Effect of crystal habit and superstructure on modulus of elasticity of isotactic polypropylene by AFM nanoindentation |
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Authors: | Qamer Zia Davide Tranchida René Androsch Holger Schönherr |
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Affiliation: | 1.Fraunhofer Institute for Mechanics of Materials IWM,Halle/Saale,Germany;2.Center of Engineering Sciences,Martin-Luther-University Halle-Wittenberg,Halle/Saale,Germany;3.Department of Physical Chemistry I,University of Siegen,Siegen,Germany;4.Borealis Polyolefine GmbH,Linz,Austria |
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Abstract: | In this study the effects of crystal habit, crystallinity and superstructure on the modulus of elasticity of isotactic polypropylene
films were analyzed by atomic force microscope (AFM) nanoindentation. The modulus of elasticity, evaluated on the nanometer
scale by AFM, showed a qualitatively similar dependence on the crystal habit, crystallinity and superstructure as the modulus
of elasticity measured by dynamic-mechanical analysis and tensile testing. The observed values of both the surface stiffness
measured by AFM and the macroscopic/bulk stiffness were distinctly larger in the presence of non-isometric lamellae organized
in spherulite than in the presence of isometric nodular crystals, not organized in a spherulitic superstructure. The experimental
data showed that the modulus of elasticity is not primarily influenced by the presence or absence of spherulite but by the
molecular-deformation constraint associated to the crystal habit. |
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