Quiescent crystallization kinetics and morphology of isotactic polypropylene resins for injection molding. I. Isothermal crystallization

Carvalho, Benjamim de Melo; Bretas, Rosário Elida Suman

doi:10.1002/(sici)1097-4628(19980516)68:7<1159::aid-app13>3.0.co;2-t

Cited by 26 publications

(38 citation statements)

References 7 publications

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“…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%

“…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] . 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] .…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Introductionmentioning

confidence: 99%

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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“…the formation of the final structure. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] For example, when high flow and high cooling rates exist, oriented structures, such as shish kebab or lamellae row structures, are preferably formed. In addition, Varga et al [6,7] found that the supermolecular structure formed in the vicinity of the sheared layer is generally rich in the b-modification of isotactic polypropylene (iPP).…”

Section: Introductionmentioning

confidence: 99%

Processing, Morphology, and Mechanical Properties of Liquid Pool Polypropylene with Different Molecular Weights

Stern

Frick

Weickert

et al. 2005

Macro Materials & Eng

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Summary: The processability, morphology, and resulting mechanical properties of novel polypropylene (PP) samples of varying molecular weight ($\overline M _{\rm w}$) were studied. A series of homopolymer PP in a wide $\overline M _{\rm w}$ range from 101 000 to 1 600 000 g · mol−1 was polymerised in a liquid pool (LP) under defined conditions. The LP‐PP with a well‐known polymerisation history was manufactured into micro dumbbell specimens by means of a micro injection‐moulding process. The morphology and mechanical properties of the samples were studied by light microscopy, transmission and scanning electron microscopy, and a quasi‐static tensile test. Simulation of the filling behaviour of the molten polymer inside the mould shows that the shear rate increases as the molecular weight increases, up to a maximum shear rate of 750 000 s−1. In addition, the present crystallisation time of the high‐molecular‐weight PP samples is clearly lower than their retardation time; the long macromolecules do not have sufficient time to retard while cooling. As a result of the shear‐induced crystallisation, a highly oriented crystalline structure is formed as a function of the acting shear rate. SEM and TEM investigations show the existence of an oriented shish kebab structure. The density of the shish kebab increases as the molecular weight increases. Evaluations of the shear rate and the morphological structure indicate a critical shear rate of about 300 000 s−1. Above this shear rate level, shish kebab structures are favourably formed. The shear‐induced crystallisation and, therefore, the preferred formation of a highly oriented shish kebab structure lead, obviously, to unusual solid‐state properties of the analysed LP‐PP samples. With a tensile strength up to 100 N · mm−2 and an attainable strain at break of more than 30%, the mechanical performance is much higher than results ever reported in literature.True strain–stress behaviour of moulded the LP‐PP samples of different molecular weight.magnified imageTrue strain–stress behaviour of moulded the LP‐PP samples of different molecular weight.

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“…In three previous works of the present authors, the Master Curve Approach proposed by Isayev et al 1 was applied to calculate the non-isothermal crystallization rate constant K(T) for modified polypropylenes 2,3 (maleic anhydride and acrylic acid grafted polypropylenes) and for a heterophasic polypropylene sample (Polypropylene/Ethylene-propylene rubber PP/EPR) 4,5 . The non-isothermal crystallization rate constant obtained by this method was used to calculate the curves of relative crystallinity as a function of temperature at different cooling rates.…”

Section: Introductionmentioning

confidence: 99%

Determination of non-isothermal crystallization rate constant for pseudo-experimental calorimetric data

2009

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Quiescent crystallization kinetics and morphology of isotactic polypropylene resins for injection molding. I. Isothermal crystallization

Cited by 26 publications

References 7 publications

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

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

Processing, Morphology, and Mechanical Properties of Liquid Pool Polypropylene with Different Molecular Weights

Determination of non-isothermal crystallization rate constant for pseudo-experimental calorimetric data

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