Plastic deformation behavior of β phase isotactic polypropylene in plane‐strain compression at elevated temperatures

Abstract

Isotactic polypropylene (iPP) rich in β crystal modification was deformed by plane‐strain compression at T = 55–100 °C. The evolution of phase structure, morphology, and orientation were studied by DSC, X‐Ray, and SEM. The most important deformation mechanisms found were interlamellar slip operating in the amorphous layers, resulting in numerous fine deformation bands and the crystallographic slip systems, including the (110)[001]β chain slip and (110)[$1{\bar {1}}0$]β transverse slip. Shear within deformation bands leads to β→α solid state phase transformation in contrast to β→smectic transformation observed at room temperature. Newly formed α crystallites deform with an advancing strain by crystallographic slip mechanism, primarily the (010)[001]α chain slip. As a result of deformation and phase transformation within deformation bands β lamellae are locally destroyed and fragmented into smaller crystals. Deformation to high strains, above e = 1, brings further heavy fragmentation of lamellae, followed by fast rotation of crystallites with chain axis towards the direction of flow FD. This process, together with still active crystallographic slip, leads to the final texture with molecular axis of both crystalline β and α phase oriented along FD. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 92–108, 2008

Phase Transition in β-nucleated Isotactic Polypropylene Induced by Combination of Annealing and High Pressure

“…One is a melt-recrystallization mechanism and the other is a solid-to-solid transition mechanism. The processing mode used here for β-iPP makes the solid-to-solid transition impossible happen; if it did, the transition should be related directly to the pressure or to something like shear bands [56] which were not discovered in this work. The solid-to-solid phase transition of β-iPP would occur during the tensile process possibly due to the tensile stress being favorable to the transformation of chain segment conformations and/or the occurring of crystallographic slip in the lamellae.…”

“…The solid-to-solid phase transition of β-iPP would occur during the tensile process possibly due to the tensile stress being favorable to the transformation of chain segment conformations and/or the occurring of crystallographic slip in the lamellae. [54][55][56]68] According to the previous description, it can be deduced that the main transition of β-iPP in this work should be ascribed to the meltrecrystallization mechanism. Under the high pressure, the loose crystal structure of β-iPP becomes tighter and the space for the motion of chain segments in the crystal is decreased.…”

“…[51][52][53] However, in terms of a molecular mechanism, Xu et al [54] recently claimed that the β→α transition is a solid-to-solid phase transition mechanism accomplished via a simultaneous solid transition involving slip along (110) β and (120) β planes and shear of the crystal lattice in the presence of conformational defects. On the other hand, Lezak et al [55,56] claimed that the most important mechanisms were interlamellar slip operating in the amorphous layers, resulting in numerous fine deformation bands due to localization of deformation, and the crystallographic slip systems, including the (110) induced by advanced deformation within the deformation bands. Furthermore, our previous work showed that the degree of the β→α transition during uniaxial tensile deformation depends upon the crystalline morphology of the β-spherulites.…”

Influence of oriented β‐lamellae on deformation and pore formation in β‐nucleated polypropylene

“…On the contrary, with ascending DDR, the azimuthal intensity curves exhibit stronger diffraction peak at the transverse direction (TD, which is perpendicular to the MD), while the intensity at longitudinal direction (MD, which is parallel to the MD) maintains the minimum, indicating that the b-lamellae perpendicular to the MD highlights gradually with increasing DDR and PP-24 has the most conspicuous anisotropy, which is accorded with SEM results. 11,18,[40][41][42] This means a series of b-iPP samples with gradually highlighted anisotropy and high content of b-crystal (>99%) have been successfully prepared.…”

Effect of magnesium malonate on the formation of the β crystalline form in isotactic polypropylene

“…Varga and co-workers [25,26,32,[34][35][36][37][38] also found that calcium substrate is a highly active b-nucleating agent for PP. The calcium salts of pimelic acid and suberic acid were also used as specific b-nucleating agent by Li and Cheung [39], Huy et al [40], Lezak et al [41][42][43], Li et al [44], and Dou [45,46] to produce b-iPP. The other dicarboxylates having b-nucleating activity are listed as follows: disodium phthalate [47], calcium terephthalate [44], calcium glutarate [46]; the Na [39,45], Zn [45,48], and Ba [45] salts of pimelic acid; and the Ca salts of phthalic acid [44,48] and pyromellitic acid [48].…”