elastomeric fibers are fibers which have a property of extreme extencibility and elastic recovery. this seminar describes major properties and applications of elastomeric fibers.
3. Introduction
Elastomers, or rubbers, are high polymers that typically contain chemical and/or
physical crosslinks.
The predominant property of elastomers is elastic recovery after deformation in
compression or tension.
Besides, elastomers are characterized by
great toughness under static or dynamic stresses
better abrasion resistance than that of steel,
impermeability to air and water and in many cases
high resistance to swelling in solvents and attack by chemicals.
4. Pre history
The natives of South America got the idea to exploit
the latex of the Hevea Brasiliensis rubber tree
Intending to produce waterproof footwear among
other products from soaking their feet in the liquid.
The word rubber originates from the early
applications of rubber to rub out pencil writing.
In the 18th century, when rubber appeared in
Europe, it was used for the fabrication of suspenders
and straps.
5. Prior to World War II, hevea rubber accounted for
over 99% of all elastomers used, but synthetic
elastomers account for more than 70% of all rubber
used today.
Over 5.5 billion pounds of synthetic rubber is
produced annually in the United States.
6. Types of elastomers
based on nature
Natural rubbers
Synthetic rubbers
Elastomers have been classified
in groups according to similarity
of properties and applications.
• Based on origin
• Based on the set of temperature
7. Natural rubbers
Natural rubber can be isolated from more than
200 different species of plants.
It is obtained from latex, which is the emulsion
of cis-1,4-polyisoprene and water.
also contains a few percent of non-rubber
constituents such as resins, proteins, sugars and
fatty acids,
which can function as weak antioxidants and
accelerators in the natural rubber.
8. features
Applications
tires (60 - 70%)
Tubes, conveyor belts and V-belts
Coatings
Gaskets
Latex products
Footwear
Adhesives
Advantage
Good process ability
Excellent elastic properties
Good tensile strength
High elongation
Good tear and wear resistance
Excellent cold resistance
Good electrical insulator
9. Disadvantages of Natural Rubber:
Poor weather and ozone resistance
Restricted high temperature resistance
(short-time maximum temperature 100°C)
Swelling in oils and fuels: low oil and fuel
resistance
10. Synthetic rubbers
DIENE-BASED ELASTOMERS
ETHYLENE–PROPYLENE RUBBERS
POLYURETHANES
SILICONE ELASTOMERS
Synthetic fibers have many
types based on the building
monomers.
11. DIENE-BASED ELASTOMERS
Polymerization of conjugated dienes like butadiene,
isoprene, and chloroprenes involves activation of either
or both of the double bonds
The residual unsaturation in the polymer chains
provides convenient sites for the introduction of
elastomeric network of cross-links (vulcanization).
conjugated dienes are the source of some of the most
important commercially available synthetic rubbers or
elastomers.
12.
13. ETHYLENE–PROPYLENE RUBBERS
Copolymerization of ethylene with propylene results in a random, noncrystalline
copolymer that is a chemically inert and rubbery material.
To incorporate sites for vulcanization, an unsaturated terpolymer can be prepared
from ethylene, propylene, and a small amount (3 to 9%) of a nonconjugated diene
(EPDM).
Ethylene–propylene elastomers are made by solution polymerization of ethylene
and propylene in a solvent such as hexane using catalysts.
14.
15. POLYURETHANES
Polyurethane is the generic name of polymers with the urethane inter unit linkage in the
chain.
There are two main synthetic routes for the preparation of linear urethane homopolymer.
The condensation reaction between a bischloroformate and a diamine
the addition reaction of a diisocyanate with diol:
Polyurethanes are used in four principal types of products: foams, elastomers, fibers, and
coatings.
16. Polyurethane elastomers have
high strength;
extremely good abrasion resistance;
good resistance to gas, greases, oils, and
hydrocarbons;
and excellent resistance to oxygen and ozone.
17. SILICONE ELASTOMERS
Silicone elastomers (Polysiloxanes) can be
prepared by the hydrolysis of dichlorosilanes
such as dimethydichlorosilanes
They are credited for
high temperature and oxidative stability,
low temperature flexibility,
good electrical properties,
high resistance to weathering and oil.
18. Based on set of temperature
Thermoset
The principal feature the presence of a
cross-linked network structure
network structure formed exclusively by
covalent bonds.
the presence of these cross-links prevents
gross mobility of molecules, but local
molecular mobility is still possible.
Thermoplastic
Thermoplastic elastomers are a polymer
group whose main properties are elasticity
and easy process ability.
Thermoplastic elastomers are a wide
group of materials.
Thermoplastic elastomers contain two or
more distinct phases and
their properties depend on these phases
being intimately mixed and small
19. Properties of thermoplastics
In order that the material be a
thermoplastic elastomer at least
one phase must be soft or flexible under the
operating conditions and
at least one phase is hard with the hard
phase(s) becoming soft (or fluid) at higher
temperatures.
Often the hard segments or phases are
crystalline thermoplastics
while the soft segments or phases are
amorphous.
21. Thermosets
the major commercial thermosets
include
epoxies,
polyesters, and
polymers based on formaldehyde.
Thermosets, on the other hand,
have a network structure formed
exclusively by covalent bonds.
Formaldehyde-based resins,
which are the most widely used
thermosets
22. General properties of elastomers
Thermal expansion
the linear thermal expansion coefficient of elastomeric materials is five 5 to 20 -fold
compared with e.g. that of steels. Consequently, the heat shrinkage of molded elastomer
products can be several percent.
Hardness
Hardness is commonly quantified using the IRHD or Shore 0 to 100 scale. The hardness of
a conventional elastomeric product is around 50 to 70 IRHD.
Electrical property
Most general-purpose elastomers, like natural rubber and a variety of synthetic elastomers
exhibit very low electrical conductivity and are therefore suitable as electrical insulating
materials.
23. Dynamic properties
Elastomers are viscoelastic materials. It means that part of the deformation is recovered
after the load is removed and part of the deformation is permanent.
depend on temperature, type frequency of loading and amplitude of deformation.
Abrasion resistance
Most rubbers have exceptionally good abrasion resistance, which is a consequence of the
ability of rubbers to creep over the irregularities of the wearing counterpart in sliding.
Buthyl and ethylene-propylene rubbers, on the other hand, have the best abrasion resistance
at elevated temperatures.
24. Manufacturing processes of elastomers
The raw rubber will be build up from
different polymers and go through
polymerization
The manufacturing process of
synthetic rubber starts with
the manufacturing raw
rubber.
26. Applications of elastomers
Elastomers have varieties of applications
Apparel, most of the time under wears
and leggings
Protective clothings
Tyres
Bushings
Mounts
gaskets
latex products
footwear
adhesives