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STYRENE BUTADIENE RUBBER

 STYRENE-BUTADIENE RUBBER-SBR



 

SBR is a general-purpose synthetic rubber, produced by emulsion polymerization using copolymers Styrene and Butadiene. If the emulsion polymerization is done at a low temperature like 5°C, then the produced polymer is called cold SBR, while if the polymerization takes place at an elevated temperature around 50°C is referred to as hot SBR.





Atypical recipe for cold emulsion SBR polymerization at 5°C

Ingredient                                                    Parts by weight                        Function

Butadiene                                                                72                                    Monomer

Styrene                                                                    28                                    Monomer

di-isopropyl benzene hydroperoxide                       0.08                                Initiator

Ferrous sulfate                                                         0.04                               Activator of initiator

n-dodecyl mercaptan                                                0.2                                  Modifier

Potassium pyrophosphate                                         0.18                               Buffer

Rosin acid soap                                                         4.0                                 Emulsifier

Water                                                                        180


Atypical recipe for hot emulsion SBR polymerization at 50°C

Ingredient                                                    Parts by weight                        Function

Butadiene                                                                75                                    Monomer

Styrene                                                                    25                                    Monome

Potassium peroxydisulphate                                    0.3                                  Initiator

n-dodecyl mercaptan                                                0.5                                  Modifier

Rosin acid soap                                                        5                                     Emulsifier

Water                                                                        180


Differences between cold and hot SBR's

  • Hot SBR has wide molecular weight distribution whereas cold SBR has a narrow molecular weight distribution
  • As a result of molecular weight distribution differences, cold SBR has better strength properties than hot SBR
  • Cold SBR can be easily extended with petroleum oils
  • Hot SBR can be processed more easily than cold type
SBR is the highest consumed synthetic rubber, abundantly in automobile and truck tires. SBR can be regarded as a general-purpose replacement for natural rubber in many applications, the choice directly depends on the price factor. The SBR properties include excellent abrasion resistance, crack resistance, and better-aging properties. Due to unsaturation in the Carbon backbone, SBR is easily attacked by Oxygen and Ozone. Apart from that like natural rubber, SBR is swollen and weakened by hydrocarbon oils. The most important limitation of SBR is poor physical properties in gum stocks, where no reinforcing fillers are used, low resilience, low tear strength, and poor tack. Comparatively, SBR requires a longer cure time due to its lower level of unsaturation, unless it contains a higher level of the accelerator.
However, the strength properties and abrasion resistance of SBR can easily be enhanced by the addition of filler carbon black. This determines the SBR used as a major polymer in tire treads. 
Apart from the solid form of SBR, it is produced in latex form exclusively for manufacturing rubber adhesives and latex-based products.


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