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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

DSC cooling thermograms of PP and PP/PS systems with PP droplets crystallized under high pressure of 200 MPa. Prior to cooling the samples were heated to 230 °C. Heating and cooling rate 10 °C min−1
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Fig9: DSC cooling thermograms of PP and PP/PS systems with PP droplets crystallized under high pressure of 200 MPa. Prior to cooling the samples were heated to 230 °C. Heating and cooling rate 10 °C min−1

Mentions: High-pressure crystallization behavior of the PP dispersions can be correlated with their crystallization under atmospheric pressure. Figure 9 compares DSC cooling thermograms of PP and PP/PS dispersions, which were annealed under high pressure and next re-melted and cooled in the DSC. The thermograms are similar to those shown in Fig. 2 indicating that the high-pressure treatment did not change temperature ranges in which the materials crystallized during cooling in the DSC. The thermograms of PP control sample shows a single crystallization peak at 114 °C, whereas that of PP/PS-b is featured by a main peak at 113 °C with low temperature shoulder and a trace of peak at 74 °C. The all other PP/PS systems exhibited fractionated crystallization as before the high-pressure annealing, with the same peak positions, with accuracy of 1.5 °C. It can be noticed that the crystallization exotherm of PP/PS-200 started to rise at similar temperature as those of PP control sample and PP/PS-b, which implies that in a significant fraction of PP droplets the nucleation was of the same nature as in these two systems.Fig. 9


High-pressure crystallization of isotactic polypropylene droplets.

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

DSC cooling thermograms of PP and PP/PS systems with PP droplets crystallized under high pressure of 200 MPa. Prior to cooling the samples were heated to 230 °C. Heating and cooling rate 10 °C min−1
© Copyright Policy
Related In: Results  -  Collection

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

Fig9: DSC cooling thermograms of PP and PP/PS systems with PP droplets crystallized under high pressure of 200 MPa. Prior to cooling the samples were heated to 230 °C. Heating and cooling rate 10 °C min−1
Mentions: High-pressure crystallization behavior of the PP dispersions can be correlated with their crystallization under atmospheric pressure. Figure 9 compares DSC cooling thermograms of PP and PP/PS dispersions, which were annealed under high pressure and next re-melted and cooled in the DSC. The thermograms are similar to those shown in Fig. 2 indicating that the high-pressure treatment did not change temperature ranges in which the materials crystallized during cooling in the DSC. The thermograms of PP control sample shows a single crystallization peak at 114 °C, whereas that of PP/PS-b is featured by a main peak at 113 °C with low temperature shoulder and a trace of peak at 74 °C. The all other PP/PS systems exhibited fractionated crystallization as before the high-pressure annealing, with the same peak positions, with accuracy of 1.5 °C. It can be noticed that the crystallization exotherm of PP/PS-200 started to rise at similar temperature as those of PP control sample and PP/PS-b, which implies that in a significant fraction of PP droplets the nucleation was of the same nature as in these two systems.Fig. 9

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