styrene-butadiene rubber (sbr)

Styrene Butadiene Rubber(SBR)

Syed Mohammed Sajl

Semester 6B Tech – PS & E

Tuesday, April 11, 2023 1Review Seminar - Semester 5

Introduction

• Styrene-butadiene or styrene-butadiene rubber (SBR) describe families of synthetic rubbers derived from styrene and butadiene.

• These materials have good abrasion resistance and good aging stability when protected by additives.

• In 1929, E Tchunkur and A Bock discovered that mixtures of butadiene and styrene.

• The styrene/butadiene ratio influences the properties of the polymer: with high styrene content, the rubbers are harder and less rubbery.


• In the 1930’s, the first emulsion polymerized SBR known as Buna S was prepared by I. G. Farbenindustrie in Germany.

• The U. S. Government in 1940 established the Rubber Reserve Company to start a stockpile of natural rubber and a synthetic rubber program.

• About 50% of car tires are made from various types of SBR

Tuesday, April 11, 2023 Review Seminar - Semester 5 3


Figure: Structure of Styrene-Butadiene


Production

E-SBR (Cold Rubber)

• The Emulsifiers for the dispersion of monomers during polymerization are of an anionic nature.

• The ratio of butadiene to styrene is mostly 76.5% to 23.5% by weight.

• The free radicals required for the initiation step are obtained by the reaction of Iron (II) salts with p-menthane hydroperoxide.


• For redox activators, one uses chelating agents, like Sodiun Salt of Ethylene-diaminetetraactic acid, together with Sodium formaldehyde sulfoxylate.

• The pH of the reaction medium is usually adjusted to about 11 to 12.

• Tertiary Dodecyl Mercaptan is mostly used as a chain modifier, it only terminates itslef when all the monomer has reacted.

• Prior to coagulation, stabilizers are added to the latex depending on desired qualitites.


OE-E-SBR Caron Black Master batch

• With some SBR grades, extender oils (OE-E-SBR) and Carbon Black Master batch are added at the end of polymerization stage.

• The oil extension, the rubber is usually produced to higher molecular weights.

• The oils is co-precipitated with rubber from the latex, acts as plasticizer during processing.

• Post dispersion in the latex, after co-precipitation, it is possible to incorporate carbon black finely dispersed in the rubber.


E-SBR (Hot Rubber)

• The Processes are very similar for both Hot and Cold Rubbers.

• We use soaps from fatty acids or alkylaryl sulfonates. The polymerization temperature is normally about 50OC or even higher.

• The free radicals are created from Potassium Persulfate and Mercaptaqn to initiate Polymerization.


The following parameters are important for the production of SBRs:• Monomer Ratio (mostly 23.5% styrene)• Polymerization Temperature• Chain modifiers• Emulsifier• Stabilizer• Coagulant• Oil, type and amount • Carbon Black, type and amountTuesday, April 11, 2023 Review Seminar - Semester 5 10

L-SBR

• Solution-SBR is produced by an anionic polymerization process.

• Polymerisation is initiated by alkyl lithium compounds. Water is strictly excluded.

• The process is homogeneous (all components are dissolved), which provides greater control over the process, allowing tailoring of the polymer.


• The organolithium compound adds to one of the monomers , generating a carbanion that then adds to another monomer, and so on.

• Relative to E-SBR, S-SBR is increasingly favored because it offers improved wet grip and rolling resistance, which translate to greater safety and better fuel economy, respectively



Properties

Properties of E-SBR

• E-SBR is commercially available in Mooney viscosities ranging from 30 to about 120 (ML1+4@125OC).

• Lower Mooney viscosity E-SBR grades band more easily on the mill, incorporate fillers and oil more readily, show less heat generation during mixing, are calendared more easily, shrink less, give higher extrusion rates and have superior extrudate appearance than the higher Mooney viscosity grades.

• On the other hand, the high Mooney viscosity SBR’s have better green strength, less porosity in the vulcanizate, and accept higher filler and oil loadings.


• As the molecular weight of the SBR increases, the vulcanizate resilience and the mechanical properties, particularly tensile strength and compression set, improve.

• The processability of SBR improves as its molecular weight distribution broadens. Formation of high molecular weight fractions with the increase in the average molecular weight can however, prevent improvements in the processability.

• This is due to the fact that the tendency for gel formation also increases at higher molecular weights.


• In addition to the polymer viscosity, polymerization temperature also plays an important role in shaping the processability.

• E-SBRs produced at low polymerization temperatures have less chain branching than those produced at higher temperature.

• The styrene content of most emulsion SBR varies from 0% to 50%. The percent styrene of most commercially available grades of E-SBR is 23.5%.

• In vulcanizates of SBR, as styrene content increases, dynamic properties and abrasion resistance decrease while traction and hardness increase.


MECHANICAL PROPERTIES:• SBR lacks the self-reinforcing qualities of natural

rubber due to stress induced crystallization, gum vulcanizates of SBR have lower tensile properties.

• The tensile property of E-SBR vulcanizates depends in great measure on the type and amount of filler in the compound.

• Cured gum stocks have only 2.8 to 4.2 MPa tensile strength, while fine particle carbon black loadings can produce tensile strength of 27.6 MPa.

• Though the compression set of some of the common E-SBR compounds is high, by proper compounding and blending, it is possible to obtain E-SBR vulcanizates with a low compression set.


ELECTRICAL PROPERTIES• SBR is a non-polar polymer and its

vulcanizates are poor conductors of electricity. The electrical properties of E-SBR depend to a large extent on the amount and type of emulsifier and coagulating agent(s) used.

RESISTANCE TO FLUIDS• While E-SBR vulcanizates are resistant to

many polar solvents such as dilute acids and bases, they will swell considerably when in contact with gasoline, oils, or fats. Due to this limitation, SBR cannot be used in applications that require resistance to swelling in contact with hydrocarbon solvents.


Properties of L-SBR

L-SBR with Random Distribution of Styrene:• These compounds have low hysteresis, less heat

buildup and superior abrasion resistance than E-SBR.

• L-SBRs are purer than E-SBR as they do not contain residual emulsifier.

• They have lower water absorption and particularly good electrical properties.

• They are odor free and light colored.L-SBR with Blocky Monomer Distribution:• They have good elastic properties, low water

absorption and low electrical conductivity


L-SBR with SBS Triblocks:• At Room Temperature, it has high elasticity

and tensile strength.• The SBS polymers are physical in nature

and due to the separation of styrene into discrete phases, these can be used in products which require only a low heat resistance.

• Above 70OC, the SBS polymers lose their elasticity and strength.

• The resistance to organic solvents is also poor.



Application & Uses

Application & Uses

E-SBR• E-SBR is predominantly used for the production of

car and light truck tires and truck tire retread compounds.

• A complete list of the uses of SBR includes housewares mats, drain board trays, shoe sole and heels, chewing gum, food container sealants, tires, conveyor belts, sponge articles, adhesives and caulks, automobile mats, brake and clutch pads, hose, V-belts, flooring, military tank pads, hard rubber battery box cases, extruded gaskets, rubber toys, moulded rubber goods, shoe soling, cable insulation and jacketing, pharmaceutical, surgical, and sanitary products, food packaging, etc.


Random L-SBR:• It is used in blends with E-SBR to improve

the extrudability and specifically, the sharpness of edges and the surface smoothness of extrudates.

Blocky L-SBR:• The preferred use is in hard shoe soling,

roll covering and special technical rubber products

Thermoplastic L-SBR:• It is used in instances where products

require low heat resistances have to produced in great quantity in roofing, shoe applications and nipples of babu bottles



References & Acknowledgements

Acknowledgements

•Rubber Technology Handbook – Werner Hofmann•www.wikipedia.com•www.google.com



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