RUBBERRUBBERRUBBERRUBBER

What is rubberWhat is rubber

Natural rubber is obtained from Natural rubber is obtained from rubber trees called rubber trees called Hevea brasiliensisHevea brasiliensis which was first brought to Malaysia in which was first brought to Malaysia in year 1887.year 1887.

A natural rubber is a natural polymer.A natural rubber is a natural polymer.

Natural polymer is a polymer that Natural polymer is a polymer that

exists as naturally.exists as naturally.

Examples of natural Examples of natural polymerpolymer

Natural Natural polymerpolymer

MonomerMonomer

Natural rubberNatural rubber IsopreneIsoprene

StarchStarch GlucoseGlucose

CelluloseCellulose GlucoseGlucose

ProteinProtein Amino acidAmino acid

Composition of RubberComposition of Rubber Natural rubber is obtained from latex .Natural rubber is obtained from latex .

Latex is a while milk-like fluid. Latex is a while milk-like fluid.

Natural rubber is actually poly(isoprene).Natural rubber is actually poly(isoprene).

Its monomer is Its monomer is 2-Methylbuta-1,3- diene or Isoprene2-Methylbuta-1,3- diene or Isoprene..

Each isoprene molecule contains two pairs of Each isoprene molecule contains two pairs of double bonds.double bonds.

Thus, the isoprene molecule undergo addition Thus, the isoprene molecule undergo addition polymerization to produce a long-chain molecule polymerization to produce a long-chain molecule called poly( isoprene).called poly( isoprene).

The value of The value of monomer is about 10,000.monomer is about 10,000.

Structure of Isoprene/ Structure of Isoprene/ monomermonomer

CHCH33

HH22C = C – CH = CHC = C – CH = CH22

Conclusion, composition of rubber:

Rubber consist of carbon and hydrogen atoms

When isoprene form When isoprene form polymerpolymer

CHCH33

HH22C - C =CH - CHC - C =CH - CH22[[

[[or

PROCESSING OF PROCESSING OF RUBBERRUBBER

Coagulation process of Coagulation process of latexlatex

Latex needs to be turned into a solid for it to Latex needs to be turned into a solid for it to be used in daily purposes. be used in daily purposes.

This process is known as coagulation.This process is known as coagulation.

When latex is exposed to air, it will slowly When latex is exposed to air, it will slowly coagulate to form a white soft solid.coagulate to form a white soft solid.

Latex is a colloid. It consists of rubber Latex is a colloid. It consists of rubber particles dispersed in water. particles dispersed in water.

Each rubber particle is made up of many Each rubber particle is made up of many long-chain rubber molecules enclosed by a long-chain rubber molecules enclosed by a protein- like membrane which is negatively protein- like membrane which is negatively charged.charged.

Coagulation processCoagulation process The coagulation of latex will also occur when The coagulation of latex will also occur when

it is exposed to air. This is because the it is exposed to air. This is because the bacteria from the air enter the latex.bacteria from the air enter the latex.

The growth and spread of bacteria produce The growth and spread of bacteria produce lactic acid that causes the coagulation of lactic acid that causes the coagulation of latex. latex.

Due to the Due to the slowslow bacterial action, the bacterial action, the coagulation of latex a coagulation of latex a longer timelonger time to occur. to occur.

However, latex can be preserved in the liquid However, latex can be preserved in the liquid state if ammonia, NHstate if ammonia, NH33 solution is added. solution is added.

Ammonia solution contains bacteria. Hence Ammonia solution contains bacteria. Hence the rubber particles remain negatively the rubber particles remain negatively charged and the coagulation is prevented.charged and the coagulation is prevented.

PROPERTIES OF PROPERTIES OF RUBBERRUBBER

Properties of natural Properties of natural rubberrubber

Natural rubber exists as a white solid at Natural rubber exists as a white solid at room temperature. The presence of double room temperature. The presence of double bonds in the polymer greatly affects the bonds in the polymer greatly affects the properties of natural rubber. properties of natural rubber.

Natural rubber has the following Natural rubber has the following propertiesproperties..i. Elasticity decreases over time.i. Elasticity decreases over time.ii. Softii. Softiii. Sensitive to heat.iii. Sensitive to heat.iv. Easily oxidized by airiv. Easily oxidized by airv. Insoluble in water.v. Insoluble in water.vi. Soluble in organic solvent.vi. Soluble in organic solvent.

USES OF RUBBERUSES OF RUBBER

Uses of rubberUses of rubber11 Mixture of latex cement and Mixture of latex cement and

rubberised bitumen for tarring rubberised bitumen for tarring roads.roads.

22 Insulators for electrical Insulators for electrical appliances and cablesappliances and cables

33 Friction enhancers such as shoe Friction enhancers such as shoe soles and door stoppersoles and door stopper

44 Rubber hoses, rubber caps and Rubber hoses, rubber caps and rubber bandsrubber bands

55 GlovesGloves

Uses of rubberUses of rubber Natural rubber is processed to become Natural rubber is processed to become

vulcanised rubber which has better vulcanised rubber which has better properties- more elastic and more stable to properties- more elastic and more stable to heat and oxidation.heat and oxidation.

Vulcanised rubber is use to make tyres, Vulcanised rubber is use to make tyres, gloves and tubbinggloves and tubbing

Carbon is added to vulcanised rubber in Carbon is added to vulcanised rubber in tyres to make them tougher while tyres to make them tougher while maintaining their elasticity.maintaining their elasticity.

Uses of rubberUses of rubber The use of rubber is further extended by combaining The use of rubber is further extended by combaining

natural rubber with other materials such as synthetic natural rubber with other materials such as synthetic rubber and plastics.rubber and plastics.

Carbon is added to vulcanised natural rubber in tyres to Carbon is added to vulcanised natural rubber in tyres to make them tougher while maintaining their elasticity.make them tougher while maintaining their elasticity.

Even though natural rubber is facing stiff competition Even though natural rubber is facing stiff competition from synthetic rubber, there are many uses whereby from synthetic rubber, there are many uses whereby there are no better alternative. there are no better alternative.

For example, only natural rubber can take the For example, only natural rubber can take the tremendous stress, strength and heat produced during tremendous stress, strength and heat produced during landing and taking off of aircraft. Thus aircraft tyres landing and taking off of aircraft. Thus aircraft tyres must be made from natural rubber.must be made from natural rubber.

Vulcanization of rubberVulcanization of rubber What is vulcanization process?What is vulcanization process?

In this process, about 1-3% by weight of In this process, about 1-3% by weight of sulphur is added to raw rubber and the sulphur is added to raw rubber and the mixture is carefully heated.mixture is carefully heated.

Sulphur atoms form cross-links between Sulphur atoms form cross-links between adjacent chains of rubber polymer at the adjacent chains of rubber polymer at the carbon-carbon double bonds.carbon-carbon double bonds.

The number of sulphur atoms in the cross-The number of sulphur atoms in the cross-links is usually one to four.links is usually one to four.

Vulcanization or rubberVulcanization or rubber The cross-linking improved the properties of raw The cross-linking improved the properties of raw

rubber such as:rubber such as:

i. More tougher material that is more resistant to i. More tougher material that is more resistant to oxidation.oxidation.

ii. More elastic as the cross-linked chains can ii. More elastic as the cross-linked chains can revert revert

back to their original positions.back to their original positions.

iii. More heat resistant which means the iii. More heat resistant which means the vulcanized vulcanized

rubber is less soft and sticky on warming.rubber is less soft and sticky on warming.

iv. Less soluble in organic solvent.iv. Less soluble in organic solvent.

TO THINK !!!TO THINK !!! Name the monomer of rubber?

Draw the structural formula for the monomer of rubber?

What is the types of reaction that joins the monomers together to form natural rubber?

Briefly describe how coagulation of latex takes place when an acid is added?

State three properties in which vulcanised rubber is better than unvulcanised rubber?