Polymerisation
A natural and artificial substance that are made from combination of small
simple molecules of same of different types in a regular manner to form a
large or long chain molecule is known as polymer , The process of formation
of polymer by combination of monomer is called polymerisation. The simple
molecules which combine together are called monomers
nM
-(M)-n
e.g
According to source , the polymer are natural or synthetic polymer .The
polymer obtained from nature ( plants and animals) are natural polymer .eg
starch cellulose protein natural rubber.
The polymer which are prepared in the laboratory are called synthetic polymer
.They are also called man made polymer.eg polyethene, nylon Bakelite,
Terylene, synthetic rubber .etc
Living organism are mostly composed of polymerised amino acid, protein,
nucleic acid ( DNA and RNA) and other biopolymers. The most powerful
computer i.e our brain is mostly just a complex polymeric material socking in
the salty water. Synthetic polymer are commercially produced on a large scale
and have a wide range properties and uses.
Polymer on the basis on nature of monomer are classified into homopolymer
and co polymer. The polymer formed from one type of monomer is called
homopolymer .For example, polyethene is homopolymer of ethane. Other
PVC, Teflon, polystyrene etc. The polymer formed from two or more different
monomer is called co-polymer. Or mixed polymer. Eg. Bakelite. Terylene etc.
Types of polymer:
a. Organic polymer
b. Inorganic polymer.
Organic polymer: polymer are macromolecules built by the linking together of
large number of small molecules called monomer. If the main chain is made up
of carbon atom it is called organic polymer.
The number of repeating units ( n) in a chain formed in polymer is known as
the degree of polymerisation. On the basis of mode of polymerisation organic
polymer is divided into
a. Addition polymerisation:
The polymer formed by repeated addition of monomer unit without
removal of any bi- product molecule is called addition polymerisation.
Monomeric unit contains one or more double bond and addition
polymerisation takes place by application of heat, light, or catalyst for
breaking down the bond of monomer. The molecular mass of polymer is
exact multiple Teflon, PVC, etc. are the example of addition
polymerisation. The monomers adding maybe the same type or
different. Generally, alkenes, alkadienes and their derivatives are
used. In this mode, lengthening of chains occurs as a result of the
formation of either free radicals or ionic species.
Mechanism :
Free Radical Mechanism
Many of the monomers like alkenes or dienes and their derivatives are
polymerized in the presence of free radicals. In the polymerization of
ethene to polythene by heating or exposing to light by using a small
amount of benzoyl peroxide initiator. The phenyl free radical formed by
peroxide is added to the ethene double bond and hence formed a new
larger free radical
It is called a chain initiation step. This newly formed radical will reacts
with another molecule of ethene to form another new free radical and so
on. This repeated formation of a new free radical is called chain
propagation. Finally, at some stage, the polymerized product will be
formed and this step is called a chain termination step. The steps are
given below.
Characteristics
Many monomers bond together via rearrangement of bonds
There is no loss of atoms or molecules when monomers bind
Most of the common addition polymers are formed from unsaturated monomers
(usually having a double bond)
Addition polymers are generally chemically inert. This is as a result of very
strong C-C and C-H bonds and lack of polarisation within many addition
polymers. For this reason they are non-biodegradable and hard to recycle.
Condensation polymerisation:
The process of formation polymer formed by combination of two or more
same or different types monomer with the elimination of simple
molecules like H2O HCl ,NH3 methanol etc as a by-product . Is
condensation polymerisation. Or a form of a step-growth polymerization
Characteristics:
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The molecules should have one or two functional groups (like
alcohol, amine, or carboxylic acid groups).
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The reaction occurs between two similar or different functional
groups or monomers. Smaller molecules usually combine to form
larger molecules.
Mixed properties of both the molecules and functional groups are
taken into consideration.
A linear polymer is obtained as the condensation product when
both functional groups are di-functional.
When one of the functional groups is tri- or tetra-functional, the
polymer formed will be a cross-linked polymer having a threedimensional network.
The average molecular weight decreases when monomers are
added with one reactive group.
Formation nylon 66
Plastic polymer: Plastic polymer is an organic material of high molecular
weight which can be moulded into any desired form when subjected to
heat and pressure in the presence of catalyst. They are thermoplastics
and thermosetting plastics
Thermoplastic polymers: These are the liner or slightly changed to
branched polymers and are obtained by addition polymerisation that
can be softened on continues heating and hardening on cooling.
Their intermolecular force between the chains can be broken easily
on heating. They are usually soft weak and less brittle. Polyvinyl,
polystyrene etc are examples of thermoplastic polymers.
Thermosetting polymers: They are formed by condensation
polymerisation and have 3D structure. The cross link and bond
retains their strength on heating. So they comes under the category
of heavily branched or cross-linked, which can mould on heating and
can’t regain the original shape. So these cannot be reused. Bakelite
is an example.
Preparation properties and uses of
1. Polyethene: It is addition polymer formed by repeating of ethene
monomer at high temperature in the presence of Zeigler natta
catalyst.
It is insoluble in acid, alkali, and organic solvent .It is used to make
bag, bottles, containers, pipe electric insulator. It is non-polar
polymer and polymeric chain are interact with each other by
Vander Waal’s force. As a chains are heavily branched not straight
these intermolecular forces are relatively weak for such large
molecules .polymeric chains are not pack neatly together. When
polymeric chains are unbranched and are packed closely together
it results high density polyethene.
Low-Density Polyethene
This type of polymers is obtained by the polymerization of ethene under
the condition of high pressure of 1000 to 2000 atmospheres at 350 to
520 k temperature in the presence of dioxygen or peroxide initiator as a
catalyst in a very small amount.
It is formed through the free radical addition. It is chemically inert in
nature and tough but flexible. It is a poor conductor of electricity. LDP is
used for the manufacture of toys, squeeze bottles and flexible pipes.
High-Density Polyethene
Prepared by the polymerization addition of ethene in the presence of a
catalyst like triethyl aluminium and titanium tetrachloride ( Zeigler natta
catalyst). The process takes place in a hydrocarbon solvent, in a
condition of low pressure of 3 to 4 atmospheres and 343 k temperature.
Like the LDP it is chemically inert but comparatively tougher and harder.
It is used for the manufacture of buckets, dustbins, pipes, etc.
Polytetrafluoroethylene (Teflon)
It is also known as Teflon and is manufactured by heating of
tetrafluoroethene with a free radical addition mechanism at high
pressure in the presence of benzoyl peroxide as a catalyst.. Teflon is
chemically inert and less corrosive due to the resistive property against
the corrosive agents. It is resistant towards heat , actions of chemicals
like acid, base. It is bad conductor of electricity. It is used for gaskets
seals, valve, bearing, and not stick surface coated utensils.
Poly vinyl chloride: The monomer unit of PVC is vinyl chloride
( chloroethene).It is addition polymer . It is prepared by heating vinyl
chloride in an inert solvent in the presence of peroxide, benzoyl
peroxide.
It is hard and rigid but addition of phthalate ester make it soft.
PVC has a linear structure
It is generally transparent, odourless, inflammable, resistant to light, air,
inorganic acid, alkali, and soluble in hot chlorinated hydrocarbon.
Unplasticized PVC It is used for making tank lining, safety helmets, and tyres
for cycle and motorcycle, wastepipe, superior chemical resistance in the place
of non- ferrous metal
Plasticized PVC is used for making raincoat, handbags, toys, artificial flooring,
insulating material, electrical goods,
Nylon-6,6
It is prepared by the method of condensation polymerisation process.
Hexamethylenediamine combines with adipic acid to give the
macromolecule Nylon-6,6 with the elimination of water molecule.
• It has long molecular chains resulting in more hydrogen
bonds, creating chemical springs and making it very
resilient.
• It is an amorphous solid so it has a large elastic property
and is slightly soluble in boiling water.
• It is very stable in nature.
• It is very difficult to dye but once it is dyed it has a high
colourfastness and is less susceptible to fading.
• Its chemical properties does not allow it to be affected by
solvents such as water, alcohol etc. .
• Nylon 6, 6 is a light material, it is used in parachutes.
• Nylon 6, 6 is waterproof in nature so it is also used to
make swimwear.
• Nylon 6, 6 having a high melting point make it more
resistant to heat and friction so it is suitable to be used in
airports, offices and other places which are more liable to
wear and tear.
• It being waterproof in nature is used to make machine
parts.
• It is also used in the following like airbags, carpets, and
ropes. Hoses etc.
• It is used for making bristles of brushes
• It is blended with wool to make socks and sweaters
• For manufacturing automobiles tubes
Nylon 1, 1
Nylon 11 is produced by polymerisation of 11-aminoundecanoic acid at ~
215 °C and has commercial application in both fibre and engineering
plastic end uses.
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Nylon 11
Nylon 6
Nylon 6 is produced by ring-opening chain growth polymerization of
caprolactam in the presence of water vapour and an acid catalyst at the
high temperature. After removal of water and acid, the nylon 6 is melt
spun at 250°–260°C into fibres.
Terylene (Polyester)
It is prepared by the condensation polymerization of ethylene glycol and
Terephthalic acid with removal of water. This reaction is performed at
temperature 420-460 K in the presence of a catalyst such as zinc
acetate and antimony trioxide. Terylene is also called Dacron,
Terylene is also called polyester.
• Terylene is a very strong fibre and will suffer very little loss in strength
when wet.
• It is elastic in nature and possess the property of resist creasing.
• Terylene is mainly used in making plastic bottles and clothing
• It is also used for making-Terylene fibre is used as polyester tricot knit
as a fashion garments fabric, for the laundry usage as an automatic
clothing vacuum packaging machine.
Polyurethane
Polyurethanes are one of the most versatile plastic materials. Polyurethanes are
formed by reacting a polyol (an alcohol with more than two reactive hydroxyl
groups per molecule) with a di-isocyanate or a polymeric isocyanate in the
presence of suitable catalysts and additives. Because a variety of diisocyanates
and a wide range of polyols can be used to produce polyurethane, a broad
spectrum of materials can be produced to meet the needs of specific
applications.
Applications of Polyurethane
Some important applications of polyurethane are listed below.
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The primary application of polyurethane is in the production of
foams. These foams are used in a variety of materials such as
domestic furniture, and refrigerator sheets.
Polyurethane is also used in some garments.
Polyurethane mouldings are also used in columns and door
frames..
The low-density foams of polyurethane which exhibit flexibility are
widely used in mattresses and other forms of bedding. They are
also used in automobile seats and upholstery.
Flexible polyurethane is also used in the manufacture of partially
elastic straps and bands.
The low-density elastomers of polyurethane are widely used in the
footwear industry.
Another notable application of polyurethane is in the manufacture
of bathroom and kitchen sponges. It is also used in seat cushions
and couches.
Bakelite
Bakelite is a polymer made up of the monomers phenol and
formaldehyde. This phenol-formaldehyde resin is a thermosetting
polymer. Bakelite is the commercial name for the polymer obtained by
the polymerization of phenol and formaldehyde.. The condensation
reaction of the two reactants in a controlled acidic or basic medium
results in the formation of ortho and para hydroxymethyl phenols and
their derivatives.
In second step small amount of hexa-methylene tetra-amine is added
at the steam temperature and the chain length is increased and three
dimensional resin is formed which crosslinks the structure. Thus
soluble novolac gets converted into insoluble Bakelite
These phenolic resin are rigid hard and water resistant they are
resistant to organic solvent, non-oxidising acid but are susceptible to
alkali. They usually producing insulating properties. Melting point and
solubility changes with molecular mass
• It can be used in manufacturing electrical switches and machine
parts of electrical systems.
• . Phenolic resins are also extensively used as adhesives and
binding agents.
• They are further used for protective purposes as well as in the
coating industry.
• Bakelite has been used for making the handles of a variety of
utensils
• . It is one of the most common and important polymers that are
used to make different parts of many objects.
Inorganic Polymer:
Inorganic polymer are macro molecules having skeleton made up of
atoms (like Si, P, S, N etc.,) other than carbon. Elements in these polymer
are joined together by single or double covalent bond. Examples:
Silicones, polyphosphazines, polythiazyl , chalcogenide glass, etc. Most
of the inorganic polymer contains two different elements of alternate
structure but side chain contains carbon atom with other elements like
alkyl or phenyl group etc. Broadly speaking, inorganic polymers are
hybrid systems that have advantages of metals, ceramics and organic
polymers, while at the same time have minimum disadvantages.
Polyphosphazine
Characteristics of inorganic polymers
• They have higher softening point as compared to organic polymers
• . Inorganic polymers with cross-links are usually stiffer ( not flexible ),
harder and more brittle than organic polymers. The segments between the
cross links are usually shorter; therefore, they do not allow intercalation
with solvent molecules
• These polymers have highly polar repeat units, so dissolve in polar
solvents
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They possess lesser tensile strength as compared to organic polymers.
• They are solid or liquid with high density and are generally transparent.
• They don’t burn except sulphur based polymer which burn at above 6000c
• Polythiazyl is electrically conducting polymer.
On the basis of nature of elements present in monomer, they are classified as
Polyphosphazine
Sulphur based polymer
Silicones
Silicones
Silicones are inorganic polymers consisting of Silicon –Oxygen alternate
structure which has organic radical as side chain attached with silicon atom in
the skeleton. Silicones may be cyclic, linear or cross linked polymer. They can
be obtained in the form of oils, rubbers, or resin depending upon the extent of
polymerisation. It depends on reaction condition and nature of alkyl group. The
stating material for the manufacture of silicones are alkyl or aryl substituted
chlorosilane.
They have a wide variety of commercial uses as fluids, oils, elastomers
(rubbers), and resin. They are now produced on a larger scale than any other
group of organometallic compounds. Silicones are fairly expensive but have
many desirable properties
Where R is alkyl group (CH3) or phenyl group ( C6H5)
Preparation of Silicones:
For the preparation of silicones, firstly silicon is reacted with alkyl halide
or silicon halide with Grignard reagent to obtain mixture of different
organo-silicon halide. And then different organo-silicon halide are
separated by fractional distillation. Finally different silicones are prepared
by careful controlled hydrolysis followed by polymerisation.
Si + CH3Cl→ CH3SiCl3, or (CH3)2SiCl2
SiCl4+ CH3MgBr→ (CH3)3SiCl, or
(CH3)4Si + MgCl2
Mono-methyl silicon tri-chloride (CH3SiCl3,)
The hydrolysis of methyl tri chlorosilane gives a very complex crosslinked polymer. The ratio of CH3SiCl3 in the starting mixture will
determine the amount of cross linking in the polymer.
Di-methyl silicon di-chloride (CH3)2SiCl2,)
Di-methyl silicon di-chloride (CH3)2SiCl2, on hydrolysis followed by
polymerisation produce very long linear chain of dimethyl silicon polymer or
silicon rubber As compared to organic rubber, silicone rubber has Si-O bond in
its structure, and hence, it has better:
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Heat resistance
Chemical stability
Electrical insulation
Abrasion resistance
Weatherability as well as Ozone resistance
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It also form cyclic trimer or tetramer.
Trimethylsilicon chloride (CH3)3Cl is also known as chain stopper. It is
used to limit the chain length
(CH3)3Cl + H2O→ (CH3)3OH→
Hexamethyldisiloxane
Tetramethyl silicon (CH3)4Si) functional group less that is why it does not
form any polymer or does not polymerise
Properties of silicones
. Depending on the proportion of various alkyl silicon halides used during the
preparation, silicones may be liquid, viscous liquids, semi-solid (grease), rubber
and solids.
ii. Because of the oxygen-silicon bonds they exhibit outstanding stability at
high temperature than organic polymer.
iii. Because of the presence of alkyl groups surrounding the silicon atoms
makes the molecule hydrophobic and gives water repelling tendency of
silicones.
iv. Their physical properties are less affected by the change of temperatures,
oxygen, ozone, UV radiations, most chemicals.
v. They are non-toxic.
They have high gas permeability so it cannot be used where gas tight seal is
necessary.
Uses
Straight chain polymers are used as water repellent for treating buildings,
glassware and fabrics. They are also included in car and shoe polish.
Silicones fluids are nontoxic and have low surface tension; therefore, addition
of a few parts per million of it greatly reduces foaming in sewage disposal,
textile dyeing, beer making and frothing of cooking oil in making potato crisps
and chips.
Silicone oils are used as dielectric insulating material in high voltage
transformers. They are also used in hydraulics fluid
Silicone greases are made by mixing silicones oil with lithium stearate soaps
and are used as lubricants where high and low temperatures are encountered.
They are used in making tyres of aircraft and racing cars, as sealing material in
search lights and aircraft engines, in making lubricants, paints and protective
coatings.
For making boots for the use at very low temperature (Neil Armstrong used
silicones rubber boots while walking on the moon)
They are used in making high voltage insulator, making printed circuit boards
and to encapsulate integrated circuits chips and resistors.
They are also used as non-stick coatings for pans, moulds for making car tyres
etc.
Different Types of silicones and their uses
1.Liquid silicones/ silicone oil
They are generally dimethyl silicones of lower molecular weight silicones. They
possess low surface tension, very small change in viscosity with temperature
and great wetting power for material.
Uses
They are use as high temperature lubricant.
Use as antifoaming agent, water repellent, finishing for leather and textile.
Use in cosmetics and polishes
Used as hydraulic fluid.
Used as dielectric insulating material in high voltage transfermor.
2. Silicone grease
They are modified form of silicone oils which are prepared by mixing dimethyl
silicon with filler like silica, carbon black. Lithium soap, wood flour, china clay
etc.
Uses
They are particularly used in the form of lubricant in situation where very high
and very low temperature are encountered.
3. Solid silicon resin Silicone resins are highly cross linked rigid polymer rather
like Bakelite .They are made by dissolving a mixture of dimethyl silicon
dichloride( bifunctional) mono -methyl silicon tri-chloride( trifunctional) in
toluene and hydrolysing with water. The party hydrolysed product is washed to
remove HCl then it is shaped or moulded.
They are thermosetting polymer with outstanding heat resistant.
They are good electrical insulator
They are chemically stable
They are used for making high temperature insulating foams for making high
voltage insulator.
4. Silicone rubber:
Silicone rubber is a durable & highly-resistant elastomer (rubber-like material)
composed of silicone (polymer) containing silicon together with other molecule
like carbon, hydrogen and oxygen. Its structure always comprises siloxane
backbone (silicon-oxygen chain) and an organic moiety bound to the silicon.
The properties of silicone rubber can vary greatly depending on the:
Organic groups (methyl, vinyl, phenyl, or other groups) and Chemical structure
As compared to organic rubber, silicone rubber has Si-O bond in its structure,
and hence, it has better: Heat resistance, chemical, stability, Electrical
insulation Abrasion resistance Weatherability as well as Ozone resistance
Silicone rubbers can withstand temperature ranging from -50°C to 350°C .Parts
made of silicone rubber when exposed to wind, rain and UV rays for long
periods result in virtually no change in physical properties. Unlike most organic
rubbers, silicone rubber is not affected by ozone as well. Silicon rubber are
made of long straight chain polymer ( dimethyl polysiloxane) between 60006000000 silicon units long mixed with a filler usually finally divided SiO 2 or
occasionally graphite They are usually prepared by hydrolysis of dimethyl
dichlorosilane ( CH3)2SiCl2 unit with KOH .Great care must be taken to exclude
chain blocking and cross linking.
By oxidising with a small amount of benzoyl peroxide containing curing agent
(cross linking agent) which produces the dimethyl bridge between methyl
groups of adjacent chain.
Properties
The strong Si-O chemical structure and high bond energy give Si Elastomers
their unique performance properties. Several benefits of silicone rubbers
include:
Can be used wide temperature range (-Si-O-Si- binding energy is higher than CC bonds)
Have excellent resistance to attack by oxygen, ozone and sunlight
Readily resistant to electromagnetic and particle radiation (UV, alpha, beta and
gamma rays)
Excellent non-stick and non-adhesive properties
Low toxicity
Flexible at low temperatures due to their low glass transition temperature (Tg).
Optical transparency
Good excellent insulation properties
Low chemical reactivity
High bio-compatibility
Excellent mechanical properties (high tear strength, high elongation)
Uses:
Plz see the uses of silicone polymer
Rubber:
Rubber is a material which can stretch and shrink .It is a polymer. Natural
rubber is made from white sap of some tree such as Hevea brasiliensis .Other
elastomer are synthetic rubber made by chemical process.
Natural rubber: These are the elastomers which are obtained naturally.
Natural rubber is made up of solid particles suspended in a milky white
liquid (called latex) that drips from the bark of certain tropical and
subtropical trees mainly found in countries like Brazil, India, Indonesia,
Malaysia, and Sri Lanka.
It is made by the polymerization of isoprene (2 methyl-1, 3-butadiene)
which has a chemical formula (C5H8) n and it is known as cis- 1, 4polyisoprene. They are made by loosely joining the monomers of
isoprene (C5H8) in the form of a long tangled chain.
CH2=C (CH3) CH=CH2
- (CH2-C (CH3) = CH-CH2 -)
2 methyl-1, 3-butadiene
polyisoprene
Processing of natural rubber:
Rubber tapping – The milky white liquid latex which contains 25-45% of
rubber is collected from the rubber trees in a cup by making a slight Vcut on the tree bark. The collected latex is washed, filtered and reacted
with acids to congeal the rubber particles. A grown tree continues to
yield for as long as 40 years about 3-6 pound every year. The flow of
latex from the cut diminishes with time so removal of another thin layer
of bark is known as taping.
Latex is treated in two ways to obtain rubber goods.
The crude rubber is coagulated from it by acid or heat and then
processed
The latex itself is mixed with appropriate compounding material and then
precipitated directly from solution in the to be used
The latex of rubber is an aqueous dispersion of rubber containing 2540% rubber hydrocarbon stabilised by small quantity of protein material
(about 2%).The rubber droplets are quite small, the emulsion may be
broken by the action of enzymes or by addition of coagulating agent.
Generally small amount of ammonia is added as a preservative to the
latex collected. The latex is then coagulated by the addition of 5%
solution of acetic acid or 90% formic acid or potassium alum are also
added as coagulants .The coagulum is washed and dried then it is
subjected to any of the following process
Crepe rubber: It is prepared by adding small amount of sodium
bisulphite to bleach the rubber and the coagulum is then rolled out into
sheet of about 1mm thickness and dried in air at about 500c
Smoked rubber: It is made by eliminating the bleaching with sodium
sulphite and rolling the coagulum into somewhat thicker sheet .These
are then dried in smokehouse at 500c in the smoke from burning wood or
coconut shells. Crude rubber does not have all desirable properties, It
becomes soft and stick in hot summer while in cold weather it becomes
hard and brittle. Both of these properties are harmful for many
application .However its properties can be substantially improved by
addition of suitable material.
Mastication – The rubber obtained from the tapping process is still not
ready to be used. When it is cold it is very brittle in nature, it becomes
very gluey when subjected to severe mechanical working. This process
is called mastication. To remove the brittle nature and strong odour of
the rubber, it is allowed to pass through the rollers and is pressed to
make it softer and flexible to work. This process is repeated based on
the properties that are required for the rubber. In this process, extra
chemical ingredients are also added to enhance the properties of rubber.
Mastication is accompanied by marked decrease in molecular weight.
Oxidative degradation is an important factor in mastication. Since the
decrease in viscosity, and other change in properties do not take place if
rubber is masticated in the absence of oxygen .After mastication is
complete, corresponding ingredients are added and rubber mix is
prepared for vulcanisation process.
Calendaring is a process which is mainly performed to provide shape to
the rubber using rollers (after proper mixing of the chemical ingredients).
The final product obtained is then extruded to make hollow tubes by
passing them through specially designed holes in an extrusion machine.
Vulcanization: The natural rubber has many drawbacks while using for
different purposes
They have plastic nature i.e becomes soft at high temperature so it
cannot be used at high temperature.
It is too weak having tensile strength 200kg/cm3
It has larger water absorption capacity
It is not resistance to non-polar solvent
It is easily attacked by oxidising agent like HNO3, H2SO4
When stretched strongly it gets permanently deformed
To remove the above mention properties of natural rubber and hence to
enhance all these properties like tensile strength, elasticity , and
resistance to swelling sulphur is added to the rubber and it is heated at
a temperature ranging from 373 K to 415 K. This process is known as
vulcanization.
The sulphur combines chemically at the double bond in the rubber
molecules bringing about excellent change in its properties like
resistance to change in temperature, increased elasticity, tensile
strength, durability, and chemical resistance. Vulcanisation is an
irreversible process which do not melt on heating so they are placed
away from the class of thermoplastic material which is fundamental
difference between rubber and thermoplastic.
Vulcanisation brings about stiffening (making rigid) of rubber by coordinating
and restricting the intermolecular movement of rubber springs. This id due to
chemical combination of the sulphur at double bonds of different rubber
springs and providing cross linking between the chains. The stiffness of
vulcanised rubber depends on the amount of sulphur added.
The vulcanisation can be carried out in several ways
The article to be vulcanised are heated with steam under pressure.
The article is immersed in hot water under pressure
By heating articles in air or in carbon dioxide
By passing steam directly into article.
By vulcanizing the articles in the mould in which it is shaped.
Condition for vulcanised rubber:
The temperature used in 1100-1400c
The curing time is few minutes to three hours .Over cured decrease
stretch and tensile strength where under cured is too soft with excessive
stretch but lower tensile strength.
The amount of sulphur used for ordinary soft vulcanized rubber is 1-5%
whereas for hard rubber 40-50% of the sulphur.
Other volcanizing agents are S2Cl2, Benzoyl chloride, tri-nitrobenzene,
alkyl phenol
Uses of Rubber
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It is used for lining chutes, bins and industrial mixers. Because of
its water-proof and resilient property, it can be made into a good
insulator.
In the clothing industry, it can be used as wetsuits and expandable
clothes such as gym and cycling shorts etc.
Rubbers are also used for flooring purposes it gives padding and
prevents fatigue along with being waterproof and slip-resistant.
In the automobile industry, its use can be witnessed in tires,
padding in brakes, airbags, seats, and roof etc.