2. Rubber is a polymer, which is a word that is derived from the Greek
meaning “many parts”.
Natural rubber is a naturally occurring polymer obtained from the latex of
rubber trees.
Natural rubber (NR) is also known as cis-1,4-poly(isoprene).
Natural rubber is found in the latex that comes from the rubber trees.
It is collected in a cup mounted on each tree, by slashing the bark to
reach the latex vessels.
The liquid is 30-40% rubber.
3.
4. The commercial source of natural rubber latex is the
Para rubber tree (Hevea brasiliensis).
Other plants containing latex include:
Gutta-percha (Palaquium gutta)
Rubber fig (Ficus elastica)
Panama rubber tree (Castilla elastica)
Spurges (Euphorbia spp.)
Common dandelion (Taraxacum officinale)
Russian dandelion (Taraxacum kok-saghyz)
5. The physical and chemical properties of the rubber are
influenced by the presence of the non-rubber
substances.
NR is a natural polymeric substance having high
molecular weight, possessing visco-elastic properties.
Natural rubber is cis-1,4-polyisoprene, i.e. a diene,
because of this, it shows all the reactions of an
unsaturated compound.
It gives addition compounds with hydrogen chloride,
halogens, ozone and several other reactants that
combine with olefins.
6. An interesting reaction of NR is its combination with
sulphur, called ‘vulcanization’.
This reaction converts the raw rubber into an elastic
material.
Vulcanized rubber possesses high tensile strength,
hardness and abrasion resistance.
Because of the unique combination of these
properties, NR finds application in the manufacture
of various types of products.
10. Production of rubber is followed by processing into final
products consists of :
Compounding
Mixing
Shaping
Vulcanizing.
Processing techniques for natural and synthetic rubbers
are virtually the same, differences being in the
chemicals used to effect vulcanization.
11. COMPOUNDING
Rubber is always compounded with additives to satisfy
the given application in terms of properties, cost, and
processability
Compounding adds chemicals for vulcanization.
Mainly used reinforcing filler used in NR is carbon
black.
Other additives include antioxidants , antiozonants
colouring pigments, plasticizers and softening oils,
blowing agents in the production of foamed rubber; and
mold-release compounds
12. MIXING
The additives must be thoroughly mixed with the base
rubber to achieve uniform dispersion of the ingredients.
A two-stage mixing process is usually employed.
In the first stage, carbon black and other non vulcanizing
additives are combined with the raw rubber.
After thorough mixing has been accomplished, and time for
cooling has been allowed, the second stage is carried out in
which the vulcanizing agents are added.
Equipment for mixing includes the Two-roll mill and internal
mixers such as the Banbury mixer
13. SHAPING
Shaping processes for rubber products can be divided
into four basic categories:
Extrusion
Calendering
Coating
Molding and Casting
VULCANIZATION
o Vulcanization is a chemical process for converting
natural rubber or related polymers into more durable
materials via the addition of sulphur or other equivalent
curatives or accelerators.
14. NR Composites and Nanocomposites based on
Conventional Fillers
NR Composites and Nanocomposites Reinforced with Carbon
Black
NR Composites and Nanocomposites Reinforced with Silica
NR Composites and Nanocomposites Based on Carbon
Nanotubes
NR Composites and Nanocomposites Based on Graphene
NR Composites and Nanocomposites Based on Natural
Fillers
Fibre-Reinforced NR Composites and Nanocomposites
(glass, rayon, aramid, asbestos and cellulose as fibres)
Starch-Reinforced NR Composites and Nanocomposites
NR Composites and Nanocomposites Reinforced with
Natural Mineral Fillers
15. NR Composites and Nanocomposites Based on Metal
or Metallic Compound Fillers
Metal nanoparticles and metallic compound powders are
most widely used in polymers to strengthen the polymers,
and improve their thermal stability and gas barrier
properties.
NR is often reinforced with various kinds of metal
nanoparticles and metallic compound powder.
NR Composites and Nanocomposites Based on Hybrid
Fillers
NR composites filled with hybrid fillers possess outstanding
mechanical properties that are not caused by only one filler.
16. Glass Fibre/NR Composite
Glass fibres are the most common of all reinforcing
synthetic fibres for polymeric matrix composites (PMCs).
The major advantages of glass fibres are high tensile
strength, low cost, high chemical resistance and excellent
insulating properties.
The disadvantages are relatively low tensile modulus and
high density, high hardness,sensitivity to abrasion during
handling which tends to decrease its tensile strength,
relatively low fatigue resistance.
Fibre-reinforced NR composites are manufactured by
various processes, the most common being extrusion,
injection moulding and compression moulding.
17. MECHANICAL PROPERTIES OF GLASS FIBRE/NR COMPOSITES
The mechanical properties of glass fibre/NR
composites strongly depend on properties of glass
fibres.
It is seen from the table that E-glass fibre has better
tensile properties than A-glass fibre.
It is expected that E-glass/NR composites will show
better tensile properties than A-glass/NR composites.
It is often observed that increase in fibre content leads
to an increase in the strength and modulus of a fibre
reinforced polymer matrix composite
18. Mechanical properties also depend on fibre
orientation.
It varies for unidirectional and non-unidirectional
arrangements and for long and short fibres also.
Strength of glass fibre/NR composites can be
improved by modification of NR and glass fibre.
Modified NR can also give higher strength and
better adhesion properties.
Modification of glass fibre helps to improve the
fibre/matrix adhesion.
19. The main use of natural rubber is in automobiles.
Sixty per cent of all rubber consumed is for automobile
tyres and tubes.
In heavy duty tyres, the major portion of the rubber
used is NR.
Uses of NR in hoses, footwear, battery boxes, foam
mattresses, balloons, toys etc., are well known.
NR now finds extensive use in soil stabilization, in
vibration absorption and in road making.
20. Non-tyre rubber items include industrial products
(for example, transmission and elevator belts,
hoses and tubes, industrial lining, and bridge
bearings)
Consumer products (like golf or football balls and
other recreational and sports goods, erasers,
footwear and other apparel)
Articles for use in the medical and health sector
(notably, condoms, catheters and surgical gloves)
Latex articles (typically condoms, gloves, threads,
adhesives, and moulded foams) could be included
in different categories in terms of end-use.
