Plastic deformation behavior of polypropylene sheet with transversal orientation

Abstract

The deformation behavior of a polypropylene (PP) sheet, in which c-axis of b-form PP orients perpendicular to the flow direction in the sheet [transverse direction (TD)], is studied focusing on the mechanical anisotropy. The deformation mechanism of this sample is found to be strongly dependent on the stretching direction. Shear yielding is dominant in TD stretching, indicating that reorganization and phase transformation of crystalline form occur easily with low yield stress. On the contrary, in machine direction (MD) stretching, numerous microvoids appear with the transformation of crystalline form as well as the rotation of c-axis. Moreover, the crazing process, initiated at the orientation defects, occurs locally with remaining undeformed region in which b-form PP orients to TD. The deformation behavior is applicable to a microporous film. V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 897-906

Morphology, structure, and properties of poly(lactic acid) microporous films containing poly(butylene terephthalate) fine fibers fabricated by biaxial stretching

“…[5][6][7][8][9][10] In case of isotactic polypropylene (PP), it has been known that a microporous film is prepared by stretching an extruded sheet containing a large amount of b trigonal crystalline form. [5][6][7][8][9][10] In case of isotactic polypropylene (PP), it has been known that a microporous film is prepared by stretching an extruded sheet containing a large amount of b trigonal crystalline form.…”

“…11 During the stretching, the crystalline phase transformation from b-to a-form occurs. 6,7 The alternative routes to obtain microporous films include stretching a composite filled with rigid particles 13,14 or immiscible polymer blends. 6,7 The alternative routes to obtain microporous films include stretching a composite filled with rigid particles 13,14 or immiscible polymer blends.…”

Control of Chain Orientation in Blends of Polypropylene and Polybutene‐1

“…Because the needle‐shaped crystals orient to the flow direction by the hydrodynamic force, PP chains orient perpendicular to the flow direction upon extrusion. This orientation behavior has been confirmed by infra‐red dichroic ratio and birefringence measurements, transmission electron microscopy, 2D wide‐angle X‐ray analysis, and mechanical anisotropy measurements . Upon injection‐molding, moreover, the PP chains orient toward the flow direction, i.e., machine direction (MD), in the skin layer, but orient perpendicular to the flow direction in the core layer because of the preferential crystal growth from the flow direction‐aligned needle‐shaped nucleating agent crystals.…”

“…Among the reported nucleating agents, N , N′ ‐dicyclohexyl‐2,6‐naphthalenedicarboxamide is one of the most well‐known commercially available nucleating agents for β‐modification. According to previous studies, this nucleating agent is dissolved into molten PP and appears as needle‐shaped crystals during the cooling process. PP undergoes epitaxial crystallization on the surface of these needle‐shaped crystals, during which the chain‐axis of the PP molecules orients perpendicular to the long axis of the needles .…”

“…Isotactic polypropylene (PP) is a polymorphic material that has several crystalline forms, including α monoclinic, β trigonal, and γ orthorhombic forms . Although α‐form crystals are known to be dominant in most conventional products, the structure and properties of PP containing a large amount of β‐form crystals have been increasingly studied recently with the development of effective nucleating agents for β‐modification . As revealed by Karger‐Kocsis, marked mechanical toughness, which is lacking in α‐form PP, is expected for β‐form PP through a pronounced energy dissipation mechanism during plastic deformation owing to a crystalline phase transformation from the β‐ to α‐form .…”