SBR - Styrene Butadiene Rubber
Styrene-butadiene or styrene-butadiene rubber (SBR) is a synthetic rubber copolymer consisting of styrene and butadiene.
It has good abrasion resistance and good aging stability when protected by additives, and is widely used in car tyres, where it may be blended with natural rubber.
Its common physical characteristics are - Black in color, other colors can be compounded upon volume special request, 70 +/- 5 Durometer (hardness rating), excellent tensile strength and abrasion resistance at higher temperatures.
A chemist called Fritz Hofmann discovered the elastic material methyl isoprene in 1909; many happenings have influenced the development of SR -- the Industrial Revolution, progress of motor transportation, two World Wars, growing demand for rubber and inability of natural rubber (NR) to meet entirely the world elastomer requirements.
This synthetic material had opened the door to numerous innovations in previous decades – in automotive engineering, energy generation, medicine, sports, and even the aerospace industry.
Industrial manufacture began during World War II, where it was used extensively by the USA to replace the Far-East natural rubber supplies captured by the Japanese.
Asahi Kasei, Lanxess, LG Chem, Polimeri Europa, Sinopec and are some of the leading producers of SBR in the world.
Global capacity of SBR (emulsion) in 2015 was around 5.6 MMT while SBR (solution) was 1.7 MMT.
In 2011 SBR capacity in India was 20 KTA and is expected to touch 290 KTA in 2016-17. The demand for SBR in India is projected at 313 KTA for 2016-17 .
India’s first large-scale styrene butadiene rubber (SBR) plant was built at Panipat by Indian Synthetic Rubber – a joint venture between Indian Oil, Taiwan’s TSRC and Japan’s Marubeni.
Reliance Industries Ltd. began production at its new 150 KTA SBR plant at Hazira in 2015-16, which is the largest in India. The plant has capability to produce entire range of dry as well as oil extended grades of emulsion SBR.
Typical applications are sealing requirements for hydraulic braking systems. Additionally, it is used in some rubber cutting boards.
The elastomer is used widely in pneumatic tires, shoe heels and soles, gaskets and even chewing gum. It is a commodity material which competes with natural rubber. Latex (emulsion) SBR is extensively used in coated papers, being one of the most cost-effective resins to bind pigmented coatings. It is also used in building applications, as a sealing and binding agent behind renders as an alternative to PVA, but is more expensive. In the latter application, it offers better durability, reduced shrinkage and increased flexibility, as well as being resistant to emulsification in damp conditions.
SBR can be used to 'tank' damp rooms or surfaces, a process in which the rubber is painted onto the entire surface (sometimes both the walls, floor and ceiling) forming a continuous, seamless damp proof liner; a typical example would be a basement.
1. Emulsion Polymerization of SBR:
Typically, an emulsion system for polymerization contains water, monomer, initiator, and an emulsifier. The polymerization process was initially done at 50 degrees celsius, but improved technology allowed for “cold” processes to be developed with reaction temperatures at 5 degree celsius. The polymerization of cold SBR is initiated by the reaction of a hydroperoxide with ferrous icons, which furnishes free radicals for polymer formation. Polymerization is stopped at 60 percent conversion with a short stop agent such as hydroquinone. Higher conversion percentages generally lead to polymers with inferior physical properties, most likely due to unwanted chain cross-linking. The latex is warmed, and the excess butadiene and styrene is recovered for recycling by either steam stripping or distillation.
2. Solution Polymerization of SBR:
The processes to produce SBR & PBR by solution are very similar. A catalyst is added to a thoroughly dried mixture of monomer and hydrocarbon solvent. After reacting and polymerizing in one or more reactors, a shortstop is added to limit the conversion of the polymer.