Heterophasic propylene-ethylene copolymers

To illustrate the potential of the method, we present in Figure 7 the 2D ESRI perspective plot of a phantom sample consisting of nitroxide biradicals derived from Tinuvin 770 (obtained by oxidation of the amine) in two different environments in a plaque of heterophasic propylene-ethylene copolymers (HPEC). One side of the plaque was doped with the biradical by contact with a biradical solution in toluene. The same biradical solution was placed on transparent tape and the solvent was evaporated the tape was then folded and attached to the other side of the plaque. The corresponding spectral slices are... 

Fig. 4. The ID ESRI at 340 K of a cylindrical sample (height 3 mm, diameter == 4 mm) of heterophasic propylene-ethylene copolymer (HPEC) containing a nitroxide derived from a hindered amine stabilizer (HAS). X-band ESR spectrum recorded in the absence (a) and in the presence of a vertical magnetic field gradient of 206 G cm b).

Our laboratory developed ID and 2D spectra-spatial ESRI for the study of het-erophasic systems, such as poly(acrylonitrile-butadiene-styrene) (ABS) and heterophasic propylene-ethylene copolymers (HPEC) containing bis(2,2,6,6-tetram-ethyl-4-piperidinyl) sebacate (Tmuvin 770) as the HAS, and exposed to thermal treatment and UV irradiation.The major objectives were to examine polymer degradation under different conditions to assess the effect of rubber phase (polybutadiene in ABS and ethylene-propylene rubber in HPEC) on the extent of degradation and to evaluate the extent of stabilization by HAS. The repeat units in ABS and the formula of Tinuvin 770 are shown in Fig. 2. 

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... 

This section presents the ID and 2D ESRI study of thermally and UV-treated heterophasic propylene-ethylene copolymers (HPEC) polymers. Two polymers, coded HPECl and HPEC2, differing in ethylene content, were investigated. The ethylene content was 25% wt in HPECl and 10% wt in HPEC2, within 2%, as determined by FTIR. Morphologically, HPEC systems are more complex compared to ABS, because of the presence of amorphous and crystalline domains. 

Figure 14 presents the 2D spearal-spatial ESRI perspective plot and corresponding virtual slices for nitroxide radicals derived from hindered amine stabilizers (HASs) generated during the UVB irradiation of heterophasic propylene-ethylene copolymers (HPEC). " Note that the ESR spectra shown in the spectral slices consist of two spectral components, F and S, whose relative intensities vary as a function of sample depth, from about 22% near the irradiated side to about 45% at the other sample extremity. Data such as those shown in Figure 14... 

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. 

Product specifications The process can produce a broad range of propylene-based polymers, including homopolymer polypropylene, random copolymers and terpolymers, heterophasic impact and specialty impact (up to 25% bonded ethylene) copolymers as well as high stiffness, high-clarity copolymers. 

An attempt has been made (56) to understand the role of the structural factor when MAH was grafted to heterophase PP. The latter was a mixture of highly crystalline homopolypropylene, which made the matrix and copolymers dispersed in the PP matrix similar to rubber particles. During fractionation of the heterophase PP, three fractions were separated PP ( 50 wt%), EPR with irregular distribution of ethylene units ( 43 wt%), and ethylene-propylene block copolymer (EPM) ( 2 wt%). Peroxide initiators were DTBP (di-tert-butyl peroxide), S =... 

During polymerization, this porous structure is used to produce heterophasic or impact copolymers by dispersing an elastomeric ethylene-propylene polymer in the initially generated homopolymer granule... 

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... 

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. 

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. 

Ethylene propylene copolymers and their blends exhibit diverse degradation behavior under the influence of light, heat and radiation. In spite of many papers in this area, little, if any, mechanistic data on degradation and stabilization of this important class of materials is available in the literature. The present paper reviews the published literature in this area organised under five distinct class of materials, namely, thermoplastic, elastomeric, and heterophasic copolymers, thermoplastic elastomer and blends. Of this, elastomeric ethylene-propylene copolymers appears to have been most exhaustively studied. Very few studies have reported on thermoplastic copolymers, both random as well as heterophasic as well as thermoplastic elastomers and blends. Specific mechanisms of degradation and stabilization of each of these classes of materials are discussed. 

The crystalline copolymers of propylene with ethylene are thermoplastic materials. They can be further classified as random and block or heterophase copolymers. 

Products The process can produce a broad range of propylene-based polymers, including mono-and bimodal (medium/wide/very wide molecular weight distribution) homopolymer PP, high stiffness homopolymers, random copolymers and terpolymers, high-clarity random copolymers as well as two compositions copolymer/random copolymer, twin-random or random/heterophasic copolymer). Conventional heterophasic impact copolymers (with improved stiffness/impact balance) can be produced with the second additional gas phase reactor, with ethylene/ propylene rubber content up to 40%. 

ICP = blends of isotactic propylene homopolymer with ethylene-propylene rubber. These materials are commonly called "impact copolymers," "heterophasic copolymers," or, incorrectly, "block copolymers." These are typically prepared during the polymerization process using a series of reactors. L = low rubber (less than about 15% rubber by weight typically witli an ethylene content of less than about 10%). H = high rubber content blends (greater than about 15% rubber by weight typically with an ethylene content of at least 7%). 

Impact copolymers (heterophasic copolymers), also known as block copolymers, are made in a two reactor system where the homopolymer matrix is made in the first reactor and then transferred to the second reactor where ethylene and propylene are polymerized to create ethylene propylene rubber (EPR) in the form of microscopic nodules dispersed in the homopolymer matrix phase. These nodules impart impact resistance both at ambient and cold temperatures to the compound. This type has intermediate stiffness and tensile strength and is quite cloudy. In general, the more ethylene monomer added, the greater the impact resistance with correspondingly lower stiffness and tensile strength. 

Fracture characteristics and deformation behavior of heterophasic ethylene-propylene copolymers as a function of the disprersed phase comp>osition. Polymer, Vol.46, No.22, (October 2005), pp. 9411-9422, ISSN 0032-3861 Ernst H. A. Paris, P.C. Landes J.D. (1981). Estimations on J-integral and Tearing Modulus T from a single specimen test record. Fracture Mechanics Thirteenth Conference ASTM STP 743, Roberts R., (Ed.), p>p. 476-502. 

Impact copolymers, also known as heterophasic copolymers or rTPOs, usually contain up to about 40% ethylene-propylene rubber (EPR), distributed inside the semicrystalline PP homopolymer matrix. This copolymer phase is added to increase the impact strength of the product at low temperatures. As a result of its glass transition temperature the impact strength of polypropylene homopolymer is often unacceptable for use in low temperature applications, such as packaging or automotive applications. 

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. 

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. 

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