Post on 04-Jun-2018
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Elastomers
MFG 355
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Elastomeric Materials
Highly amorphous
Highly random orientation
High elongation
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Elastomeric Materials
Elongation at break
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Stress
Strain
Elastomeric Materials
Metals
Conventional Plastics
Elastomers
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Elastomeric Materials
No Stress
Stressed
In tension
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Elastomer Processing
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Aliphatic Thermoset Elastomers
These are the most common elastomers
These have a double bond after
polymerization has occurred
These are noncrystalline
These are highly flexible
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Natural Rubber
C C
C C
C
H
H
H
H
H
HH
H
C
C C
C
C
H
H
H
H
H
H
H
H
Hevea Rubber
(cis-polyisoprenene)
Gutta percha or Balatta(trans-polyisoprene)
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Natural Rubber
Raw material extracted from trees
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Natural Rubber
Material is processed
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Natural Rubber
Latex is then dried, sorted and smoked
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Natural Rubber
The difficulties with natural rubber
Strength
Availability
Bacterial breakdown
Creep
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Natural Rubber
Creep
Solved by Goodyear in the 1800's
Discovered that the polymer could be
crosslinked (cured or vulcanized) by heating
with sulphur
C C
C C
C
H
H
H
H
H
HH
H
Sulphur attacks this double bond
- As many as 8 sulphur atoms mightbe in the bridge between molecules
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Synthetic Polyisoprene or Isoprene
Rubber
Need
Supply of natural rubber disrupted during
WWI and WWII
Used in tires for bicycles and early cars
Used the Ziegler-Natta catalyst system to
improve properties
The trans- or cis- nature of the rubber could becontrolled up to 90% in either direction
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Butadiene Rubber (BR)
C C
C CH
HH
H
H
H
How is this polymer different from natural rubber?
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Butadiene Rubber (BR)
No cis or trans isomers
Lower mechanical strength because of no
of pendant methyl group but also more
flexibility
Lower cost (all synthetic from cheap
monomer)
Improvement of low-temp flexibility
Compatibility with other polymer materials
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Styrene Butadiene Rubber (SBR)
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Oil-Resistant Elastomers
NBRNitrile Butadiene Rubber
Copolymerization of butadiene and
acrylonitrile
More expensive than SBR or BR
CRChloroprene rubber (neoprene)
Thermal stability
Non-flammable
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Many of the properties of thermoset elastomers
Resiliency
Elasticity
More easily processed Injection molding, extrusion and other standard
thermoplastic processes
Highly compatible with polyolefins
EPDM is crosslinked very lightly and may not be
capable of being melted
Thermoplastic Elastomers (EPM
and EPDM)
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Thermoplastic Olefin Elastomers
(TPO)
Block tripolymers (such as SBS) with hard
and soft domains
Poor compatibility with other rubbers
Melt processible
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Flouroelastomers
C C
F
HH
H
Vinylidene fluoride monomer
C C
F
FF
F
Tetrafluoroethylene monomer
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Flouroelastomers
Many of the desirable properties of
flouropolymers
Low solvent effects
Excellent for chemical and petroleum handling
applications
High thermal stability
Good for gaskets and seals
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Silicones
S O
C
C
H H
H
H H
H
( )n ()n
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Silicones
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Elastomer Processing
Compounding
Banbury mixer
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Elastomer Processing
Preforming
Molding
Dipping
Impact Toughness Guide
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Impact Toughness GuideResin Izod (ft-lb) Reasoning
Polyurethane (x-link) 25 High elongation and strength
Polycarbonate 16 High strength
SMC 7 Reinforced and toughened
ABS 6 Toughened with rubber
HDPE 3 High elongation, flexible
Acetal 2 Can be toughened
Nylon 6/6 2 Can be toughened
PET 1 Can be alloyed
PP 1 Some crystallinity
LDPE 1 Low strength
Polystyrene 0.3 Pendent group
Acrylic 0.3 Short link, large pendent group
Phenolic, w/fiberglass 0.3 Crosslinked
Epoxy, unreinforced 0.2 Crosslinked
Crosslinked polyester 0.2 Crosslinked
Increasing
Toug
hness
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Thank You