Blends with Other Elastomers

Blends of CR and other elastomers are desirable in order to achieve special properties either of a CR-based compound or of a compound mainly based on the second 

Lowest dynamic loss factor, highest elasticity 

M-grades XD-grades. Both of slow crystallization S-grades 

---

Latices and solutions are used to produce adhesives, carpet backings, upholstery foam, gloves, condoms and medical devices such as catheters. NR is also frequently used in blends with other elastomers. 

Rubber Blends For Automotive Applications. The ionomers from Exxpro elastomer can be blended with other elastomers such as Neoprene(CR), Nitrile(NBR), and Acrylics(VAMAC) for selected automotive applications, e.g., hoses, air springs, and belts. 

The major use of SBR is in the production of tires, particularly passenger-car and light-truck tires, and in other automotive applications where SBR is blended with other elastomers. These applications include belts, hoses, seals, and various extruded and molded items. Nontire and nonautomotive uses of SBR are in industries that require hoses, belts, gaskets, or seals. Others include footwear (shoe soles) various kinds of solid wheels roll covers coated fabrics and electrical (wire and cable) insulation. 

Very rarely is polybutadiene used by itself. It is generally used as a blend with other elastomers to impart better resiliency, abrasion resistance, and/or low-temperature properties, particularly in the manufacture of automobile tire treads, shoe heels and seals, gaskets, seals, and belting. 

Halobutyl rubber (HIIR) is used primarily in tire innerliner and white sidewalls. These elastomers are best for tire air retention owing to lower air permeability as well as aging and fatigue resistance. The chlorinated (CIIR) and brominated (BUR) versions of isobutylene isoprene rubber (HR) can be blended with other elastomers to improve adhesion between HIIR compounds and those based on general purpose elastomers, and improve vulcanization kinetics [16]. 

Polybutadiene (ER) is the second largest volume synthetic rubber produced, next to SER (Scheme 21.3). The major use of polybutadiene is in tires, with over 70% of the polymer produced going into treads and sidewalls. Cured ER imparts excellent abrasion resistance (good tread wear), and low rolling resistance (good fuel economy) due to its low glass transition temperature (T. The low Oower than -90 °C) is a result of the low vinyl content of polybutadiene. Due to the fact that the low leads to poor wet traction properties, polybutadiene is usually blended with other elastomers, such as natural rubber or SER for tread compounds. 

Crosslinked nitrile rubbers (ACN 30%) are used in blends with other elastomers and plastics such as ABS and PVC. 

There are no objections to the use of certain processing aids, of which there are many on the market. For appUcations and handling, the suppliers recommendations must be followed. In addition to stearic acid and commercial process aids, low-molecular weight polyethylene, waxes, and wax-like materials, and blends with other elastomers (e.g., BR) are commonly employed. 

When selecting the grade of polysulfide to use for a given application the service conditions are the key criteria to consider. Thiokol FA, as previously indicated, is used mainly in covered rolls and specialty hose where its excellent solvent resistance may be needed. It is often blended with other elastomers such as polychloroprene if some sacrifice in solvent resistance can be tolerated, or with a high acrylonitrile NBR if a minimal loss in solvent resistance is dictated. 

Polysulhdes often are blended with other elastomers such as nitrile rubber, NBR, or neoprene, CR, for improved physical properties and factory processing. Traditionally, Thiokol FA is blended with neoprene for improved strength and processing for rollers, at some sacrihce in solvent resistance. Table 11.9 has information on Thiokol FA blends. If minimal loss in chemical resistance is indicated, then a blend with a high ACN nitrile is employed. A cure system that is compatible with both rubbers needs to be used in all cases. The zinc peroxide-cure system is NBR specihc, hence it is important that the recommended one be used or others be tested since many NBRs do not cure with zinc peroxide. Best results are obtained with blends if separate masterbatches are made with the individual polymers, which are then blended in the... 

Double-Bond Cure Sites. The effectiveness of this kind of reactive site is obvious. It allows vulcanization with conventional organic accelerators and sulfur-based curing systems, besides vulcanization by peroxides. Fast and controllable vulcanizations are expected so double-bond cure sites represent a chance to avoid post-curing. Furthermore, blending with other diene elastomers, such as nitrile mbber [9003-18-3] is gready faciUtated. 

Because the polybutadiene component is liable to oxidation, ABS materials are embrittled on prolonged exposure to sunlight. By replacing polybutadiene rubber with other elastomers that contain no main chain double bonds it has been possible to produce blends generally similar to ABS but with improved weathering resistance. Three particular types that have achieved commercial status are ... 

In common with other polymers the polycarbonates have been blended with other polymers in recent years. The most well-known blends are those with ABS but more recently elastomer-modified grades have made their appearance, some of which may be copolymers (See Section 20.8). 

Chlorobutyl rubber is prepared by chlorination of butyl rubber (chlorine content is about 1 wt%). This is a substitution reaction produced at the allylic position, so little carbon-carbon double unsaturation is lost. Therefore, chlorobutyl rubber has enhanced reactivity of the carbon-carbon double bonds and supplies additional reactive sites for cross-linking. Furthermore, enhanced adhesion is obtained to polar substrates and it can be blended with other, more unsaturated elastomers. 

The copolymerization of butadiene in trans configuration with suitable comonomers represents a second route for obtaining a wide range of strain induced crystallizable elastomers, with melting point tailorable in a wide range of temperatures. These copolymers can be used, in particular, in blends with other crystallizable rubbers (e.g. synthetic cis-l,4-polyisoprene) in order to improve their "green strength". 

Heat-shrinkable tubing is made typically from polyolefins, PVC, polyvinyl fluoride, PTFE, their blends, or blends with other plastics and elastomers. The formulations may be designed for chemical resistance, heat resistance, flame resistance, etc. ... 

Blends of elastomers are routinely used to improve processability of unvulcanized rubbers and mechanical properties of vulcanizates like automobile tires. Thus, cis-1,4-polybutdiene improves the wear resistance of natural rubber or SBR tire treads. Such blends consist of micron-sized domains. Blending is facilitated if the elastomers have similar solubility parameters and viscosities. If the vulcanizing formulation cures all components at about the same rate the cross-linked networks will be interpenetrated. Many phenolic-based adhesives are blends with other polymers. The phenolic resins grow in molecular weight and cross-link, and may react with the other polymers if these have the appropriate functionalities. As a result, the cured adhesive is likely to contain interpenetrating networks. 

Blending either ABS-MA or EPR-MA, with amine-terminated PA or PEST resulted in alloys with excellent performance [Akkapeddi et ai, 1990, 1992]. Similarly, either ABS-MA or ABS-GMA copolymer was used to compatibilize and to toughen PA blends with other resins, viz. PC, PEST, or PAr [Yuichi and Suehiro, 1989]. Recently the role of elastomer, its type and location in the PA-66/SAN/Elastomer system has been studied [Nair et al, 1998]. 

PP blends with PE have already been discussed. PP blends with elastomers will be discussed in the following parts. In Table 1.48 few examples of PP blends with other PO s are given. 

One of the major areas for potential involves the synthesis of polyolefin block copolymers. A PP-EPR-PP or PE-EPR-PE block copolymer could have large potential as is or in blends with other polyolefins. PE-EPR-PE block copolymers have been synthesized via anionic polymerization of butadiene-isoprene-butadiene ABA block copolymers followed by hydrogenation [Mohajer et al, 1982 Rangarajanout et al., 1993]. These materials would have utility in hot melt adhesive formulations as well as general-purpose thermoplastic elastomer applications. Improvements on the synthesis procedures to offer viable approaches to polyolefin block copolymers could open up a new class of commercial polyolefins. In summary, several opportunities exist for new combinations of commercial blends from the list of commodity polymers. 

---