Direct Evaluation of Local Dynamic Viscoelastic Properties of Isotactic Polypropylene Films Based on a Dynamic μ-Beam...

Area of Science:

• Materials Science
• Polymer Physics
• Crystallography

Background:

• Understanding local mechanical properties of crystalline polymers is crucial for material design.
• Traditional methods often lack the resolution to probe micro-scale variations within polymer structures.
• Isotactic polypropylene (iPP) with distinct spherulites provides a model system for heterogeneous mechanical analysis.

Purpose of the Study:

• To evaluate the local mechanical properties of crystalline polymers using advanced synchrotron X-ray diffraction.
• To determine local dynamic viscoelastic functions (storage and loss moduli) within and outside iPP spherulites.
• To correlate mechanical response with crystallite orientation and deformation.

Main Methods:

• Utilized synchrotron radiation X-ray diffraction with 10 μm lateral resolution.
• Performed in situ wide-angle X-ray diffraction (WAXD) on an iPP film under sinusoidal strain.
• Calculated local dynamic storage (E') and loss (E") moduli from stress-strain relationships derived from lattice spacing changes.

Main Results:

• Observed reversible changes in crystal plane spacing corresponding to applied strain.
• Quantified local storage modulus (E') inside spherulites at 1.8 GPa (110 plane) and 6.0 GPa (1̅13 plane).
• Determined E' outside spherulites to be 1.1 GPa (110 plane), highlighting anisotropic mechanical behavior.

Conclusions:

• Synchrotron X-ray diffraction is effective for measuring local mechanical properties (E') in crystalline polymers.
• Mechanical properties vary significantly within and outside iPP spherulites, influenced by crystallite orientation.
• The technique provides both structural and local mechanical insights into material deformation.