Styrene-butadiene rubber tearing

Polymers can be modified by the introduction of ionic groups [I]. The ionic polymers, also called ionomers, offer great potential in a variety of applications. Ionic rubbers are mostly prepared by metal ion neutralization of acid functionalized rubbers, such as carboxylated styrene-butadiene rubber, carboxylated polybutadiene rubber, and carboxylated nitrile rubber 12-5]. Ionic rubbers under ambient conditions show moderate to high tensile and tear strength and high elongation. The ionic crosslinks are thermolabile and, thus, the materials can be processed just as thermoplastics are processed [6]. 

FIGURE 1.12 Master curve of tear energy Gc versus rate R of tear propagation at Tg for three cross-linked elastomers polybutadiene (BR, Tg — —96°C) ethylene-propylene copolymer (EPR, Tg — —60°C) a high-styrene-styrene-butadiene rubber copolymer (HS-SBR, Tg — —30°C). (From Gent, A.N. and Lai, S.-M., J. Polymer Sci., Part B Polymer Phys., 32, 1543, 1994. With permission.)... 

FIGURE 26.56 Log Abrasion loss by a blade (solid lines) and log cut growth rate (dashed hnes) of noncrystallizing rubber compounds as function of log frictional and log tearing energy, respectively isomerized natural rubber (NR), 2 styrene-butadiene rubber (SBR), and 3 acrylate-butadiene rubber (ABR). (From Champ, D.H., Southern, E., and Thomas, A.G., Advances in Polymer Friction and Wear, Lieng Huang Lee (ed.), Plenum, New York/London, 1974, p. 134.)... 

These may be used for low hardness compounds in areas where impact abrasion is predominant. EPDM is at times referred as crackless rubber5 since it has high tear resistance. For producing high hardness compounds blends with natural rubber, styrene-butadiene rubber (SBR) and high styrene resins are recommended. 

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. 

Compared with similar natural rubber compositions of the same hardness, styrene butadiene rubber (SBR) formulations are characterized by lower tensile strength, elongation, and resilience, lower resistance to tear, flexing, abrasion, ozone, and sunlight, and higher permanent set. The freeze resistance and permeability to gases of styrene butadiene are equivalent to those of comparable natural rubber, and so are the electrical characteristics. 

Polybutadiene rubber (BR) is similar to natural rubber in its properties but it is more costly to process into intricate shapes than rubbers such as styrene butadiene rubber. Hence, it is essentially used as an additive in order to increase the tear resistance of other rubbers. 

Styrene-Butadiene Rubber. Styrene-butadiene rubber (SBR) is made by either an emulsion or solution process (eq. 2). The classification systems for emulsion SBR is shown in Table 5. In the emulsion process, it is more difficult to control polymer microstructure and the final product is not as pure as the solution form. However it tends to show a higher tensile strength and tear strength, and is easier to process. It is used in applications such as tire treads, sidewalls, bead... 

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). 

Fig. 5.60 Dependence of tearing energyy 2T upon rate and temperature for a gum styrene-butadiene rubber. (After Greensmith and Thomasy J. Polym. Sci.y 18, (1955) 189.)...

Non- or semi-reinforcing fillers These are usually added to reduce cost. In natural rubber or polychloroprene, they may be used alone, but with non-crystallizing polymers such as butadiene - acrylonitrile or styrene - butadiene copolymers, they can only be used in conjunction with a reinforcing filler. Their effect is to reduce tensile strength and elongation, tear resistance and resistance to set. The effect on modulus varies according to choice of filler, but it is always much weaker than that of a reinforcing filler. 

B. N. Dinzburg, V. P. Popova, V. G. Dynunina, and A. E. Chalykh, Effect of the Structure of Styrene-Butadiene Copolymers on the Properties of Resins in Admixture with Rubbers, Kolloidn. Zh. 38(2), 338 (1976). SBR(High S)/SBS block copolymer (80%S)/PS, sulfur vulcanized. Improved tearing resistance. 

Non-oil Resistant (swelling or Natural rubber Styrene-Butadiene GRS Elastic cord, tires -65 to 220 High resilience, abrasion resistance, tear strength... 

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