Rubbers
Natural Synthetic
Rubbers Rubbers
Isoprene units (cis 1,4-)
Butadiene Styrene Nitrile Isoprene
Rubbers Butadiene Rubbers Rubbers (IR)
(BR) Rubbers(SBR) (NBR)
Polychloroprene (CR)
Neoprene Rubber (NR) Butyl Rubber
(BR)
Definitions
all product from rubber are made
" In beginning produced from materials
from natural rubber that
natural rubber tree called latex.
from
rubber_are produced from reactions of
Synthetic monomer
materials called
low molecular weight
molecule called polymer
chain
to produced long
produced by mix raw rubber
Elastic properties_are
additives
during rubber
with specific
compounding
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Definitions
When rubber was heated the chemical reactions occur
callvulcanization (crosslinking occur) or curing.
Process were rubber molecules were tied together at
specific place called crosslinks
Elastomer are elastic materials that can deformed
when forced being applied and back to the original
shape when release the forced.
The words elastomer comes from 'elastic polymer'.
Elastomers
1. The material must be macromolecular (long chain polymers).
2. Must be amorphous (at least at low strains).
3. Tg must be below the operating temperature.
4. Must have low secondary forces between molecules
(crosslinking bonds) so as to obtain the requisite flexibility.
Polyisoprene (Natural Rubber)
Raw material extracted from trees
Poly-cis-isoprene (40%) in water Me Me
-Natural rubber in unfilled form
"Very large elastic deformations CiS trans
"Very high resilience,
" Resistance to cold flow
cis polyisoprene
Resistance to abrasion, wear, and fatigue.
T, = 28°C, T, = -70°C
trans polyisoprene (gutta percha)
Natural rubber does not have good intrinsic T, = 68°C, T, = -70°C
resistance to sunlight, oxygen, ozone, heat
aging, oils, or fuels (reactive double bond).
Vulcanizes with 4% sulfur
Vulcanization can be defined as the curingof
elastomers, with the terms 'vulcanization' and
curing' sometimes used interchangeably in
this context. It works by formingcross-links
between sections of the polymer chain which
results in increased rigidity and durability, as
well as other changes in the mechanical and
electrical properties of the material, 2]
Vulcanization, in common with the curing of
other thermosetting polymers, is generaly
irreversible.
The word was suggested by William
Brockedon (a friend of Thomas Hancock who
attained the British patent for the process)
coming from the god Vulcan who was
associated with heat and sulfur in
volcanoes. l3)
In contrast with thermoplastic processes (the
melt-freeze process that characterize the
behaviour of most modern polymers),
vulcanization, in common with the curing of
other thermosetting polymers, is generally
irreversible. Five types of curing systems are
in common use:
1. Sulfur systems
2. Peroxides
3. Metallic oxides
4. Acetoxysilane
5. Urethane crosslinkers
CH3 ÇH3
-CH,-=ECH-CH,-CH,-CCH-CH,
+
-CH,-ÇECH-CH,-CH,CCH-CH,
CH3 H,
+
Sulphur
CH, CHg
CH,- -çH-CH-CH,-ÇH-CHy
S
Sulphur cross linkage
S
CH,-Ç -H-CH-CH,-¢ -H-CH,
H, CH3
