On the differences in micro‐deformation mechanism between isotactic polypropylene and β‐nucleated isotactic polypropylene as revealed by the confocal laser scanning microscopy

Abstract

To understand the toughness enhancement of β‐nucleated isotactic polypropylene (iPP) in comparison with iPP, the differences in the micro‐deformation mechanisms between the neat iPP and β‐nucleated iPP were visualized using the confocal laser scanning microscopy (CLSM). Structure of the α‐ and β‐spherulites situated close to the tip of the sharp starter crack has been investigated during tensile deformation in the viewing field of the CLSM. In the α‐spherulite of the neat iPP, highly localized inter‐ and intra‐spherulitic micro‐shear bands have been observed. In the β‐nucleated iPP, relatively uniform distribution of diffuse shear bands has been observed in the β‐phase, while the α‐phase remained relatively undeformed exhibiting only narrow intra‐spherulitic shear bands in the direction perpendicular to the loading direction. Delocalization of plastic deformation into diffuse shear bands in β‐nucleated iPP can explain its enhanced crack resistance compared with the neat iPP exhibiting highly localized shear banding. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Plastic deformation behavior of polypropylene sheet with transversal orientation

“…Moreover, it should be notified that our experimental results contradict with several reports on microvoid (crazes and/or small cracks) formation during plastic deformation of β‐form PP . According to them, a volume contraction of the crystalline phase due to the β‐to‐α transformation is responsible for the void formation.…”

“…Lezak et al carried out plane‐strain compression experiments of β‐form PP and found that interlamellar slippage leads to numerous fine deformation bands and the crystallographic slip systems, including chain slip and transverse slip. Jancar et al investigated the deformation behavior by a confocal laser scanning microscope and clarified that β‐PP shows diffuse shear band while α‐PP exhibits localized shear band.…”

“…There have been also a lot of researches on the microvoid formation during plastic deformation, which will be important information on the process of microporous films with self‐shutdown system beyond the melting point . Chu et al found that the crystalline phase transformation and microvoid formation depend strongly on the stability of the β‐form crystals in a film.…”