Styrene-butadiene rubber general properties

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. 

Copolymerization, which, in its objective, may be compared to alloying in metallurgy, is very useful for synthesizing polymer with the required combination of properties. For example, polystyrene is brittle, and polybutadiene is flexible therefore copolymers of styrene and butadiene should be more flexible than polystyrene but tougher than polybutadiene. The general purpose rubber SBR (styrene-butadiene rubber), the first practical synthetic rubber, is a copolymer of styrene and butadiene. 

There are two classes of polyolefin blends elastomeric polyolefin blends also called polyolefin elastomers (POE) and nonelastomeric polyolefin blends. Elastomeric polyolefin blends are a subclass of thermoplastic elastomers (TPEs). In general, TPEs are rubbery materials that are processable as thermoplastics but exhibit properties similar to those of vulcanized rubbers at usage temperatures (19). In TPEs, the rubbery components may constitute the major phase. However, TPEs include many other base resins, which are not polyolefins, such as polyurethanes, copolyamides, copolyesters, styrenics, and so on. TPEs are now the third largest synthetic elastomer in total volume produced worldwide after styrene-butadiene rubber (SBR) and butadiene mbber (BR). 

Polybutadiene rubbers generally have a higher resilience than natural rubbers at room temperature, which is important in rubber applications. On the other hand, these rubbers have poor tear resistance, poor tack, and poor tensile strength. For this reason polybutadiene rubbers are usually used in conjunction with other materials for optimum combination of properties. For example, they are blended with natural rubber in the manufacture of truck tires and with styrene-butadiene rubber (SBR) in the manufacture of automobile tires. 

The fatigue of NR and styrene-butadiene rubber (SBR) is an enormous industrial problem, as important mechanical properties of these materials deteriorate quickly when stressed. Although fatigue may describe the deterioration of certain material properties, it is generally believed that the term also describes failure... 

Addition of fillers can dramatically change mechanical properties of elastomer materials. For example, a pure gum vulcanizate of general purpose styrene-butadiene rubber (SBR) has a tensile strength of no more then 2.2 MPa but, by mixing in 50 parts per hundred weight parts of rubber (p.p.h.r) of a active CB, this value rises more than 10 times to 25 MPa. How CB, being fine powder of practically no mechanical strength, can make reinforcement in rubbers, similar to... 

The natural rubber does not generally exhibit all the desired properties for use in the rubber industry. Thus, it is possible to obtain better mechanical and physical properties at a lower cost by blending natural rubber with synthetic rubbers. Normally, natural rubber is deteriorated by ozone and thermal attacks due to its highly unsaturated backbone, and it also shows low oil and chemical resistances due to its non-polarity. However, these properties can be achieved by blending it with low unsaturated ethylene propylene diene monomer rubber, styrene butadiene rubber, carboxylate styrene butadiene rubber, nitrile butadiene rubber, chloroprene rubber, chlorosulfonated polyethylene rubber, and acrylonitrile butadiene rubber. 

Styrene butadiene rubber is generally marketed at lower viscosity grades than NR and this permits its use in rubber compounding without premastication. Mechanical or chemical peptizing (or dispersing as a colloid, or suspension) is not required in SBR rubber. While most properties of SBR are comparable with NR, in some respects, such as heat build up, tack and gum tensile strength, SBR is inferior but addition of resins and reinforcing fillers improves these properties acceptably. 

Polybutadiene vulcanizates (see Table 18.1 for typical properties) are superior to those of natural rubber with respect to resilience, heat build-up and abrasion resistance. These properties are particularly significant in tyres. On the other hand, polybutadiene vulcanizates have lower tensile strength and tear resistance and polybutadiene tyres have relatively poor road-adhesion in wet conditions. For these reasons and to aid processing, butadiene rubbers are generally used in blends with natural or styrene-butadiene rubbers such blends usually contain less than 50% polybutadiene. Because of their use in tyre production, butadiene rubbers have become significant tonnage rubbers (Table 18.2). 

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