Crystallization Polypropylene

Term N J, Fairclough P A, Towns-Andrews E, Komanshek B U, Young R J and Ryan A J 1998 Density fluctuations the nucleation event in isotactic polypropylene crystallization Polymer 29 2381- 5... 

Brosse et al. [41] modified isotactic polypropylene and other polyolefins by a cold plasma. In isotactic polypropylene, plasma treatment results in a polypropylene crystallization of paracrystalline or smectic form into a a-crystalline form. Further, the active films are susceptible to react with monomers in a postgrafting reaction. 

Syndiotactic polypropylene became commercially available about ten years ago with the advent of single-site catalysts. Unlike its atactic and isotactic counterparts, its manufacture presented serious challenges to polymer scientists and engineers. Even under the best conditions, its syndiotacticity rarely exceeds 75%, based on pentad sequences. It typically has both a lower melting point (approximately 138 °C relative to approximately 155 to 160 °C) and density (0.89 g/cm3 relative to 0.93 g/cm3) than isotactic polypropylene. Syndiotactic polypropylene crystallites have a much more complex structure than the isotactic form, which impedes its crystallization. Therefore, in general, the syndiotactic form of polypropylene crystallizes very slowly. 

Kuo SW, Chan SC, Chang FC. Correlation of material and processing time scales with structure development in isotactic polypropylene crystallization. Macromolecules 2003 36 6653-6661. 

Helical conformations occur frequently in macromolecular crystals. Isotactic polypropylene crystallizes as a 3] helix because the bulky methyl substituents on every second carbon atom in the polymer backbone force the molecule from a trans/trans/trans... conformation into a trans/gauche/trans/gaiiche... sequence with angles of rotation of 0° trans) followed by a 120° (gauche) twist. 

Fillers affect the nucleation rate as polypropylene crystalizes. The addition of 2.5 wt% titanium dioxide reduces the size of spherulite by a factor of 3 due to an in-... 

Dynamic mechanical results for polypropylene crystal aggregates (40) grown at 60°C. from 0.1% xylene and for poly(1-butene) crystals (95) from a 2% Decalin solution have been obtained at temperatures from 210°K. For these specimens the peak caused by the principal amorphous transformation at 300°K. (103 c.p.s.) (64, 91) is greatly reduced while a loss maximum closer to the melting point is found at 390°K. (102 c.p.s.) for polypropylene and 340°-360°K. (102 c.p.s.) for poly(-l butene) these maxima are attributed to motion in the crystalline regions. 

The spherulites of polypropylene crystals (80 pm) were larger than those of polypropylene/epoxy blends. This is because epoxy resin particles acted as nucleating sites, increased the number and decreased the size of PP spherulites in the blends. The normalized dynamic DSC cooling curves of polypropylene/epoxy blends are shown in Fig. 21.7 and the data from the DSC studies are summarized in Table 21.5. 

Isotactic polypropylene crystallizes below 350 K on quick cooling from the melt increasingly as condis glass This conformationally disordered polypropylene had first been described as bdng smectic mesomorphic or paracrystalline ... 

Explain how the 2 3/1 helical conformation of polypropylene molecules spaces out the methyl side groups along the helix. Give reasons why the polypropylene crystal has a lower modulus in the c direction than the polyethylene crystal. 

B.R Grady, F. Pompeo, R.L. Sbambaugh, and D.E. Resasco, Nucleation of polypropylene crystallization by single-walled carbon nanotubes, J. Phys. Chem. B, 106, 5852-5858 (2002). 

Differential scanning calorimetry is used in this study to examine the crystallization behavior of polypropylene. Crystallization exotherms are analyzed according to the procedure outlined by Gupta et al where the parameters shown in Figure 1 are defined as follows ... 

Figure 4. (a) Heat capacity of polypropylene crystal, glass and liquid in J/K per mole of -CH2-CH2(CH3)-repeat units, from refs. 35 and 36 compared with the same properties of 3-methyl pentane (1/2 mole) from ref. 37. The comparison shows how the postponement of the glass transition to the higher tem rature, consequent on the extension of the carton chain, completely changes the relation between liquid and glass heat capacities, causing polymers to appear... 

PRA Pradhan, D. and Ehrlich, P., Morphologies of microporous polyethylene and polypropylene crystallized from solution in supercritical propane, J. Polym. Sci. Part B Polym. Phys., 33, 1053, 1995. 

It is intermediate between the extreme values of 67 x 10 and 15 x 10 which are theoretically calculated by Keedy et al. using the Denbigh and the Bunn-Daubeny values of bond polarisability, respectively. This is reasonable since the internal field within a polypropylene crystal might be expected to be intermediate between that in a normal paraffin crystal (Bunn-Daubeny) and a normal paraffin vapour (Denbigh). 

During the formation of fibres the crystallization takes place in non-isothermal conditions in the field of high tensile stress. Cooling rate and tensile stress strongly affect polypropylene crystallization. 

The formation of the p form is confirmed by WAXS measurements. In the WAXS pattern of polypropylene crystallized by addition of the quinacridone pigment characteristic p peaks... 

Fig. 2. WAXS pattern of polypropylene crystallized in the presence quinacridone pigment.

The investigated a form of phthalocyanine promotes mostly formation of the a form of polypropylene. On the wide-angle X-ray scattering (WAXS) pattern for polypropylene crystallized in the presence of phthalcoyanine pigment, aystalline peaks characteristic for the a form are observed (Fig.3). 

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