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High-pressure crystallization of isotactic polypropylene droplets.

Zapala K, Piorkowska E, Hiltner A, Baer E - Colloid Polym Sci (2012)

Bottom Line: Only the largest PP droplets, with average sizes of 170 μm, crystallized predominantly in the γ form.The results showed that the γ phase formed only in the droplets sufficiently large to contain the most active heterogeneities nucleating PP crystallization under atmospheric pressure.It is concluded that the presence of nucleating heterogeneities is necessary for crystallization of PP in the γ form under high pressure.

View Article: PubMed Central - PubMed

Affiliation: Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90 363 Lodz, Poland.

ABSTRACT
Dispersions of isotactic polypropylene (PP) particles in polystyrene (PS) were produced by interfacially driven breakup of nanolayers in multilayered systems that were fabricated by means of layer-multiplying coextrusion. The droplet size was controlled by the individual PP layer thickness ranging from 12 to 200 nm. In addition, PP was melt blended with PS to produce PP droplets larger than those formed by breakup of nanolayers. The dispersions of PP particles in the PS matrix were melted and annealed under high pressure of 200 MPa. Only the largest PP droplets, with average sizes of 170 μm, crystallized predominantly in the γ form. In the 42-μm droplets obtained by breakup of 200 nm layers, a minor content of the γ form was found whereas the smaller droplets obtained by breakup of the thinner nanolayers contained the α form and/or the mesophase. The results showed that the γ phase formed only in the droplets sufficiently large to contain the most active heterogeneities nucleating PP crystallization under atmospheric pressure. It is concluded that the presence of nucleating heterogeneities is necessary for crystallization of PP in the γ form under high pressure.

No MeSH data available.


Related in: MedlinePlus

WAXD diffractograms of PP control sample crystallized in the γ form under high pressure of 200 MPa and the same sample heated and crystallized in the α form during cooling in DSC
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Fig6: WAXD diffractograms of PP control sample crystallized in the γ form under high pressure of 200 MPa and the same sample heated and crystallized in the α form during cooling in DSC

Mentions: Identification of the PP phase structure is possible via X-ray diffraction. Most of the peaks characteristic of the α and γ phases are located at nearly the same positions. Therefore, identification of the crystallographic forms has to involve analysis of diffraction curves for 2θ ranging from 18 to 21°, where two well-separated diffraction peaks of (130) plane of α crystals (2θ = 18.55°) and (117) plane of γ crystals (2θ = 20.07°) are located. According to Turner-Jones [10], the content of the γ modification, Kγ, in the crystalline phase of PP sample containing both α- and γ phases can be calculated based on the following equation:1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ K_{\gamma } = I_{\gamma } {\left( {117} \right)}/{\left[ {I_{\gamma } {\left( {117} \right)} + I\alpha {\left( {130} \right)}} \right]} $$\end{document}where Iγ(117) and Iα(130) denote integral intensities of the (117)γ and (130)α diffraction peaks, respectively. Kγ ranges from 0 to 1 for PP with the γ phase contents from 0 to 100 %. Figure 6 compares diffraction curve recorded for the PP control specimen annealed under high pressure with that for the same PP specimen subsequently melted and crystallized under atmospheric pressure. As can be seen from Fig. 6, the PP specimen annealed under the high pressure showed only the γ form, as can be concluded from the presence of (117)γ peak and absence of (130)α peak, whereas the same specimen re-melted and crystallized under atmospheric pressure during cooling in the DSC contained exclusively the α modification.Fig. 6


High-pressure crystallization of isotactic polypropylene droplets.

Zapala K, Piorkowska E, Hiltner A, Baer E - Colloid Polym Sci (2012)

WAXD diffractograms of PP control sample crystallized in the γ form under high pressure of 200 MPa and the same sample heated and crystallized in the α form during cooling in DSC
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3472077&req=5

Fig6: WAXD diffractograms of PP control sample crystallized in the γ form under high pressure of 200 MPa and the same sample heated and crystallized in the α form during cooling in DSC
Mentions: Identification of the PP phase structure is possible via X-ray diffraction. Most of the peaks characteristic of the α and γ phases are located at nearly the same positions. Therefore, identification of the crystallographic forms has to involve analysis of diffraction curves for 2θ ranging from 18 to 21°, where two well-separated diffraction peaks of (130) plane of α crystals (2θ = 18.55°) and (117) plane of γ crystals (2θ = 20.07°) are located. According to Turner-Jones [10], the content of the γ modification, Kγ, in the crystalline phase of PP sample containing both α- and γ phases can be calculated based on the following equation:1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ K_{\gamma } = I_{\gamma } {\left( {117} \right)}/{\left[ {I_{\gamma } {\left( {117} \right)} + I\alpha {\left( {130} \right)}} \right]} $$\end{document}where Iγ(117) and Iα(130) denote integral intensities of the (117)γ and (130)α diffraction peaks, respectively. Kγ ranges from 0 to 1 for PP with the γ phase contents from 0 to 100 %. Figure 6 compares diffraction curve recorded for the PP control specimen annealed under high pressure with that for the same PP specimen subsequently melted and crystallized under atmospheric pressure. As can be seen from Fig. 6, the PP specimen annealed under the high pressure showed only the γ form, as can be concluded from the presence of (117)γ peak and absence of (130)α peak, whereas the same specimen re-melted and crystallized under atmospheric pressure during cooling in the DSC contained exclusively the α modification.Fig. 6

Bottom Line: Only the largest PP droplets, with average sizes of 170 μm, crystallized predominantly in the γ form.The results showed that the γ phase formed only in the droplets sufficiently large to contain the most active heterogeneities nucleating PP crystallization under atmospheric pressure.It is concluded that the presence of nucleating heterogeneities is necessary for crystallization of PP in the γ form under high pressure.

View Article: PubMed Central - PubMed

Affiliation: Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90 363 Lodz, Poland.

ABSTRACT
Dispersions of isotactic polypropylene (PP) particles in polystyrene (PS) were produced by interfacially driven breakup of nanolayers in multilayered systems that were fabricated by means of layer-multiplying coextrusion. The droplet size was controlled by the individual PP layer thickness ranging from 12 to 200 nm. In addition, PP was melt blended with PS to produce PP droplets larger than those formed by breakup of nanolayers. The dispersions of PP particles in the PS matrix were melted and annealed under high pressure of 200 MPa. Only the largest PP droplets, with average sizes of 170 μm, crystallized predominantly in the γ form. In the 42-μm droplets obtained by breakup of 200 nm layers, a minor content of the γ form was found whereas the smaller droplets obtained by breakup of the thinner nanolayers contained the α form and/or the mesophase. The results showed that the γ phase formed only in the droplets sufficiently large to contain the most active heterogeneities nucleating PP crystallization under atmospheric pressure. It is concluded that the presence of nucleating heterogeneities is necessary for crystallization of PP in the γ form under high pressure.

No MeSH data available.


Related in: MedlinePlus