The opposite trend units to the each curve. It can also be seen from these data that there is co-crystallization between the two polyeth- the crystallization would have occurred far from ylenes in most blends. Further morphological investiga- temperatures, indicating that there may be a co- tions will be carried out using microscopic tech- crystallization and hence miscibility at all composi- niques such as scanning electron microscopy tions.
The presence of similar morphologies of these SEM.
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LDPE blends also indicates that the molar masses or melt flow indices are not significant in controlling the morphology. However, the long-chain branches in VLDPE2 are expected to contribute more to the rheologic characteristics than the morphology. Sukhadia, A. Figure 9 The plots of onset crystallization tempera- 2. Schlund, B. Bode, W. The symbol X indicates 4. Rudin, A.
Speed, C. Plast Eng , July, Kyu, T. Seoul, Korea ; p. Ree, M. J Polym Sci, Part B: Lee, S. Prasad, A. Polym Eng Sci , 38, J Indust Eng Chem , 4, Mathot, V. Calorimetry and Thermal Analysis Rana, D. Zhao, Y. Macromol Chem Phys Woo, L. Polym Preprints , 39, Cran, M.
Garbassi, F. Polym News , International Symposium on Macromolecules, 19, July, Gold Coast, Australia , p. Adams, J. Beagan, C. AN- R. Shih, H. Karol, F. In Metallocene-Catalyzed Polymers: Galante, M. Poly- Materials, Properties, Processing and Markets; mer , 39, Benedikt, G. Stein, R.
Knight, G. Polym Conference Proceed , Preprints , , Chum, P.
Plast Eng Westphal, S. In , June, Metallocene-Catalyzed Polymers: Materials, Prop- Leaversuch, R. Modern Plast Int , April, York, ; p Hill, M.
J Appl Polym Sci , 65, Kim, B. J Polym Eng , 11, Organ, S. Thermochim Butler, T. J Plast Film Sheet- Acta , , Joskowicz, P. Alamo, R. Polym Macromol Chem Phys , , Prepr , 35, Paukkeri, R.
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Polymer , 34, Schellenberg, J. Adv Polym Technol , 16, Shanks, R. Unlike polyethylene, crystalline and amorphous regions differ only slightly in their density. However, the density of polyethylene can significantly change with fillers. Polypropylene is normally tough and flexible, especially when copolymerized with ethylene. This allows polypropylene to be used as an engineering plastic , competing with materials such as acrylonitrile butadiene styrene ABS. Polypropylene is reasonably economical. Polypropylene has good resistance to fatigue.
The melting point of polypropylene occurs in a range, so the melting point is determined by finding the highest temperature of a differential scanning calorimetry chart. The thermal expansion of polypropylene is very large, but somewhat less than that of polyethylene. Polypropylene at room temperature is resistant to fats and almost all organic solvents , apart from strong oxidants.
Non-oxidizing acids and bases can be stored in containers made of PP. At elevated temperature, PP can be dissolved in nonpolar solvents such as xylene , tetralin and decalin. Most commercial polypropylene is isotactic and has an intermediate level of crystallinity between that of low-density polyethylene LDPE and high-density polyethylene HDPE.
The measure helps to determine how easily the molten raw material will flow during processing. Polypropylene with higher MFR will fill the plastic mold more easily during the injection or blow-molding production process. As the melt flow increases, however, some physical properties, like impact strength, will decrease.
There are three general types of polypropylene: homopolymer , random copolymer, and block copolymer. The comonomer is typically used with ethylene. Ethylene-propylene rubber or EPDM added to polypropylene homopolymer increases its low temperature impact strength. Randomly polymerized ethylene monomer added to polypropylene homopolymer decreases the polymer crystallinity, lowers the melting point and makes the polymer more transparent.
Polypropylene can be categorized as atactic polypropylene PP-at , syndiotactic polypropylene PP-st and isotactic polypropylene PP-it. In case of atactic polypropylene, the methyl group -CH 3 is randomly aligned, alternating alternating for syndiotactic polypropylene and evenly for isotactic polypropylene.
This has an impact on the crystallinity amorphous or semi-crystalline and the thermal properties expressed as glass transition point T g and melting point T m. The term tacticity describes for polypropylene how the methyl group is oriented in the polymer chain. Commercial polypropylene is usually isotactic. This article therefore always refers to isotactic polypropylene, unless stated otherwise. The tacticity is usually indicated in percent, using the isotactic index according to DIN The index is measured by determining the fraction of the polymer insoluble in boiling heptane.
The tacticity effects the polymers physical properties. As the methyl group is in isotactic propylene consistently located at the same side, it forces the macromolecule in a helical shape , as also found in starch. An isotactic structure leads to a semi-crystalline polymer.