Isotactic Poly(propylene) Crystallization: Role of Small Fractions of High or Low Molecular Weight Polymer

Elmoumni, Aadil; Gonzalez-Ruiz, Ramon A.; Coughlin, E. Bryan; Winter, H. Henning

doi:10.1002/macp.200400130

Cited by 24 publications

(24 citation statements)

References 23 publications

(29 reference statements)

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“…In that work, SAXS-WAXD data demonstrated that only when the concentration of flow induced nuclei is, at least, of the same order of magnitude of those naturally present in the system, the effects of flow can be appreciated. in literature [24][25][26][27][28][29][30][31], when a given shear condition is applied, a low molecular weight should result in a low molecular orientation of the system and, thus, in a reduced enhancement of crystallization rate.…”

Section: Flow Induced Crystallizationmentioning

confidence: 99%

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Flow induced crystallization of LDPE nanocomposites: A rheological and morphological characterization

Azzurri

Stagnaro²,

Conzatti³

et al. 2011

E-Polymers

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Abstract:The flow induced crystallization behaviour of a LDPE:PE-g-MA:D72T 90:9:1 nanocomposite has been investigated by in-situ Rheo-SALS technique and data have been compared with those obtained from a reference LDPE:PE-g-MA 90:9 sample. Rheo SALS results, confirming thermal analysis findings, indicate that under mild shear flow fields the organoclay exhibits a negligible nucleating effect. Both nucleation density and, as a consequence, crystallization rate, are not appreciably affected by the application of external flow field for both the examined systems, revealing that no evident synergic effects between the organoclay and the shear flow are present. On the other hand, Rheo SALS analysis indicates that the nanocomposite submitted to flow exhibits a higher level of crystal orientation. TEM morphological analyses support this observation suggesting that the orientation of the nanofiller along the flow direction templates the growth of oriented crystals.

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Section: Flow Induced Crystallizationmentioning

confidence: 99%

“…FIC studies have been addressed to investigate the role of molecular parameters (composition [21][22][23], molar mass [24][25][26][27][28][29][30][31], etc) and flow conditions [11][12][32][33][34] on the crystallization kinetics of polymers, mainly of polyolefins.…”

Section: Introductionmentioning

confidence: 99%

Flow induced crystallization of LDPE nanocomposites: A rheological and morphological characterization

Azzurri

Stagnaro²,

Conzatti³

et al. 2011

E-Polymers

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show abstract

“…21 However, it is known that the high molecular weight tail of the distribution dictates the crystallization in sheared systems. 26,[29][30][31][32] Therefore, because of the wide molecular wide distribution of the previously used samples, the precise role of molecular dimensions on the lifetime of nucleation precursors still needs to be addressed with better accuracy.…”

Section: Introductionmentioning

confidence: 99%

Insights into Formation and Relaxation of Shear-Induced Nucleation Precursors in Isotactic Polystyrene

2008

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Rheooptical experiments on narrow isotactic polystyrene (i-PS) fractions have been carried out to investigate temperature and molar mass dependence of the lifetime of shear-induced nucleation precursors. Similar to i-poly(1-butene) and i-polypropylene, the survival of the flow-induced structures lasts very long, even at temperatures well above the measured melting point of the crystals. It has been observed that the decrease of concentration of nucleation precursors follows a first-order kinetics with a strongly temperature-dependent rate constant. The apparent activation energy of the overall relaxation process is around 400 kJ/mol, of the same order of magnitude previously found for other semicrystalline polymers. A comparative analysis of the apparent activation energy data for different polymers, coupled with morphological evidence, suggests that the rate-determining step in the evolution of the system toward the equilibrium state in the melt is the detachment of stems from the lateral surface of flow-induced oriented bundles, present either as isolated entities, in the case of pointlike nuclei, or as rows alternated by disordered nanodomains, in the long threads of the shish. Thanks to the monodisperse character of the investigated samples, the molar mass dependence of lifetime of oriented nucleation precursors has also been established.

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“…Different configurations (isotacticity and head-to-tail sequences) or addi-tion of small monomeric units and nucleating agents can also influence the final structure. [18][19][20][21][22][23][24][25] Influence of molecular weight on polymer crystallization is controversial. Stem length indeed interferes with entanglement density, thus determining a rate-controlled segregation regime of topological constraints in noncrystalline regions.…”

Section: Introductionmentioning

confidence: 99%

Crystallization kinetics of iPP: Influence of operating conditions and molecular parameters

Carrubba

Piccarolo

Brucato

2007

J of Applied Polymer Sci

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An analysis of the crystallization kinetics of different grades of isotactic polypropylene (iPP) is here presented. To describe the crystallization kinetics as a function of molecular and operating parameters, the methodological path followed was the preparation of quenched samples of known cooling histories, calorimetric crystallization isotherms tests, differential scanning calorimetry cooling ramps, wide angle X-ray diffraction (WAXD) measurements, and density determination. The WAXD analysis performed on the quenched iPP samples confirmed that during the fast cooling at least a crystalline structure and a mesomorphic one form. The diffractograms were analyzed by a deconvolution procedure, to identify the relationship between the cooling history and the distribution of the crystalline phases. The whole body of results (including calorimetric ones) provides a wide basis for the identification of a crystallization model suitable to describe solidification in polymer-processing operations, based on the KolmogoroffAvrami-Evans nonisothermal approach. The kinetic parameters, determined for all the materials, are discussed, highlighting the effect of molecular parameters on the crystallization kinetics: molecular mass and distribution, tacticity, nucleating agents, and ethylene units content.

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Isotactic Poly(propylene) Crystallization: Role of Small Fractions of High or Low Molecular Weight Polymer

Cited by 24 publications

References 23 publications

Flow induced crystallization of LDPE nanocomposites: A rheological and morphological characterization

Flow induced crystallization of LDPE nanocomposites: A rheological and morphological characterization

Insights into Formation and Relaxation of Shear-Induced Nucleation Precursors in Isotactic Polystyrene

Crystallization kinetics of iPP: Influence of operating conditions and molecular parameters

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