Unexpected Shish-Kebab Structure in a Sheared Polyethylene Melt

Hsiao, Benjamin S.; Yang, Ling; Somani, Rajesh H.; Ávila‐Orta, Carlos A.; Zhu, Lei

doi:10.1103/physrevlett.94.117802

Cited by 269 publications

(259 citation statements)

References 17 publications

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“…44 Subsequent studies of stress-induced crystallization of polyethylene elucidated this mechanism and revealed the detailed structure of these morphological units, which were called shish kebabs. [45][46][47][48][49][50][51][52] The detailed structure of polyethylene shish kebabs were revealed in recent studies, showing that the shish were sub-lm to $10 lm in length, $2-3 lm in diameter and contained $10-50 extended chain segments. 51,52 Also, a blend study revealed that mainly ultra-high molecular weight polyethylene chains ($5-6 Â 10 6 weight-average molecular weight) were involved in shish formation by a coil-stretch mechanism.…”

Section: Stress-induced Crystallizationmentioning

confidence: 99%

“…51,52 Also, a blend study revealed that mainly ultra-high molecular weight polyethylene chains ($5-6 Â 10 6 weight-average molecular weight) were involved in shish formation by a coil-stretch mechanism. 51 Further, multiple shish were observed to connect adjacent lamellar kebabs 51 in contrast to the earlier view that only one shish connected adjacent kebabs. 53 The formation of the shish structures was attributed to heterogeneous primary nucleation.…”

Section: Stress-induced Crystallizationmentioning

confidence: 99%

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Crystallization and melting of polyethylene copolymers: Differential scanning calorimetry and atomic force microscopy studies

Mirabella

2006

J Polym Sci B Polym Phys

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ABSTRACT:The HoffmanLauritzen theory of secondary, surface nucleation and growth was primarily relied upon for about 40 years after its introduction in about 1960 to rationalize the crystallization of flexible chain polymers into lamellar crystals. However, in about 1998, Strobl and coworkers introduced a different model for crystallization, based on the stagewise formation of lamellae. Two major components of this model were as follows: (1) the concept of the formation of a mesomorphic melt as a precursor to crystallization and (2) the control of the melting temperature range of lamellar crystals of homogeneous polyolefin copolymers by an inner degree of order or perfection rather than on the crystal thickness. The first concept is in disagreement with the HL theory and the second with the Gibbs-Thomson theory, which associates melting temperature with lamella thickness. In the present study, differential scanning calorimetry and atomic force microscopy were successfully employed to monitor the in situ quiescent crystallization of polyethylene homopolymer and copolymer. In the present study, evidence was not found to support the concept of lamellae with equal thickness melting over a broad temperature range. Some evidence was found that might be interpreted to support the concept of a mesomorphic melt as a precursor to crystallization. At present, the model promoted by Strobl and coworkers appears to be at an uncertain stage at which strong proof or disproof are not available. However, this alternative model has injected a new vitality into the study of crystallization of flexible chain polymers.

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Section: Stress-induced Crystallizationmentioning

confidence: 99%

Section: Stress-induced Crystallizationmentioning

confidence: 99%

Crystallization and melting of polyethylene copolymers: Differential scanning calorimetry and atomic force microscopy studies

Mirabella

2006

J Polym Sci B Polym Phys

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“…The surface area of a kebab on which both parent and daughter morphology can grow is denoted by ψ 1,p . Reproduced with permission of the copyright owner [5] For such experiments, a shear cell is combined with in-situ X-ray diffraction (XRD) [4,[48][49][50][51][52][53], birefringence [18,23,43], or light scattering [46], or examined ex-situ with microscopy [4]. The critical flow conditions are usually expressed in terms of stress [4,44], mechanical work [35,45], or shear rate for a fixed strain [43].…”

Section: State Of the Artmentioning

confidence: 99%

Modeling Flow-Induced Crystallization

Roozemond

Drongelen

Peters

2016

Polymer Crystallization II

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A numerical model is presented that describes all aspects of flow-induced crystallization of isotactic polypropylene at high shear rates and elevated pressures. It incorporates nonlinear viscoelasticity, including viscosity change as a result of formation of oriented fibrillar crystals (shish), compressibility, and nonisothermal process conditions caused by shear heating and heat release as a result of crystallization. In the first part of this chapter, the model is validated with experimental data obtained in a channel flow geometry. Quantitative agreement between experimental results and the numerical model is observed in terms of pressure drop, apparent crystallinity, parent/daughter ratio, Hermans' orientation, and shear layer thickness. In the second part, the focus is on flow-induced crystallization of isotactic polypropylene at elevated pressures, resulting in multiple crystal phases and morphologies. All parameters but one are fixed a priori from the first part of the chapter. One additional parameter, determining the portion of β-crystal spherulites nucleated by flow, is introduced. By doing so, an accurate description of the fraction of β-phase crystals is obtained. The model accurately captures experimental data for fractions of all crystal phases over a wide range of flow conditions (shear rates from 0 to 200 s À1 , pressures from 100 to 1,200 bar, shear temperatures from 130 C to 180 C). Moreover, it is shown that, for high shear rates and pressures, the measured γ-phase fractions can only be matched if γ-crystals can nucleate directly on shish.

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“…Hence, bimodal blends of polymers composed of small fraction of long-chain molecules in a short-chain polymer matrix have been explored to simplify the task. [21][22][23] Even though industrial polymers and bimodal blends of controlled polydispersity demonstrate qualitatively similar results in the onset of oriented morphologies, it is not clear to what extent the longest molecular chains in polymer ensemble control the crystallization of polymer, and how the rest of the molecules influence the flow-induced crystallization. The aim of this study is to understand the interaction between different kinds of chains in a polydisperse system and illustrate how the interaction between these chains affects the conditions required for the flow-induced nucleation in polydisperse polymers.…”

mentioning

confidence: 97%

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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Unexpected Shish-Kebab Structure in a Sheared Polyethylene Melt

Cited by 269 publications

References 17 publications

Crystallization and melting of polyethylene copolymers: Differential scanning calorimetry and atomic force microscopy studies

Crystallization and melting of polyethylene copolymers: Differential scanning calorimetry and atomic force microscopy studies

Modeling Flow-Induced Crystallization

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

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