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  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Equilibrium and non-equilibrium melting of branched polyethylene relating to defect incorporation within crystals (1987)
    Springer
    Colloid & polymer science 265 (1987), S. 239-245 
    Details
    ISSN: 1435-1536
    Keywords: Branchedpolyethylene ; equilibriummelting point ; enthalpy offusion ; surface free energy ; kinks ; chain defects
    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 New equilibrium melting point data, for polyethylene containing chain defects, are tested in the light of random copolymer predictions. A simplified expression for the melting point depression of random copolymers containing small amounts of non-crystallizable units is derived. Non-equilibrium melting data for rapidly quenched polyethylene samples are also reported. The fusion enthalpyΔH∘(X), and the surface free energyσ e for crystals containing defects are evaluated using crystallinity, equilibrium meltingtemperatures and X-ray long period data. It is shown that increasing defect penetration within crystals induces a decrease ofΔH∘(X) withX in accordance with theoretical predictions. Finallyσ e is, similarly, shown to decrease with increasing number of chain defects attached to the crystal surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01412713
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Microhardness and surface free energy in linear polyethylene: The role of entanglements (1990)
    Springer
    Colloid & polymer science 268 (1990), S. 440-446 
    Details
    ISSN: 1435-1536
    Keywords: Microhardness ; polyethylene ; molecularweight ; folded-chainlamellae ; melting ; surfacefreeenergy ; entanglements
    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 microhardness of a series of melt crystallized samples of linear polyehtylene was investigated in a wide range of molecular weights. The x-ray long period was analyzed to study the variation of the hardness-derived constantb as a function of molecular weight (M η). It is pointed out thatb offers a measure of the hardness depression due to the finite thickness of the lamellar crystals. The data obtained show that the increase and final leveling-off (forM η 200 000) ofb withM η parallels the concurrent increase of the surface free energy, as derived from DSC experiments. Results are discussed using the concept og chain folded lamellae as thermodynamically stable non-homogeneous microphases. Comparison of experimental and calculated data supports the view that the number of molecular entanglements, segregated onto the defective surface boundary of the heterogeneous crystals influence the shearing mechanism within the “mesocrystals” and thereby control the yield behavior of the material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01411002
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Microhardness-structure correlation of iPP/EPR blends: influence of molecular weight and EPR particle content (1998)
    Springer
    Colloid & polymer science 276 (1998), S. 786-793 
    Details
    ISSN: 1435-1536
    Keywords: Key words Microhardness ; poly(propylene) ; ethylene-co-propylene rubber ; blends ; surface free energy
    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 influence of molecular weight on the mechanical properties of isotactic poly(propylene) (iPP) and iPP blended with ethylene-propylene copolymers has been investigated by means of the microhardness technique. The hardness (H) of iPP is shown to slightly decrease with increasing molecular mass, within the range of molecular weights investigated. The H-decrease is correlated to a loss of crystallinity as the average molecular weight increases. On annealing, the mechanical properties are enhanced as a consequence of an increase in both, the degree of crystallinity and the crystalline lamellar thickness. A value of H ∞ c for iPP crystals of infinite thickness in the α-form is proposed for the first time. The inclusion of EPR particles in the iPP matrix softens the material. This result could be explained in terms of an increase in the basal surface free energy of the iPP crystals with increasing amount of rubber content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003960050311
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    Paper (German National Licenses)
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