Isotactic polypropylene—continued

The majority of spunbonded fabrics are based on isotactic polypropylene and polyester (Table 1). Small quantities are made from nylon-6,6 and a growing percentage from high density polyethylene. Table 3 illustrates the basic characteristics of fibers made from different base polymers. Although some interest has been seen in the use of linear low density polyethylene (LLDPE) as a base polymer, largely because of potential increases in the softness of the final fabric (9), economic factors continue to favor polypropylene (see OlefinPOLYMERS, POLYPROPYLENE). 

In rubber-plastic blends, clay reportedly disrupted the ordered crystallization of isotactic polypropylene (iPP) and had a key role in shaping the distribution of iPP and ethylene propylene rubber (EPR) phases larger filler contents brought about smaller, less coalesced and more homogeneous rubber domains [22]. Clays, by virtue of their selective residence in the continuous phase and not in the rubber domains, exhibited a significant effect on mechanical properties by controlling the size of rubber domains in the heterophasic matrix. This resulted in nanocomposites with increased stiffness, impact strength, and thermal stability. 

Voyiatzis and Andrikopoulos discuss adding an orientation-sensitive, resonant Raman additive to a polymer mixture prior to drawing in order to calculate molecular orientation continuously. The approach was tested with poly(vinyl chloride) (PVC), isotactic polypropylene (iPP), and poly(vinylidene fluoride) (PVF2). The ratio of a band from the additive to the orientationally insensitive CH2 bending mode at 1435 cm-1 in the polymer was computed. While the addition of such an additive is unreasonable for many industrial processes, the authors note a favorable alternative for industrial PVC samples. 

Figure 4 shows that the orientation of the two chains follow similar paths. The similarity suggests that the local environment is very much the same for both blend constituents. In contrast, a phase-separated binary mixture of polymer segments will exhibit a different orientation for each component. For example, high-density polyethylene and isotactic polypropylene form multiphase systems when blended together (16). When the incompatible blends are deformed, the component which constitutes the continuous phase always orients to a higher degree than... 

The tensile properties of isotactic polypropylene materials reinforced with continuous nylon fibers were measured. Less than 10 vol % of the fibers leads to an increased yield strength and yield elongation. As little as 3 vol % of the nylon fibers increased the elongation at necking from 10 to 20%. This retarded necking arises from the fiber-matrix debonding which delocalizes the microscopic yielding processes. 

If isotactic polypropylene is quenched from the melt to room temperature a so-called smectic modification is formed which shows only two crystal reflexions. Cabarcos, Bbsecke, and Zachmann investigated the kinetics of the transition from this modification into the a-modification. Fig. 54 shows the change of wide angle scattering during isothermal annealing at 90 °C. One sees that the 040-reflexion of the a-modification appears after about 200 sec and continues to increase in intensity afterwards. The time until the constant temperature is reached is about 150 sec. Therefore we can say that most of the process occurs at constant temperature. If the same is done at 130 °C the process occurs so rapidly that it is almost finished as constant temperature is reached. 

Table 6.1.8 (continued). Compounds identified in the pyrogram of isotactic polypropylene as shown in Figure 6.1.16. 

U.V. Makedonov, A.Z. Margolin, H.la. Rapoport, LS. Shibriaeva About the reasons of the change of effective constants of the rate of reactions of continuation and chains breaks in the period of oxidation induction of isotropic and oriented isotactic polypropylene////zg/zzzzo/eczz/z7r compounds (1986), 28 (A), No 7, 1380-1386 (in Russian). 

The original, simplest polyolefins, polyethylene and polypropylene, continue to dominate the scene, even after two decades, to such an extent that no other polyolefin even appears on the production charts. Nevertheless, a great many (we may assume all) available olefins have been tested, and many have been found capable of being converted to stereoregular polymers. As was mentioned above, poly(l-butene) and poly(4-methy1-1-pentene) are being offered commercially and may be expected to achieve significant volume in the future. Isotactic and syndiotactic polystyrene are of much theoretical interest (26) but are not yet commercial products. 

In slurry, bulk-monomer, or gas-phase processes, the polymer is usually of higher density or crystallinity (e.g.. high-density polyethylene, linear-low-density polyethylene, isotactic polypropylene) and is thus insoluble in the reactor diluent or fluidizing gas stream. The continuous operation of these processes suggests the use of morphologically uniform catalyst particles which can be fed into the reactor smoothly without clumping, which in turn implies fixing the solution-soluble catalyst on an insoluble carrier. 

The synthesis of polypropylene brought a new scenario and major efforts at that time concentrated on controlling the stereoregularity, synthesizing the most regular isotactic polypropylene, and understanding its polymorphism these efforts have continued for many years. 

Makedonov Yu.V., Margolin A.L., Rapoport N.Ya. and al. (1986)." On the causes of changes in the effective rate constants continue and chain termination in the induction period of oxidation of isotropic and oriented isotactic polypropylene". Vysoconwlek. Soedin. V.28 A. No 7. PP.1380-1385. (In Russian)... 

The transcrystallization in isotactic polypropylene occitrs beginning from a network of nucleating agents. The network provides continuous reinforcing stractures, which could be used to improve fiber-matrix adhesion and resist crack propagation. ... 

He spent the next two years as a full professor at the University of Pavia and left to accept a position as professor of physical chemistry at the University of Rome. In 1938, after a year as head of the Institut of Industrial Chemistry at Turin, he returned to Milan and spent the rest of his professional life as a consultant for Montecatini Chemical Company and much of his success in the discoveiy of isotactic polypropylene may be attributed to continued financial support from that lai e chemical firm. 

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