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  • curing kinetics  (2)
  • Nylon-12, dry and water-saturated, dielectric properties of  (1)
  • absorption of water and dielectric relaxation of Nylon-12  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Relaxations in thermosets. XIX. Dielectric effects during curing of diglycidyl ether of bisphenol-A with a catalyst and the properties of the thermoset (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 299-311 
    Details
    ISSN: 0887-6266
    Keywords: dielectric relaxation ; curing kinetics ; thermoset ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Changes in the dielectric permittivity ε′ and loss epsiv;″ during the curing of DGEBA catalyzed by 10 mole % dimethylbenzylamine have been studied from sol to gel to glass formation regions at different temperatures from 323 to 390 K. The ε′ monotonically decreases with time of cure, and ε″ initially decreases by several orders of magnitude and then increases to reach a peak value before finally decreasing to a low value characteristic of the glassy state. The features shift to shorter times and the peak vanishes as the curing temperature is increased. The decrease of ε″ at the initial stage of cure has been analyzed in terms of dc conductivity σ0, which follows a power law, σ0 ∝ (tg-t)x, as well as a new singularity equation, σ0 ∝ exp[-B/(t0-t)] where tg, x, B, and t0 are empirical constants that vary with the curing temperature; tg is close to the time for gelation; and t0 ≥ time for vitrification. The dielectric properties of the thermoset formed after different periods of cure have been studied from 77 to 325 K. Similar studies of the thermosets formed at different temperatures have been made. Increase in the curing period decreases the heights of both the γ-and α-relaxation peaks and increases their separation, while a β-relaxation peak emerges. Isothermal curing at high temperatures decreases the height of the γ peak to a vanishingly small value and increases that of the β peak from a vanishingly small value. In both the uncured and fully cured states, there is only one sub-Tg relaxation process named γ for the uncured and β for the cured state. These results are discussed in terms of our general physical concepts of local mode motions in an amorphous matrix. © 1993 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1993.090310308
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  • 2
    Electronic Resource
    Electronic Resource
    The dielectric properties of dry and water-saturated nylon-12 (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 30 (1992), S. 341-348 
    Details
    ISSN: 0887-6266
    Keywords: Nylon-12, dry and water-saturated, dielectric properties of ; dielectric properties of dry and water-saturated Nylon-12 ; absorption of water and dielectric relaxation of Nylon-12 ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The dielectric relaxation of 30% crystalline Nylon-12 of molecular weight 20,000 has been studied at frequencies from 12 Hz to 0.1 MHz and temperatures from 77 to 375 K, and the effect of water on the relaxation spectra has been investigated. Absorbed water increases both the rate and the intensity of both its α-and β-relaxation processes and increases the rate but decreases the intensity of its γ-relaxation process. These results are interpreted in terms of the hydrogen bonding effects of water on localized motions of dipoles in Nylon-12. The relatively large half-width of the α-relaxation, which becomes better resolved at high temperatures, is attributed mainly to the random distribution of crystalline regions in the polymer. It is suggested that water lowers the steric hindrance for the localized mode of dipolar reorientation and causes a redistribution of local sites such that the β-relaxation process grows at the expense of the γ-process.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1992.090300404
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  • 3
    Electronic Resource
    Electronic Resource
    Relaxations in thermosets. XXVI. Ultrasonic studies of the temperature dependence of curing kinetics of diglycidyl ether of bisphenol-A with catalyst (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 1465-1474 
    Details
    ISSN: 0887-6266
    Keywords: ultrasonics ; curing kinetics ; diglycidyl ether of bisphenol-A ; thermosets ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Longitudinal velocity and attenuation of the unreacted diglycidyl ether of bisphenol-A and dimethylbenzylamine mixture have been measured for 1 MHz ultrasonic frequency. These are combined with our earlier data [Alig et al., Acta Polymerica, Vol. 40, p. 590 (1989)], which were measured during the curing process of the thermoset, and then analyzed in terms of a process involving a negative feedback between molecular diffusion and chemical reaction. The complex plane plots of the real and imaginary components of the longitudinal modulus are fitted to a stretched exponential relation, and the structural relaxation time is calculated at different stages of curing at temperatures in the range 333-403 K. The results are compared against the calorimetric, dielectric, and viscosity measurements and it is shown that, at least for two cases, gelation time can be observed from the longitudinal modulus data. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1994.090320818
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