Flow-induced shish-kebab precursor structures in entangled polymer melts

Somani, Rajesh H.; Yang, Ling; Zhu, Lei; Hsiao, Benjamin S.

doi:10.1016/j.polymer.2005.06.034

Cited by 438 publications

(485 citation statements)

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“…The application of flow (shear or elongation) can change drastically the crystallization kinetics and the morphology of semicrystalline polymers (Kumaraswamy et al, 2004;Somani et al, 2005;Kimata et al, 2007;Balzano et al, 2008). Fibrillar precursors, composed of bundles of stretched molecules, are formed when some critical flow conditions are exceeded.…”

Section: Shear-induced Crystallization Using a Slit Rheometermentioning

confidence: 99%

Polymer crystallization studies under processing-relevant conditions at the SAXS/WAXS DUBBLE beamline at the ESRF

et al. 2013

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Recent developments on the experimental infrastructure and the acquisition of new detectors on the Dutch-Belgian beamline BM26B at the ESRF offer novel and promising possibilities for synchrotron X-ray experiments in the field of polymer crystallization under processing-relevant conditions. In this contribution, some of the most recent experiments mimicking conditions similar to those relevant for the plastics processing industry are discussed. Simultaneous thermal analysis and wide-angle X-ray scattering (WAXS) experiments, at the millisecond time-frame level, on -nucleated isotactic polypropylene (i-PP) samples subjected to ballistic cooling up to 230 K s À1 , show that the efficiency of the nucleating agent can be suppressed when quenched cooling rates higher than 130 K s À1 are used. In situ WAXS experiments using small-scale industrial equipment during a real film blowing process reveal the dependence of the onset of crystallinity (the so-called freeze line) and the crystal orientation as a function of different take-up and blow-up ratios. In situ small-angle X-ray scattering (SAXS) experiments during high-flow fields reveal the formation of shish and kebab structures in i-PP as a function of the imposed stress. Quantitative analysis of i-PP flow-induced structures is presented. The beamline specifications required to obtain high quality and industrially relevant results are also briefly reported.

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Section: Shear-induced Crystallization Using a Slit Rheometermentioning

confidence: 99%

Polymer crystallization studies under processing-relevant conditions at the SAXS/WAXS DUBBLE beamline at the ESRF

et al. 2013

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“…Here, the chain extension via flow or elongation processes, form the shish and at a later time the coiled chains then go on to form the crystalline outgrowths or kebabs [4,56]. This model is now widely accepted as the process by which crystallization in entangled polymer melts occurs under all types of flow.…”

Section: Crystallization Processes In the Extruded Tapementioning

confidence: 99%

“…This results in the formation of the shish structures. The critical strain rate at a fixed temperature, is a function of the molecular weight distribution; higher molecular weight chains can be stretched at lower strain rates and lower molecular weight chains at much higher strain rates [15,56]. At constant strain rate a portion of molecules above the molecular weight threshold (M*) will stretch fully, whereas chains below M* will not stretch and remain as random coils.…”

Section: Crystallization Processes In the Extruded Tapementioning

confidence: 99%

Effect of processing parameters on the morphology development during extrusion of polyethylene tape: An in-line small-angle X-ray scattering (SAXS) study

Heeley

Gough

Hughes

et al. 2013

Polymer

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Ray scattering (SAXS). AbstractThe in-line development of crystalline morphology and orientation during melt extrusion of low density polyethylene (LDPE) tape at nil and low haul-off speeds has been investigated using Small-Angle X-Ray Scattering (SAXS). The processing parameters, namely haul-off speed and distance down the tape-line have been varied and the resulting crystalline morphology is described from detailed analysis of the SAXS data. Increasing haul-off speed increased orientation in the polymer tape and the resulting morphology could be described in terms of regular lamellar stacking perpendicular to the elongation direction. In contrast, under nil haul-off conditions the tape still showed some orientation down the tape-line, but a shish-kebab structure prevails. The final lamellae thickness (~50 Å) and bulk crystallinity (~20%), were low for all processing conditions investigated, which is attributed to the significant shortchain branching in the polymer acting as point defects limiting lamellae crystal growth.2

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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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Flow-induced shish-kebab precursor structures in entangled polymer melts

Cited by 438 publications

References 115 publications

Polymer crystallization studies under processing-relevant conditions at the SAXS/WAXS DUBBLE beamline at the ESRF

Polymer crystallization studies under processing-relevant conditions at the SAXS/WAXS DUBBLE beamline at the ESRF

Effect of processing parameters on the morphology development during extrusion of polyethylene tape: An in-line small-angle X-ray scattering (SAXS) study

Modeling Flow-Induced Crystallization

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