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  • 1
    Electronic Resource
    Electronic Resource
    Changes in defect concentration within polymer crystals: annealing of isotropic and drawn polyethylene (1986)
    Springer
    Colloid & polymer science 264 (1986), S. 123-127 
    Details
    ISSN: 1435-1536
    Keywords: Polyethylene ; chain defects ; lattice constants ; annealing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An estimation of the changes in the level of chain defects (branches) accommodated within crystals of undrawn and drawn branched polyethylene, subsequently annealed, is carried out in the light of unit cell expansion data. The results reveal that annealing affects the estimated crystalline defect concentration differently depending on whether the material was drawn or undrawn. Thus, annealing of drawn polyethylene with a defect concentration of 3 % results in a healing of crystal defects, due to a preferential rejection of branches from the crystals. In contrast, annealing of melt crystallized branched polyethylene does not influence the average concentration of chain defects within the crystal despite the increase in lamellar thickness. The branches are trapped into the much wider lamellar crystals with fewer grain boundaries available and defect sequences cannot diffuse out of the crystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01414837
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  • 2
    Electronic Resource
    Electronic Resource
    Degradation of nitric acid-trbeated bulk polyethylene (1983)
    Springer
    Colloid & polymer science 261 (1983), S. 626-630 
    Details
    ISSN: 1435-1536
    Keywords: Low-density polyethylene ; differential scanning-calorimetry ; long period ; fuming nitric acid ; dicarboxylic acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract LDPE samples with differing branching content were treated with fuming nitric acid for times up to 180 h at 60°C. The samples were examined by differential scanning calorimetry and small angle X-ray diffraction. While the crystal thickness derived from the X-ray long period remains practically constant throughout treatment timet, a conspicuous sharpening and shifting of the melting curves to higher temperatures witht is observed. It is suggested that the shift in melting peak is caused by the contribution of the dicarboxylic groups attached to the crystal surface after treatment. It is further shown that the shift depends inversely on the crystal thickness. The comparison of melting points for long time nitric acid treated PE samples with data from dicarboxylic acids has permitted the derivation of an expression for the melting temperature of longer molecular diacids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01415031
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Hardness of nitric acid treated polyethylene followed by recrystallization (1987)
    Springer
    Colloid & polymer science 265 (1987), S. 37-41 
    Details
    ISSN: 1435-1536
    Keywords: Microhardness ; polyethylene ; fuming nitric acid ; dicarboxylic acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The hardness variation of melt crystallized polyethylene as a consequence of controlled fuming nitric exposure has been investigated using the microindentation technique. This study complements previous results obtained using other reagents (H2SO4, ClHSO3). After HNO3 exposure the microhardness of polyethylene decreases very rapidly, instead of increasing after the first hours of treatment. The hardness decrease is correlated to the volume fraction of interlamellar microvoids arising through selective acid digestion. For longer treatment times (t〉40 h) the fragility of the material increases and the sample collapses under the indenter. The hardening of the degraded material after recrystallization from the melt is followed as a function of treatment time. The results are discussed in the light of the molecular mechanisms involved. Comparison of the experimental data with hardness calculations for ideal PE lamellar structures and chain extended dicarboxylic crystals implies that the major contribution to hardening is due to electron dense groups attachment at the surface of a mixed lamellar structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01422661
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    A study of diffractometer line shapes in melt crystallized polyethylene (1984)
    Springer
    Colloid & polymer science 262 (1984), S. 361-365 
    Details
    ISSN: 1435-1536
    Keywords: Polyethylene ; chain defects ; diffraction profiles ; paracrystalline lattice distortions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Wide angle X-ray diffraction scans of isothermally crystallized samples of polyethylene containing known levels of chain defects have been investigated. An analysis of scattering curves using a powder diffractometer is reported. The analytical deconvolution of Lorentz and Lorentz squared profiles for the PE experimental scattering curve and the standard is performed to give the pure profile for the polymer. The separate contribution of paracrystalline lattice distortions and coherently diffracting domains, in different crystallographic directions, to the broadening of the diffraction profiles is discussed in the light of the level of defects present.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01410253
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Real-time X-ray scattering study during heating of oriented injection-molded polyethylene (1991)
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 2 (1991), S. 57-61 
    Details
    ISSN: 1042-7147
    Keywords: Orientation ; Injection-molding ; X-ray scattering ; Polyethylene ; 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
    Notes: Highly oriented linear polyethylene was prepared by elongational flow injection molding. The changes in crystal orientation were investigated as a function of temperature by real-time wide-angle X-ray diffraction. Additionally, the influence of molecular weight upon the microstructure and the changes in orientation, during heating near the melting point, and after cooling have been examined. A shish-kebab structure is inferred for the high molecular weight samples (Mw≥105) from SAXS observations, while for samples with Mw〈105 only an oriented lamellar structure is found. Consequently, a higher thermal stability is shown by the higher molecular weight samples. Furthermore, a recovery of crystal orientation on rapid cooling of the samples from the melt is only observed for samples with Mw≥105. The results are discussed in terms of a preferential recrystallization of chain-folded lamellae, on cooling, onto the shish fibrils which survive at high temperature.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pat.1991.220020201
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    Paper (German National Licenses)
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