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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.

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)

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.

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.

Physical properties of NR.

Chemical resistance of NR

Mechanical properties of NR

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.

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

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

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.

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

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.

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.

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

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.

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.

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.

http://www.allsealsinc.com/Natural_Rubber-popup.html

http://www.tutorvista.com/content/chemistry/chemistry-ii/carbon-compounds/natural-rubber.php

http://rubberboard.org.in/ManageCultivation.asp?Id=196

Natural Rubber Materials: Volume 2: Composites and Nanocomposites edited by Sabu Thomas, Chin Han Chan, Laly A Pothen, Jithin Joy, Hanna Maria

Fundamentals of Modern Manufacturing: Materials, Processes, and system

Mikell P. Groover