Transcript
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Alejandro Moreno
Ty Van Tran
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Definition of Rubber
History and source of Rubber Properties and Classification of Rubber
Natural Rubber
Synthetic Rubber
Elastomer and elasticity
Vulcanization
Manufacture
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Elastomer = Rubber
Material has the remarkable ability to substantially
return to its original shape after being stretched
considerably.
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0 B.C Aztecs and Mayas Shoe soles, play balls, coated fabrics
18th century EU Rubber
1823 Macintosh Naphtha
1830 Thomas Hancock 1st internal mixing machine
1841 Charles Goodyear Vulcanization process
1843 Hancock Vulcan = the god of fire
1889 John Dunlop 1st pneumatic tire for bicycles
1904 Carbon black Increasing mechanical properties
1910
Motor car Uses and price of NR exploded
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1870s Polyisoprene Europe, in labs
WW I Polybutadiene, Russia, in commercial
1930s Neoprene, Buna-S US and Germany
WW 2GRS copolymer of
butadiene and styreneUS
1960 SNR Shell, Goodyear
2005 58% of rubber is synthetic
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1
2
3
4
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High elasticity
Low Tg Sensitive to oxygen, ozone, light
Not oil resistant
Resistant to inorganic chemicals
Unsuitable for use with organic liquids
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Synthetic rubberNatural rubber
Synthetic natural rubber (SNR)
Butyl Rubber (BR)
Chloroprene Rubber (Neoprene)
Nitrile Rubber (NBR)
Styrene-Butadiene Rubber (SBR)
Thermoplastic elastomers
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C
C C
C
C
H
H
H
H
H
H
H
H
H
H
Hevea Rubber
(cis-polyisoprenene)
Natural rubber
M = 200,000 - 500,000
Proteins, sugars, fatty acids
Potassium, manganese,
phosphorus, copper and iron
Hevea Brasiliensis
Latex
30 40% wt. dry rubber
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Tg = -72oC
Need to be cross-linked to obtain
the high elasticity
Be cross-linked by sulfur, sulfur
donor systems, peroxides, isocyanate
cures and radiation
Easily blended with various fillers
and elastomers
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Transportation Industrial Consumer Hygiene and
medical
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Polyisoprene
Ziegler-Natta catalyst
More uniform and lighter in color than NR
Less of a tendency to crystallize
Application:
Used interchangeably with NR
Used in blends with PB, and SBR
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Monomer: butadiene
The cis 1,4 and 1,2 vinyl
contents govern the
performance of polymers
Lower cost
C C
C CH
H H
H
H
H
H
Appli ti s:
I l i it t r l r, :
Reduce eat uild-up
I pr es t eabrasi resistance, and
t e fricti n n ice f inter tires
I pr eabrasi nand l temperature
flexibilit
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Randomcopol mer,
st rene
Requires reater
reinforcement
ower resilience t an R
Application :
Blend with NR and PB: Tire
production
Conveyor belts, molded rubber
goods,
Carpet backing
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NBRNitrile Butadiene Rubber
Copolymer of butadiene and acrylonitrile
More expensive than SBR or BR
CRChloroprene rubber (neoprene)
Thermal stability
Non-flammable
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A class of copolymers or a physical mix of polymers which consist
both thermoplastic and elastomeric properties
The crosslink in TP polymers: a weaker dipole or hydrogen bond or
takes place in one of the phases of the material
More easily processed: extrusion and injection molding
Be used where conventional elastomers cannot provide the range
of physical properties needed in the product
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Physical Characteristics:
Amorphous Material Generally T > Tg.
Thermodynamic Equilibrium
Dont crystalize
Regarded as liquids
One huge macromolecule
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I Thermoplastic T < Tg
II Elastomer T > Tg
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Retraction force of
Elastomers is dominated
by entropy
Ideal Elastomer
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Main Hypothesis: Micro scale the
deformation is proportional than at
Macro scale
Second Hypothesis: All the chains in
the elastomer network have the samemolar Mass
Third Hypothesis: The material is
incompressible
Elastic modulus depend on the
temperature, density and Ms which is
the mass of chains between two cross
linked points.
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Vulcanized Rubber
Unvulcanized Rubber
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A process which increases
the retractile force and
reduces the amount of
permanent deformationremaining after removal of
the deforming force
Increases elasticity while
decreases plasticity
How?
Crosslinked molecular
networks
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Rubber becomes
essentially insoluble.
Hysteresis is a
measure of
deformation energy
that is not stored but
that is converted to
heat.
These properties are
not functions only of
crosslink density.
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IMPORTANT CHARACTERISTICS
Time elapsed before crosslinking starts Sufficient scorch resistance!
Rate of crosslink formation Fast!
The extent of crosslinking at the end of the process Controlled
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Vulcanization by sulfur without accelerator is no longer of
much commercial significance , but its chemistry has been the
object of much research and study.
A concentration of 8 parts per 100 parts of rubber (phr) requires 5
hours at 140C.
The addition of zinc oxide reduced the time to 3 hours.
The use of accelerators in concentrations as low as 0.5phr has
since reduced the time to asshort as 1 to 3 minutes.
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Accelerated-sulfur
vulcanization is the most
widely used method.
Rapid crosslinking
Good delayed action
required for processing
before the formation of the
vulcanized network.
It is used to vulcanize
natural rubber, synthetic
isoprene rubber, styrene-
butadiene rubber, nitrile
rubber, etc.
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VULCANIZATION BY THE ACTION OF METAL OXIDES
Chlorobutadiene
VULCANIZATION BY THE ACTION OF ORGANIC PEROXIDES
Elastomers
DYNAMIC VULCANIZATION
Vulcanization of one polymer during its molten-state mixing with another
polymer or with other polymers.
The polymers are first thoroughly mixed and then, during further mixing,
one of the polymers is obliged to become crosslinked, whereas the
remaining other polymeric material remains uncross.
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Mills Internal Mixing Machines
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Extruders Calenders
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MOLD.- At least two pieces of material,
which when fitted together from a cavity,
resembling the shape of the product.
Mold dimensions are around 1.5 % greater
than required.
Molding is the most important process
during rubber manufacturing.
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Transfer Molding
utocla e curing
Transfer Molding
Compression Molding
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