NATURAL RUBBER

HAFIS PS6 PS&E

INTRODUCTION 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.

STRUCTURE

SOURCES 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)

RUBBER TAPPING

Rubber tapping is the process by which the latex is collected from a rubber tree. An incision is made in the tree's bark, which cuts through the latex vessels, from which the product then flowsis the process by which the latex is collected from a rubber tree. An incision is made in the tree's bark, which cuts through the latex vessels, from which the product then flows

PROPERTIES 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

PROCESSING OF NR Production of rubber is followed by processing into final

products consists of :

CompoundingMixingShapingVulcanizing.

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:

ExtrusionCalenderingCoatingMolding 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 BASED COMPOSITES NR Composites and Nanocomposites based on

Conventional Fillers

Carbon Black Silica Carbon Nanotubes Graphene

NR Composites and Nanocomposites Based on Natural Fillers

Glass, rayon, aramid, asbestos and cellulose as fibres Starch-Reinforced 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.

EXAMPLE 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.

APPLICATIONS OF NR BASED COMPOSITES 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.

REFERENCES http://www.allsealsinc.com/Natural_Rubber-popup.ht

ml

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