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1. SYNHETIC RUBBER
MNUFCTURING
BY: SYED MEHRAN FARID

2. We will learn today :
 Introduction
 Classification
 Natural Rubber Brief
 Synthetic Rubber Intro.
 Industrial Processing

3. INTRODUCTION
Rubber, elastic substance obtained
from the exudations of certain tropical
plants (natural rubber) or derived
from petroleum and natural
gas (synthetic rubber).
Because of its elasticity, resilience,
and toughness, rubber is the
basic constituent of the tires used in
automotive vehicles, aircraft, and
bicycles.

4. RUBBER
• NATURAL RUBBER SYNTHETIC RUBBER
• Isoprene Polyisoprene Buna-S (GRS)
H2C CH2 Buna-N (GRA)
C = C Neoprene
CH3 H Butyle Rubber

5. NATURAL RUBBER
• Natural rubber is obtained from a tree
called Hevea brasiliensis as an
aqueous suspension.
• Low plasticity
• Low tensile strength(load bearing capacity)
• High water absorption (weak)
• High unsaturation(more reactive)
These problems can be overcome by Vulcanization.

6. SYNTHETIC RUBBER
• Created in 1909 by Fritz Hofmann.
• 2/3 of today’s rubber is synthetic.
Synthetic rubber Obtained From Butadiene Are :
Buna Rubbers
• As a result of polymerization
of butadiene with acrylonitrile or styrene
• Buna – Bu stands for Butadiene, na for Sodium
S and N for styrene & nitrile(acrylonitrile)
respectively.

7. FILLERS
Carbon Black
Silica
Cellulose filler
Clay filler
Sulphur

8. PROCESSING
1. Mastication/Compounding
2. Mixing
3. Shaping
4. Curing/Vulcanization

9. 1. MASTICATION
• The process of softening by means of mechanical shearing
is known as mastication.
• Rubber is always compounded with additives(carbon black)
• Mastication shortens rubber
Molecular chains,
Resulting in a reduced molecular weight and
Reduces its viscosity
Improve Plasticity.
• This process involves the use of special mechanical
equipment and additives at low temperatures.

10. MASTICATION CONT….
OTHER FILLERS AND ADDITIVES
• China clay – Hydrous Alumina Silicates ,used when black is not
acceptable
• other polymers, such as styrene, pvc, and phenolics.
• recycled rubber added in some rubber products, but usually 10% or less.
• coloring pigments; plasticizers and softening oils; blowing agents in
the production of foamed rubber; and mold release compounds.

11. 2. MIXING
• the additives must be thoroughly mixed with the base rubber to
achieve uniform dispersion of ingredients.
• uncured rubbers have high viscosity so mechanical working of
the rubber can increase its temperature up to 150 C (300 F).

12. MIXING CONT…
• to avoid premature vulcanization, a two-stage mixing process
is usually employed
stage 1 - carbon black and other non-vulcanizing
additives are combined with the raw rubber.
 The term master batch is used for this first-stage mixture
stage 2 - after stage 1 mixing has been completed, and
time for cooling has been allowed, stage 2 mixing is carried out in
which vulcanizing agents are added

13. 3. SHAPING & RELATED PROCESSES
• Shaping processes for rubber products can be
divided into four basic categories:
1. Extrusion
2. Calendering
3. Coating
4. Molding and Casting
• Some products require several basic processes
plus assembly work
-- Example: tires

14. SHAPING CONT…..
CALENDERING ROLLER DYE PROCESS COATING
Rubber sheet
thickness determined
by final roll gap.
Combination of extrusion
and calendering that results
in better quality product.
Industrial process for
producing automobile tires,
conveyor belts, and
waterproof cloth tents and
rain coats

15. 4. VULCANIZATION
The treatment that accomplishes cross-linking
of elastomer molecules,
so that the rubber becomes stiffer & stronger
but retains extensibility
-- A typical soft rubber has 1 or 2 cross-links
per 1000 units (mers)
-- As the number of cross-links increases, the polymer
becomes stiffer and behaves more and more like
a thermosetting plastic (hard rubber)

16. VULCANIZATION CHEMICALS
• As it was first invented by Goodyear in 1839, vulcanization used sulfur
(about 8 parts by weight of S mixed with 100 parts of NR) at 140c (280f)
for about 5 hours
- Vulcanization with sulfur alone is no longer used today, due to the
long curing times
• various other chemicals are combined with smaller doses of sulfur
accelerate and strengthen the treatment
-The resulting cure time is 15-20 minutes