Relationship between crystallization regimes and melting phenomena in isotactic polypropylene

Celli, Annamaria; Fichera, A.M.; Marega, Carla; Marigo, Antonio; Paganetto, Guglielmo; Zannetti, Roberto

doi:10.1016/0014-3057(93)90305-y

Cited by 13 publications

(16 citation statements)

References 20 publications

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“…The growths in regime II and III are basically controlled by the surface nucleation process and the transition from II to III means the roughening of the growth front at larger supercoolings (lower temperatures) in regime III with more and more surface nucleation events simultaneously occurring on the growth surface. [19][20][21][22][23] Basically, there is no reason for the simultaneous occurrence of growth regime transition for different growth faces and the respective growth directions because the growth kinetics on different types of crystallographic plane should be different. In this sense, it will be reasonable to have negligible inflection in G b at the lower inflection temperature of G a * .…”

Section: Growth Ratementioning

confidence: 99%

“…[19] In the case of iPP, an inflection of the temperature dependence of growth rate has been reported at supercoolings around 47 • C by a number of researchers. [20][21][22][23][24] This inflection was often explained by the regime II-III transition, but in a recent study, Nakamura et al suggested that the inflection could be due to the change of crystalline structure, that is, from α1 to α2, of the growing crystals. [25] The α1 and α2 forms crystallize at lower and higher T c , respectively.…”

Section: Introductionmentioning

confidence: 96%

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Morphology and Growth of Single Crystals of Isotactic Polypropylene from the Melt

Yamada

Kajioka

Nozaki

et al. 2010

Journal of Macromolecular Science, Part B

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Isolated single crystals of isotactic polypropylene (iPP) grown from the melt were studied by optical microscopy and atomic force microscopy (AFM). The single crystals had a well-known rectangular shape when crystallized at high temperatures (T c ) above 155 • C. The width increased with decreasing T c , and the shape became hexagonal below 130 • C. The single crystals were sectored with thickness difference between them. The growth rate along the a * -axis, G a * , agreed well with the growth rate of spherulites, as expected. G a * had two inflection points on the plots against (T T) −1 . The lower temperature inflection corresponds to the regime II-III transition, and the higher temperature one is accompanied by an inflection of the growth rate in the b-axis direction, G b , which has been measured for the first time. The inflection of G b at the lower inflection temperature of G a * was much smaller than that of G a * and may not exist. The crystals are basically surrounded with flat surfaces and no indications of kinetic roughening in the regime III were recognized in the AFM images. The inflections of G a * and G b caused a complicated shape change of the aspect ratio, having a minimum at around 135 • C.

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Section: Growth Ratementioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Morphology and Growth of Single Crystals of Isotactic Polypropylene from the Melt

Yamada

Kajioka

Nozaki

et al. 2010

Journal of Macromolecular Science, Part B

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“…The discontinuity in the growth rate has been interpreted as a II-III regime transition. [24][25][26][27][28] However, the crystal growth rate is influenced by several factors, such as crystal phase transition, change in radial growth direction, tacticity and molecular weight. Among these factors, a change of the crystal phase has a major impact on the temperature dependence of the crystal growth rate.…”

mentioning

confidence: 99%

Temperature Dependence of Crystal Growth Rate for α and β Forms of Isotactic Polypropylene

Nakamura

Shimizu

Umemoto

et al. 2008

Polym J

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The crystal growth rate of the 1 , 2 and forms of isotactic polypropylene (iPP) and their morphological changes were studied in a wide range of crystallization temperatures. The temperature dependence of the crystal growth rate of the 1 form showed a bell-shaped curve with the maximum growth rate (G max ) at 70 C. The crystal growth rate of the form induced by calcium pimelate also showed a bell-shaped curve with G max at 79 C. Two crossover points on the growth rate curve from the 1 form to the form or vice versa were observed at 90 C and 133 C, respectively. Tear-drop shaped spherulites were observed at temperatures between the two crossover points. Electron diffraction patterns showed the high ordered structure of the 2 form for thin films crystallized at 140 C. The 2 fraction became detectable in X-ray diffraction pattern for temperatures above 110 C. The 2 fraction increased with crystallization temperature and saturated to 100% at about 140 C. In the temperature region from 110 C to 140 C, several crystal growth rates were found at the same crystallization temperature. The growth rate variations could be associated with the co-crystallization of the 1 and 2 forms. Above 140 C, the growth rate variations disappeared, since the fraction of the 2 reached to 100%. The extrapolated G max of the 2 showed at 72 C.KEY WORDS: Isotactic Polypropylene / -Form / -Form / Crystal Growth Rate / Crossover / Isotactic polypropylene (iPP) is one of the most widely used commercial polymeric materials and has been extensively investigated for it academic and industrial interest. iPP displays different structural polymorphism, such as form (monoclinic), form (trigonal), form (orthorhombic) and smectic form, which all consist of 3 1 helical conformations with a 0.65 nm chain axis periodicity. The form is the most common crystal structure, which is produced by crystallization from the melt or solution.1-5 The form can be obtained from temperature gradient crystallization, 6 crystallization under molecular orientation 7 or can be induced by selective -nucleating agent. 8-10The crystal structure of the form was first determined by Natta and Corradini. 11 Mencik 12 and Hikosaka and Seto 13showed that the structure has two limiting modifications named 1 and 2 forms. Extensive works on these crystalline forms have been also reported. 14-16 The 1 form space group (C2/c) is the limit-disordered structure and the 2 form (P2 1 /c) is the limit-ordered structure. They are characterized by either regular alternation of the up and down orientations of the methyl group along the chain ( 2 ) or random orientation. A transition from the 1 form to the 2 form is observed by annealing at a higher temperature. [17][18][19][20][21][22] The crystal structure of the form has been analyzed by Meille et al. 23 and refined by D. L. Dorset et al. 9Many studies about the crystallization behavior and morphology of iPP have been reported. When iPP was crystallized from the melt in a wide temperature range, Keith and Padden found four distinct spherulites,...

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“…Due to its technical importance isotactic poly-(propylene) is most often studied. This phenomenon of different spherulitic growth behaviour has been thoroughly investigated and the different spherulitic species have been characterized by their birefringence, temperature dependent radial growth rate, melting behaviour, and the organisation of crystal lamellae [4][5][6][7][8][9][10][11][12][13][14][15] . It usually crystallizes in a spherulitic manner, where spherulites can appear in four different species, as first observed by Keith and Padden 2,3) .…”

Section: Introductionmentioning

confidence: 99%

“…At least between type I and II the distinctive difference is given by point (iii). It is our aim to quantitatively describe the isotactic poly-(propylene) spherulitic growth by solid-state 13 C NMR measurements. The effect is usually interpreted in terms of regime transitions of secondary nucleation 16,17) or by epitaxial growth of daughter lamellae at an angle of 80 8 6,18,19) .…”

Section: Introductionmentioning

confidence: 99%

Solid-state 13C NMR of microscopic order in transcrystalline films of isotactic poly(propylene)

Hegemann¹,

Veeman²

1999

Macromol. Chem. Phys.

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SUMMARY: The microscopic orientational order in a variety of transcrystalline films of isotactic poly(propylene) was investigated by means of two-dimensional solid-state NMR. From the experimental results the orientation distribution function of the microcrystallites relative to the macroscopic growth direction was determined. The NMR measurements were performed at room temperature on samples that had been crystallized at conditions at which the morphology of spherulitic crystallization changes as a function of temperature or composition. For transcrystalline samples of isotactic poly(propylene) crystallized in the a-modification a drastic breakdown of molecular order was observed at a crystallization temperature of 137 8C, with the absolute degree of order depending on the molecular mass of the polymer. For samples crystallized in the bmodification a small stepwise decrease of molecular order was observed at a crystallization temperature of 128 8C. A continuous decrease of the orientational order of the isotactic part was observed by blending isotactic poly(propylene) with atactic poly(propylene).

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Relationship between crystallization regimes and melting phenomena in isotactic polypropylene

Cited by 13 publications

References 20 publications

Morphology and Growth of Single Crystals of Isotactic Polypropylene from the Melt

Morphology and Growth of Single Crystals of Isotactic Polypropylene from the Melt

Temperature Dependence of Crystal Growth Rate for α and β Forms of Isotactic Polypropylene

Solid-state 13C NMR of microscopic order in transcrystalline films of isotactic poly(propylene)

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