Natural rubber is a natural polymer obtained from the latex of the rubber tree Hevea brasiliensis. It is composed of polyisoprene, which is a long chain of the monomer isoprene. Latex is a white fluid that is coagulated to form solid natural rubber through the addition of bacteria or acids that lower the pH. Vulcanization improves the properties of natural rubber by adding sulfur to form cross-links between polymer chains, making the rubber more durable and elastic.

1. RUBBERRUBBERRUBBERRUBBER

2. What is rubberWhat is rubber
 Natural rubber is obtained from rubber trees calledNatural rubber is obtained from rubber trees called
Hevea brasiliensisHevea brasiliensis which was first brought towhich was first brought to
Malaysia in year 1887.Malaysia in year 1887.
 A natural rubber is a natural polymer.A natural rubber is a natural polymer.
 Natural polymer is a polymer thatNatural polymer is a polymer that
exists as naturally.exists as naturally.

3. Examples of natural polymerExamples of natural polymer
Natural polymerNatural polymer MonomerMonomer
Natural rubberNatural rubber IsopreneIsoprene
StarchStarch GlucoseGlucose
CelluloseCellulose GlucoseGlucose
ProteinProtein Amino acidAmino acid

4. 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 isIts monomer is 2-Methylbuta-1,3- diene or Isoprene2-Methylbuta-1,3- diene or Isoprene..
 Each isoprene molecule contains two pairs of double bonds.Each isoprene molecule contains two pairs of double bonds.
 Thus, the isoprene molecule undergo addition polymerizationThus, the isoprene molecule undergo addition polymerization
to produce a long-chain molecule called poly( isoprene).to produce a long-chain molecule called poly( isoprene).
 The value ofThe value of monomer is about 10,000.monomer is about 10,000.

5. Structure of Isoprene/ monomerStructure of Isoprene/ monomer
CHCH33
HH22C = C – CH = CHC = C – CH = CH22
Conclusion, composition of rubber:
Rubber consist of carbon and hydrogen atoms

6. When isoprene form polymerWhen isoprene form polymer
CHCH33
HH22C - C =CH - CHC - C =CH - CH22
[[
[[
or

7. PROCESSING OF RUBBERPROCESSING OF RUBBER

8. Coagulation process of latexCoagulation process of latex
 Latex needs to be turned into a solid for it to be used inLatex needs to be turned into a solid for it to be used in
daily purposes.daily purposes.
 This process is known as coagulation.This process is known as coagulation.
 When latex is exposed to air, it will slowly coagulate to formWhen latex is exposed to air, it will slowly coagulate to form
a white soft solid.a white soft solid.
 Latex is a colloid. It consists of rubber particles dispersedLatex is a colloid. It consists of rubber particles dispersed
in water.in water.
 Each rubber particle is made up of many long-chain rubberEach rubber particle is made up of many long-chain rubber
molecules enclosed by a protein- like membrane which ismolecules enclosed by a protein- like membrane which is
negatively charged.negatively charged.

9. Coagulation processCoagulation process
 The coagulation of latex will also occur when it is exposedThe coagulation of latex will also occur when it is exposed
to air. This is because the bacteria from the air enter theto air. This is because the bacteria from the air enter the
latex.latex.
 The growth and spread of bacteria produce lactic acid thatThe growth and spread of bacteria produce lactic acid that
causes the coagulation of latex.causes the coagulation of latex.
 Due to theDue to the slowslow bacterial action, the coagulation of latex abacterial action, the coagulation of latex a
longer timelonger time to occur.to occur.
 However, latex can be preserved in the liquid state ifHowever, latex can be preserved in the liquid state if
ammonia, NHammonia, NH33 solution is added.solution is added.
 Ammonia solution contains bacteria. Hence the rubberAmmonia solution contains bacteria. Hence the rubber
particles remain negatively charged and the coagulation isparticles remain negatively charged and the coagulation is
prevented.prevented.

10. PROPERTIES OF RUBBERPROPERTIES OF RUBBER

11. Properties of natural rubberProperties of natural rubber
 Natural rubber exists as a white solid at room temperature.Natural rubber exists as a white solid at room temperature.
The presence of double bonds in the polymer greatly affectsThe presence of double bonds in the polymer greatly affects
the properties of natural rubber.the properties of natural rubber.
 Natural rubber has the followingNatural rubber has the following propertiesproperties..
i. Elasticity decreases over time.i. Elasticity decreases over time.
ii. Softii. Soft
iii. Sensitive to heat.iii. Sensitive to heat.
iv. Easily oxidized by airiv. Easily oxidized by air
v. Insoluble in water.v. Insoluble in water.
vi. Soluble in organic solvent.vi. Soluble in organic solvent.

12. USES OF RUBBERUSES OF RUBBER

13. Uses of rubberUses of rubber
11 Mixture of latex cement and rubberisedMixture of latex cement and rubberised
bitumen for tarring roads.bitumen for tarring roads.
22 Insulators for electrical appliances andInsulators for electrical appliances and
cablescables
33 Friction enhancers such as shoe soles andFriction enhancers such as shoe soles and
door stopperdoor stopper
44 Rubber hoses, rubber caps and rubberRubber hoses, rubber caps and rubber
bandsbands
55 GlovesGloves

14. Uses of rubberUses of rubber
 Natural rubber is processed to become vulcanised rubberNatural rubber is processed to become vulcanised rubber
which has better properties- more elastic and more stable towhich has better properties- more elastic and more stable to
heat and oxidation.heat and oxidation.
 Vulcanised rubber is use to make tyres, gloves and tubbingVulcanised rubber is use to make tyres, gloves and tubbing
 Carbon is added to vulcanised rubber in tyres to make themCarbon is added to vulcanised rubber in tyres to make them
tougher while maintaining their elasticity.tougher while maintaining their elasticity.

15. Uses of rubberUses of rubber
 The use of rubber is further extended by combainingThe use of rubber is further extended by combaining
natural rubber with other materials such as synthetic rubbernatural rubber with other materials such as synthetic rubber
and plastics.and plastics.
 Carbon is added to vulcanised natural rubber in tyres toCarbon 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 competitionEven though natural rubber is facing stiff competition
from synthetic rubber, there are many uses whereby therefrom synthetic rubber, there are many uses whereby there
are no better alternative.are no better alternative.
 For example, only natural rubber can take the tremendousFor example, only natural rubber can take the tremendous
stress, strength and heat produced during landing andstress, strength and heat produced during landing and
taking off of aircraft. Thus aircraft tyres must be made fromtaking off of aircraft. Thus aircraft tyres must be made from
natural rubber.natural rubber.

16. Vulcanization of rubberVulcanization of rubber
 What is vulcanization process?What is vulcanization process?
In this process, about 1-3% by weight of sulphur is added toIn this process, about 1-3% by weight of sulphur is added to
raw rubber and the mixture is carefully heated.raw rubber and the mixture is carefully heated.
 Sulphur atoms form cross-links between adjacent chains ofSulphur atoms form cross-links between adjacent chains of
rubber polymer at the carbon-carbon double bonds.rubber polymer at the carbon-carbon double bonds.
 The number of sulphur atoms in the cross-links is usually oneThe number of sulphur atoms in the cross-links is usually one
to four.to four.

17. Vulcanization or rubberVulcanization or rubber
 The cross-linking improved the properties of raw rubberThe cross-linking improved the properties of raw rubber
such as:such as:
i. More tougher material that is more resistant to oxidation.i. More tougher material that is more resistant to oxidation.
ii. More elastic as the cross-linked chains can revertii. More elastic as the cross-linked chains can revert
back to their original positions.back to their original positions.
iii. More heat resistant which means the vulcanizediii. More heat resistant which means the 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.

20. 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?