Abstract
In-situ small-angle X-ray scattering (SAXS), and wide-angle X-ray diffraction (WAXD) were carried out to investigate the deformation-induced structure changes of isotactic polypropylene (iPP) films during uniaxial stretching at varying temperatures (room temperature, 60 °C and 160 °C). From the WAXD data, mass fractions of amorphous, mesomorphic and crystal phases were estimated. Results indicate that at room temperature, the dominant structure change is the transformation of folded-chain crystal lamellae (monoclinic α-form) to oriented mesomorphic phase; while at high temperatures (>60 °C); the dominant change is the transformation of amorphous phase to oriented folded-chain crystal lamellae. This behavior may be explained by the relative strength between the interlamellar entangled network of amorphous chains, which probably directly influence the tie chain distribution, and the surrounding crystal lamellae. It appears that during stretching at low temperatures, the interlamellar entanglement network is strong and can cause lamellar fragmentation, resulting in the formation of oriented mesomorphic phase. In contrast, during stretching at high temperatures, the chain disentanglement process dominates, resulting in the relaxation of restrained tie chains and the formation of more folded-chain lamellae.
Original language | English |
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Pages (from-to) | 6867-6880 |
Number of pages | 14 |
Journal | Polymer |
Volume | 48 |
Issue number | 23 |
DOIs | |
State | Published - Nov 2 2007 |
Externally published | Yes |
Funding
The authors acknowledge the financial support from the National Science Foundation (DMR-0405432) and the Dow Chemical Company. The assistance of Dr. Igors Sics and Dr. Lixia Rong for synchrotron SAXS and WAXD experimental setup is also greatly appreciated.
Keywords
- Deformation
- Entanglement
- Polypropylene