With a combination of extensional rheology and in-situ small-angle X-ray scattering measurements, the protocol of two-step extension is proposed to investigate the early stage of flow-induced crystallization (FIC) in supercooled isotactic polypropylene melt at 138 °C. After both step strains, the crystallization half-time presents a nonmonotonic dependence on the interval time between two extensional operations, based on which three different stages of structural evolution are defined. In stage I, both nucleation and chain relaxation occur, which enhances the crystallization rate but reduces the final lamellar crystal orientation. In this stage, each part of the melt is considered to have approximately the same dynamics to respond homogeneously to the second extension and thus the system is still dominated by a chain-network. When entering into stage II, the sparse large-scaled crystal is formed to construct a heterogeneous crystal-network superimposed on the chain-network, which decelerates the second extension induced crystallization by causing stress concentration on the crystal-network at low faction. In stage III, the crystal-network dominates the sample deformation due to the formation of abundant lamellar crystal, which recreates the approximately same dynamics for each part of sample and brings about an enhancement of crystallization rate again. The transition from chain- to crystal-network revealed in this work demonstrates a dynamical coupling of chain relaxation, crystal nucleation, and growth in FIC of polymers.
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July 2017
Research Article|
July 01 2017
Transition from chain- to crystal-network in extension induced crystallization of isotactic polypropylene
Special Collection:
Flow-Induced Crystallization
Zhen Wang;
Zhen Wang
National Synchrotron Radiation Lab, CAS Key Laboratory of Soft Matter Chemistry,
University of Science and Technology of China
, Hefei, China
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Fengmei Su;
Fengmei Su
National Synchrotron Radiation Lab, CAS Key Laboratory of Soft Matter Chemistry,
University of Science and Technology of China
, Hefei, China
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Youxin Ji;
Youxin Ji
National Synchrotron Radiation Lab, CAS Key Laboratory of Soft Matter Chemistry,
University of Science and Technology of China
, Hefei, China
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Haoran Yang;
Haoran Yang
National Synchrotron Radiation Lab, CAS Key Laboratory of Soft Matter Chemistry,
University of Science and Technology of China
, Hefei, China
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Nan Tian;
Nan Tian
a)
MOE Key Laboratory of Space Applied Physics and Chemistry, Shaanxi Key Laboratory of Macromolecular Science and Technology, School of Science,
Northwestern Polytechnical University
, Xi'an 710072, People's Republic of China
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Jiarui Chang;
Jiarui Chang
National Synchrotron Radiation Lab, CAS Key Laboratory of Soft Matter Chemistry,
University of Science and Technology of China
, Hefei, China
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Lingpu Meng;
Lingpu Meng
National Synchrotron Radiation Lab, CAS Key Laboratory of Soft Matter Chemistry,
University of Science and Technology of China
, Hefei, China
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Liang bin Li
Liang bin Li
b)
National Synchrotron Radiation Lab, CAS Key Laboratory of Soft Matter Chemistry,
University of Science and Technology of China
, Hefei, China
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a)
Electronic mail: tiannan@nwpu.edu.cn
b)
Author to whom correspondence should be addressed; electronic mail: lbli@ustc.edu.cn
J. Rheol. 61, 589–599 (2017)
Article history
Received:
December 26 2016
Accepted:
April 17 2017
Citation
Zhen Wang, Fengmei Su, Youxin Ji, Haoran Yang, Nan Tian, Jiarui Chang, Lingpu Meng, Liang bin Li; Transition from chain- to crystal-network in extension induced crystallization of isotactic polypropylene. J. Rheol. 1 July 2017; 61 (4): 589–599. https://doi.org/10.1122/1.4982703
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