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  • 1
    Electronic Resource
    Electronic Resource
    Solid-state phase behavior and molecular-level mixing phenomena in a strongly interacting polymer blend (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 28 (1990), S. 1261-1274 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: This research contribution addresses mixing phenomena in a polymer blend that exhibits strong intermolecular association and bieutectic phase behavior. Molecular-level observations of specific interactions between dissimilar blend components have been obtained from high-resolution solid-state proton and carbon-13 nuclear magnetic resonance (NMR) experiments at ambient temperature. Results illustrate mixing effects on the isotropic chemical shifts of the critical component in a completely or partially phase-mixed blend. Perturbations in the NMR spectra result from conformational changes, hydrogen bonding, molecular complexation, or altered packing geometries that occur concomitantly with the mixing process. More convincing evidence that two components of a strongly interacting blend reside in a near-neighbor environment is obtained from the measurement of proton spin diffusion between dissimilar species. Proton spin diffusion is measured directly via the high-resolution CRAMPS experiment (Combined Rotation and Multiple Pulse Spectroscopy) in a molecular complex of poly (ethylene oxide) and resorcinol. A primary objective of this research endeavor is to bridge the gap between macroscopic and molecular-level probes of phase behavior and intermolecular association in mixtures that form molecular complexes. In this respect, the temperature -composition projection of the thermodynamic phase diagram is generated for binary mixtures of poly (ethylene oxide) and resorcinol, whose interaction sites are characterized via solid-state NMR. Under fortuitous conditions that are related to the overall mixture composition, two morphologically and crystallographically inequivalent phenolic 13C NMR signals are identified for resorcinol when the blends exist in a two-phase region below the eutectic solidification temperature. The success of this proposed structure-property relationship scheme, which bridges molecular-level mixing phenomena (via NMR) with solid-state phase behavior (via differential scanning calorimetry) depends on our ability to understand material properties at a level where continuum hypotheses are no longer valid.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1990.090280805
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Interfacial adhesion between ionic copolymers and high-modulus surface-treated carbon fibers (1989)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 10 (1989), S. 122-133 
    Details
    ISSN: 0272-8397
    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
    Notes: High-modulus carbon-fiber-reinforced thermoplastic composites typically fail at the interface due to poor adhesion between fiber and matrix. To increase interfacial strength, the research described herein focuses on modifying the fiber surface (via high-temperature acid treatment or zinc electrolysis) to facilitate chemical functional groups on the fiber that might increase fiber-matrix inter-actions. The thermoplastic matrix materials used in this study were random copolymers of ethylene and methacrylic acid in which the carboxyl groups in the methacrylic acid segments were neutralized with either sodium or zinc counterions. Mechanical tests were performed to determine the macroscopic effects of fiber pretreatment on the ultimate mechanical properties of the composites. Fabrication was designed such that fiber-matrix separation provides the dominant contribution to mechanical gracture. Composites containing fibers treated with nitric acid, or a mixture of nitric and sulfuric acids exhibit a 20 to 25 percent increase in transverse (tensile) fracture stress relative to composites fabricated with as-received fibers. Scanning electron microscopy of the fiber-matrix interface at fracture allows one to “zoom-in” and obtain qualitative details related to adhesion. Fracture surface micrographs of the above-mentioned acid-treated fiber-reinforced composites reveal an increase in the amount of matrix material that adhered to the fiber surface relative to the appearance of the fracture surface of composites fabricated with as-received fibers. The presence of acid functionality in the matrix, rather than the divalent nature of the zinc counterions, produces the largest relative enhancement of transverse (tensile) fracture stress in the above-mentioned composites containing surface-treated carbon fibers.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750100210
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  • 3
    Electronic Resource
    Electronic Resource
    Deformation of rubber-toughened polycarbonate: Macroscale analysis of the damage zone (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 52 (1994), S. 177-193 
    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: Two commercial core-shell rubbers were used as impact modifiers for polycarbonate (PC). Specimens with a single semicircular edge notch were stretched uniaxially in order to study the prefracture damage evolution of blends under a triaxial tensile stress state. The irreversible deformation of modified PC included a cavitation mechanism in addition to the three shear modes of unmodified PC. At the macroscopic level, the cavitation condition could be described by a mean stress concept. The corresponding critical volume strain for cavitation in PC blends was determined to be independent of rubber content but differed for the two impact modifiers. The critical volume strain for cavitation was used as an index of cavitation resistance for the impact modifiers. The effect of rubber content and temperature on Izod impact strength of the PC blends was also reported. From the relationship between the cavitation resistance and the Izod impact strength, it was proposed that impact modifiers with a higher cavitation resistance impart better toughness to blends with PC. © 1994 John Wiley & Sons, Inc.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1994.070520206
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    Paper (German National Licenses)
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