Plastic deformation of polypropylene in relation to crystalline structure

Abstract

ABSTRACT:The tensile drawing behavior of quenched and annealed films of isotactic polypropylene is investigated as a function of draw temperature and strain rate. A strain-induced structural change from the smectic to the monoclinic form is observed for the quenched films. A kinetic interpretation is proposed for the phenomenon. Data of thermal activation volume at the yield point indicate two regimes of plastic flow for the quenched sample, between 25 and 60°C, but only one regime for the annealed sample. Homogeneous and heterogeneous crystal slip processes are proposed to account for these regimes in relation to the nucleation and propagation of screw dislocations. The basic mechanism of molecular motion in the polypropylene crystal is suggested to be a wormlike motion of conformational defects along the 3/1 helix chains that allows a 120°rotation and a c/3 translation. The occurrence of the smectic form as a transitory state in the deformation pathway is discussed in terms of plasticity defect generation.

Rheooptical Fourier transform infrared spectroscopy of the deformation behavior in quenched and slow‐cooled isotactic polypropylene films

“…To review, it is expected for quenched samples to be mostly amorphous, with a small quantity of smectic crystallites as shown by WAXS 60,63,66 and for the slow-cooled samples to possess a greater degree of well-defined monoclinic crystals, also shown by WAXS. 60,63,66,69,71 In this article, we discuss the responses of the amorphous and crystalline regions.…”

“…The crystal structure of quenched iPP films is discussed by Seguela et al 63 Their WAXS data suggest that these samples form somewhat illdefined smectic crystals that do not transform to the more-stable monoclinic ␣ crystals, even at 250% strain at room temperature. Our quenching procedure is the same as that of these researchers.…”

“…Previous WAXS data have shown that these samples would be expected to form monoclinic crystals. 60,63,66,69,71 The stronger dichroism response is consistent with the higher degree of crystallinity. In contrast with the quenched sample, the saturation in the crystalline orientation occurs well beyond 50%.…”

Influence of annealing on microstructure & molecular orientation, thermal behaviour, mechanical properties and their correlations of uniaxially drawn iPP thin film

“…It is widely used in many different applications such as for appliances, packaging, textiles, reinforcing fibers, monofilaments, film, automotive parts, reusable containers of various types, and other durable items for home and garden uses. Additionally, the ranges of properties and applications for PP may extend in various ways by physical treatments, for example, thermal treatment [1][2][3] and plastic deformation [4,5]. PP can be also modified by adding fillers and/or blended with other polymers [6][7] and recently was used as a matrix polymer to blend with nanoparticles/carbon nanotubes to form nanocomposite materials [8,9], in which the main field of attention is the enhancement of mechanical properties.…”

“…The α species are characterized by the presence of transverse crystallites in addition to the main structure of radial lamellae, the so-called "cross-hatching" morphology. Also, the wide angle X-ray diffraction (WAXD) patterns of α-form show the characteristic peaks at 2θ about 14.1 (110), 17.0 (040), 18.5 (130), 21.3 (111) and 21.8° (041) [3,5,11,12,18]. The β-form is less prevalent because of its lower stability than α-form and results from crystallization under a temperature gradient, under shear during processing or in the presence of specific nucleating agent [13][14][15].…”