Styrene-butadiene rubber black-reinforced

Although a large number of synthetic elastomers are now available, natural rubber must still be regarded as the standard elastomer because of the excellently balanced combination of desirable qualities. The most important synthetic elastomer is styrene-butadiene rubber (SBR), which is used predominantly for tires when reinforced with carbon black. Nitrile rubber (NR) is a raudom copolymer of acrylonitrile and butadiene and is used when an elastomer is required that is resistant to swelling in organic solvents. 

Styrene butadiene rubber (SBR) is, quantitatively, the most important synthetic rubber. It is a copolymer of styrene and butadiene in such a ratio that its rubbery nature predominates, vulcanization is carried out with sulphur, reinforcement with carbon black. It is used at a very large scale in tyres for passenger cars, thanks to its excellent combination of abrasion resistance and friction on the road. In large tyres it can not replace natural rubber because of its heat development (hysteresis losses). 

Despite the introduction of synthetic elastomers, ceramics and other abrasion resisting metals such as manganese, natural rubber holds a dominant position in this field of application and is the primary choice for abrasion resistance. Synthetic rubbers (particularly styrene-butadiene rubber which is dominant in the tyre industry sector) are used in dry abrasion application such as general purpose abrasion resistant sheets and conveyor belt covers, since the rubber can be reinforced with fine particles of carbon blacks to achieve dry abrasion resistance close to that of natural rubber. It should be noted that styrene-butadiene rubber is inferior to natural rubber in cutting and chipping resistance. 

Improvement of Mechanical Properties. The most important application of SAS, and one of the oldest, is the control of the mechanical properties of rubber. SAS are important additives for both styrene-butadiene rubber (SBR) and natural rubber (NR), second in importance only to carbon black (51, 52). Figure 5 demonstrates the increase in tensile strength at room temperature for silicone rubber with various reinforcing fillers and kieselguhr. An improvement is also brought about in the mechanical strength of fluoroelastomers and other special kinds of rubber (51). Table VI summarizes the improvements that may be achieved in other fields. 

For example, Kraus and Gruver (6) found such effects studying thermal expansion, free volume, and molecular mobility of HAF carbon black reinforced styrene-butadiene rubber (SBR) see Section 9.16.2. The SBR elastomer bonds to carbon black through a variety of secondary bonding modes. Thus, the train portion (see Figure 12.20) of the polymer chains in contact with the carbon black is relatively large and held to the surface rather firmly through multiple secondary bonds. 

Styrene-butadiene rubbers have characteristics very similar to those of natural rubber. They are compounded and processed in much the same way and may be vulcanized with either sulphur systems or peroxides. The styrene-butadiene chain is irregular and there is little tendency to crystallize on stretching (in contrast to natural rubber) thus gum vulcanizates have low tensile strength. However, reinforcement with carbon black leads to vulcanizates which resemble... 

Fig. 4 Experimental data on carbon black-reinforced styrene butadiene rubber Iot tensile (circle) and pure shear (square) tests [57]. The ratio of the tangent stiffiiess around the undeformed configuration, i.e., nominal strain equal to 1, is approximately equal to 3...

Although natural rubber has satisfactory properties in many applications there are now many synthetic alternatives available. Natural rubber is rather prone to chemical degradation by ozone and has poor resistance to solvents. Synthetic rubbers are usually better in these respects. The most important use of rubbers is in motor vehicle tyres in which styrene-butadiene rubber (a random copolymer, SBR), is mainly used along with a variety of additives such as carbon black. This reinforces the rubber and improves the strength, stiffness and abrasion resistance. 

Styrene-butadiene rubber (SBR). It has higher abrasion resistance and better aging behavioiu and is commonly reinforced with carbon black. It is widely used as tire rubber. 

Elastomers. Elastomers are polymers or copolymers of hydrocarbons (see Elastomers, synthetic Rubber, natural). Natural mbber is essentially polyisoprene, whereas the most common synthetic mbber is a styrene—butadiene copolymer. Moreover, nearly all synthetic mbber is reinforced with carbon black, itself produced by partial oxidation of heavy hydrocarbons. Table 10 gives U.S. elastomer production for 1991. The two most important elastomers, styrene—butadiene mbber (qv) and polybutadiene mbber, are used primarily in automobile tires. 

A typical tire rubber formulation for tire tread will contain various rubbers, mainly styrene-butadiene (50%) and cA-polybutadiene (12%), various processing aids (2%), softeners (3%), vulcanizing agent (mainly sulfur 1%), accelerators, and reinforcing filler (namely carbon black 30%) so that by bulk, carbon black is the second most used material. 

Figure 12.6. Volume resistivity against filler loading for SBR composites filled with MWNTs and mixtures (10 phr CB + x phr (MWNTs) (A) and TEM image of a styrene-butadiene copolymer (SBR) containing a dual filling (5 phr CB + 5 phr MWNTs) (B). [Reprinted from L. Bokobza, M. Rahmani, C. Belin, J.-L. Bruneel, N.-E. El Bounia "Blends of carbon blacks and multwall carbon nanotubes as reinforcing fillers for hydrocarbon rubbers", Journal of Polymer Science Part B Polymer Physics, 46,1939,2008, permission from John Wiley and Sons].

Autohesion of polyisoprene rubber (Natsyn 2200, a synthetic high-cis-l,4-polyiso-prene) and styrene-butadiene copolymer has been studied. Both elastomers were reinforced by carbon black and crossHnked by a sulfur-based system (see Table 24.1) [3]. The glass transition temperatures of the elastomers were not significantly changed by crossHnking and were equal to -66°C and -53°C for the IR and SBR, respectively, as measured by DSC analysis. 

For instance, Kraus and Gruver (1970) found that the Tg of a styrene-butadiene copolymer increased only 0.2°C for every ten parts per hundred by weight of reinforcing carbon black added, and that the coefficient of thermal expansion of the polymer component in the rubbery region was substantially unaffected by the presence of filler. While Yim and St. Pierre (1969) found that the Tg of silicone rubber increased up to 8 C with the addition of 40 parts per hundred by weight of reinforcing silica, this effect is still rather modest. 

The development of highly reinforcing furnace blacks paralleled the creation of the synthetic-rubber industry. Improved cold butadiene-styrene elastomers reinforced with these new blacks give vulcanizates that are superior to natural rubb m tire treads. 

Figure 3.408. Dependence of reinforcing effect, under tearing conditions, by temperature 1) poly(butadiene-co-styrene) rubber with black carbon 2) idem with chalk 3) idem with cellophane 4) idem mixture with polyamide [464].

Figure 3.415. Curves of stress relaxation, at 30 °C of the vulcanised poly(butadiene-co-styrene) rubber reinforced with 30% black carbon [1202].

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