SBR vulcanizates

Mechanical properties depend considerably on the stmctural characteristics of the EPM/EPDM and the type and amount of fillers in the compound. A wide range of hardnesses can be obtained with EPM/EPDM vulcanisates. The elastic properties are by far superior to those of many other synthetic mbber vulcanizates, particularly of butyl mbber, but they do not reach the level obtained with NR or SBR vulcanizates. The resistance to compression set is surprisingly good, in particular for EPDM with a high ENB content. 

As shown in Figure 18.1, in the stress-strain curve of the real unfilled SBR vulcanizate, the stress upturn does not appear and as a result, tensile strength and strain at break are only about 2 MPa and 400%-500%, respectively. Nevertheless, the stress-strain curve of the SBR vulcanizate filled with carbon black shows the clear stress upturn and its tensile stress becomes 30 MPa. This discrepancy between both vulcanizates is actually the essential point to understand the mechanism and mechanics of the carbon black reinforcement of mbber. 

Han, S.C. and Han, M.H., Fracmre behavior of NR and SBR vulcanizates fibed with ground rubber having uniform particle size, J. Appl Polym. Sci., 85, 2491, 2002. 

Rubber-Clay Nanocomposites Some Recent Results Table 7 Recipes for the S-SBR vulcanizates... 

The morphology of these two systems is shown in Figures 1 and 2, respectively. Figure 1 shows electron photomicrographs of fracture replicas of SBR vulcanizates containing polystyrene fillers of two different particles sizes, and the existence of the individual polystyrene particles is easily confirmed. Figure 2 shows a schematic of the morphology of a styrene-diene-styrene block copolymers, in which the formation of a... 

Figure 5. Failure envelope for filled SBR vulcanizates. Filled points refer to 25° C and 20 inches/min.

The characterization of the SBR vulcanizates containing these fillers is shown in Table II. The low values of sol content indicate the presence... 

Figure 6 is also useful in demonstrating the difference in viscoelastic response of polybutadiene and SBR vulcanizates. The higher values of tensile strength of the latter, at any given temperature, can obviously be ascribed to the substantially higher Tg of the SBR since the crosslink densities of the two vulcanizates are similar. 

Pullout Tests. The method to determine the adhesion between the dipped cords and the SBR vulcanizate was the tire cord adhesion test (L/,75), Figure 1. Here, two cords are embedded (to a depth of 10 mm) into opposite ends of a rubber block (76 mm x 13 mm x 6.4 mm). Samples are then cured 23 min at 155 °C and allowed to rest 1 day. Bond strengths are determined by clamping the two free cord ends in an Instron and pulling at the rate of 50 mm/min. 

This paper presents the results of an investigation of some of the above materials and other structurally related aryl diamine chemicals. Data are also presented on the comparative inhibiting properties of three representative protectant chemicals used as additives in typical SBR vulcanizates. 

Figure 4. EfFect of antiozonants (8 p.h.r.) on surface cracking of SBR vulcanizates...

Hamed, G.R. Gibala, D. Zhao, J. Tensile behavior of an sbr vulcanizate containing a single rubber particle. Rubber Chem. Technol. 1998, 71, 861. 

SBR filled with intercalated montmorillonite had substantially lower toluene uptake compared with the same rubber filled with carbon black (see Figure 15.42). Figure 5.28 shows that the diffusion coefficient of kerosene, which defines penetration rate, decreases when the concentration of carbon black in SBR vulcanizates is increased. Figure 15.33 compares the uptake rate of benzene by unfilled rubber and by silica and carbon black filled rubber. Both fillers reduce the solvent uptake but carbon black is more effective. 

Due to the high reactivity of ozone with unsaturated hydrocarbons moieties, surface cracking of stressed or flexed NR, BR, NBR, and SBR vulcanizates arises. Rubber goods designed for outdoor applications must therefore be stabilized against both C>2 and 0 attacks. Antioxidant protection mechanisms have been discussed in detail ( 1). Discussions dealing with antiozonant mechanism involve some contradictory experimental observations. 

Both phenyl-1- and 2-naphthylamines are highly effective discolouring AO imparting a good fatigue resistance to natural rubber (NR), but a low resistance to styrene-butadiene rubber (SBR) vulcanizates. PNA have no antiozone protection... 

Fillers in Rubber. Carbon black and calcium silicate are able to reinforce rubber. For example, the tensile strength of an SBR vulcanizate can be raised from 350 to 3500 Ib/in. by compounding with 50% of its weight of carbon black (54). The activity of the carbon black depends on particle size and shape, porosity, and number of active sites, which are less than 5% of the total surface. Elastomers of a polar nature, such as chloroprene or nitrile rubber, will interact more strongly with filler surfaces having dipoles, such as -OH and -CCX)H groups or chlorine atoms. 

FIGURE 10.20 Breaking stress, for an SBR vulcanizate versus rate of elongation, e. (From Smith (1958).)... 

FIGURE 10.24 Tensile strength of SBR vulcanizates versus degree of crosslinking, represented by Ve. (From Bueche and Dudek (1963).) Broken curve author s estimate of threshold strength under nondissipative conditions. 

Under practical aspects and by considering the viscoelasticity of polymeric materials, the testing conditions such as loading time (speed) and temperature are of special interest. The following Figs. 5.10 and 5.11 demonstrate the influence of the pendulum hammer speed and the testing temperature by using filler-reinforced EPDM and SBR vulcanizates, respectively. 

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