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RUBBER
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• Rubber is an elastic material used for various engineering
purposes.
• It is utilized to manufacture tires and tubes for cars,
trucks, buses, tractors, bicycles, airplanes, and more.
• These qualities make it suitable for engineering
applications, especially when combined with asbestos
and similar materials.
• Other applications of rubber include belts, pipes, sheets,
gaskets, toys, and more.
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Different Types of Rubber:
1. Natural
2. Synthetic
Natural Rubber:
• Natural rubber is obtained from the latex of certain
plants.
• More than 95% of rubber is obtained from Hevea
brasiliensis, also known as the rubber tree.
• Latex is a milky colloidal fluid containing 30% to 40%
rubber; the remaining portion is primarily water, along
with a small amount of protein and resinous material.
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What do you mean by vulcanization? What are the special properties of synthetic
rubber? 20/4/25
Latex is treated in two ways to obtain rubber goods.
1. The latex is coagulated with organic acid and then
processed- Crude Rubber.
2. The latex is mixed with appropriate compounding
materials and then precipitated directly from solution in
the shape to be used.
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• Crude rubber is a tough, strong, elastic substance
composed of 92% or more of a hydrocarbon chain
polymer, polyisoprene (C5H8).
• At low temperatures, rubber becomes stiff; when frozen,
it attains a fibrous structure.
• It is typically obtained from latex by coagulating it with
organic acids, washing, coagulating with water as it
passes between the rolls, and finally drying the washed
sheet.
• When rough rolls are used and the rubber is dried in the
open air, the product is known as pale crepe rubber.
• When smooth rolls are employed and the rubber is dried
in a smokehouse, the product is called smoke sheet.
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Pale Crepe Rubber Smoke Sheet
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• They are also known as 'elastomers'.
• They are rubber-like materials that have many of the
characteristic properties of rubber and some of which
resemble rubber in their chemical structure.
• Some elastomers are more resistant to sunlight than
rubber, while others have greater solvent resistance and
elasticity.
• They are derived from raw materials such as coal,
limestone, petroleum, natural gas, salt, alcohol, sulphur,
ammonia, and coal tar.
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1. Neoprene
2. Nitrile rubber
3. Butyl rubber
4. Silicon rubber
5. SBR polymers
6. Urethane polymers
7. Polysulphide elastomers
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During hot weather, pure rubber becomes soft and sticky,
while in cold weather, it becomes hard and brittle. In
these conditions, it is useless for its common purpose. Its
properties can be improved by adding other materials,
which can be processed with suitable heat or other
treatments.
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• Vulcanization is the process of manufacturing commercial
rubber. Almost all rubber today is vulcanized.
• Charles Goodyear developed this process of
manufacturing rubber in 1839, which significantly
accelerated the rubber industry.
• This process involves mixing sulfur with pure or crude
rubber and heating the mixture to a temperature (about
300°F) above the melting point of sulfur, where it
combines with rubber.
• The chemistry of vulcanization is not yet fully understood.
As the mixture of rubber and sulfur is heated in a steel
vessel, the sulfur first melts and chemically combines with
rubber.
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5% of sulphur- tyre rubber
20-25% of sulphur- ebonite rubber
30% of sulphur- battery case
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The effects of vulcanization are:
• Increase in tensile strength,
• Increase in resistance to weathering (less affected by
temperature changes than pure rubber
• More elastic,
• Good flexibility,
• Improved resistance to solvents, and
• Good dimensional stability for a longer period.
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Rubber finds a wide field of application because of the
following properties:
• It is elastic; because of this property, a rubber band can be
stretched to nine or ten times its original length, and when the
load is removed, it regains its original length.
• It is strong and tough. Because of this property, it can be
used even under abnormal conditions.
• It is highly impermeable to both water and air, so it can be
used to retain water, such as in rubber bottles and hoses.
• It exhibits great resistance to abrasion, tearing, and cutting
over a wide temperature range, from -7 to 115 °C.
• It is a poor conductor of heat.
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• It can contain liquids and gases.
• The synthetic rubber offers great resistance to acids,
petroleum products, and other substances.
• Its properties, such as hardness, strength, and abrasion
resistance, can be modified to the desired extent
through compounding techniques.
• When two fresh surfaces of milled rubber are pressed
together, they coalesce to form a single piece. This
property, known as tackiness, makes the manufacturing
of composite articles, such as a tire made from a
separate piece, very simple.
• By vulcanizing the rubber, its mechanical properties can
be considerably improved.
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• The electrical insulating properties of pure rubber are
inferior to those of vulcanized rubbers.
• Although rubber is practically water and gas tight, its
electrical characteristics are affected by moisture.
• For standard rubbers, the maximum operating
temperature is typically 55°C; for rubbers with high heat
resistance, it is 65°C, and for butyl rubbers, it is 90 °C.
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• Thermal insulation
• Lining for reservoir
• Rain water and flexible tubing
• Belting of all types
• Tires and tubes
• Adhesive
• Hose pipes, printing rollers etc.
• Mounting material
• As a buffer
• Gasketing material
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