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  • Chemistry  (6)
  • Polymer and Materials Science  (6)
  • INSTRUMENTATION AND PHOTOGRAPHY  (1)
  • Analytical Chemistry and Spectroscopy
  • 1985-1989
  • 1975-1979  (8)
  • 1970-1974
  • 1976  (8)
Collection
Keywords
Publisher
Years
  • 1985-1989
  • 1975-1979  (8)
  • 1970-1974
Year
  • 1
    Electronic Resource
    Electronic Resource
    The effect of molecular weight on the physical and mechanical properties of ultra-drawn high density polyethylene (1976)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 16 (1976), S. 200-203 
    Details
    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 on the effects of molecular weight on the physical and mechanical properties of cold-extruded high density polyethylene. Prior data indicate that such ultra-drawn strands contain a significant fraction of extended-chain crystals. Four samples, spanning the molecular weight range of 59,000 to 147,000, were cold-extruded under the same conditions and were examined with respect to their melting point, degree of crystallinity, linear expansion coefficient, Young' modulus, strain to break, and tensile strength. The degree of crystallinity, linear expansion coefficient, and modulus did not change significantly with molecular weight. The melting point, strain to break, and tensile strength do increase with increasing molecular weight. This leads to the conclusion that the amount of extended-chain crystals is invariant with molecular weight. Higher molecular weight polymers are seen as providing a greater number of the chains, thus giving the fiber a higher tensile strength.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760160313
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    A comparison of equations for the effect of pressure on the viscosity of amorphous polymers (1976)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 20 (1976), S. 1199-1208 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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 equations which are used to predict the pressure coefficient of viscosity for amorphous polymers have been examined on the basis of type of information required and equation reliability. These equations can be useful in accounting for pressure effects observed in tubular flow and in other shear geometries. The correlations of Penwell and Porter and of Miller are evaluated and in the perspective of expressions by Matheson and by Eyring. Data on linear amorphous polystyrene (PS), polyisobutylene, poly(vinyl acetate), poly(methyl methacrylate) (PMMA), natural rubber, and polycarbonate are examined and presented. Predictions from the Penwell-Porter and Miller equations are compared with experimental coefficients at one atmosphere for all data available. For PS and PMMA, it was found that Miller's equation tends to predict values somewhat higher than experiments but is closer to the data on PS and on a high molecular weight PMMA. The Penwell-Porter equation, on the other hand, tends to predict values somewhat lower than experiments and does a slightly better job for lower molecular weight PMMA. Both equations require WLF or Vogel coefficients and Tg-pressure-molecular weight data. Miller's equation also requires compressibilities at Tg and at the temperature of interest, although an alternate method can be used which only requires average “K” values without Tg-pressure or compressibilities at Tg.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1976.070200506
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Polystyrene degradation in model extrusion experiments (1976)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 20 (1976), S. 1301-1312 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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 has been made of the magnitude and the source of degradation of polystyrene in model extrusion experiments. A preformed solid plug of a narrow-distribution, high molecular weight polystyrene (M̄w = 2 × 106) was used for each experiment. The extrusions were performed with an Instron capillary rheometer at constant temperatures from 160° to 220°C. The molecular weight changes occurring in the capillary reservoir during the pass of the capillary and in the hot extrudate were evaluated. Molecular weights and distributions were obtained by gel permeation chromatography. A significant degradation was observed in the capillary reservoir. The degree of degradation was independent of polymer flow. The polystyrene near the walls reacted more extensively than that closer to the axis, but a constant degradation was observed along the axis. The molecular weight profile across the capillary reservoir was attributed to a selective thermo-oxidative degradation (160° and 190°C). Changes in molecular weight due to mechanical degradation in the capillary were observed only at 160°C. This reaction was referred to as a mechano-oxidative process, as no degradation could be detected in the absence of oxygen. At 160°C, selective migration of macromolecules (fractionation) during extrusion did not occur to any significant extent, nor could any thermo-oxidative degradation of the extrudate be detected. When a small amount of antioxidant (Ionol) was added to the polystyrene, no selective degradation did occur at the walls of the capillary reservoir during extrusion at 160° and 190°C.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1976.070200513
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  • 4
    Electronic Resource
    Electronic Resource
    Rheological properties of partially hydrolyzed ethylene-vinyl acetate copolymers (1976)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 20 (1976), S. 1321-1330 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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 have been made of steady-shear and dynamic viscosities for melts of two ethylene-vinyl acetate copolymers and their partially hydrolyzed derivatives using a Weissenberg rheogoniometer over the temperature range of 123-150°C with some tests at 160°C. The flow activation energy of all samples studied was essentially independent of shear stress. The introduction of hydroxyl groups in controlled concentrations, however, produced a complicated flow behavior. At low concentrations, there is a marked increase in Newtonian viscosity, flow activation energy, and shear dependence of viscosity. In contrast to previous reports, a further increase in all three functions was not observed with increasing vinyl alcohol concentration. Dynamic viscosities, in contrast, show monotonic increases with increasing hydroxyl group content, as do activation energies derived from the temperature dependence of the dynamic viscosity. These data may result from an increased chain cohesion due to hydrogen bonding of hydroxyl groups.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1976.070200515
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  • 5
    Electronic Resource
    Electronic Resource
    Shear degradation of polyisobutene (1976)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 20 (1976), S. 1289-1300 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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 polyisobutene of M̄w 1.98 × 106, M̄w/M̄n 1.8, was extruded in an Instron capillary rheometer. Shear degradation occurred at high shear stresses, approaching melt fracture, and was more prominent at lower extrusion temperatures for tests at 60-140°C. The capillary was 2.0 in. long with a length/diameter ratio of 66.7 and a 90° entrance angle. Repetitive extrusions at constant shear rate caused a decrease in a molecular weight and a simultaneous narrowing of the molecular weight distribution. Extrudate expansion was measured after each successive capillary pass for tests at 80°C. Extrudate swelling correlated well with (M̄z+1) M̄z/M̄w, except for the two first passes, where melt fracture was pronounced. The correlation with equilibrium extrudate expansion was almost as good for (M̄z/M̄w)3.7 (Mill's correlation) and for M̄z+1 alone. The efficiency of bond rupture is low, with the energy required to rupture 1 mole of bonds being about 200,000 kcal at 80°C.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1976.070200512
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  • 6
    Electronic Resource
    Electronic Resource
    Structure and properties of oriented polymers, I. M. Ward, Ed., Halsted Press, a division of John Wiley & Sons, Inc., New York, 1975, 500 pp. $57.50 (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Letters Edition 14 (1976), S. 116-118 
    Details
    ISSN: 0360-6384
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1976.130140213
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  • 7
    Electronic Resource
    Electronic Resource
    Polystyrene degradation induced by stresses resulting from the freezing of its solutions (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 14 (1976), S. 553-564 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solutions of polystyrene in p-xylene were frozen in liquid nitrogen. No changes in molecular weight and distribution were caused by freezing solutions for a series of narrow distribution polystyrenes with molecular weights of near 2 × 106 and lower. Likewise a commercial polystyrene of M̄w = 234,000 showed no change, even after 45 cycles of freezing and thawing. However, an ultrahigh molecular weight polystyrene (M̄w = 7.3 × 106) showed appreciable degradation even after a few freezing cycles of its solutions. The changes in molecular weight and distribution were analyzed by gel-permeation chromatography. The results depended very much on the choice of solvent, cooling rate, and concentration. The extent of degradation was found to depend on polymer concentration in two distinct ways. Indeed, two different degradation mechanisms have been distinguished at low and at high concentrations. The change between mechanisms took place between 1.0 and 2.5 g/l. for polystyrene in p-xylene. This appears to provide a rare measure of polymer-polymer interactions (entanglements) in dilute solutions. Degradation in the entanglement region proceeded via a random chain-scission mechanism as tested by the Scott method. In contrast, at low concentrations degradation was characterized by the formation of appreciable amounts of low molecular weight polystyrene. The presence of an antioxidant (Ionol) during freezing did not change the extent of degradation significantly.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1976.170140304
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  • 8
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    Microwave radiometer for subsurface temperature measurement (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A UHF radiometer, operating at a frequency of 800 MHz, was modified to provide an integral, three frequency voltage standing wave ratio (VSWR) circuit in the radio frequency (RF) head. The VSWR circuit provides readings of power transmission at the antenna-material interface with an accuracy of plus or minus 5 percent. The power transmission readings are numerically equal to the emissivity of the material under observation. Knowledge of material emissivity is useful in the interpretation of subsurface apparent temperatures obtained on phantom models of biological tissue. The emissivities of phantom models consisting of lean beefsteak were found to lie in the range 0.623 to 0.779, depending on moisture content. Radiometric measurements performed on instrumented phantoms showed that the radiometer was capable of sensing small temperature changes occurring at depths of at least 19 to 30 mm. This is consistent with previously generated data which showed that the radiometer could sense temperatures at a depth of 38 mm.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-CR-137827
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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