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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 265 (1987), S. 37-41 
    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
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 268 (1990), S. 440-446 
    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
    Library Location Call Number Volume/Issue/Year Availability
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