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  • 1
    Electronic Resource
    Electronic Resource
    Studies of epoxy resin systems: Part B: Effect of crosslinking on the physical properties of an epoxy resin (1982)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 22 (1982), S. 1213-1220 
    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: An epoxy system consisting of diglycidyl ether of butanediol, DGEB, cured with 4-4′ diaminodiphenyl sulfone, DDS, has been used for a study of the effect of crosslinking density on the properties of the epoxy resin. Because of the low curing rate at room temperature and the low glass-transition temperature, this system was amenable to a wide range of controlled cross-linking density. The crosslinking density was monitored by FTIR (Fourier transform infrared spectroscopy), which followed the change in concentration of the epoxy groups during the curing reaction. The bulk density was found to increase linearly with the crosslinking density. The modulus, the upper yield point, the lower yield point, and the degree of retraction of a deformed sample all increased with the degree of crosslinking. The thermally stimulated depolarization (TSD) β-peak was found to vary with crosslinking density, but the γ-peak was not changed. The TSD a peak was found to decrease in strength, but increased in temperature as the crosslinking density increased. This observation suggests that TSD measurements arc a good monitor of crosslinking density of epoxy resins, particularly near the final stage of the crosslinking reaction.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760221807
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  • 2
    Electronic Resource
    Electronic Resource
    Flow-induced crystallization of polypropylene in stretched ribbons (1976)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 16 (1976), S. 217-221 
    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: Ribbons of molten polypropylene have been extruded into a thermostatted chamber and subjected to elongations ranging as high as 4400-fold. Some of these ribbons have been shown to possess the unusual ability of recovering nearly all of the strain from large levels of stretch (≤100 percent). This property, as well as the magnitude of the tensile yield drop, has been found to be directly proportional to the uniaxial character of the flow present at the moment of crystallization. The structure in the final solid films has been characterized by wide angle X-ray diffraction and crystal orientation distribution. Both of these factors have been found to be proportional to the character of flow at the moment of crystallization. Finally, the temperature in the thermostatted chamber has been shown to affect the character of the flow.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760160316
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  • 3
    Electronic Resource
    Electronic Resource
    Studies of epoxy resin systems: Part A: A study of the origins of the secondary relaxations of epoxy resins by thermally stimulated depolarization (1982)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 22 (1982), S. 1205-1212 
    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: The relaxation behavior of several epoxy resin systems, which have systematic structural differences, has been studied by the thermally stimulated discharge (TSD) technique. Two TSD peaks centered at about 115°K (β peak) and 185°K (β peak) were found for epoxy resins cured with a diamine. Structural change, either in the epoxy resin molecule or the amine molecule, did not seem to affect those two peaks. The TSD thermogram of the DGEBA (diglycidyl ether of disphenol A) epoxy resin part only showed a small new peak at 160°K instead of the ft peak at 185°K. This result, together with the fact that postcuring increased β peak height, leads to the conclusion that the ft peak is most likely due to the newly-created molecular segment during the curing reaction. The peak at 160°K was assigned to the epoxy group. This assignment was based on the fact that the 160°K peak of an epoxy homopolymer, which has fewer epoxy groups, was smaller than that of the parent DGEBA. The β and γ peaks were found to be of distributed characteristics, and the distribution of activation energy was studied by the partial heating method.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760221806
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  • 4
    Electronic Resource
    Electronic Resource
    Development of stress-crystallized morphology during melt-spinning of polypropylene fibers (1973)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 13 (1973), S. 295-299 
    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: Melt-spinning of isotactic polypropylene was performed in an effort to assess how the flow field that exists within a filament affects final as-spun fiber morphology. It was concluded that the molten filament deforms chiefly by elongational flow, with some small amount of shearing flow bearing localized near the filament periphery. The resulting crystal texture is mostly comprised of lamellae oriented perpendicular (chain direction parallel) to the fiber axis, but a minority population of crystallites whose orientation is orthogonal (chain direction perpendicular) to the primary population is also present in these fibers. Post-drawing steps initially cause crystallites to rotate toward the axial direction, while the chains within them undergo intralamellar slip and become better oriented parallel to the fiber axis. At larger extensions, lamellar crystallites are pulled into microfibrillar units.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760130409
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  • 5
    Electronic Resource
    Electronic Resource
    Monodisperse polyethylenes: Crystallization kinetics (1979)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 19 (1979), S. 436-440 
    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: Crystallization kinetics of hydrogenated monodisperse polybutadienes have been measured using hot-stage microscopy, and the data have been analyzed in terms of crystallization half-time and Avrami exponent. Results obtained from hydrogenated polybutadienes having M̄w's in the range 5,100 to 340,000 were compared with what was obtained from several commercial polyethylenes. A four-branch star hydrogenated polybutadiene was also included in this study. Crystallization half-time at constant undercooling was found to go through a minimum when expressed as a function of M̄w; such behavior is consistent with polyethylene data already reported in the literature. It was found that crystallization half-times for all polyethylene homopolymers studied (hydrogenated polybutadienes as well as commercial polyethylenes with their broad molecular weight distributions) exhibit similar exponential dependences on undercooling.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760190613
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  • 6
    Electronic Resource
    Electronic Resource
    Crystal nucleation in sheared polymer melts (1978)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 18 (1978), S. 215-221 
    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 semiquantitative procedure has been developed for analyzing crystal nucleation in undercooled polymer melts that are undergoing flow. This analysis was applied to the specific ease of molten high density polyethylene experiencing low levels of shearing flow. A custom-made concentric cylinder viscometer, which could be operated by the Rheometrics mechanical spectrometer instrument, was used to make simultaneous measurements of transmitted torque and optical anisotropy in isothermal melts, The result of the analytical procedure developed here was molecular Size-dependence of chain distensions caused by prevailing shear. This distribution function was verified by testing against experimentally obtained values of birefringence. Total entropy reduction resulting from this distorted state was then calculated, and the corresponding increase in free energy was found to be at least enough to account for comparable crystal nucleation rates in flowing melts at higher temperatures and in quiescent melts at lower temperatures.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760180308
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