Synchrotron investigation on the sheared structure evolution of syndiotactic polypropylene crystallization process

Area of Science:

• Polymer Science
• Materials Science
• Crystallography

Background:

• Syndiotactic polypropylene (sPP) is a versatile polymer with applications influenced by its crystalline structure.
• Understanding how processing conditions like shear affect polymer morphology is crucial for material property control.

Purpose of the Study:

• To investigate the effects of shear on the final crystalline structure of molten syndiotactic polypropylene (sPP).
• To elucidate the relationship between shear conditions and the multiscale crystalline structures in sPP.

Main Methods:

• Synchrotron small-angle X-ray scattering (SAXS) was employed to analyze structural changes.
• Wide-angle X-ray diffraction (WAXD) was used to assess crystalline form and orientation.
• Experiments were conducted on molten sPP under varying shear conditions.

Main Results:

• WAXD data revealed no change in crystalline form, but a slight difference in the orientation of the 200 reflection.
• SAXS data indicated that shear did not affect lamellar thickness or long period.
• Lamellar orientation was found to be dependent on shear conditions.

Conclusions:

• Shear primarily influences the lamellar orientation in sPP, not its thickness or long period.
• The findings suggest the presence of a mesophase structure in sheared sPP melt.
• This mesophase structure is critical for understanding shear-induced modifications to sPP's multiscale crystalline architecture.