Ethylene-propylene rubbers applications

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. 

Polyethylene is sometimes blended with ethylene-propylene rubber (see Chapter 11). In this application it is most commonly used as an additive to the rubber, which in turn is added to polypropylene to produce rubber-modified... 

The use of ABS has in recent years met considerable competition on two fronts, particularly in automotive applications. For lower cost applications, where demands of finish and heat resistance are not too severe, blends of polypropylene and ethylene-propylene rubbers have found application (see Chapters 11 and 31). On the other hand, where enhanced heat resistance and surface hardness are required in conjunction with excellent impact properties, polycarbonate-ABS alloys (see Section 20.8) have found many applications. These materials have also replaced ABS in a number of electrical fittings and housings for business and domestic applications. Where improved heat distortion temperature and good electrical insulation properties (including tracking resistance) are important, then ABS may be replaced by poly(butylene terephthalate). 

The static and dynamic mechanical properties, creep recovery behaviour, thermal expansion and thermal conductivity of low-density foams made of blends of LDPE and EVA were studied as a function of the EVA content of the blends. These properties were compared with those of a foam made from a blend of EVA and ethylene-propylene rubber. A knowledge of the way in which the EVA content affects the behaviour of these blend foam materials is fundamental to obtaining a wide range of polyolefin foams, with similar density, suitable for different applications. 9 refs. 

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. 

Since compounds of the type XVII have shown comparable activity in a number of systems including cis-polybutadiene, styrene-butadiene rubber, and ethylene-propylene rubber, they have some commercial promise, and development work on these compounds is continuing. Nevertheless, they are not completely nondiscoloring, and in certain applications, particularly carboxylated styrene-butadiene latex films, yellow discoloration caused by the antioxidant is a serious drawback. We therefore turned our attention to ortho-linked compounds derived from 2,4-dialkylphenols. 

In addition to the polyolefin blends designed for thermoplastic elastomer applications, a great deal of interest also has centered on other kinds of blends of polyolefins as has been reviewed recently (see chapter 21 of Ref. 10 by Plochocki). In a recent paper (84), we showed that blends involving polypropylene-high density polyethylene-low density polyethylene in various proportions and combinations exhibit additivity of tensile strength however, there are serious losses in ductility in some cases such that the blends are less ductile than either pure component. It is interesting to note, however, that these losses in ductility can largely be restored by addition of rather small amounts of an amorphous ethylene-propylene rubber (84). 

Very Low Density (VLDPE) and Ultra Low Density (ULDPE) Polyethylenes. These are made by copolymerization with increasing amounts of comonomers, especially 1 -octene, reducing regularity/crystallinity (density 0.91- 0.86) down toward ethylene/propylene rubber. These are soft and flexible enough to compete with plasticized polyvinyl chloride and thermoplastic elastomers in some applications. 

The major general purpose rubbers are natural rubber, styrene-butadiene rubber, butadiene rubber, isoprene rubber, and ethylene-propylene rubber. These rubbers are used in tires, mechanical goods, and similar applications. Specialty elastomers provide unique properties such as oil resistance or extreme heat stability. Although this differentiation is rather arbitrary, it tends also to classify the polymers according to volumes used. Styrene-butadiene rubber, butadiene rubber, and ethylene-propylene rubber account for 78 percent of all synthetic rubber consumed. 

There are a number of grades of fluorocarbon rubber (copolymers, terpolymers and tetrapolymers) and they are mainly used in applications where the temperatures would degrade ethylene-propylene rubber products. They are able to withstand prolonged use at temperatures up to 200 °C. Typical conditions are high temperature (<150 °C) gaskets under flow or static conditions, in contact with aqueous or fatty foods (including oils). 

Figure 2. Product map (average molecular mass vs. copolymer composition) and applications. EPR = ethylene/propylene rubber PE = polyethylene HD = high-density ...

In this section, the future developments will be discussed that might be expected in commercial polymer blends comprising at least one of the constituents from the class of commodity polymers. Generally, the commodity polymers considered include polyethylene (and variants LDPE, HOPE, LLDPE, VLDPE and ethylene copolymers), polypropylene (PP), ethylene-propylene rubber (EPR and EPDM), polyvinylchloride (PVC), polystyrene (PS), ABS, and poly(methyl methacrylate) (PMMA). Elastomeric polymers commonly used in tire and associated applications are important in polymer blends as many tire component constructions employ polymer blends to maximize performance. However, these will not be considered here. Thermosetting polymers which could be classified as commodity polymers (urethane, phenolics, epoxies) will also not be covered, but will be mentioned in a later section discussing new polymer blends designed for specific applications (e.g., water based coatings). 

It was found that this method is applicable also for reception of ethylene-propylene rubbers, where the stage of solvent saturation by gaseous monomers proceeds in diffusion regime. 

Ethylene-propylene rubber possesses many properties superior to those of natural rubber and conventional general-purpose elastomers. In some applications, it will perform better than other materials, whereas in other applications, it will last longer or require less maintenance and may even cost less. 

Ethylene-propylene rubber finds application in the electrical industry and in the manufacture of electrical equipment. One of the primary applications is as an insulating material. It is used for medium-voltage (up to 35 kV) and secondary network power cable, coverings for line and multiplex distribution wire, jacketing and insulation for types S and SJ flexible cords, and insulation for automotive ignition cable. 

Adhesive applications can be widespread including contact cmnents, pressure-sensitive adhesives and hot melts. In solid compounded articles footwear is a large volune application such as molded-ln-place soling or unit soles to be cemented to uppers. Additional uses are in toys, milk tubing, cove base, mats and miscellaneous coatings or molded parts. Potential uses include blends with ethylene-propylene rubber and ethylene-vinyl acetate copolymers to provide ozone-resistant fomulations or blends to improve crack- or impact-resistance of plastics. 

Uses of Ethylene-Propylene Rubbers. EPDM and EPR vulcanizates are used in extruded profiles, cable insulation and jacketing, and roofing membranes. There are many automotive uses radiator hose, door and trunk seals, insulation, jacketing, and others. These elastomers are also used in applications such as window and architectural profiles, dock fenders, and washing-machine hoses. In short, their applications are extensive and diverse. Ethylene-propylene rubbers may be the most versatile of general-purpose rubbers. In addition, EP rubbers are added to polyolefin plastics as impact modifiers and as components of certain thermoplastic elastomer compositions (e.g., thermoplastic vulcanizates, which are discussed later in this chapter). 

Catalysts that form ethylene-propylene copolymers can be used to produce a material known as ethylene-propylene rubber (EPR). If an isospecific catalyst for the formation of polypropylene incorporates a small amount of ethylene, a crystalline copolymer is formed that has a lower melting point than isotactic PP. If an aspecific catalyst is used, or if more ethylene is incorporated into the polymer, an amorphous ethylene-propylene rubber (EPR) is formed. EPR generally has a lower glass transition temperature than atactic PP, and is a useful material for low-temperature applications. Catalysts that form isotactic or syndiotactic polypropylene can also generate polymers possessing defined stereochemistry within the propylene units in an EP copolymer. 

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