Shear‐Induced Orientation and Structure Development in Isotactic Polypropylene Melt Containing Modified Carbon Nanofibers

Abstract

The shear‐induced crystallization behavior of isotactic polypropylene (iPP) nanocomposite melt containing modified carbon nanofibers (MCNFs) was investigated by rheo‐SAXS (small‐angle X‐ray scattering) and rheo‐WAXD (wide‐angle X‐ray diffraction) techniques using synchrotron radiation. Under quiescent conditions, the nucleating effect of MCNFs on crystallization of iPP was pronounced and the system exhibited a remarkably low saturation point (ca. 0.05 wt% of MCNF). In‐situ SAXS and WAXD results showed the development of shear‐induced crystalline structures and lamellar morphology in nanocomposite melts. Under the same shear conditions, the filled system exhibited notably faster kinetics compared with the unfilled system. The oriented crystalline fraction was found to decrease with the MCNF loading, indicating the competition between oriented crystals (induced by shear) and unoriented crystals (due to the nucleating effect of MCNF). At the early stages of crystallization, the amount of the oriented crystals increased with the MCNF concentration, suggesting that the nanofiller hindered the motion of polymer chains after the cessation of flow resulting in the delayed relaxation of stretched polymer segments.

Dedicated to Prof. Phillip H. Geil's seventy‐fifth birthday.

Keywords:

• shear
• crystallization
• polypropylene
• carbon nanofibers
• nanocomposites
• SAXS
• WAXD

Acknowledgment

The financial support of this work was provided by the Office of Naval Research (N000140310932) and the National Science Foundation (DMR‐0405432). The authors acknowledge the assistance of Dr. Lixia Rong for synchrotron WAXD experimental setup.

Notes

Dedicated to Prof. Phillip H. Geil's seventy‐fifth birthday.