Towards a rheological classification of flow induced crystallization experiments of polymer melts

Meerveld, Jan van; Peters, Gwm Gerrit; Hütter, Markus

doi:10.1007/s00397-004-0382-7

Cited by 193 publications

(230 citation statements)

References 100 publications

(131 reference statements)

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“…Since it is widely recognized that it is the high molecular weight tail of the material to be crucial for flow-induced crystallization [41][42][43][44][45][46][47], only the longest mode (related to the HMW tail) is taken as representative in calculating the molecular stretch as follows: …”

Section: Rheologymentioning

confidence: 99%

Application of a multi-phase multi-morphology crystallization model to isotactic polypropylenes with different molecular weight distributions

Troisi

Arntz

Roozemond

et al. 2017

European Polymer Journal

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A B S T R A C TFlow-induced crystallization at elevated pressure of a set of metallocene isotactic polypropylenes (iPP) possessing different molecular weight distributions is studied using extended dilatometry experiments in an apparatus able to apply elevated pressure (up to 1200 bar) and strong shear flow (shear rates up to 180 s −1 ). The effect of flow on the crystallization temperature was quantified and the samples were analyzed using X-ray diffraction to measure the relative amounts of different crystal phases.The experimental results were used to test a flow induced crystallization model framework recently developed in our group which can describe the complex crystallization behavior of iPP and includes formation of multiple morphologies (spherulites, shish-kebab structure with lamellar branching) and crystal phases (α β , and γ ). Almost all model parameters were left unchanged, except for the temperature description of the quiescent crystal growth rate and nucleation density (experimentally measured using optical microscopy) and an extra parameter which takes into account the fraction of high molecular weight for the creation of flow-induced nuclei.The model describes rather good the experimentally observed trends for what regards crystallization temperature and amount of α and γ -phase but substantial discrepancies were found in the amount of β-phase formed. This could be related to the presence of 2,1 insertion errors in metallocene samples which could inhibit the formation of this crystal phase.

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Section: Rheologymentioning

confidence: 99%

Application of a multi-phase multi-morphology crystallization model to isotactic polypropylenes with different molecular weight distributions

Troisi

Arntz

Roozemond

et al. 2017

European Polymer Journal

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“…Close examination of various flow-induced crystallization experiments indicate that the stretch of the chain backbone ␣ is a critical parameter for the formation of the shish-kebab structure. 44 Using this hypothesis, we denote the value above which shish formation is observed by ␣ S , whereas kebabs can only form if the chain stretch is below a threshold value, ␣ K . If ␣ K Ͻ ␣ S , there is only sequential shish and kebab growth, while for ␣ K Ͼ ␣ S a range of stretching exists in which simultaneous shish and kebab growth occurs.…”

Section: Shish-kebab Growth: Revisitedmentioning

confidence: 99%

Crystal shapes and crystallization in continuum modeling

Hütter

Armstrong

2004

Physics of Fluids

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A crystallization model appropriate for application in continuum modeling of complex processes is presented. As an extension to the previously developed Schneider equations [W. Schneider, A. Köppel, and J. Berger, "Non-isothermal crystallization of polymers," Int. Polym. Proc. 2, 151 (1988)], the model presented here allows one to account for the growth of crystals of various shapes and to distinguish between one-, two-, and three-dimensional growth, e.g., between rod-like, plate-like, and sphere-like growth. It is explained how a priori knowledge of the shape and growth processes is to be built into the model in a compact form and how experimental data can be used in conjunction with the dynamic model to determine its growth parameters. The model is capable of treating transient processing conditions and permits their straightforward implementation. By using thermodynamic methods, the intimate relation between the crystal shape and the driving forces for phase change is highlighted. All these capabilities and the versatility of the method are made possible by the consistent use of four structural variables to describe the crystal shape and number density, irrespective of the growth dimensionality.

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“…Extensive research during the past decade into the phenomenon of FIC has indicated that flow-enhanced point-like nucleation is dominated by the chains at the high end of the molecular weight distribution [21,29,106]. Following earlier experiences by Steenbakkers and Peters [21], Roozemond and Peters [29], Custódio et al [66], and van Erp et al [82], the creation rate of point-like nuclei is coupled in a phenomenological way to the momentary stretch in the high molecular weight tail of the material (corresponding to the mode having the longest relaxation time; mode 7 in Table 3) on a continuum level,…”

Section: Structure Formationmentioning

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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Towards a rheological classification of flow induced crystallization experiments of polymer melts

Cited by 193 publications

References 100 publications

Application of a multi-phase multi-morphology crystallization model to isotactic polypropylenes with different molecular weight distributions

Application of a multi-phase multi-morphology crystallization model to isotactic polypropylenes with different molecular weight distributions

Crystal shapes and crystallization in continuum modeling

Modeling Flow-Induced Crystallization

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