Effects of the catalyst system on the crystallization of polypropylene*

Gahleitner, Markus; Bachner, Claudia; Ratajski, Ewa; Rohaczek, Gerald; Neil, Wolfgang

doi:10.1002/(sici)1097-4628(19990919)73:12<2507::aid-app19>3.0.co;2-v

Cited by 49 publications

(38 citation statements)

References 23 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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“…It was shown that spherulitical growth of iPP is not influenced by molecular weight. Similar results were obtained by Eder et al [21] and Gahleitner et al [32]. Magill [33] reported the opposite for poly(tetramethyl-p-silphenylene)-siloxane (TMPS), but the dependence became less for higher molecular weights.…”

Section: Measurement Of Flow-induced Crystallizationsupporting

confidence: 82%

“…Magill [33] reported the opposite for poly(tetramethyl-p-silphenylene)-siloxane (TMPS), but the dependence became less for higher molecular weights. A decrease in growth rate with decreasing tacticity was shown by Gahleitner et al [32]. Duplay et al [31] showed that the growth rate increased during shear and correlated with molecular weight.…”

Section: Measurement Of Flow-induced Crystallizationmentioning

confidence: 84%

Stress Induced Crystallization in Elongational Flow

Swartjes

Peters

Rastogi

et al. 2003

International Polymer Processing

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Stress-induced crystallization is studied in an extensional flow device (a cross-slot flow cell) for an isotactic Polypropylene (iPP) by measuring the micro-structure that develops after flow. Birefringence and Wide Angle X-ray experiments were performed. The birefringence experiments with flow below the melting temperature showed the occurrence of a fiber-like structure around the outflow centerline and, later in time, of 'streamlines'. The latter are explained by the influence of shear gradients close to the optical windows. The WAXS experiments also showed the fiber-like structure around the outflow centerline, having orientations in the (110), (040) and (130) reflections, with a width of about 80 lm. This dominance of the elongational flow around the stagnation line could not be observed in experiments with flow above and subsequent crystallization below the melting temperature. Structure development in this cell was numerically predicted using the Leonov and the extended Pompom (XPP) model. The oriented structures can be predicted. Moreover, process conditions are found with less influence of the (unwanted) shear gradients. Finally, it was concluded that the strain hardening behavior in the Leonov model over-estimates the first component of the Finger tensor, and thus the number of flow-induced nuclei. Therefore it is recommended to use the extended Pompom model as a more realistic basis for a quantitative flow-induced crystallization model. IPP_ipp1719 -2.4.03/druckhaus köthen FIBER AND FILM Intern. Polymer Processing XVIII (2003) 1  Hanser Publishers, Munich 53

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“…The properties of crystalline polymers are determined by their structure which can be modified by two main approaches, namely, (1) to control molecular structure and increase chain regularity 6,7 and (2) to use nucleating agents. [8][9][10][11][12][13][14] Modern polymerization and catalyst technology reached very high levels, further progress is difficult.…”

Section: Introductionmentioning

confidence: 99%

Effect of molecular architecture on the crystalline structure and stiffness of iPP homopolymers: Modeling based on annealing experiments

Horváth

Menyhárd

Doshev

et al. 2013

J of Applied Polymer Sci

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Five PP homopolymers were selected and their molecular structure was thoroughly characterized to determine the effect of molecular architecture on their annealing behavior and on the ultimate stiffness achieved by heat treatment. Molecular mass and its distribution were characterized by rheological measurements, while chain regularity was determined by calorimetry, by the stepwise isothermal segregation technique (SIST). The samples were annealed in two different ways. Tensile bars were treated in an oven at 165 °C for increasing times to determine changes in stiffness. Various defects developed during the annealing of tensile specimens that did not allow the reliable determination of modulus by direct measurement. On the other hand, the second approach, the annealing of small samples in a DSC cell clearly showed the changes occurring in crystalline structure and also the effect of nucleation and molecular architecture on them. The large molecular weight fraction used to facilitate nucleation hinders crystal perfection, while the presence of a heterogeneous nucleating agent increases overall crystallinity, but does not influence recrystallization during annealing. Melting traces were transformed into lamella thickness distributions, from which average lamella thickness was derived. Lamella thickness and crystallinity, the independent variables of the empirical equation used for the calculation of modulus, were extrapolated to infinite annealing time to predict maximum stiffness. The Full paper submitted for publication in Journal of Applied Polymer Science 2 value obtained, 3.5 GPa, is very far from the theoretically predicted 40 GPa of oriented crystals, which cannot be achieved under practical conditions.

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Effects of the catalyst system on the crystallization of polypropylene*

Cited by 49 publications

References 23 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

Stress Induced Crystallization in Elongational Flow

Effect of molecular architecture on the crystalline structure and stiffness of iPP homopolymers: Modeling based on annealing experiments

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