Pros And Cons Of Styrene Butadiene Rubber

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2.7 Styrene Butadiene Rubber
Styrene Butadiene Rubber (SBR) belongs to the synthetic rubbers families that are derived from Styrene and Butadiene.[53] SBR is an aqueous dispersion of (25%) Styrene (CH2=CHC6H5) and (75%) Butadiene (CH2=CH-CH=CH2) copolymer as shown in Figure (2-1).
The copolymerization of these two polymers may done by different ways. Mostly they copolymerized in an emulsion process, by dispersing a soap like surface acting agent where the materials are in water solution.[54] Figure (2-1) The chemical structure of SBR[55]

2.7.1 Properties of SBR
Recently the using of SBR becomes widespread in the world instead of natural rubber.[56] It is characterized by wide range of desirable properties including excellent crack and abrasion resistance, good aging stability. Unlike the natural rubber, the oxidation increases the linkage of polymer chains. This effect tends to harden it with age instead of softening. The main properties of SBR is shown in Table (2-2).
The main limitations and drawbacks of SBR are poor strength without reinforcement by fillers, low tear strength at high temperature and low resilience. Like natural rubber SBR is swollen and weakened by hydrocarbon oils and is degraded over time
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This polymerization is initiated by the free-radical initiators such as Alkyl Lithium compounds in the presence of stabilizers which serves as a deterioration preventive for the final product. In this process the water is entirely excluded. The process is homogeneous since all components are dissolved and this offers greater control over the process allowing fitting of the polymer. The free-radical initiators compound are sequentially added to monomers. Relative to Emulsion-SBR the Solution-SBR is increasingly favored because it offers enhanced wet grip and resistance to rolling, which in turn lead to greater safety and better fuel economy,

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