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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 with PP droplets. Prior to cooling the samples were heated to 230 °C. Heating and cooling rate 10 °C min−1
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Fig2: DSC cooling thermograms of PP and PP/PS with PP droplets. Prior to cooling the samples were heated to 230 °C. Heating and cooling rate 10 °C min−1

Mentions: Figure 2 compares differential scanning calorimetry (DSC) cooling thermograms of PP and PP/PS dispersions prepared by the breakup of PP layers after subtracting the PS contribution. Only the thermogram of PP bulk is featured by a single crystallization exotherm at about 114 °C. The thermogram of melt blend PP/PS-b shows the main crystallization peak at 113 °C, with a shoulder on a descending slope, and a trace of additional peak at about 74 °C. The all other PP/PS systems exhibited pronounced fractionated crystallization with peaks at lower temperatures related to crystallization of the droplets from different nuclei as reported by Jin et al. [30]. The crystallization exotherm of PP/PS −200 was featured by two peaks centered at 105 and at 91 °C. The other PP/PS systems exhibited exotherms at about 90, 70, 65, and near 40 °C. For PP/PS-40 and PP/PS-20, the exotherm at 70 °C showed up as a shoulder on an ascending slope of the peak centered at 65 °C. In general, the temperature range of crystallization was reproducible for each material although ratios of crystallization enthalpies associated with the peaks changed to some extent. A pronounced peak at about 40 °C was observed for PP/PS-12, similarly as reported by Jin et al. [29,30], who identified this exotherm with homogeneous nucleation in the submicron PP droplets leading to formation of the mesophase, whereas the exotherms at higher temperatures seen for larger droplets were attributed to crystallization in the α form from heterogeneous nuclei.Fig. 2


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 with PP droplets. 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

Fig2: DSC cooling thermograms of PP and PP/PS with PP droplets. Prior to cooling the samples were heated to 230 °C. Heating and cooling rate 10 °C min−1
Mentions: Figure 2 compares differential scanning calorimetry (DSC) cooling thermograms of PP and PP/PS dispersions prepared by the breakup of PP layers after subtracting the PS contribution. Only the thermogram of PP bulk is featured by a single crystallization exotherm at about 114 °C. The thermogram of melt blend PP/PS-b shows the main crystallization peak at 113 °C, with a shoulder on a descending slope, and a trace of additional peak at about 74 °C. The all other PP/PS systems exhibited pronounced fractionated crystallization with peaks at lower temperatures related to crystallization of the droplets from different nuclei as reported by Jin et al. [30]. The crystallization exotherm of PP/PS −200 was featured by two peaks centered at 105 and at 91 °C. The other PP/PS systems exhibited exotherms at about 90, 70, 65, and near 40 °C. For PP/PS-40 and PP/PS-20, the exotherm at 70 °C showed up as a shoulder on an ascending slope of the peak centered at 65 °C. In general, the temperature range of crystallization was reproducible for each material although ratios of crystallization enthalpies associated with the peaks changed to some extent. A pronounced peak at about 40 °C was observed for PP/PS-12, similarly as reported by Jin et al. [29,30], who identified this exotherm with homogeneous nucleation in the submicron PP droplets leading to formation of the mesophase, whereas the exotherms at higher temperatures seen for larger droplets were attributed to crystallization in the α form from heterogeneous nuclei.Fig. 2

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