PBR – Poly Butadiene Rubber
Polybutadiene is a term used to denote homopolymer of butadiene C4H6. Polybutadiene is a synthetic rubber that is a polymer formed from the polymerization process of the monomer 1,3-butadiene. Depending upon the disposition of the double bonds present in the polymer chain, PBR can be classified into five configuration cis- 1,4;
trans-1,4; vinyl-l,2-isotactic; vinyl-l,2-syndiotactic ; and vinyl-1,2 atactic. Depending on the choice of catalyst system, PBR can be prepared ranging from almost 100% cis to 100 % trans or 100% vinyl. Out of these configurations, medium and high cis varieties are of commercial importance.
The Russian chemist Sergei Vasilyevich Lebedev was the first to polymerize butadiene in 1910. In 1926 he invented a process for manufacturing butadiene from ethanol, and in 1928, developed a method for producing polybutadiene using sodium as a catalyst. The government of the Soviet Union strived to use polybutadiene as an alternative to natural rubber and built the first pilot plant in 1930, using ethanol produced from potatoes. The experiment was a success and in 1936 the Soviet Union built the world's first polybutadiene plant in which the butadiene was obtained from petroleum. By 1940, the Soviet Union was by far the largest producer of polybutadiene with 50,000 tons per year. Following Lebedev's work, other industrialized countries such as Germany and the United States developed polybutadiene and SBR as an alternative to natural rubber. In 1980, researchers from Zeon discovered that high-vinyl polybutadiene (over 70%), despite having a high liquid-glass transition, could be advantageously used in combination with high cis in tires. This material is produced with an alkyllithium catalyst. In addition to the Japanese company Zeon, the American company Firestone produces high-vinyl polybutadiene as well. JSR Corporation markets a type of polybutadiene with 90% vinyl, giving it the properties of an elastomeric thermoplastic: elastic at room temperature but a fluid at high temperatures, which makes it possible to process it using injection molding.
Polybutadiene rubber is prepared by either emulsion or solution polymerisation. In general these processes are based on organo-lithium compounds or co-ordination catalysts. Polymerization is carried out using pure dry butadiene and a solvent. When the desired conversion is achieved, the catalyst is deactivated and polybutadiene is recovered from the unreacted butadiene and solvent, washed to remove the catalyst residue, and dried.
In early 1970s, IPCL set up PBR manufacturing facilities with the know-how from Polymer Corporation of Canada. The commercial production in this plant with the installed capacity of 20,000 TPA started in 1978. Now, Reliance is the sole manufacturer of PBR having a capacity of 0.074 MMT which is expected to touch 0.164 MMT in 2016.
Leading producers of PBR around the world include Lanxess, Korea Kumho, Michclin, Ncgromcx, Nippon Zeon, Petkim, Turkey, Petrochim, Rcpson Ouimica, Taiwan Synthetic, Ube and Romania, and CIS. Global capacity in 2011 was 3.8 MMT and is expected to touch 4.8 MMT in 2016.
Polybutadiene is largely used in various parts of automobile tyres; the manufacture of tyres consumes about 70% of the world production of polybutadiene, with a majority of it being high cis. The polybutadiene is used primarily in the sidewall of truck tyres, this helps to improve fatigue to failure life due to the continuous flexing during run. As a result, tyres will not blow out in extreme service conditions. It is also used in the tread portion of giant truck tyres to improve the abrasion, i.e. less wearing, and to run the tyre comparatively cool, since the internal heat comes out quickly. Both parts are formed by extrusion. Its main competitors in this application are styrene-butadiene rubber (SBR) and natural rubber. Polybutadiene has the advantage compared to SBR in its lower liquid-glass transition temperature, which gives it a high resistance to wear and a low rolling resistance. This gives the tyres a long life and low fuel consumption. However, the lower transition temperature also lowers the friction on wet surfaces, which is why polybutadiene almost always is used in combination with any of the other two elastomers. About 1 kg of polybutadiene is used per tire in automobiles, and 3.3 kg in utility vehicles.
About 25% of the produced polybutadiene is used to improve the mechanical properties of plastics, in particular of high-impact polystyrene (HIPS) and to a lesser extent acrylonitrile butadiene styrene (ABS). The addition of between 4 and 12% polybutadiene to polystyrene transforms it from a fragile and delicate material to a ductile and resistant one. Most golf balls are made of an elastic core of polybutadiene surrounded by a layer of a harder material. Polybutadiene is preferred to other elastomers due to its high resilience. Polybutadiene rubber can also be used in the cover of hoses, mainly pneumatic and water hoses. This rubber can also be used in railway pads, bridge blocks, etc. It is also used as a fuel in combination with an oxidizer in various Solid Rocket Boosters such as Japan's H-IIB launch vehicle.
Solution Polymerization of PBR:
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.