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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Chemistry of materials 4 (1992), S. 1240-1245 
    ISSN: 1520-5002
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Brookfield, Conn. : Wiley-Blackwell
    Journal of Vinyl and Additive Technology 16 (1994), S. 96-101 
    ISSN: 0193-7197
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The use of multiphase polymers is of growing importance given their inherent economical and technological benefits. Unplasticized PVC is brittle and heat sensitive. Improved impact resistance is often attained by using rubber additives. However, the rubber contributes to increasing viscosity, and, consequently, limited processability. Research efforts are concentrated on the development of a PVC matrix blend that has good heat stability and processability. While traditional PVC modification has concentrated on using plasticizers to aid processing, in this project, the use of three styrenic copolymers has been investigated. Miscibility of the systems has been established using the Rheometrics Mechanical Spectrometer by determining the number of transitions in the resultant blends. Long range time-temperature effects have been established via generation of master curves for the two component systems. The shift factor data has been analyzed to determine the corresponding activation energies associated with different transitions. These indicate a methodology to design optimum blend systems.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Brookfield, Conn. : Wiley-Blackwell
    Journal of Vinyl and Additive Technology 1 (1995), S. 88-93 
    ISSN: 0193-7197
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In an effort to improve the utility and processing of PVC, additives like heat distortion modifiers and plasticizers are often added. While the economics of using PVC are highly favorable, they are limited in their dimensional stability at high temperatures. Blending with a component having better dimensional stability at higher temperatures is therefore investigated. In this paper, use of a styrenic copolymer, styrene acrylonitrile (SAN), and a substituted styrenic copolymer, alpha methyl styrene acrylonitrile (αMSAN), is studied. The glass transition-composition behavior is studied through dynamic mechanical measurements. Heat distortion test results of the blend in compositions of 0-100 in 10% increments indicate enhanced DTUL above certain compositions. Rheological characterization is done both in the low strain steady shear and dynamic mode. High shear rate testing was done. In general it was found that while the styrenic copolymer exhibits a plasticization of the PVC glass transition, the substituted styrene, by maximizing the repulsive interaction effects, pushes the system to a limited partial miscibility.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 1635-1642 
    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: By using an advanced epoxy resin of 22,500 weight average molecular weight two bimodal systems of 6300 weight average molecular weights were prepared. By altering the curing procedure normally used to cure epoxy resins and high molecular weight resins we have succeeded in minimizing the difficulty associated with preparing bimodal epoxy resin systems. The ultimate Tg of these bimodal systems is associated with the phase morphology and controlled by the curing conditions employed. For the completely phase separated bimodal system a Tg of 473 K is reported and for the partially phase separated system a Tg of 466 K is reported. Equations were developed for predicting the equilibrium shear modulus of these bimodal systems. Theoretical predictions based on these equations were found to be consistent with experimental results.
    Additional Material: 9 Ill.
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  • 5
    Publication Date: 1992-11-01
    Print ISSN: 0897-4756
    Electronic ISSN: 1520-5002
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 6
    Publication Date: 2013-08-31
    Description: The materials made available through the Long Duration Exposure Facility (LDEF) satellite provide a set of specimens that can be well characterized and have a known exposure history with reference to atomic oxygen and ultraviolet radiation exposure. Mechanical characteristics measured from control samples and exposed samples provide a data base for predicting the behavior of polymers in low earth orbit. Samples of 1.0 mil thick low density polyethylene were exposed to the low earth orbit environment for a period of six years. These materials were not directly exposed to ram atomic oxygen and offer a unique opportunity for measuring the effect of atomic oxygen and UV radiation on mechanical properties with little concern to the effect of erosion. The viscoelastic characteristics of these materials were measured and compared to the viscoelastic characteristics of control samples. To aid in differentiating the effects of changes in crystallinity resulting from thermal cycling, from the effects of changes in chemical structure resulting from atomic oxygen/UV attack to the polymer, a second set of control specimens, annealed to increase crystallinity, were measured as well. The resulting characterization of these materials will offer insight into the impact of atomic oxygen/UV on the mechanical properties of polymeric materials. The viscoelastic properties measured for the control, annealed, and exposed specimens were the storage and loss modulus as a function of frequency and temperature. From these datum is calculated the viscoelastic master curve derived using the principle of time/temperature superposition. Using the master curve, the relaxation modulus is calculated using the method of Ninomiya and Ferry. The viscoelastic master curve and the stress relaxation modulus provide a direct measure of the changes in the chemical or morphological structure. In addition, the effect of these changes on long-term and short-term mechanical properties is known directly. It should be noted that the dependence on directionality for the polymer films was considered since these films were manufactured by a blown-film process.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. Part 3: Second Post-Retrieval Symposium; p 849-866
    Format: application/pdf
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  • 7
    Publication Date: 2013-08-29
    Description: One of the trays aboard LDEF was an experiment having the objective of assessing the effects of long term exposure of candidate balloon films, tapes, and lines to the hostile environment of space. The fortuitous location of these materials on LDEF minimized direct impact by atomic oxygen thus providing an opportunity to study the effects of low earth orbit environments on polymeric materials without the worry of atomic oxygen abrasion. The resulting chemical, morphological, and thermomechanical changes for polyethylene specimens are reviewed. In addition, preliminary data for fluorinated ethylene/propylene copolymers used for thermal blankets is presented. Polyethylene is observed to crosslink and branch from exposure to atomic oxygen and/or ultraviolet with a decrease in crystallinity.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. First Post-Retrieval Symposium, Part 2; p 705-722
    Format: text
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  • 8
    Publication Date: 2019-01-25
    Description: Changes in polymer properties which result after exposure to an atomic oxygen-rich environment of a flowing afterglow are presented. Dynamic mechanical and Fourier Transform Infrared (FTIR) spectra as well as scanning electron microscopy micrographs were employed to monitor variations in mechanical properties and chemical and physical structure. Polymers analyzed include polystyrene, PEKK, and a polyester.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA, Langley Research Center, First LDEF Post-Retrieval Symposium Abstracts; p 55
    Format: text
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  • 9
    Publication Date: 2019-01-25
    Description: The initial results of analysis performed on a number of polymeric materials which were exposed aboard the Long Duration Exposure Facility (LDEF) are discussed. These materials include two typical high altitude balloon films (a polyester and a polyethylene) and silver-backed Teflon from thermal control blanket samples. The techniques used for characterizing changes in mechanical properties, chemical structure and surface morphology include Fourier Transform Infrared (FTIR) spectroscopy, scanning electron microscopy, and dynamic mechanical analysis.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA, Langley Research Center, First LDEF Post-Retrieval Symposium Abstracts; p 54
    Format: text
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  • 10
    Publication Date: 2019-01-25
    Description: Preliminary results of thin film polymers exposed to low-Earth orbit aboard the Long Duration Exposure Facility (LDEF) are discussed. Dynamic testing of a 0.92/0.92 mil. polyester laminate film indicated that the modulus loss of the exposed specimens may be very small. When the storage modulus of the exposed specimen was compared to the storage modulus of a control specimen over a temperature range of minus 150 degrees to 100 degrees, there was very little change. Fourier Transform Spectroscopy performed on the same exposed material indicated crosslinking of the polyethylene, which was verified by an increase in the storage modulus above the glass transition temperature. Optical microscopy of the sample showed micrometeoroid strikes and contamination in spots by what is thought to be silicon outgassed from a nearby experiment.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA, Langley Research Center, First LDEF Post-Retrieval Symposium Abstracts; p 53
    Format: text
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