Heterophasic polypropylene

Ethylene-propylene resins, random heterophasic polypropylene (PP) copolymer 0.890 Coextruded form/fill/seal film, hot fill, heavy duty sacks, medical and personal care films, blends with other PP or PE grades Soft poly(vinyl chloride), nonpolymer packaging, LDPE, LLDPE... 

The improvement in toughness (impact strength) when EPR is added to PP matrix normally results in a reduction of its stiffness, which is usually related to a decrease in flexural modulus, yield stress, and an increase in the yield strain. A balance between toughness and stiffness is always required for optimum performance of the rubber-toughened polymer. The mechanical performance, shrinkage, and processing behavior of heterophasic polypropylene is influenced by rubber particle size, rubber composition, and rubber content. 

The rubber particle size of heterophasic polypropylene can be described by molecular weight. The molecular weight of an ethylene propylene copolymer can be described by its intrinsic viscosity, as measured by the XS fraction. The p of an ethylene propylene copolymer is generally determined at 135°C using decaline as a solvent, see Fig. 2.21. 

Rubber particle size characterized by intrinsic viscosity influences the flow behavior, shrinkage, and mechanics of heterophasic polypropylene. At equal rubber concentrations, a high IV yields a greater decrease in the MFI when compared to low IV materials. The influence on increased impact properties is also higher. 

The composition of the rubber phase is important in respect to the mechanical properties. Varying the ethylene-propylene ratio in an ethylene-propylene rubber can have a large effect on the heterophasic polypropylene properties. 

BAR Bartke, M., KrSner, S., Wittebrock, A., Reichert, K.-H., llhopoulus, I., and Dittrich, C.J., Sorption and diffusion of propylene and ethylene in heterophasic polypropylene copolymers, Macro/wo/. Symp., 259, 327, 2007. 

Heterophasic polypropylene copolymers are used in large automotive parts that must withstand high temperatures without distortion. Heterophasic copolymers are formed when a rubber phase, usually ethylenopropylene rubber, is polymerized with the homopolymer phase during manufacture. The addition of rubber increases the impact resistance of the material, while the homopolymer provides... 

Polypropylene polymers are typically modified with ethylene to obtain desirable properties for specific applications. Specifically, ethylene—propylene mbbers are introduced as a discrete phase in heterophasic copolymers to improve toughness and low temperature impact resistance (see Elastomers, ETHYLENE-PROPYLENE rubber). This is done by sequential polymerisation of homopolymer polypropylene and ethylene—propylene mbber in a multistage reactor process or by the extmsion compounding of ethylene—propylene mbber with a homopolymer. Addition of high density polyethylene, by polymerisation or compounding, is sometimes used to reduce stress whitening. In all cases, a superior balance of properties is obtained when the sise of the discrete mbber phase is approximately one micrometer. Examples of these polymers and their properties are shown in Table 2. Mineral fillers, such as talc or calcium carbonate, can be added to polypropylene to increase stiffness and high temperature properties, as shown in Table 3. 

Random insertion of ethylene as comonomer and, in some cases, butene as termonomer, enhances clarity and depresses the polymer melting point and stiffness. Propylene—butene copolymers are also available (47). Consequendy, these polymers are used in apphcations where clarity is essential and as a sealant layer in polypropylene films. The impact resistance of these polymers is sligbdy superior to propylene homopolymers, especially at refrigeration temperatures, but still vastiy inferior to that of heterophasic copolymers. Properties of these polymers are shown in Table 4. 

Some of the most difficult heterophase systems to characterize are those based on hydrocarbon polymers such as mbber-toughened polypropylene or other blends of mbbers and polyolefins. Eecause of its selectivity, RuO staining has been found to be usehil in these cases (221,222,230). Also, OsO staining of the amorphous blend components has been reported after sorption of double-bond-containing molecules such as 1,7-octadiene (231) or styrene (232). In these cases, the solvent is preferentially sorbed into the amorphous phase, and the reaction with OsO renders contrast between the phases. 

Figure 12-3. The Himont Inc. Spheripol process for producing polypropylene in a liquid-phase (1) tubular reactor, (2,4) two-stage flash pressure system (to separate unreacted monomer for recycle), (3) heterophasic copolymerization gas-phase reactor, (5) stripper.

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. 

Polypropylene polymers are typically modified with ethylene to obtain desirable properties for specific applications. Specifically, ethylene-propylene rubbers are introduced as a discrete phase in heterophasic copolymers to improve toughness and low temperature impact resistance. 

Application To produce polypropylene-based polymers, including homopolymer polypropylene, random, heterophasic impact and specialty dual composition copolymers, using Spherizone process technology. 

Application To produce propylene-based polymers including homopolymer polypropylene, random and heterophasic impact and specialty impact copolymers using Spheripol process technology. 

Application The Borstar polypropylene (PP) process is a versatile technology. Through the choice of reactor combinations, homopolymers, random copolymers, heterophasic copolymers, and very high-rubber content heterophasic copolymers can be produced. 

Description Polypropylene with a melt flowrate ranging from 0.1 to 1,200 can be produced with the Borstar PP process. Currently, Ziegler Natta catalysts are used, but there is a potential to use single-site catalysts latter. When producing homopolymers and random copolymers, the process consists of a loop reactor and a gas-phase reactor in series. One or two gas-phase reactors are combined with this arrangement when heterophasic copolymers are produced. Propylene, catalyst, cocatalyst, donor, hydrogen, and comonomer... 

Borealis A/S Polypropylene Propylene, ethylene Slurry-loop and a series gas-phase reactor produce tailor-made MW and enhanced PPs, homopolymers, high-comonomers, heterophasic compolymers 1 1999... 

Blends of EPDM rubbers with polypropylene in suitable ratios have been marketed as thermoplastic elastomers (TPE), also commercially known as thermoplastic polyolefin elastomers (TPO). These heterophasic polymers, characterized by thermoreversible interaction among the polymeric chains, belong to a broad family of olefinic alloys that can now be produced directly during the polymerization phase, unlike blended TPE and TPO, and various compositions (with various compounding additives) can be formulated which are primarily tailored to meet different requirements of most of car applications. The TPE-based synthetic leather and foam sheets are typical examples. 

From the three basic categories of polypropylene, namely, homopolymers, heterophasic copolymers, and random copolymers (with ethylene), there are specialty resins with enhanced capabilities for specific applications. Producers of large blow-molded or thermoformed parts can thus utilize grades with high melt strength to fabricate heat-resistant under-the-hood automotive parts. 

The advantages of localizing the reaction centers of heterophase catalytic systems on the surface or in a thin surface layer of polymer were emphasized in Section 12.3.1. The same conclusion is valid for the hydroformylation of hexene-1 in the presence of Rh(AcAc)(CO)2 supported on the surface of polypropylene-gr-poly(styryldiphenylphosphine) [160]. Under mild conditions (338 K, 1.6 MPa) the ratio between n- and wo-aldehydes for this system is at least 3.5 times higher than that for the homogeneous analogue. 

These relationships have been found particularly correct when the amount of the dispersed phase is quite low and each particle is isolated from the other. In this situation the competitive process of particle coalescence, always present in unstable polymeric hetero phase systems, is drastically reduced indeed. Taking into account this set of requirements, proper technologies and formulations can be developed to control the morphology and characteristics of polymer blends. This paper reviews the results of our research activity on a typical heterophase systems based on isotactic polypropylene (PP) and ethylene-propylene rubber (EPM) blends. 

Figure 3. Cross-section of polypropylene-EFR heterophasic copolymer. (X 11.800)...

Figure 5. Interpenetration polymer lattice network structure of "soft" polypropylene heterophasic copolymers. 

The a-nucleated polypropylene is suitable for power cable insrrlation. A polymeric a-nucleating agent which comprises monomer units is derived from a vinyl conrporrrrd. The nucleating agent is present in the heterophasic polymer composition in an amorrrrt of 0.0002 to 0.05 wt%. ... 

Heterophasic copolymer resins (so called because their morphology typically shows two or more phases) have lower stiffness and improved toughness at low temperature, down to -40°C (depending on the dispersed phase type and amount). These resins often demonstrate more complex thermal behavior (e.g., two or more melting points and reduced stiffness at elevated temperature). You can find examples of typical grades of polypropylene resins in Table 1.7. Chapter 2 describes propylene structure-property relationships that suit a variety of end-use applications. 

Heterophasic propylene-ethylene copolymers (HPEC) consist of crystalline polypropylene (PP) modified by an elastomeric component, typically ethylene-propylene rubber (EPR), and are prepared by polymerization of propylene (P) in the presence of catalysts, and sequential polymerization of a propylene-ethylene mixture with... 

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