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  • 1
    ISSN: 0449-2986
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Blends of polycarbonate (PC) and linear low density polyethylene (LLDPE) of different compositions, in the form of slabs obtained by melt extrusion, have been examined by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). DSC measurements show that the melting, crystallization and glass transition temperatures of the two polymeric components in the blends are slightly affected by the composition. On the contrary, large differences are observed in the melting behaviour of layers cut at various depths, parallel to the slab surfaces of samples. This supports the occurrence of different crystal morphologies and distribution of the two components within the samples. The study of the crystallization kinetics from the melt blends shows that the crystallization processes of LLDPE are affected by the presence of PC. The dynamic mechanical analysis indicates that modulus, transitions and relaxational behaviour of the polymer components are scarcely affected by the composition. Some variations of the damping factor have been interpreted as due to the phase heterogeneity of the system, arising from the processing conditions and rheological behaviour of the blends.
    Type of Medium: Electronic Resource
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  • 3
    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 results of dynamic mechanical and broad-line proton magnetic resonance studies carried out over a broad, temperature range on a series of aromatic polyamides are presented. At temperatures lower than 300 K, the NMR data show no relaxation for the all-meta linked benzene rings polyamide, whereas processes for the other polyamides are found, the magnitude of which is dependent on the polymer structure. Between 400 and 500 K further decreases in the second moment take place for all materials. Two secondary mechanical loss peaks are evident in these polymers, one in the 200-380 K region (β) and one in the 380-500 K region (β*), at about 104 cps. In particular, the relaxation strength of the β* peak depends on the conditions of isolation of the polymers from solution. The results are discussed in terms of possible motional processes of these polymers characterized by a long range intramolecular uniaxial order. An attempt is made to correlate the relaxational properties of aromatic polyamides to the existence of a phase of low regularity such as the nematic or smectic mesophases.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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  • 4
    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: Morphology and mechanical properties of (amine terminated butadiene acrylonitrile rubber/diglycidyl ether of bis-phenol-A epoxy resin) blends of different compositions, cured in wide range of temperatures, are described. Curing at low temperature promoted formation of homogeneous materials with poor fracture resistance. On the contrary, at high temperature tough heterogeneous blends were obtained. Such blends showed phase inversion above 20 percent of rubber. The volume fraction of precipitated phase, determined on SEM micrographs, was higher than the amount of added rubber. A fracture mechanism to account for this is proposed. Extensive voiding and interface damage were observed in the low temperature cured materials. Such phenomena did not contribute to the fracture energy.
    Additional Material: 25 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    ISSN: 0887-6266
    Keywords: dielectrometry ; epoxy ; cross-linking ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The dielectric behavior of an epoxide/ethylenediamine formulation has been studied during cross-linking in the frequency range 103-1010 Hz at 25°C and 70°C. Dielectric data were collected both in the frequency and in the time domains and analyzed in terms of a combination of two Havriliak-Negami functions. A complete description of the evolution of the relaxation parameters during the reaction was obtained. The nature of the information yielded by dielectrometry on the dynamics of the system is discussed. © 1995 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
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  • 6
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Mechanical dynamic properties of some polythenes with different degrees of crystalinity have been measured over a temperature range from -70°C. to above room temperature, at frequencies in the range 5-30 kcps. At room temperature Young's modulus and resonance coefficient increase with increasing crystallinity. A transition temperature, independent of the degree of crystallinity, at about -24°C. is found in partially amorphous polythenes. The transition region is sharper for more amorphous samples. The modulus increases with increasing degree of crystallinity at temperatures above the transition point but appears to decrease somewhat with increasing degree of crystallinity below the transition point.
    Additional Material: 2 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 31 (1958), S. 189-191 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 1 Ill.
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  • 8
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Through determination of dynamic mechanical properties (sound velocity and damping factor) over the temperature range from -160 to 200°C. and frequency range from 4 to 16 kcycles/sec. evidence is found for the existence of two isophasic transition temperatures in polytrifluorochloroethylene: one at -58°C. and the other at 50°C. Both transitions are associated with motion in the main chain of the polymer, which is first excited at -58°C. for the molecular segments which are more freely rotating (because they are located near network defects) and at 50°C. for the majority of the chain elements in the amorphous regions. The transition point at -58°C. is regarded as the glass transition temperature for polytrifluorochloroethylene. The experimental results are discussed on the basis of the structure of the polymer examined, and a comparison is made between dynamic mechanical data and data obtained by measurements of specific volume, nuclear magnetic resonance, and dielectric losses.
    Additional Material: 1 Ill.
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  • 9
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dynamic mechanical properties of eight samples of polyethylene irradiated to various extents have been determined over a temperature range from -70 to +280°C. and a frequency range from 103 to 2 × 104 cycles/sec. At room temperature, minimum values in Young's modulus and maximum values in damping factor are observed for a critical radiation dose. Three transition points Tg, Ts, and Tm are exhibited by the sound velocity-temperature curves; these may be associated with the transition from the glass state, the softening of the amorphous regions, and the melting of the crystallites, respectively. With increasing dose, Tm, decreases and Tg, increases, while Ts shows a minimum for a radiation dose equal to the critical value. At temperature above the melting point of the crystallites Tm, lightly crosslinked samples show rubber-like elasticity, but highly crosslinked samples show the same dynamic mechanical behavior as highly crosslinked amorphous materials. Results are discussed and explained on the basis of the partial crystallinity of polyethylene and of the changes that irradiation causes on the molecular structure.
    Additional Material: 5 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 57 (1962), S. 617-628 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dynamic mechanical properties of polyisobutylene, butyl rubbers, Paracril, cis-1,4-polybutadiene, reinforced with EPC black, were determined in the temperature range -150-+170°C., in the frequency range 2-20 kcycles/sec. In the amorphous polymers, reinforcement causes an increase of sound velocity at any temperature, while the glass transition point Tg and the thermal coefficient of sound velocity dV/dT remain practically unchanged. Only at high temperatures, near the softening region, are lower values of the damping factor Q-1/dT found for the filled samples, as compared with the corresponding unfilled ones. Addition of reinforcing carbon black to cis-1,4-polybutadiene causes an increase of sound velocity at any temperature, and a little shift of the maximum damping point toward lower temperatures. In the reinforced sample, the Q-1 - T curve, in the region of high dissipation, becomes more unsymmetrical, showing a flat region at temperatures just above the maximum. A comparison of the mechanical spectra of the unfilled vulcanized samples of cis-1,4-polybutadiene with those of the corresponding filled vulcanized ones (with the same sulfur content and the same heat treatment) shows a shift of the glass transition point and of the maximum damping toward lower temperatures with addition of the filler. The experimental results are discussed and the conclusion is drawn that neither structural changes nor appreciable variations of chain mobility are caused by addition of carbon black in the examined rubbers.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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