A revisit to the flow and pressure jointly induced thick lamellae in isotactic polypropylene: A synchrotron radiation small‐ and wide‐angle X‐ray scattering study. Issue 1 (30th November 2018) - Yang, Shu‐Gui
Abstract: The mutual influence of flow and pressure, two key parameters in polymer processing, on the lamellar structure of semicrystalline polymers is vital important but still far from clear. Here, we studied the lamellar structure of isotactic polypropylene (iPP) crystallized under shear flow (3–30 s –1 ) and pressure (100 MPa). Under 100 MPa, the oriented thick lamellae with a thickness of 28 nm are produced when the shear rate is greater than or equal to 17 s –1 . These oriented thick lamellae with a high melting temperature (177 ºC) are testified to be parallelly oriented α‐parent lamellae. Intriguingly, the oriented thick α‐parent lamellae have a small lattice spacing of (130) crystallographic planes (0.473 nm, a shrinkage of approximately 0.4% comparing to the α‐form formed at 0 s –1 and at 100 MPa), implying that the chains are densely stacked within the crystal. The oriented thick α‐parent lamellae with compact stacking of molecular chains are shown to generate from flow‐induced nuclei, accompanying with the growth and lamellar thickening during the isothermal crystallization period. The current study examines the lamellar structure of iPP crystallized under the coexistence of flow and pressure, and the approach can be used for fabricating high performance iPP products with thick lamellae. Abstract : The mutual influence of flow and pressure, two key parameters in polymer processing, on the lamellar structure of semicrystalline polymers is vitally important but still far from clear. Here, the authors studied the lamellar structure of isotactic polypropylene (iPP) crystallized under shear flow (3‐30 s −1 ) and pressure (100 MPa). Under 100 MPa, the oriented thick lamellae with a thickness of 28 nm are produced when the shear rate ( γ ˙ ) is greater than or equal to 17 s −1 . These oriented thick lamellae with a high melting temperature (177°C) are testified to be parallelly oriented α‐form parent (α‐parent) lamellae. Intriguingly, the oriented thick α‐parent lamellae have a small lattice spacing of (130) crystallographic planes (0.473 nm, a shrinkage of approximately 0.4% compared to the α‐form formed at γ ˙ < 17 s −1 and at 100 MPa), implying that the chains are densely stacked within the crystal. The oriented thick α‐parent lamellae with compact stacking of molecular chains are shown to generate from flow‐induced nuclei, accompanying with growth and lamellar thickening during the isothermal crystallization period. The current study examines the lamellar structure of iPP crystallized under the coexistence of flow and pressure, and the approach can be used for fabricating high performance iPP products with thick lamellae. Flow and pressure jointly induced oriented thick lamellae (28 nm) in isotactic polypropylene (iPP) have been studied using the synchrotron radiation small‐ and wide‐angle X‐ray scattering technologies. The oriented thick lamellae are shown to be parallelly oriented α‐parent lamellae, which are generated from flow‐induced nuclei, accompanying the lamellar thickening during the isothermal crystallization period.