Rubber Types
The most common chemical elements in rubber are carbon (c) and hydrogen (H). The Polymers of
natural rubber are mainly built of these elememts. In synthetic rubber these elements are
products from the petrochemical industry.
Natural Rubber (NR) – Production and Properties:
The rubber trees grow in tropical climates and is cultivated in many countries.
The biggest producers are Thailand, Indonesia and Malaysia, which combined produce
80% of world consumption. Plantations can also be found in South America and Africa.
When tapping the tree, a cut is made through the bark and the latex drips into a cup.
A tree with a good yield could give 30 to 35 grams of rubber per day the contents of cups
are emptied to the containers and transported to a rubber factory. Acetic acid is added to
promote coagulation. To manufacture smoked sheets, the rubber is made into sheets in
a mill, washed dried and smoked and finally classified. With the exception of Butadiene
rubber, natural rubber has the best elasticity of all rubber types. It has very good
resistance to abrasion and fatigue .Among the drawbacks are the materials poor
resistance ozone (weather) and oils and fuels.
Natural rubber is mainly used in the production of heavy duty tires , vibration dampers,
springs and bearings. For special purposes it is used in hoses seals , conveyor belts,
coated fabrics and other products.
Styrene-butadiene rubber (SBR) the most common type of synthetic rubber:
When the automobile industry developed , demands for rubber increased sharply. Many
trials were made to produce a man made rubber. The first synthetic rubber could not
match the natural rubber , but in the course of time several rubber types were developed
that had many properties comparable with natural rubber, In some cases even better.
Styrene butadiene rubber, the most common and cheapest synthetic rubber, serves as an
example of the manufacturing principles.The basic material is derived from petroleum
(oil) Which is a fossil formation from organisms that have been dead for millions of years.
In the distillation process at the oil refineries, styrene and butadiene are produced, which
are then used as raw materials for the production of styrene and butadiene rubber.
The first step is to let styrene and butadiene react together, the new material consist of
about 25% styrene, with butadiene making up the remainder. The result is synthetic
rubber that in principle has the same properties as natural rubber Heat resistance is
better but low temperature flexibility and tensile strenght are less than for natural rubber.
At Trelleborg, around 60% of the polymers used are synthetic, while 40% is natural
rubber.
Styrene and butadiene rubber is used in many of same products as natural rubber, it is
also used to cover different types of hose and in a number of other products. For
practical reasons, abbreviations of various rubber types have been internationally
approved. The abbreviations are used in this presentation.
Isoprene Rubber (IR) Very much as natural rubber:
Isoprene rubber has chemical structure as natural rubber( polyisoprene). However it does not
contain proteins ,fatty acids and other substances that are present in natural rubber. The
physical properties of isoprene rubber are in general some what inferior to those of natural
rubber but, in principle the two types are very alike . Isoprene rubber is used in the same type of
products as natural rubber.
Butadiene Rubber (BR):
Butadiene rubber is polymerized butadiene . It is used in blends with other rubber types for
improved elasticity, wear resistance and low temperature properties. A typical application is a
blend of butadiene rubber and natural rubber in truck tires.
SPECIAL RUBBER TYPES:
The above mentioned rubber types are so called general purpose. Many other types are
available , each with its own special properties. The most common special types in our
products are ethylene-propylene, butyl, chloroprene and nitrile rubber.
Ethylene –Propylene ruber (EDM/EPDM):
For manufacture of sheeting used at high temperatures, ethylene propylene rubber , with
above abbreviation EPDM ,is used. The first two letters means that the rubber consists of
ethylene and propylene , but the letter of D tells us that a diene is also present. That third
monomer makes it possible to cure the rubber with sulfur since it introduces double
bonds in the structure, thereby changing the structure to an unsaturated polymer. Since
ethylene –propylene does not crack outdoors(Good ozone resistance) is widely used for
seals in buildings and in the Automotive industry. Steam Hose, high temperature
–resistant seals and roll covers are other applications.
Butyl Rubber (IIR)-when low gas permeation is needed:
Products used to prevent gases from passing through the material based onbutyl rubber.
The polymer consists of isobutene with a minor part of isoprene . This isoprene makes
the rubber unsaturated and possible to vulcanize. The gas permeability increases with
increased temperature for all rubber types , but for butyl rubber it is very low, up to 160-
175F.The inner tubes are made of butyl rubber.
Chloroprene rubber (CR) - resistant to oil and weather:
Most chloroprene rubber types consists solely of polymerized chloroprene monomers.
The polymers has good resistants to the outdoor climate and reasonable oil resistance. It
is therefore used product exposed to oil based fuels and weather.
Nitrile rubber (NBR) – For use with Oil:
Nitrile rubber is co polymer of Acrylonitrile and Butadiene. It is a most common polymer
for products that are in contact with oil and weather.