Styrene-butadiene rubber tensile strength

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 18.2 Tensile strength of styrene-butadiene rubber (SBR) as a function of network chain density. (From Bueche, F. and Dudek, T.J., Rubber Chem. Tech., 36, 1, 1963.)... 

Radiation vulcanization of carbon fiber reinforced styrene-butadiene rubber causes a substantial increase in crosslink density (Figure 11.4) and tensile strength (Figure 11.5). This magnitude of change is possible only when the interaction between the filler and the matrix is improved. When irradiated in the presence of air, carbon fibers gain functionality which substantially increases their adhesion resulting in a spectacular improvement in properties. SEM studies show that as the dose of radiation increases, the adhesion of the... 

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. 

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. 

Figure 15.1 Effect of polymerization tenqroatiire upon the tensile strength of styrene-butadiene rubber vulcanizates containiirg SO parts per 100 parts by mass of rubbtf of a reinfotcing carbon black (Howland et aL [12])- The different styles of points denote results for vulcanizates prepared using rubbos obtained from different polymerization systems...

Commercial high-impact polystyrene usually contains 5-20% styrene-butadiene rubber. The particle size ranges from 1-10 fim. High-impact polystyrene may have as much as seven times the impact strength of polystyrene, but it has only half its tensile strength, lower hardness, and a lower softening point. 

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... 

At the same time Bala et al. studied the filler effects of organomodified dodecyl alkylammonium intercalated montmorillonite (12C-MNT) for natural rubber (NR) and styrene butadiene rubber (SBR). The results showed that tensile strength, modulus, and elongation at break increased significantly as compared to pure vulcanized NR and SBR when 4 wt% of 12C-MNT was used as filler. In the case of NR, these properties decreased drastically for 1 wt% of pure Na-MNT [122]. 

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. 

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... 

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). 

---