title: Shear-Induced Precursor Relaxation-Dependent Growth Dynamics and Lamellar Orientation of β-Crystals in β-Nucleated Isotactic Polypropylene.
abstract: Although a shear flow field and β-nucleating agents (β-NAs) can separately induce the formation of β-crystals in isotactic polypropylene (iPP) in an efficient manner, we previously encountered difficulty in obtaining abundant β-crystals when these two factors were applied due to the competitive growth of α- and β-crystals. In the current study, to induce the formation of a high fraction of β-crystals, a strategy that introduces a relaxation process after applying a shear flow field but before cooling to crystallize β-nucleated iPP was proposed. Depending on the relaxation state of the shear-induced oriented precursors, abundant β-crystals with a refined orientation morphology were indeed formed. The key to producing these crystals lay in the partially dissolved shear-induced oriented precursors as a result of the relaxation process's ability to generate β-crystals by inducing the formation of needlelike β-NAs. Therefore, the content of β-crystals gradually increased with relaxation time, whereas the overall crystallization kinetics progressively decreased. Moreover, more time was required for the content of the β-phase to increase to the (maximum) value observed in quiescent crystallization than for the effect of flow on crystallization kinetics to be completely eliminated. The c-axis of the oriented β-lamellae was observed to be perpendicular, rather than parallel, to the fiber axis of the needlelike β-NAs, as first evidenced by the unique small-angle X-ray scattering patterns obtained. The significance of the relaxation process was manifested in regulating the content and morphology of oriented β-crystals in sheared, β-nucleated iPP and thus in the structure and property manipulation of iPP.
authors.affiliation: †Department of Applied Chemistry, School of Science, Northwestern Polytechnical University, Xi'an 710129, China.|‡College of Polymer Science and Engineering and State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065, China.
authors.forename: Yan-Hui
authors.initials: YH
authors.lastname: Chen
authors.affiliation: §Department of Chemistry, Stony Brook University, Stony Brook, New York 11794-3400, United States.
authors.forename: Du-Fei
authors.initials: DF
authors.lastname: Fang
authors.affiliation: ‡College of Polymer Science and Engineering and State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Lei
authors.affiliation: ∥National Synchrotron Radiation Lab and College of Nuclear Science and Technology, CAS Key Laboratory of Soft Matter Chemistry, University of Science and Technology of China, Hefei 230022, China.
authors.forename: Liang-Bin
authors.initials: LB
authors.lastname: Li
authors.affiliation: §Department of Chemistry, Stony Brook University, Stony Brook, New York 11794-3400, United States.
authors.forename: Benjamin S
authors.initials: BS
authors.lastname: Hsiao
authors.affiliation: ‡College of Polymer Science and Engineering and State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065, China.
authors.forename: Zhong-Ming
authors.initials: ZM
authors.lastname: Li