Isotacticity effect on crystallization and melting in polypropylene fractions. II. Linear crystal growth rate and morphology study

Janimak, James J.; Cheng, Stephen Z. D.; Giusti, Paul A.; Hsieh, Eric T.

doi:10.1021/ma00009a020

Cited by 134 publications

(117 citation statements)

References 6 publications

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“…Two main observations can be extracted from the experimental results: the growth rates of the LMW material are practically the same as the bimodal, whereas the HMW grade shows slightly slower growth in the investigated temperature range. The influence of molecular weight on the maximum growth rates has been investigated in literature [54][55][56], and a decrease with increasing molecular weight is expected, in line with our experimental observations. In this work we use an empirical relation to describe the growth rate of each crystal phase (α β , and γ), which, similarly to the widely used Lauritzen-Hoffman theory [57], translates to a bell-shaped curve to describe the temperature dependence of the growth rate:…”

Section: Crystallization Model Frameworksupporting

confidence: 89%

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: Crystallization Model Frameworksupporting

confidence: 89%

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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show abstract

“…An increase in crystallinity can lead to an increase in the lamellar thickness which leads to higher storage modulus and stiffiness values [2][3][4] . The effects of molecular weight [5][6][7][8] , molecular weight distribution [9] and tacticity [10][11][12][13] on the crystallization have been investigated by several authors. Cheng et al [6] showed that the linear growth rate of crystals decreases with the increase of molecular weight, but the overall crystallization rate might increase because an increasing number of intramolecular folded-chain nuclei could result in a higher nucleation density [7] .…”

Section: Introductionmentioning

confidence: 99%

“…Cheng et al [6] showed that the linear growth rate of crystals decreases with the increase of molecular weight, but the overall crystallization rate might increase because an increasing number of intramolecular folded-chain nuclei could result in a higher nucleation density [7] . For samples with similar molecular weights and different tacticities the linear crystal growth rate might increase by three orders of magnitude when the isotacticity (mmmm %) of isotactic polypropylene increases from 78.7 to 98.8% [11,14] . The degree of crystallinity of isotactic polypropylene is commonly in the range of 40 to 70% [1] .…”

Section: Introductionmentioning

confidence: 99%

Molecular weight and tacticity effect on morphological and mechanical properties of Ziegler–Natta catalyzed isotactic polypropylenes

2015

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SbstractThe morphological and mechanical properties of Ziegler-Natta catalyzed isotactic polypropylenes as influenced by the molecular weight and tacticity was investigated. Polypropylene samples were injection moulded into standard disks with a HAAKE MiniJet II injection moulder at 190 °C and 200 bar for morphological and mechanical tests. The morphological and mechanical properties of specimens were investigated by means of optical microscope (OM), scanning electron microscopy (SEM), microhardness (MH) and dynamic mechanical analysis (DMA). The samples exhibited a typical α-modification spherulite structure of isotactic polypropylenes crystallized from the melt. It was found that the most important factor affecting the structure and properties of these polymers is the isotacticity content. A clear molecular weight effect was also found for samples with low molecular weights. The microhardness and storage modulus values increased as crystallinity did. Accordingly, isotacticity degree is considered as the main parameter affecting the crystallinity of samples.

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“…At the crystallization temperature used in the experiments, iPP crystallizes in regime III [43], which makes it possible to use Equation (29) or (30) given in the previous analysis. In the Equation (29) or (30) the expression for /G 0 is given by Equation (20) and the remaining parameters can be found in literature [2,3,47]. However, the reported values, especially for " u and " e , widely scatter [13] and limit a useful calculation of K g and /G 0 .…”

Section: Analysis Of the Crystallization Behaviour Of The "-And !-Phamentioning

confidence: 99%

The influence of chain defects on the crystallisation behaviour of isotactic polypropylene

Meer¹,

Varga²,

Vancso³

2015

Express Polym. Lett.

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Isotacticity effect on crystallization and melting in polypropylene fractions. II. Linear crystal growth rate and morphology study

Cited by 134 publications

References 6 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

Molecular weight and tacticity effect on morphological and mechanical properties of Ziegler–Natta catalyzed isotactic polypropylenes

The influence of chain defects on the crystallisation behaviour of isotactic polypropylene

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