Styrene-Butadiene Rubber (SBR)

Styrene Butadiene Rubber
(SBR)

Syed Mohammed Sajl
Semester 6
B Tech – PS & E

Thursday, March 07, 2013 Review Seminar - Semester 5 1

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


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
O
temperature is normally about 50 C 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 amount


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@125 C). O

• 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

• 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 70 C, the SBS polymers lose their
O

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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Styrene-Butadiene Rubber (SBR)

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