal/mole. These values are similar to other glassy polymers. The equilibrium water sorption, C∞, was found to increase with temperature and R.H. The isotherm at 100°C was determined to be: C∞ = 0.005945 [R.H.]. When samples immersed in a water bath at 100°C were transferred into room-temperature water, visible aqueous microcavities were formed due to the condition of super-saturation, and under stress may become crack initiation sites. For the polycarbonate investigated here, it was found that the decrease in weight-average molecular weight (M̄)w was a first-order process under a constant R.H. and temperature, and that hydrolytic embrittlement, i. e., (M̄)w 〈34,000, was reached after ca. 188, 143, 99, and 66 days under 56%, 73%, 87%, and 95% R.H., respectively, at 100°C. A comparison with reported hydrolytic stability data for other polycarbonates showed large differences in their stability which are believed to be due to the extent of end-group capping (over 95% in Calibre 300) and resin purity: both phenolic end-groups and some additives (i.e., fire retardants, thermal stabilizers) are known to accelerate hydrolytic degradation.
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  • 54
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    Polymer Engineering and Science 29 (1989), S. 1766-1773 
    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 and mechanical properties of polyethylene terephthalate (PET) under normal molding conditions were found to improve significantly when it was blended with bisphenol-A-polycarbonate (PC) and polypropylene (PP) to form ternary polymer blend systems. DSC results of these blends revealed that the PET and PC components formed a miscible blend while PP being incompatible with them, formed a separate phase. PP was also found to form a sleeve around the PET-PC miscible phase and, thereby, showed a skin-core type of morphology. Variations of mechanical properties with varying amounts of PP was measured keeping the ratio of PET and PC constant. Tensile and flexural properties of the blends decrease with the amount of PP. Notched impact strength increases up to a certain level of PP and then decreases, while the unnotched values decrease gradually. The effect of annealing on the mechanical properties of these blends have been discussed on the basis of the increased crystallinity of some of the components.
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  • 55
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1786-1795 
    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 possible multimodal sorption mechanisms in glassy amorphous poly-ether-ether-ketone (PEEK) are presented. By varying the penetrant-polymer affinity, experimental temperature, and external solvent activity, a broad range of sorption behaviors from ideal Fickian diffusion to limiting relaxation controlled kinetics is observed. In particular, water, methylene chloride, and n-heptane sorption kinetics are analyzed and interpreted on the basis of the multiple transport mechanisms. Low uptake liquid n-heptane sorption follows ordinary Fickian diffusion. Analogously, water vapor at low activity, is sorbed in small amounts in the same limiting mode while, at higher activities, the moderately higher penetrant uptakes induce slow relaxation coupled with ideal Fickian diffusion. The highly interacting methylene chloride leads to ideal Fickian diffusion only at very low activities, while anomalous non-ideal Fickian diffusion and limiting Case II and diffusion controlled swelling are observed at moderate and at high solvent activities, respectively. Limiting Case II sorption of methylene chloride in PEEK has been observed only at a very low temperature (-32°C). The optical microscopy observations of cryogenically fractured samples contacted with liquid methylene chloride at 5, 20 and 36°C revealed the presence of a sharp front moving linearly with the square root of time. Solvent induced crystallization in methylene chloride swollen samples was detected by means of differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). Finally, sorption from liquid methylene chloride/n-heptane solutions with varying compositions are presented. The progressive increase of the more high sorbing methylene chloride concentration in the solutions, leads to the same wide variety of sorption behavior observed in the methylene chloride vapor sorptions. The gas chromatographic (GC) analysis indicated that the presence of methylene chloride enhanced the n-heptane sorption in the polymer.
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  • 56
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1649-1654 
    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: Welding represents one of the key stages in the manufacture of injection molded or blow molded plastics products. One process frequently employed is heated-tool butt welding. However, the high seam quality associated with this process can only be attained through reliable process control and optimized welding parameters. This paper presents a simple new method for determining these parameters. Mathematical and physical descriptions of the individual process stages and a computer-controlled heated-tool butt welding machine serve as the basis for determining the parameters.
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  • 57
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1661-1666 
    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 measuring method is presented for process monitoring and process analysis of linear vibration welding of thermoplastics. The method works by recording and evaluating time-dependent signals that describe the process - such as the frequency-dependent signals of the displacement of the two parts being joined, the tangential force in the welding plane - and the nonperiodic signals of the welding process, i.e. the normal force in the welding plane and the melting or joining displacement of the parts being joined. It is possible to determine the energy input into the welding zone as a function of the selected machine parameters and the process sequence over time.
    Additional Material: 12 Ill.
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  • 58
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    Polymer Engineering and Science 29 (1989), S. 1699-1704 
    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 far-field ultrasonic welding of plastic parts the distance between the ultrasonic horn and the joint is greater than 6 mm. This study investigated the farfield ultrasonic welding of amorphous (acrylo butadiene styrene and polystyrene) and semicrystalline (polyethylene and polypropylene) polymers. Far-field welding worked well for amorphous polymers. Weld strength improved substantially with increasing amplitude of vibration at the joint interface. Increasing the weld pressure and/or the weld time also resulted in higher weld strengths. Far-field ultrasonic welding was not successful for semicrystalline polymers. The parts melted and deformed at the horn/part interface with little or no melting at the joint interface. A model for wave propagation in viscoelastic materials, which was developed to predict the vibration amplitude experienced at the joint interface, indicates that increasing the length of the samples to a half a wavelength should improve the far-field welding of semicrystalline polymers by maximizing the amplitude of vibration at the joint interface.
    Additional Material: 12 Ill.
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  • 59
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989) 
    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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  • 60
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1746-1758 
    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 methodological survey of preparation of microspheres and microcapsules by suspension cross-linking is presented. Thus, basic features of suspension cross-linking, i.e., the formation of small droplets of a polymer solution (or melt) in an immiscible liquid followed by hardening of these droplets by covalent cross-linking, are discussed. Typical microspherical and microcapsular products manufactured by suspension cross-linking of naturally occurring and preformed synthetic polymers, including agarose and cellulose beads, albumin microspheres and microcapsules, polystyrene beads and epoxy resin microcapsules, are described. Manufacturing parameters controlling microsphere/microcapsule characteristics are also briefly outlined.
    Additional Material: 10 Ill.
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  • 61
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989) 
    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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  • 62
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    Polymer Engineering and Science 29 (1989), S. 1325-1331 
    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 structures composed of polymer matrix composite materials, components must be joined such that the overall structure retains its structural integrity while it is performing its, intended function which can include both mechanical loads (static and dynamic) and environmental loads (temperature and humidity). The use of composite materials in complex structures almost always reduces the number of components in the structures compared to the use of metallic alloys for the same structure. Thus, using composite materials not only results in great savings in weight, but also through a reduced number of joining operations, results in significant savings in assembly, inspection, parts storage, and movement, resulting in increased reliability and lower cost. Yet joining is still required. Joining metallic structures is a mature technology involving riveting, bolting, welding, glueing, brazing, soldering, and other methods. However, for most polymer matrix composites only adhesive bonding and mechanical fastening can be utilized. Attention has been given recently, however, to localized welding of thermoplastic polymer matrix composites, and this will be discussed briefly later. Inherently, adhesive bonding is preferable to mechanical fastening because of the continuous connection, whereas in drilling holes for bolts or rivets, fibers or other reinforcements are cut, and large stress concentrations occar at each discrete fastener hole. The following is a review of much of the literature dealing with adhesive bonding of polymer matrix composite structures. It is Intended not only to be a review, but also a background for detailed study of the referenced and other documents, and a catalyst for future research.
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  • 63
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    Polymer Engineering and Science 29 (1989), S. 1488-1491 
    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: Gelation phenomenon in thermoset polymers is an area of extreme importance from the processing point of view. Gel point (GP) has traditionally been detected using rheological and mechanical techniques. We wish to report the use of dielectric and especially calorimetric techniques for detecting GP. Using a particular thermoset system, we have compared the calorimetric, dielectric, and mechanical techniques and shown how to define GP in terms of time and temperature. As a matter of convenience, we have briefly defined the gelation phenomenon in thermosets, its significance and measurement, and a critical evaluation of the techniques for detecting GP.
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  • 64
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    Polymer Engineering and Science 29 (1989), S. 1516-1523 
    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 orientation development in polystyrene film by biaxial stretching is described. Stretch ratios up to 7.2 × 7.2 were used. Mechanical properties of polystyrene films were correlated with the level of molecular orientation developed by uniaxial or biaxial stretching. Sensitivity of the mechanical properties to change due to development of orientation varied as follows: Yield strength 〈 Young's modulus 〈 Tensile strength 〈 Elongation to break. Brittle to ductile transition phenomena were observed at certain orientation values in the orientation triangle diagram. The transition occurs when f1B × f2B ∼ 0.0025 for biaxially oriented and f1B ∼ 0.015 in the machine direction for uniaxially oriented films. SEM photomicrographs show that the fracture surfaces of ductile failures exhibit many fibrils while brittle failures exhibit no fibrils.
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  • 65
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    Polymer Engineering and Science 29 (1989) 
    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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  • 66
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    Polymer Engineering and Science 29 (1989), S. 1579-1587 
    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 general kinetic model was developed to simulate the grafting of monomers such as unsaturated carboxylic acids and silanes to ethylene polymers. The polymers considered were ethylene-co-vinyl acetate (EVA), ethylene-co-butyl acrylate (EBA), and low-density polyethylene (LDPE). Grafting was assumed to proceed by a free-radical mechanism involving chain transfer. Organic peroxides having a strong tendency for hydrogen abstraction were selected as the source of primary radicals. The model simulated the grafting reaction as taking place in a single screw extruder. The residence time distribution in the extruder was experimentally determined by tracer analysis, according to which the extruder was a plug-flow reactor connected to two mixed reactors in parallel. The model is able to predict the extent of grafting in terms of predefined parameters. Comparison of model predictions with available experimental data showed slight deviations, the possible causes of which are discussed. However, the kinetic behavior expected on the basis of the input parameters was observed, and, as such, the model allowed study of the effect of process variables on grafting kinetics and provided insight into the reaction mechanism.
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  • 67
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    Polymer Engineering and Science 29 (1989), S. 1598-1603 
    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 describes characterizations performed on two types of polyethylene T-Joints as well as the starting resin from which they were manufactured. It was found that the melt flow rate of material taken from the two types of joints differed from that of the starting resin and differed from each other by as much as a factor of two. Investigation of the environmental stress-crack resistance (ESCR) and uniaxial creep behavior of material from the two joints revealed further significant differences in behavior between the two joints. These observations lead to the conclusion that subtle differences in the processing conditions can result in significant differences in the long-term mechanical behavior.
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  • 68
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    Polymer Engineering and Science 29 (1989), S. 1614-1617 
    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 tensile strength of solid-filled rubbers is predicted by the statistical model proposed in this paper, by which the maximum area fraction of the solid filler in a representative cube is calculated. The minimum net cross-section area of the rubber matrix is thus obtained, and this is used to calculate the reduction in strength of the compound in comparison to that of the unfilled rubber. The prediction is then tested by experiments using hydroxyl-terminated polybutadiene (HTPB) filled with glass spheres. After curing, tensile specimens were cut from sheets and exposed to humidity-controlled environments so as to debond the filler particles from the rubber matrix, and were tested in tension. The experimental results were found consistent with the predictions.
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  • 69
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    Polymer Engineering and Science 29 (1989), S. 1683-1688 
    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 vibration welding of thermoplastics, frictional work done by vibrating two parts under pressure, along their common interface, is used to generate heat to effect a weld. Past work on welding characterized the effects of weld parameters such as the weld frequency, the weld pressure, and the weld time, on the welding process and weld strength, and showed that the most important parameter affecting weld strength Is the weld penetration - the decrease in the distance between the parts being welded that is caused by lateral outflow of material in the molten film. However, those weld studies were based on specimens of constant nominal thickness (6.35 mm, 0.25 in). This paper is concerned with the effects of specimen thickness on the weld process and weld strength.
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  • 70
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    Polymer Engineering and Science 29 (1989), S. 1722-1729 
    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 transient two-dimensional thermal model for resistance welding of thermoplastic composites is presented. A parametric study is conducted that yields insight into the welding process enabling some critical process and material parameters to be identified. Time to melt is predicted by the model and is successfully compared to experimental observations. Local heating and meltthrough can also be explained by the transient thermal model in agreement with experimental observations. Mode I fracture toughness of unidirectional graphite reinforced poly(etheretherketone) resistance welded double cantilever beam specimens are conducted under various process conditions. Experimental results indicate that under optimum process conditions, the interlaminar fracture toughness of the bulk compression-molded thermoplastic composite material can be achieved using resistance heating as a joining technique.
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  • 71
    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: Although fibers are subject to complex deformations during processing and end use, most research has concentrated on tensile properties. We have extended our studies to include the ultimate torsional properties, i.e., the breaking twist angle (BTA), and the flexural fatigue life of single fibers. We now have sufficient data on diverse fiber types that we may compare their mechanical properties. Thus, in this paper we report the mechanical properties of the different starting, untreated, fibers, tested under fiducial conditions. We then develop and consider some interrelationships between these selected single fiber physical properties.
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  • 72
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    Polymer Engineering and Science 29 (1989), S. 1774-1785 
    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 analyzed step growth polymerization in a flat film with finite mass transfer resistance. We have shown rigorously that the molecular weight distribution (MWD) at equilibrium is given by the Flory distribution, and under reaction the form of the MWD does not change if the feed is either pure monomer or in equilibrium initially. Extensive computations have shown that it is possible to split the film into growing interfacial and shrinking bulk regions. It is possible to obtain similarity transformations of concentrations of condensation product, and polymer as time invariant profiles. Based on this finding, we have determined a solution for step growth polymerization with finite mass transfer in films. The results lie within 5% of the “exact” numerical computations, for all possible variations of parameters.
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  • 73
    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: Thermal analysis of oriented polymers involves several transitional processes which may be coupled in a complex way. The disorientation process that occurs during heating is often accompanied by dimensional shrinkage which may occur in both amorphous and crystalline oriented polymers. From differential scanning calorimetry (DSC) measurements it has been determined that shrinkage is an exothermic process. In amorphous atactic polystyrene (PS), hot drawn uniaxially, the shrinkage occurs just above Tg. In triaxially oriented polyethylene (PE) and isotactic polypropylene (iPP), shrinkage and melting take place concomitantly, producing multiple melting peaks. In rolltruded (and also in biaxially oriented) poly(ethyleneterephthalate) (PET) films, shrinkage and crystallization are found to be coupled and to occur between Tg and Tm upon heating. If the enthalpy contribution due to shrinkage is ignored, it follows that crystallinities determined by DSC are incorrect. In this study, the influence of shrinkage upon transitional changes in oriented polymers is investigated in a systematic manner.
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  • 74
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    Polymer Engineering and Science 29 (1989), S. 1534-1543 
    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 offer a detailed study on the anisotropic optical properties in uni and simultaneous biaxially stretched Poly(ethylene terephthalate) (PET) films. Cast amorphous sheets of PET were stretched to a series of extension ratios in two mutually perpendicular directions at 80, 90, and 100°C. Additionally, 0selected films were subsequently “heat-set” by annealing with their width and lengths constrained. The principal refractive indices at sodium D wavelength of these, asstretched and heat-set films were obtained using a modified Abbe refractometer. The changes in the principal refractive indices with the processing history were correlated with the orientation of PET chains and phenyl plane normals, which were determined independently by wide angle X-ray (WAXS) pole figure technique.
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  • 75
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    Polymer Engineering and Science 29 (1989), S. 1642-1648 
    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 order to achieve high fatigue strengths in heated-tool butt welds in plastic pipes used in gas and water supply lines, it is essential that optimum welding parameters be selected. In this paper, the different process phases are described by means of dimensionless characteristic parameters that have been obtained by applying similarity principles to heated-tool butt welding. On the basis of strength studies conducted on welded Joints, it is shown that the best weld quality is attained when the welding parameters are selected such that identical sheaf deformations result in the joint zones of small and large pipes. Laws for scaling data from small-pipe to large-pipe welds are then based on the values of these nondimensional numbers.
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  • 76
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    Polymer Engineering and Science 29 (1989), S. 1569-1573 
    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 gel melting temperature and crystallization kinetics of ultra-high molecular weight polyethylene (UHMW-PE)/decalin systems were investigated. Two methods were used to determine gel melting temperature; thermomechanical analysis (TMA) with a penetration probe and differential scanning calorimetry (DSC). The melting points determined from TMA and DSC were in good agreement, indicating that the crystallization of UHME-PE is an essential step for gelation. The gel melting temperature increases with UHMW-PE concentration. The change in gel melting temperature with composition results from interaction of the components in the amorphous phase. The gelation and crystallization rates increase with decreasing UHMW-PE concentration.
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  • 77
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    Polymer Engineering and Science 29 (1989), S. 1553-1559 
    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 cure of an epoxy-anhydride resin system used in pultrusion was characterized to develop an understanding of the cure behavior and to determine potential process controls parameters. Isothermal cures of neat resin formulations were monitored by differential scanning calorimetry (DSC), torsional braid analysis (TBA), and microdielectrometry (MDE). The processing conditions define a time/ temperature region in which monitoring would be applicable. Both DSC and MDE were found to yield useful information in this region, however, the events typically monitored by TBA either did not occur or occurred too quickly to be monitored. Significant ionic conductivity was observed in the fully cured resins at temperatures above the glass transition temperature and could possibly be used as a control parameter. This study revealed an apparent change in reaction mechanism with increasing cure temperature. DSC showed a change in activation energy with extent of reaction and a decrease in heat of reaction at the higher isothermal cure temperatures. The formation of a different network structure was indicated by a decreasing glass transition temperature of the cured resin with increasing cure temperature by both DSC and TBA.
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  • 78
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    Polymer Engineering and Science 29 (1989), S. 1604-1610 
    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: An investigation of the effect of physical aging on excess enthalpy of compatible polymer blends was carried out. Poly(methyl methacrylate) (PMMA) and poly(styrene-co-acrylonitrile) (SAN) were chosen for this study. Blends of different ratios of PMMA and SAN were physically aged at different times and temperatures below their glass transition (Tg) and then subjected to enthalpy relaxation measurement in a differential scanning calorimeter (DSC). An improved procedure was developed and, employed to analyze the data. The error associated with the calculation of the normalized deviation in enthalpy, known as the “Φ” function, was below 4%. The relaxation was observed to proceed faster at higher aging temperature. It was also found that at higher aging temperatures of Tg - 20 and Tg- 35°C, enthalpy relaxation in SAN-rich blends proceeds faster than in PMMA rich blends, while at the low aging temperature of Tg- 50°C the rate of relaxation becomes independent of the composition.
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  • 79
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    Polymer Engineering and Science 29 (1989), S. 1638-1641 
    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: Die-drawing techniques recently developed at Leeds University make it possible to produce oriented polymer tubes with both axial draw and hoopwise expansion. These products have increased axial stiffness, improved barrier properties, and excellent resistance to chemical reagents. Normally mechanical methods are used to join such tubes in order to preserve their orientation: however we show that electrofusion techniques produce joints of strengths such that in tensile tests, failure always occurs in the fittings, not at the joint interfaces. Optical and electron microscopy reveal different zones in the welds and indicate that only 20 percent of the wall thickness is affected by the electrofusion process. The pipe studied was biaxially drawn medium density polyethylene of outside diameter 63 mm with draw ratios of 4 in the axial direction and 2, inner hoop. Optimum welding conditions were determined using socket and saddle electrofusion fittings. The joints did not fail in a standard crush test. Careful control of welding parameters is essential in butt fusion welding when the maximum weld strength exceeds that of the undrawn polymer.
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  • 80
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1677-1682 
    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 has been made of vibration butt welds between plaques of polypropylene. The quality of the welds, as determined by impact tests, has been examined as a function of the welding variables: pressure and vibration amplitude. In addition, the microstructure of the welds has also been examined, classified, and correlated with the welding variables and weld quality. Penetration as a function of time shows three distinct regimes and It is shown that the impact strength of the welds is independent of time once the third regime is reached. The time required to reach the third regime decreases as pressure or amplitude increases and is more sensitive to amplitude of vibration than to pressure. The highest quality welds were produced at low pressure and low amplitude with corresponding long times to reach regime three and exhibited a unique, readily identifiable microstructure.
    Additional Material: 10 Ill.
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  • 81
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1705-1721 
    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 ultrasonic welding process is modeled using a five part model that includes mechanics and vibration of the parts, viscoelastic heating, heat transfer, flow and wetting, and intermolecular diffusion. The model predicts that melting and flow occur in steps, which has been confirmed by experiments. The model also indicates the possibility of monitoring joint quality by measuring the dynamic mechanical impedance of the parts during welding, which has also been verified experimentally by indirectly monitoring the magnitude of the impedance. via measurements of both the power and the acceleration of the base. When the melt fronts of the energy directors meet, at the end of welding, the dynamic impedance of the composites' interface is shown to rise rapidly. This raises the possibility of developing closed loop control procedures for the ultrasonic welding of thermoplastic composites. Ultrasonic welding of polyetheretherketone (PEEK) graphite APC-2 composites produced joints with excellent strengths.
    Additional Material: 31 Ill.
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  • 82
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1759-1765 
    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: Fluorescence spectroscopy has been employed to monitor the mixing of polymer melts with filler material. The polymer melts were low molecular weight polybutadiene and PBAN, a terpolymer consisting of 85% butadiene, 11% acrylonitrile, 4% acrylic acid, and the filler material was aluminum oxide. To carry out the fluorescence observations, a dopant chromophore was mixed into the polymer melt at very low concentrations, 10-4 to 10-6 molar or 11 to 0.11 ppm by weight. The mixing experiments were carried out using a small laboratory mixer which had glass walls for viewing the fluorescence spectra from the dopant chromophore. Fluctuations in fluorescence intensity were observed to decrease as a function of mixing time indicating that the spatial distribution of the fluorescent chromophores was becoming more uniform. Concerning the mixing of polymer melt and filler, we hypothesize that uniform mixing of ingredients is achieved when fluorescence intensity as a function of time is constant. In order to obtain quantitative support for this hypothesis, we used a fluorescence microscope to measure fluorescence intensity and optical transmittance from microscopic regions of well-mixed and poorly mixed specimens.
    Additional Material: 10 Ill.
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  • 83
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    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 5 (1989), S. 170-182 
    ISSN: 0887-3585
    Keywords: modeling ; flavodoxin ; structure prediction ; side chains ; database ; structure analysis ; protein ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The tertiary structure of flavodoxin has been model build from only the X-ray crystallographic α-carbon coordinates. Main-Chain atoms were generated from a dictionary of backbone structures. Side-chain conformations were initially set according to observed statistical distributions, clashes were resolved with reference to other knowledge-based parameters, and finally, energy minimization was applied. The RMSD of the model was 1.7 Å across all atoms to the native structure. Regular secondary structural elements were modeledmore accurately than other regions. About 40%of the ξ1 torsional angles were modeled correctly. Packing of side chains in the core was energetically stable but diverged significantly from the native structure in some regions.The modeling of protein structures is increasing in popularity but relatively few checks have been applied to determine the accuracy of the approach. In this work a variety of parameters have been examined. It was found that close contact, and hydrogen-bonding patterns could identifypoorly packed residues. These tests, however, did not indicate which residues had a conformation different from the native structure or how to move such residues to bring them into agreement. To assist in the modeling of interacting side chains a database of known interactions has been prepared.
    Additional Material: 8 Ill.
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  • 84
    ISSN: 0887-3585
    Keywords: yeast hexokinase II ; dimerization ; in vivo functions ; glucose repression ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The function of the N-terminal amino acids of Saccharomyces cerevisiae hexokinase II was studied in vivo using strains producing a form of hexokinase II lacking its first 15 amino acids (short form).This short form of hexokinase II was produced from a fusion between the promoter region of the PGK1 gene and the HXK2 coding sequence except the first 15 codons. As expected, the in vitro analysis of the short from protein by gel filtration chromatography indicates that the short protein does not form dimers under conditions where the wild-type protein dimerizes. Kinetic studies show that the enzymatic activities are very similarto wild-type behavior. The physiological experiments performed on the strains containing the fusion allele demonstrate that the short form ofthe enzyme is similar to the wild-type both in terms of phosphorylation of hexoses and glucose repression. We conclude that the N-terminalamino acids of hexokinase II are not required in vivo either for phosporylation of hexoses or for glucose repression.
    Additional Material: 4 Ill.
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  • 85
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    Proteins: Structure, Function, and Genetics 5 (1989), S. 248-257 
    ISSN: 0887-3585
    Keywords: subunit interactions ; icosahedral capsid ; electrostatic potential ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The role of the electrostatic interactions in the stability of the icosahedral β60 capsid of heavy riboflavin synthase from Bacillus Subtilis has been investigated using an approach based on the theory of Kirkwood and Tanford. The pH dependence of the electrostatic subunit interaction agrees well with experimental data. The electrostatic subunit interaction energy has a pronounced minimum at pH 8.2 for both the ligated and ligand-free capsid. The latter is characterized by a reduction of the magnitude and the pH range of the electrostatic attraction. It is found that only 8 charged groups, which form one cluster and two ion pairs, provide a significant contribution to the capsid stability. The analysis has shown that the aggregation/disaggregation equilibrium seems to be regulated by electrostatic interactions between β-subunits forming dimers, which connect the relatively stable pentamers in the β-60 capsid. The release of the ligand causesareduction of the electrostatic attraction of the dimers, which may induce disaggregation of the capsid. The electrostatic potential field due tothe titratable groups and α-helix macrodipoles has been calculated on the basic of the Coulomb relation. Two different values of the dielectric constant have been used for the protein and the surrounding solvent, respectively. The electrostatic potential shows a radially polardistribution with a positive pole at the inner capsid wall and a negative pole outside the capsid. An interesting feature of the electrostatic field is the formation of the positive potential “channels” that coincide with the channels constituted by the pentameric and trimeric β-subunit aggregates. It is supposed that the electrostatic potential field plays a role in enzyme-substrate recognition.
    Additional Material: 9 Ill.
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  • 86
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    Proteins: Structure, Function, and Genetics 5 (1989), S. 233-247 
    ISSN: 0887-3585
    Keywords: protein folding ; crystallographic data base ; structural analysis ; computer program system ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: PKB is a computer program system that combines a data base of three-dimensional protein structures with a series of algorithms for pattern recognition, data analysis, and graphics. By typing relatively simple commands the user may search the data base for instances of a structural motif and analyze in detail the set of individual structures that are found. The application of PKB to the study of protein folding is illustrated in three examples. The first analysis compares the conformations observed for a short sequential motif, sequences similar to the cell-attachment signal Arg-Gly-Asp. The second compares sequences observed for a conformational motif, a 16-residue βαβ unit. The third analysis considers a population of substructures containing ion-pair interaction, examining the relationship offrequency of occurrence to calculated electrostatic energy.
    Additional Material: 7 Ill.
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  • 87
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    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 6 (1989) 
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 88
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    Proteins: Structure, Function, and Genetics 6 (1989), S. 217-221 
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: No abstract.
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  • 89
    ISSN: 0887-3585
    Keywords: retrovirus ; bacterial expression ; high-performance liquid chromatography ; NH2- and COOH-terminal sequence analysis ; kcat ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A recombinant plasmid encompassing the human immunodeficiency virus type 1 (HIV 1) protease coding sequence and flanking regions (Ala-13 to Gly-185 of the pol open reading frame) has been expressed in two distinct strains of Escherichia coli, AR58 and AR68. In the first strain, AR58, the primary translation product, a 25 kilodalton (kDa) precursor protein, is short-lived and rapidly processes itself to the 11 kDa mature protease in vivo. In the second strain, AR68, the 25 kDa species isonly partially processed, and it, a 13 kDA intermediate, and the mature 11 kDA enzyme accumulate at a ratio of 3:4.5:2.5, respectively. The 11 kDa mature protease from AR58 and the 25 kDa precursor from AR68 have been purified to homogeneity. The yield of 11 kDa enzyme from AR58 is approximately 0.02 mg/g wet weight of E. coli cell pellet. The protease has both the expected NH2- and COOH-terminal sequences. The yield of 25 kDa enzyme from AR68 is approximately 0.1 mg/g wet weight of E. coli cell pellet. In vitro, the 25 kDa precursor enzyme rapidly (t1/2≅ 9 min) processes itself into a species with a mass of ∼13kDa and a species with a mass of ∼11 kDa. Both of these latter species can be separated by RP-HPLC, have the NH2-terminal sequence expected for the mature protease, and are active. The 11 kDa enzyme from AR58 comigrates with the 11 kDa enzyme from AR68 on RP-HPLC and SDS poly acrylamide gel electrophoresis. On extended incubation at 4°C at either neutral or acidic pH all species of the proteinexhibit further autodegradation at defined sequences. The availability of the mature, 11 kDa enzyme and the 25 kDa precursor will allow biochemical and physical studies on this critical viral enzyme.
    Additional Material: 7 Ill.
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  • 90
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    Proteins: Structure, Function, and Genetics 6 (1989), S. 215-215 
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
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  • 91
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    Proteins: Structure, Function, and Genetics 6 (1989), S. 222-230 
    ISSN: 0887-3585
    Keywords: G proteins ; p21ras ; GTPase ; cholera toxin ; GTPase-activating protein ; amino acid sequence ; protein structure ; conformational change ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The functions of G proteins - like those of bacterial elongation factor (EF) Tu and the 21 kDa ras proteins (p21ras) - depend upon their abilities to bind and hydrolyze GTP and to assume different conformations in GTP- and GDP-bound states. Similarities in function and amino acid sequence indicate that EF-Tu, p21ras, and G protein α-chains evolved from a primordial GTP-binding protein. Proteins in all three families appear to share common mechanisms for GTP-dependent conformational change and hydrolysis of bound GTP. Biochemical and molecular genetic studies of the α-chain of Gs (αs) point to key regions that are involved in GTP-dependent conformational change and in hydrolysis of GTP. Tumorigenic mutations of αs in human pituitary tumors inhibit-the protein's GTPase activity and cause constitutive elevation of adenylyl cyclase activity. One such mutation replaces a Gln residue in αs that corresponds to Gln-61 of p21ras; mutational replacements of this residue in both proteins inhibit their GTPase activities. A second class of the GTPase inhibiting mutations in αs occurs in the codon for an ARG residue whose covalent modification by cholera toxin also inhibits GTP hydrolysis by αs. This Arg residue is located in a domain of αs not represented in EF-Tu or p21ras. We propose that this domain constitutes an intrinsic activator of GTP hydrolysis, and that it performs a function analogous to that performed for EF-Tu by the programmed ribosome and for p21ras by the recently discovered GTPase-activating protein. Owing to their inherited similarities of structure and function, what we learn about αs, p21ras, or EF-tu as individual molecules helps us to understand crucial functions of other members of the super-family.
    Additional Material: 2 Ill.
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  • 92
    ISSN: 0887-3585
    Keywords: β-adrenergic recepor ; chimeric proteins ; receptor subtypes ; ligand binding ; protein structure-function ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Pharmacological analysis of ligand binding to the β-adrenergic receptor (βAR) has revealed the existence of two distinct receptor subtypes (β1 and β2) which are the products of different genes. The predicted amino acid sequence of the β1 and β2 receptors differ by 48%. To identify the regions of the proteins responsible for determining receptor subtype, chimeras were constructed from domains of the human β1 and hamster β2 receptors. Analyses of the ligand-binding characteristics of these hybrid receptors revealed that residues in the middle portion of the βAR sequence, particularly around transmembrane regions 4 and 5, contribute to the subtype specific binding of agonists. Smaller molecular replacement of regions of the hamster β2AR with the analogous regions from the avian β1AR, however, failed to identify any single residue substitution capable of altering the subtype specificity of the receptor. These data indicate that, whereas sequences around transmembrane regions 4 and 5 may contribute to conformations which influence the ligand-binding properties of the receptor, the subtype-specific differences in amine-substituted agonist binding cannot be attributed to a single molecular interaction between the ligand and any amino acid residue which is divergent between the β1 and β2 receptors.
    Additional Material: 4 Ill.
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  • 93
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    Proteins: Structure, Function, and Genetics 6 (1989), S. 382-394 
    ISSN: 0887-3585
    Keywords: immunoglobulins ; hydrogen bonding ; hairpin loops ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Loops are integral components of protein structures, providing links between elements of secondary structure, and in many cases contributing to catalytic and binding sites.The conformations of short loops are now understood to depend primarily on their amino acid sequences. In contrast, the structural determinants of longer loops involve hydrogen-bonding and packing interactions within the loop and with other parts of the protein. By searching solved protein structures for regions similar in main chain conformation to the antigen-binding loops in immunoglobulins, we identified medium-sized loops of similar structure in unrelated proteins, and compared the determinants of their conformations.For loops that form compact substructures the major determinant of the conformation is the formation of hydrogen bonds to inward-pointing main chain atoms. For oops that have more extended conformations, the major determinant of their structure is the packing of a particular residue or residues against the rest of the protein.The following picture emerges: Medium-sized lops of similar conformation are stabilized by similar interaction. The groups that interact with the loop have very similar spatial dispositions with respect to the loop. However, the residues that provide these interactions may arise from dissimilar parts of the protein: The conformation of the loop requires certain interactions that the protein may provide in a variety of ways.
    Additional Material: 11 Ill.
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  • 94
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    Proteins: Structure, Function, and Genetics 5 (1989), S. 8-12 
    ISSN: 0887-3585
    Keywords: ribonuclease A ; protein deamidation ; protein conformation ; disulfide bonds ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The effect of the folded conformation of a protein on the rate of deamidation of a specific asparaginyl residue has been determine. Native and unfolded ribonuclease A (RNase A) could be compared under identical conditions, because stable unfolded protein was generated by breaking irreversibly the protein disulfide bonds.Deamidation of the labile Asn-67 residue of RNase A was followedelectrophoretically and chromatographically. At 80°C, similar rates of deamidation were observed for the disulfidebonded form, which is thermally unfolded, and the reduced form. At 37°C and pH 8, however, the rate of deamidation of native RNase A was negligible, and was more than 30-fold slower than that of reduced, unfolded RNase A. This demonstrates that the Asn-67 residue is located in a local conformation in the native protein that greatly inhibits deamidation. This conformation is the β-turn of residues 66-68.
    Additional Material: 5 Ill.
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  • 95
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    Proteins: Structure, Function, and Genetics 5 (1989), S. 1-7 
    ISSN: 0887-3585
    Keywords: helix stabilization ; helix dipole ; charged group ; pH titration ; electrostatic interaction ; hydrogen bonding ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Interactions between the α-helix peptide dipoles and charged groups close to the ends of the helix were found to be an important determinant of α-helix stability in a previous study.1 The charge on the N-terminal residue of the C-peptide from ribonuclease A was varied chiefly by changing the α-NH2 blocking group, and the correlation of helix stability with N-terminal charge was demonstrated. An alternative explanation for some of those results is that the succinyl and acetyl blocking groups stabilize the helix by hydrogen bonding to an unsatisfied main-chain NH group. The helix dipole model is tested here with peptides that contain either a free α-NH3+ α-COO- groups, and no other charged groups that would titrate with similar pKa's. This model predicts that α-NH3α-COO- groups are helix-destabilizingand that the destabilizing interactions are electrostatic in origin. The hydrogen bonding model predicts that α-NH3 and α-COO- groups are not themselves helix-destabilizing, but that an acetyl or amide blocking group at the N- or C- terminus, respectively, stabilizes the helix by hydrogen bonding to an unsatisfied main-chain NH or CO group.The results are as follows: (1) Removal of the charge from α-NH3 and α-COO- groups by pH titration stabilizes an α-helix. (2) The increase in helix stability on pH titration of these groups is close to the increase produced by adding an acetyl or amide blocking group. (3) The helix-stabilizing effect of removing the charge from α-NH3 and α-COO- groups by pH titration is screened by increasing the NaCl concentration, and therefore the effect is electrostatic in origin. (4) Replacing the C-terminal amide blocking group with a methylester blocking group, which cannot donate a hydrogen bond, causes little change in helix stability.
    Additional Material: 6 Ill.
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  • 96
    ISSN: 0887-3585
    Keywords: template-assembled synthetic protein (TASP) ; 4-helix bundle ; β-barrel structure ; protein de novo design ; peptide synthesis ; peptide conformation ; orthogonal protection ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The construction of a template-assembled synthetic protein (TASP) designed to contain both a 4-helix bundle and a β-barrel as two folding “domains” is described. For the de novo design of proteins, amphiphilic helices (α) and β-sheets (β) are covalently attached to a template peptide (T) carrying functional side chains suitably oriented to promote intarmolecular folding of the secondary structure blocks into a characteristic packing arrangement, i.e., T8-(4α)(4β). The design of this new macromolecule was assisted by computer modeling, which suggested a low-energy conformation with tight hydrophobic packing of the secondary structure subunits. Solid-phase synthesis of the “two-domain” TASP molecule was achieved using orthogonal protection techniques. The solution properties as well as circular dichroism (CD) and infrared spectroscopy (IR) data under various experimental conditions are consistent with the folded conformation suggested by modeling.
    Additional Material: 6 Ill.
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  • 97
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    Proteins: Structure, Function, and Genetics 5 (1989), S. 313-321 
    ISSN: 0887-3585
    Keywords: protein ; electron transfer ; molecular dynamic simulations ; dielectric ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Electrostatic calculations have been carried out on a number of structural conformers of tuna cytochrome c Conformers were generated using molecular dynamics simulations with a range of solvent simulating, macroscopic dielectric formalisms, and one solvent model that explicitly included solvent water molecules. Structures generated using the lowest dielectric models were relatively tight, with-side chains collapsed on the surface, while those from the higher dielectric modelshad more internal and external fluidity, with surface side chains exploring a fuller range of conformational space. The average structure generated with the explicitly solvated model corresponded most closely with the crystal structure. Individual pK values, overall titration curves, and electrostatic potential surfaces were calculated for average structures and along each simulation. Differences between structural conformers within each simulation give rise to substantial changes in calculated local electrostatic interactions, resulting in pK value fluctuations for individual sites in the protein that very by 0.3-2.0 pK units from the calculated time average. These variations are due to the thermal side chain reorientations that produce fluctuations in charge site separations. Properties like overall titration curves and pH dependent stability are not as sensitive to side chain fluctuations within a simulation, but there are substantial effects between simulation due to markeddifferences in average side chain behavior. These findings underscore the importance of proper dielectric formalism in molecular dynamics simulations when used to generate alternate solution structures from a crystal structure, and suggest that conformers significantly removed from the averagestructure have altered electrostatic properties that may prove important inepisodic protein properties such as catalysis.
    Additional Material: 7 Ill.
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  • 98
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    Proteins: Structure, Function, and Genetics 5 (1989), S. 337-354 
    ISSN: 0887-3585
    Keywords: computer simulation ; fluctuations in proteins ; secondary structural dynamics ; lysozyme ; protein-substrate complex ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The relation between protein secondary structure and internal motions was examined by using molecular dynamics to calculate positional fluctuations of individual helix, β-sheet, and loop structural elements in free and substrate-bound hen egg-white lysozyme. The time development of the fluctuations revealed a general correspondence between structure and dynamics; the fluctuations of the helices and β-sheets converged within the 101 psec period of the simulation and were lower than average in magnitude, while the fluctuations of theloop regions were not converged and were mostly larger than average in magnitude. Notable exceptions to this pattern occurred in the substrate-bound simulation. A loop region (residues 101-107) of the active site cleft had significantly reduced motion due to interactions withthe substrate. Moreover, part of a loop and a 310 helix (residues of 67-88) not in contact with the substrate showeda marked increase in fluctuations. That these differences in dynamics of free and substrate-bound lysozyme did not result simply from sampling errors was established by an analysis of the variations in the fluctuationsof the two halves of the 101 psec simulation of free lysozyme. Concerted transitions of four to five mainchain φ and ψ angles between dihedral wells were shown to be responsible for large coordinate shifts in the loops. These transitions displaced six or fewer residues and took place eitherabruptly, in 1 psec or less, or with a diffusive character over 5-10 psec. Displacements of rigid secondary structures involved longer timescale motions in bound lysozyme; a 0.5 Å rms change in the position of a helix occurred over the 55 psec simulation period. This helix reorientation within the protein appears to be a response to substrate binding. There was little correlation between the solvent accessible surface areaand the dynamics of the different structural elements.
    Additional Material: 15 Ill.
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  • 99
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    Proteins: Structure, Function, and Genetics 6 (1989), S. 32-45 
    ISSN: 0887-3585
    Keywords: long range truncation ; molecular dynamics ; myoglobin ; truncation effects ; protein electrostatics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: This paper considers the effects of truncating long-range forces on protein dynamics. Six methods of truncation that we investigate as a function of cutoff criterion of the long-range potentials are (1) a shifted potential; (2) a switching function; (3) simple atom-atom truncation based on distance; (4) simple atom-atom truncation based on a list which is updated periodically (every 25 steps); (5) simple group-group truncation based on distance; and (6) simple group-group truncation based on a list which is updated periodically (every 25 steps). Based on 70 calculations of carboxymyoglobin we show that the method and distance of long range cutoff have a dramatic effect on overall protein behavior. Evaluation of the different methods is based on comparison of a simulation's rms fluctuation about the average coordinates of a no cutoff simulation and from the X-ray structure of the protein. The simulations in which long-range forces are truncated by a shifted potential shows large rms deviations for cutoff criteria less than 14 Å, and reasonable deviations and fluctuations at this cutoff distance or larger. Simulations using a switching function are investigated by varying the range over which electrostatic interactions are switched off. Results using a short switching function that switches off the potential over a short range of distances are poor for all cutoff distances. A switching function over a 5-9 Å range gives reasonable results for a distance-dependent dielectric, but not using a constant dielectric. Both the atom-atom and group-group truncation methods based on distance shows large rms deviations and fluctuation for short cutoff distance, while for cutoff distance of 11 Å or greater, reasonable results are achieved. Although comparison of these to distance-based truncation methods show surprisingly larger rms deviations for the group-group truncation, contrary to simulation studies of aqueous ionic solutions. The results of atom-atom or group-group list-based simulations generally appear to be less stable than the distance-based simulations, and require more frequent velocity scaling or stronger coupling to a heat bath.
    Additional Material: 7 Ill.
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  • 100
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    Proteins: Structure, Function, and Genetics 6 (1989), S. 70-85 
    ISSN: 0887-3585
    Keywords: Protein electrostatics ; protein kinases ; effector protein ; calciumbinding protein ; α-helix ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Calmodulin's calculated electrostatic potential surface is asymmetrically distributed about the molecule. Concentrations of uncompensated negative charge are localized near certain α-helices and calcium-binding loops. Further calculations suggest that these charge features of calmodulin can be selectively perturbed by changing clusters of phylogenetically conserved acidic amino acids in helices to lysines. When these cluster charge reversals are actually produced by using cassette-based site-specific mutagenesis of residues 82-84 or 118-120, the resulting proteins differ in their interaction with two distinct calmodulin-dependent protein kinases, myosin light chain kinase and calmodulin-ldependent protein kinase II. Each calmodulin mutant can be purified to apparent chemical homogeneity by an identical purification protocol that is based on conservation of its overall properties, including calcium binding. Although cluster charge reversals result in localized perturbations of the computed negative surface, single amino acid changes would not be expected to alter significantly the distribution of the negative surface because of the relatively high density of uncompensated negative charges in the region around residues 82-84 and 118-120. However, this does not preclude the possibility of single amino acid charge perturbations having a functional effect on the more intimate, catalytically active complex. The electrostatic surface of calmodulin described in this report may be a feature that would be altered only by cluster charge reversal mutations. Overall, the results suggest that the charge properties that are important for the efficient assembly of calmodulin-protein kinase signal transduction complexes in eukaryotic cells.
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