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

Yamada, Koji; Kajioka, Hiroshi; Nozaki, Koji; Toda, Akihiko

doi:10.1080/00222341003648847

Cited by 14 publications

(18 citation statements)

References 29 publications

(62 reference statements)

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“…Clearly, the Lauritzen–Hoffman plots can be divided into three regimes. The boundaries between regimes III and II and between regimes II and I locate around 140 and 151 °C, respectively, which are close to the reported values of 137 and 148 °C in earlier studies . The K g in the every regime is shown in Table .…”

Section: Resultssupporting

confidence: 87%

“…From Figure , it can be seen that around 185 °C, two fitting lines intersect. This indicates the equilibrium melting temperature of aggregates is around 185 °C, which is the same as the equilibrium temperature of iPP crystal …”

Section: Resultsmentioning

confidence: 79%

“…One is the activation energy needed for transporting the polymer chain from the melt to the spherulitic growth front, and the other one is Gibbs free energy needed for the formation of a critical surface nucleus . Thus, growth rate G can be generally expressed by the following equation:

G = G_{0} \exp [- U^{*} / R (T - T_{\infty})] \exp true[- K_{normalg} / (T Δ T) true]

where

G_{0}

is the preexponential factor,

U^{*}

is the activation energy that governs the short distance diffusion of the crystalline element across the phase boundary, R is the gas constant,

T_{\infty}

is the Vogel temperature, K g is the surface nucleation barrier, and

Δ T

represents the degree of supercooling with equilibrium melting temperature,

T_{normalm}^{0}

. Here 8.31 J/(mol·K), 6.28 kJ/mol, 231.2 K, and 185 °C were taken as values for R,

U^{*}

T_{\infty}

T_{normalm}^{0}

for iPP, respectively, which is suggested by Clark and Hoffman .…”

Section: Resultsmentioning

confidence: 99%

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Molecular mechanism leading to memory effect of mesomorphic isotactic polypropylene

Liu

Tian

et al. 2016

J Polym Sci B Polym Phys

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In this study, memory effect of mesomorphic isotactic polypropylene (iPP) was investigated using polarized optical microscope and small-angle X-ray scattering. Differing from classical memory effect, mesomorphic iPP melt had a higher growth rate and a higher memory temperature. The relative growth rate increased with increasing crystallization temperature. Lauritzen-Hoffman plots indicated that the increased growth rate arose from reduced surface nucleation barrier. The highest memory temperature was estimated to be 185 8C, which was close to the equilibrium melting point of iPP crystal. Additionally, Small-angle X-ray scattering measurements showed that a liquid crystal layer might exist between lamellar and amorphous layers. Based on above results, a crystallization model was proposed. In the mesomorphic iPP melt, there exist aggregates structurally similar to b phase except a-phase crystal residuals, which cannot act as nucleation sites or transform to b crystal through surface nucleation. The only way for the aggregate is to transform to a crystal during crystal growth. The aggregate decreases the surface nucleation barrier and promotes the helical growth, leading to higher growth rate. Only when the aggregate relaxes to polymer coils through thickening at a higher temperature, can the memory effect be erased. FIGURE 1 (a) Micrographs for growing spherulites and (b) changes in diameter of spherulites with time during isothermal crystallization at 135 8C after melting of mesomorphic iPP at 180 or 220 8C for 5 min. (c) Variety and relative variety in growth rate with isothermal crystallization temperature after heating mesomorphic iPP at 180 and 220 8C for 5 min.

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Section: Resultssupporting

confidence: 87%

Section: Resultsmentioning

confidence: 79%

G = G_{0} \exp [- U^{*} / R (T - T_{\infty})] \exp true[- K_{normalg} / (T Δ T) true]

where

G_{0}

is the preexponential factor,

U^{*}

is the activation energy that governs the short distance diffusion of the crystalline element across the phase boundary, R is the gas constant,

T_{\infty}

is the Vogel temperature, K g is the surface nucleation barrier, and

Δ T

represents the degree of supercooling with equilibrium melting temperature,

T_{normalm}^{0}

. Here 8.31 J/(mol·K), 6.28 kJ/mol, 231.2 K, and 185 °C were taken as values for R,

U^{*}

T_{\infty}

T_{normalm}^{0}

for iPP, respectively, which is suggested by Clark and Hoffman .…”

Section: Resultsmentioning

confidence: 99%

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Molecular mechanism leading to memory effect of mesomorphic isotactic polypropylene

Liu

Tian

et al. 2016

J Polym Sci B Polym Phys

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“…Single crystals of isotactic polypropylene (iPP), especially large sized crystals, have attracted the interest of researchers for many years. [1][2][3][4][5][6][7][8][9][10][11][12] However, the crystal aggregate-the so-called spherulite rather than the single crystal-is usually obtained during the conventional crystallization of iPP from the molten state. Spherulite consists of both crystalline lamella and non-crystalline amorphous regions, which are alternatively arranged with a certain periodicity, that is, long-range order.…”

Section: Introductionmentioning

confidence: 99%

“…Because of these obstacles, well-isolated iPP single crystals usually only exist during the early stage of the crystallization process. 4,12 As a natural consequence, the size of the iPP single crystal is small when iPP is crystallized from the bulk melt.…”

Section: Introductionmentioning

confidence: 99%

Giant single crystal of isotactic polypropylene showing near-equilibrium melting temperature

Asakawa

Nishida

Kanaya

et al. 2012

Polym J

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Giant single crystals of isotactic polypropylene (iPP) were obtained using a specific kinetic pathway through the mesophase of iPP; the pre-quenched iPP mesophase was heated to 166 1C at a rate of 75 1C min À1 and maintained at this temperature for 24 h. The obtained crystallites exhibited a very high melting temperature, T m , of 183.7 1C, which is B19 1C higher than the iPP's nominal T m (B165 1C); namely, the observed T m is immediately close to the literature value of iPP's equilibrium melting temperature, T m 0 (186.2 1C). The crystallites have bamboo leaf-like or needle-like morphology and are B35 lm in length and B3.5 lm in width. The thickness of the crystallites was estimated to be 88 nm according to the melting temperature. The number density of the crystallites in a unit volume was controlled by adjusting the heating rate. As the result, well-isolated single crystals of iPP with the above-mentioned morphologies were obtained.

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Crystallization of Polypropylene

Pawlak

Gałęski

2019

Polypropylene Handbook

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

Cited by 14 publications

References 29 publications

Molecular mechanism leading to memory effect of mesomorphic isotactic polypropylene

Molecular mechanism leading to memory effect of mesomorphic isotactic polypropylene

Giant single crystal of isotactic polypropylene showing near-equilibrium melting temperature

Crystallization of Polypropylene

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