Shear-induced crystallization of isotactic polypropylene with different molecular weight distributions: in situ small- and wide-angle X-ray scattering studies

Nogales, Aurora; Hsiao, Benjamin S.; Somani, Rajesh H.; Srinivas, Srivatsan; Tsou, Andy H.; Baltà‐Calleja, F. J.; Ezquerra, Tiberio A.

doi:10.1016/s0032-3861(00)00919-8

Cited by 283 publications

(272 citation statements)

References 34 publications

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“…In particular flow-induced crystallization of polymer melts can results in the formation of a so-called shish-kebab structure in semicrystaline polymers under appropriate conditions [33][34][35][36]. This special kind of chain crystalline assembly consists of foldedchain lamellae or kebabs periodically held together by fibrillar crystals or shishes [33][34][35][36][37][38][39][40][41][42][43] which is a result of a coil-to-stretch transition of polymer chains in the melt crystallization when the shear rate exceeds a critical value [33,37]. It has been predicted and observed that longer coiled-chains (longer than a critical length) of a polydisperse polymer melt can be stretch to the shishes while at the same flow rate shorter coiled-chains epitaxially grow into the kebabs.…”

Section: Flow-induced Crystallizationmentioning

confidence: 99%

“…It has been predicted and observed that longer coiled-chains (longer than a critical length) of a polydisperse polymer melt can be stretch to the shishes while at the same flow rate shorter coiled-chains epitaxially grow into the kebabs. It has been found that the flow fields are always essential for the formation of the shish, whereas the kebabs can grow on the shish in the absence of any flow [37,39,40].…”

Section: Flow-induced Crystallizationmentioning

confidence: 99%

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Crystallization of Polypropylene: Application of Differential Scanning Calorimetry Part I. Isothermal and Non-Isothermal Crystallization

Raka¹,

Bogoeva‐Gaceva²

2017

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Section: Flow-induced Crystallizationmentioning

confidence: 99%

Section: Flow-induced Crystallizationmentioning

confidence: 99%

Crystallization of Polypropylene: Application of Differential Scanning Calorimetry Part I. Isothermal and Non-Isothermal Crystallization

Raka¹,

Bogoeva‐Gaceva²

2017

Contributions

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“…[35][36][37][38][39][40][41] Thus, a quantitative characterization of the effects of flow conditions on the crystalline phase microstructure is essential to fully understand polymer solid-state structure-property relationships, which is the goal of the present work. In situ rheo-X-ray technique [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] was used to track the polymer structure in flow, both prior to and after crystallization. A relatively strong shear (rate ¼ 30 s…”

Section: Introductionmentioning

confidence: 99%

“…It was shown that a fraction of PE molecules adopted all-trans sequence configurations upon shearing, which remained stable for several hours even after cessation of shear. The recent results of the techniques that couple flow (parallel plate, [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57]66,68,[74][75][76][77][78] fiber pullout, 14,79,80 die extrusion 15,[70][71][72][73][81][82][83] ) with a physical probe of the structure development (transmitted light, [70][71][72][73][81][82][83] optical microscopy, 14,[75][76][77][78]79,80 X-ray diffraction, 42-57 atomic force microscopy, …”

mentioning

confidence: 99%

Thermal stability of shear‐induced precursor structures in isotactic polypropylene by rheo‐X‐ray techniques with couette flow geometry

Somani

Šics

Hsiao

2006

J Polym Sci B Polym Phys

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Combined in situ rheo-SAXS (small-angle X-ray scattering) and -WAXD (wide-angle X-ray diffraction) studies using couette flow geometry were carried out to probe thermal stabilty of shear-induced oriented precursor structure in isotactic polypropylene (iPP) at around its normal melting point (162 8C). Although SAXS results corroborated the emerging consensus about the formation of ''long-living'' metastable mesomorphic precursor structures in sheared iPP melts, these are the first quantitative measures of the limiting temperature at which no oriented structures survive. At the applied shear, rate ¼ 60 s À1 and duration t s ¼ 5 s, the oriented iPP structures survived a temperature of 185 8C for 1 h after shear, while no stable structures were detected at and above 195 8C. Following Keller's concepts of chain orientation in flow, it is proposed that the chains with highly oriented high molecular weight fraction are primarily responsible for their stability at high temperatures. Furthermore, the effects of flow condition, specifically the shear temperature, on the distributions of oriented and unoriented crystals were determined from rheo-WAXD results. As expected, at a constant flow intensity (i.e., rate ¼ 30 s À1 and duration, t s ¼ 5 s), the oriented crystal fraction decreased with the increase in temperature above 155 8C, below which the oriented fraction decreased with the decrease in temperature. As a result, a crystallinty ''phase'' diagram, i.e., temperature versus crystal fraction ratio, exhibited a peculiar ''hourglass'' shape, similar to that found in many two-phase polymer-polymer blends. This can be explained by the competition between the oriented and unoriented crystals in the available crystallizable species. Below the shear temperature (155 8C), the unoriented crystals crystallized so rapidly that they overwhelmed the crystallization of the oriented crystals, thus depleting a major portion of the crystallizable species and increasing their contribution in the final total crystalline phase.

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“…The geometry and temperature profile for shearing experiments were based on the methodology reported previously. 3,9,27 The shear rate _ cðrÞ applied to the sample by the parallel disks geometry is proportional to the radial position r and represented as _ cðrÞ ¼ Xr=d, where X is an angular speed of the shearing disk, and d is the gap between two parallel disks (0.5 mm was used). Consequently, one sheared sample disk has variant shear conditions of the _ cðrÞ and strain cðrÞ ¼ _ cðrÞ Á t s , where t s is a shearing time, within the radius of the sample disk (8 mm was used).…”

mentioning

confidence: 99%

Using multimodal blends to elucidate the mechanism of flow‐induced crystallization in polymers

Okura

Chambon

Mykhaylyk

et al. 2011

J Polym Sci B Polym Phys

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The effect of polydispersity on the formation of flow-induced, oriented morphology in polyolefins is investigated by polarized light imaging and small angle X-ray scattering. A torsional shear flow was applied at different temperatures to model polyethylene blends (bimodal and trimodal hydrogenated polybutadienes) comprising of two kinds of long chains with different molecular weight (1080 and 1770 kDa) in a matrix of short chains (18 KDa), and the results were compared to those of polydisperse materials. While a single boundary associated with the threshold flow conditions for the onset of oriented morphology is observed in the bimodal blends, two boundaries corresponding to the orientation of the longest chains (1770 kDa) and next longest chains (1080 kDa) are detected in the trimodal blends. The results obtained, herein, are extended by inference to polydisperse polymers. It is demonstrated that the shear rate dependence of the critical specific work parameter for the onset of oriented morphology in polydisperse polymers is dictated by the molecular weight distribution and that the longest chains mainly control the process with some contribution from shorter chains involved in the formation of flow-induced precursors at higher flow rates. KEYWORDS: crystallization; orientation; SAXS; viscoelastic properties INTRODUCTION Polyolefins are the most widely used polymer nowadays due to their excellent cost-benefit performance. The typical processing methods for semicrystalline polyolefins take a melt and shape it by means of either an extrusion or molding technique and the shape stabilization process is crystallization by cooling.1 The flow conditions in the extruder, and die or mold system have a profound effect on the morphology of the crystalline material and introduce different forms of crystals from isotropic spherulites to highly oriented ''shish-kebab structure'' in the polyolefin with the significant effect on materials through their mechanical, thermal, and optical properties.2 As processing conditions (temperature, pressure, flow rate, and duration of flow) can be adjusted and are relatively easy to control, the relationship between this group of parameters and characteristics of the polymer (chemical composition and molecular weight distribution) could significantly improve the control of structural morphologies and widen an understanding of flowinduced phenomena in polymeric materials.

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Shear-induced crystallization of isotactic polypropylene with different molecular weight distributions: in situ small- and wide-angle X-ray scattering studies

Cited by 283 publications

References 34 publications

Crystallization of Polypropylene: Application of Differential Scanning Calorimetry Part I. Isothermal and Non-Isothermal Crystallization

Crystallization of Polypropylene: Application of Differential Scanning Calorimetry Part I. Isothermal and Non-Isothermal Crystallization

Thermal stability of shear‐induced precursor structures in isotactic polypropylene by rheo‐X‐ray techniques with couette flow geometry

Using multimodal blends to elucidate the mechanism of flow‐induced crystallization in polymers

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