Flow-induced crystallization studied in the RheoDSC device: Quantifying the importance of edge effects

Roozemond, Peter C.; Drongelen, Martin van; Verbelen, Leander; Puyvelde, Peter Van; Peters, Gwm Gerrit

doi:10.1007/s00397-014-0820-0

Cited by 11 publications

(6 citation statements)

References 26 publications

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“…Rheometers are widely used to study flow-induced crystallization (FIC), since these instruments enable researchers to apply flow at elevated temperatures (> T m , the polymer nominal melting point) and to monitor crystallization via oscillatory time sweeps upon lowering temperature (< T m ). ,− Experiments on entangled melts can be challenging in commercial rotational rheometers where the torque and normal force limitations are readily exceeded. Only pressure-driven flow (capillary rheometry) has been previously reported to study the effect of flow on crystallization kinetics in the regime of high shear stress, where shish-kebab structures form and determine the final morphology.…”

Section: Introductionmentioning

confidence: 99%

“…Together with this change in crystalline morphology, crystallization occurs faster and at a higher temperature. As a direct measure of crystallization via latent heat release, differential scanning calorimetry (DSC) has proven to be a valuable complement to rheometry for the study of FIC. ,,, Polarized optical microscopy (POM) equipped with a hot stage has also been used to investigate morphological evolution in crystallizing samples with different shear histories. ,,, …”

Section: Introductionmentioning

confidence: 99%

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Two Distinct Morphologies for Semicrystalline Isotactic Polypropylene Crystallized after Shear Flow

et al. 2018

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Application of shear flow to molten, highly isotactic polypropylene (iPP) results in two different morphology transitions: (1) above a certain shear rate but below a critical shear stress σ*, flow-induced precursors nucleate many small crystallites; (2) for shear stress above σ*, shish precursors nucleate highly oriented shish-kebab morphology. Herein we study flow-induced crystallization (FIC) in iPP with different molecular weights, using rotational and capillary rheometry. Since precursors created by shear are quite stable, we can also use differential scanning calorimetry (DSC) and polarized optical microscopy (POM) to study crystallization, melting, and morphology of iPP samples with different shear histories. Above a critical shear rate (inverse of long-chain relaxation time 1/τ), the onset of crystallization on cooling shifts to higher temperatures compared to unsheared samples. POM micrographs see a clear border between the regions affected by FIC (with γ̇ > 1/τ) and regions crystallizing as though they had not been sheared. FIC results in much smaller crystallites, so-called rice grains of order 1 μm in size. Above a critical shear stress (σ* ∼ 0.11 MPa) in the rotational rheometer, the morphology transitions to a shish-kebab structure. Shish appear in micrographs as highly aligned birefringent regions; in DSC, flow-induced shish further accelerate the onset of crystallization. In the rheometer, sheared samples with σ < σ* at 170 °C (above T m) behave as a viscoelastic liquid identical to unsheared samples, whereas strongly sheared samples with σ > σ* behave as weak gels, revealing the presence of a percolating network of shish. In capillary rheometry, samples sheared above this threshold stress likewise show an abrupt increase in apparent viscosity.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Two Distinct Morphologies for Semicrystalline Isotactic Polypropylene Crystallized after Shear Flow

et al. 2018

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“…For example, the simultaneous measurement of the shear stress and heat flow will facilitate the accurate estimation of the contribution of the shearing heat flow, which can be applied to highly viscous non-Newtonian fluids. The Rheo-DSC system, which was developed for the investigation of shear-induced crystallization of polymers, [37][38][39][40] is a good reference for such improvements.…”

Section: Discussionmentioning

confidence: 99%

Calorimetry of phase transitions in liquid crystal 8CB under shear flow

et al. 2023

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“…3 of this chapter and [5,116]). Aside from the obvious goal of validating the approach of combining these models, this research is aimed at investigating two phenomenon specific to FIC of iPP:…”

Section: Formation Of Multiple Crystal Phases and Morphologiesmentioning

confidence: 94%

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 crystallization studied in the RheoDSC device: Quantifying the importance of edge effects

Cited by 11 publications

References 26 publications

Two Distinct Morphologies for Semicrystalline Isotactic Polypropylene Crystallized after Shear Flow

Two Distinct Morphologies for Semicrystalline Isotactic Polypropylene Crystallized after Shear Flow

Calorimetry of phase transitions in liquid crystal 8CB under shear flow

Modeling Flow-Induced Crystallization

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