Polymers

Polymers
You may think of polymers as being a relatively modern
invention however naturally occurring polymers have been
used for thousands of years
– wood, rubber, cotton, wool, leather, silk,.. etc.
 Artificial polymers are, indeed, relatively recent and mostly
date from after WW-II
in many cases, the artificial material is both better and
cheaper than the natural alternative
2

A polymer is a large molecule made by linking together
repeating units of small molecules called monomers
4

General Characteristics of Polymers
 Low Density.
 Low coefficient of friction.
 Good corrosion resistance.
 Good mould ability.
 Excellent surface finish can be obtained.
 Can be produced transparent or in different colors.
 Chain length - in general, the longer the chains the stronger the polymer.
 Side groups - polar side groups give stronger attraction between polymer
chains, making the polymer stronger.
 Cross-linking - if polymer chains are linked together extensively by covalent
bonds, the polymer is harder and more difficult to melt.
 Medicine; Sports; Industry

Polymers
A macromolecule is a very large molecule consisting of repeating
units called monomers. These structural units are bound together
by covalent bonds.
A collection of macromolecules is called a polymer. For example,
polyethylene

 Polymerization of ethylene to form polyethylene
H2C CH2 -CH2CH2-CH2CH2-CH2CH2-CH2CH2-
Ethylene monomer units
ethylene
polyethylene
Polymers are prepared by polymerizing a monomer. The reaction
is called polymerization
Polymerization

Some Important Terms
 Degree of polymerization: The number of repeating units
present in a polymer is called degree of polymerization.
 “n” is called degree of polymerization. When n is large, the
polymers are called high polymers. For low values of n, less
than 10, the polymers are called oligomers.
 Tacticity: relative stereochemistry/ orientation of atoms or
groups

Classification of polymers
1. Natural and Synthetic Polymers: (Based on occurrence)
Natural polymers: wood,
cellulose,, jute, cotton, wool
etc.
Synthetic polymers: PE, PVC,
epoxy resin etc.

2. Thermoplastic and thermosetting polymers
(based on thermal behavior)
Thermoplastic polymers: The polymers that soften on heating
and which can be converted into any shape on cooling are
called thermoplastics. The process of heating, reshaping, and
retaining the shape on cooling can be repeated several times
without affecting their properties much. Ex: PE, Polycarbonate
(PC), Polytetrafluoro ethylene (PTEE) etc.
Thermosetting polymers: Polymers that undergo chemical
changes and cross-linking on heating and become
permanently hard, rigid and infusible on cooling, are called
thermosetting polymers. They do not soften on reheating;
instead they undergo degradation. Ex: phenol-formaldehyde
(bakelite), urea-formaldehyde etc.

3. a) Addition polymers (Based on type of polymerization)
The polymers formed by self-addition of several monomers to
each other without elimination of byproducts are called
addition polymers. Ex: PVC, PE etc.
 Monomers add successively to a growing polymer chain
 Polyethylene and polystyrene are addition polymers.
 Only olefinic or vinyl compounds can undergo addition
polymerization.
 No elimination of byproducts.
 Double bond provides required bonding sites.
 The elemental composition of the polymer is the same as that of
monomer.
 The addition of monomers takes place rapidly.
 Polymerization is brought about by initiators like free radicals.

Addition Polymerization Example
In this type of polymerization C=C bonds of monomers react
to form larger monomers until the unit is a larger polymer
chain as seen here.
Table on the next slide shows ethylene monomer based
polymers

Examples of addition polymers.

Polymers Derived from Modified Ethylene Monomers (e.g. of addition
polymerization )

3. b) Condensation Polymer (Based on type of
polymerization)
The polymers formed by intermolecular condensation reaction by the functional
groups of monomers with continuous elimination of small molecules such as
ammonia, water etc. Ex: nylon-6,6; polyester etc.
 Polymer chain grows when monomers combine and split out water or
other small molecule.
 Nylon 6,6 and polyurethane are condensation polymers.
 The monomers having two or more reactive functional groups can
undergo condensation polymerization.
 There is continuous elimination of byproducts.
 Polymerization proceeds through intermolecular condensation.
 Polymerization is catalyzed by acids or alkali.
 The polymer chain built up is slow and stepwise.
 The elemental composition of the polymer is different from that of the
monomers.

21
4. Linear, branched and cross-linked polymers
(Based on chemical structure)

5. Organic and Inorganic polymer
Organic
Inorganic

23
Organic and Inorganic Polymers
A polymer whose backbone chain is essentially made up of carbon atoms
is termed as an organic polymer. The atoms attached to side valencies
are oxygen, nitrogen, hydrogen etc. Majority of synthetic polymers are
organic polymers, for example PE, PVC.
On the other hand, the polymers that do not contain a carbon atom in
their backbone chain are called inorganic polymers.

6. Atactic, isotactic and syndiotactic polymers (Based on
stereochemistry)
Atactic, isotactic and syndiotactic polymers
Side Group is random
Side Groups are on same side
Side Groups are on
alternating fashion

25
Elastomers, Fibers, Resins and Plastics
(7. On the basis of ultimate structure and end use)
Elastomer: The polymers which undergo very long elongation when
pulled apart, and return to their original length on release are called
elastomers. Example Natural rubber, Buna-S, etc.
Fibers: These are long, thin and thread like polymers, whose length is at
least 100 times their diameter. They do not undergo stretching and
deformation like elastomers. Example jute, wood, silk
Resins: These are low molecular weight polymers used as adhesives.
They can be in the form of liquids or powder.. Example Urea-
formaldehyde, epoxy resin.
Plastics: These are polymers, which can be molded into desired shapes
by the application of heat and pressure. Example PVC, PC, Teflon.

Homopolymers and copolymers
Homopolymers: If same type of monomers
e.g., PE, PVC etc.
Homopolymers: If two or different type of monomers
e.g., Styrene-Acrylonitrile (SAN), Styrene-butadiene (SBR),
Acyronitrile-butadiene-styrene (ABS) copolymers

Homo Polymerization
Example
In this type of polymerization C=C bonds of monomers react to
form larger monomers until the unit is a larger polymer chain as
seen here.
Table on the next slide shows ethylene monomer based polymers

Copolymerization
The polymerization of two or more different monomers resulting in the
formation of a polymer containing both monomers linked in one chain
is called copolymerization. It is considered as a type of addition
polymerization. The polymers so formed are called copolymers.
A copolymer is a polymer that has two types of monomer units in
its chain.
 Block copolymer: When repeating units of each kind appear in
blocks, it is called a block copolymer.
 Random copolymer: If the various repeating units occur
randomly along the chain structure, the polymer is called a
random copolymer.
 Graft copolymers: They are formed when chains of one kind are
attached to the backbone of a different polymer.

Methods of Polymerization
Addition Polymerization
Condensation Polymerization
30
Chain-growth polymers, also known as addition polymers, are made by
chain reactions

Step-growth polymers, also called condensation polymers, are made
by combining two molecules by removing a small molecule

Structure–Property Relationship of Polymers
 Strength: Tensile strength increase with molecular mass up to a
certain point and then become constant. Commercially a polymer
should have high tensile strength. Melt viscosity shows gradual
increase with increase in molecular mass.
 Crystallinity: Degree of crystallinity of polymer depends on its
structure. Linear polymer will have high crystallinity. Eg HDPE is more
crystalline than LDPE. LDPE is more crystalline than Polystyrene.
Isotactic, syndiotactic highly crystalline. Nylon 66 high degree of
crystallinity. Polymers having polar groups can formed hydrogen bond
with neigbouring chain.
 Elasticity: It is mainly because of uncoiling and recoiling of molecular
chains on application of force. Can be avoided by :
introducing cross linking
avoiding bulky side groups
more non-polar groups in chain

 Plastic deformation: Thermoplastic material/ polymer on
application of heat and pressure, initially become soft, flexible and
undergo deformation. On further heating above their melting point
they melt and flow. Thermoplastic exhibit plastic deformation (linear
chains , weak vanderwaals force). While thermosetting plastic doesn’t
because of cross linking.
 Chemical Resistivity: It depends on the structure of polymer and
nature of attacking reagent. When the chemicals attack on polymer, it
first softens, swells and loses its strength, and then dissolves. It also
depends on several factors such as polar and non polar groups, molar
mass, degree of crystallinity, cross linking etc.
 Non-elastic Nature of Fibers: The chain mobility is reduced by very
close packing of the polymer chain backbone without cross linking.
Polar groups and aromatic rings in the backbone chain impart high
strength to the polymer fiber.
Glass transition temperature (Tg) is the temperature below which a
polymer is hard, brittle and above which it is soft and flexible.

Glass transition temperature (Tg)
It is the temperature below which a polymer is hard, brittle and above
which it is soft and flexible. Denoted by Tg. Hard brittle state is known as
glassy state and soft flexible state is called the rubbery state.
Factors affecting Tg:
1. Flexibility: Presence of rigid groups (aromatic, bulky) in the carbon
chain backbone hinders freedom of rotation. This restriction in the chain
mobility increases the Tg value.
2. Effect of side group: Poly(-methyl styrene) has higher Tg (170°C) while
polystyrene has lower (100°C) due to presence of extra methyl group
which hinders free rotation.
3. Intermolecular forces: Presence of large number of polar groups in the
molecular chain lead to strong intermolecular cohesive forces which
restricts the segmental/molecular mobility. This leads to increase in Tg
value.

4. Branching and Cross linking: A small amount of branching will
reduce the value of Tg, because the free volume increases with
branching and thus decreases the Tg. High density of branching
brings the chain closer and thus reduces the mobility, thereby
increasing Tg.
5. Presence of Plasticizers: Addition of plasticizers reduces the Tg
value. Eg diisooctyl phthalate which is added to PVC reduces its Tg
from 80 c to below room temperature.
6. Stereo-regularity: Tg increases with stereo-regularity. Thus Tg of
isotactic polymer is greater than syndiotactic which in turn has
greater tg than atactic polymer.
7. Molecular Weight: Tg of all polymers increases with molecular
weight up to 20,000 and beyond this, the effect is negligible.

Significance of Tg
1. Tg value is a measure of flexibility.
2. Its value gives and idea of thermal expansion, heat capacity,
refractive index, electrical and mechanical properties of a
polymer.
3. Its value decides whether a polymer at room temperature will
behave like rubber or plastic.
4. It helps in choosing the right temperature for fabrication.

Structure-property relationship
40
The Structure of the polymers depends upon:
1. Size and shape of the polymer chain .
2. Chemical nature of the monomers.
The Structure of the polymers further effects the physical and
mechanical properties of polymers.
 Strength
 Crystallinity
 Elasticity
 Non-elastic Nature of Fibers
 Plastic deformation
 Chemical Resistivity

41
The tensile strength of a
material quantifies how
much stress the material
will endure before
suffering permanent
deformation.
For example, a rubber
band with a higher
tensile strength will hold
a greater weight before
snapping
Strength

42
For a polymer to be commercially useful , It should have low melt viscosity, high
tensile strength and impact strength

Crystallinity
43
Amorphous and crystalline regions in a polymer. The crystalline region
(crystallite) has an orderly arrangement of molecules.
The higher the crystallinity, the harder, stiffer.

44
Polymers containing polar groups can form H-bonding, so have higher
crystallinity.
Linear polymers have higher crystallinity, because the atoms along the
chain Permit closer approach, branched polymer will have low
crystallinity.

Advanced polymeric materials (plastic)
45

Plastics
Classification: Thermoplastic and Thermosetting
This is a cross-linked
thermosetting polymer
This is a linear thermoplastic
polymer.

Plastic Molding Techniques
 Involves conversion of the solid polymer into desirable shape
and size.
 During molding the plastic material is heated to the
appropriate temperature for it flow and material is shaped
and then cooled to preserve the desired shape.

plastic molding techniques
(only first 3 in syllabus)
1. Injection molding (for thermoplastics)
2. Extrusion molding (for thermoplastics)
3. Compression molding (for thermosetting)
4. Blow molding
5. Injection blow molding
6. Thermoforming
7. Transfer molding
8. Injection-Compression molding

 Known quantity of polymer may in the form of granules , pellet
or powder is fed to the hopper.
 Passed to a hot chamber where the polymer material soften
flows under the pressure applied by means of electrically
operated plunger.
 As the plunger moves in the forward direction ,the soften
material passes into mold through a nozzle , solidifies upon
cooling ,takes the shape of mold.
1. Injection molding

Injection molding
Injection molding with (a) plunger, (b) reciprocating rotating screw, (c) a typical part
made from an injection molding machine cavity, showing a number of parts made
from one shot, note also mold features such as sprues, runners and gates.

Materials such as polystyrene, nylon, polypropylene
and polythene can be used in a process called
injection moulding. These are thermoplastics - this
means when they are heated and then pressured in a
mould they can be formed into different shapes.
The DVD Storage unit seen opposite has been made
in one piece using this process
An animation of an injection moulding machine is
shown below. The product being produced is the
DVD / CD storage unit seen opposite.

 speed production
 Low costs in mass production
 very low loss of material
 flexibility to make parts with complex shapes
 high precision
Advantages of Injection molding

Applications
Makings
1. Bottles caps
2. Mugs
3. Dustbins
4. Automotives dashboards
5. Chairs

Injection moulding is used to create many things such
as wire spools, packaging, bottle caps, automotive parts
and components, Gameboys, pocket combs, some
musical instruments (and parts of them), one-piece
chairs and small tables, storage containers, mechanical
parts (including gears), and most other plastic products
available today.
Injection moulding is the most common modern
method of manufacturing parts; it is ideal for producing
high volumes of the same object

2. Extrusion Molding
 Production of thermoplastic material into finished articles such
as sheets, films and rod.
 Done by using machine Extruders.
 Raw materials in the form if thermoplastic pellets, granules, or
powder, placed between the screw and extruder barrel.(feed
zone)
 The barrel is equipped with a screw . As screw rotates , the
pellets are dragged forward and compressed (transition or
compaction zone)
 Heaters around the extruder’s barrels heats the pellets and
liquefies them. (molten plastic) (metering zone).
 Screw has 3-sections
• Feed section
• Melt or transition section
• Pumping section.

LDPE granules are heated and made into a molten state. The liquid is extruded
through a nozzle in the form of a tube called a 'Parison'.
The two halves of the mould close on the 'Parison' and shut tight.
Compressed air is blown into the Parison forcing the LDPE to the sides of the
mould, where it cools. The moulds open, releasing the product.

Complex shapes with constant cross-section
Solid rods, channels, tubing, pipe, window frames,
architectural components can be extruded due to
continuous supply and flow.
Plastic coated electrical wire, cable, and strips are also
extruded
Pellets :extruded product is a small-diameter rod
which is chopped into small pellets

 The screw depth is constant in both the feed and
metering zones and varies in transition zone to begin
generating pressure and to force the pellets to begin to
melt.
 Length of each zone in screws design varies according
to type of plastic being processed. Example LDPE- melt
gradually ,the overall length of the screw is roughly
divided into three zone.
 Nylon- have sharp melting point ,screw designed such
that transition zone only consist of one turn of the
screw flight.
 PVC- prone to thermal degradation and melt very
gradually may be processed with screw whose entire
length is composed of a compression zone.

Advantages
 Low initial setup
 Fast setup
 Low production cost

Application
Manufacturing of
 Tubes
 Rods
 Plumbing pipes
 Electric cable
 Door insulation seals
 Optical fibers

 Thermosetting are molded by this method.
 Known quantity of polymer (resin) which may in any
form (powder or pellet) is placed in the lower
portion of mold cavity.
 It is heated electrically or by passing steam to soften
the material.
 The mold cavity gets filled with fluidized plastic.
 The melt is compressed by the upper mold.
 compression mass gets cured and hardened and is
open after cooling and the article removed.
3. Compression Molding

Compression Molding
Types of compression molding, a
process similar to forging; (a)
positive, (b) semi positive, (c) flash
(d) Die design for making
compression-molded part with
undercuts.

Advantages and Applications
1. Low cost
2. Very low loss of materials
3. God surface finish
4. Fast setup time
1. Electrical parts
2. Cooker Handles
3. Electronic devices
4. Appliance housing and large container.

Some Important Commercial Thermoplastics
Polythylene (PE): LDPE and HDPE
Polypropylene

Polyvinyl Acetate
Polytetrafluoroethylene/Teflon

Polymethyl Methacrylate/Plexiglass

Some Important Commercial Thermosetting Resins
Phenol–Formaldehyde Resins
Engineering Chemistry
Copyright  2012 Wiley India Pvt. Ltd. All rights reserved.
Novolac resin
Resol resin

Both resol and novolac on curing with wood flour filler give highly cross-linked
product called Bakelite. (Cross linking Novolac polymer)

Elastomers (Rubber)
Natural rubber is prepared from latex of Hevea rubber
trees or gutta-percha and balata. It is a linear polymer
of isoprene and is called poly-isoprene.

• Vulcanization is the cross-linking of polymer
chains with sulfur atoms by applying heat.
• Vulcanization increases the abrasion resistance
and the useful temperature range of rubber.

A Segment of Vulcanized Rubber

• The double bonds in isoprene polymer allows for cis-trans isomers.
• Cis-trans isomers are molecules that differ only in the spatial orientation of
their atoms
• Natural rubber is cis-polyisoprene.
• Gutta-percha is trans-polyisoprene

Ethylene groups on same side = cis
Ethylene groups on opposite side = trans

Some Important Synthetic Rubbers
• Butyl rubber (GR-I rubber)
• Polychloroprene (Neoprene or GR-M rubber)
• Styrene-Butadiene rubber (SBR) (Buna-S or GR-S rubber)
• Nitrile rubber (NBR) (Buna-N or GR-A rubber)
• Polysulphide rubber
• Silicone rubber

93
Application: Making sportsgear,fishing lines,sportsequipments Making brushesandcombs.

Adhesives
Adhesive is a polymeric material used to bind together two or more
similar/dissimilar surfaces, so that the resulting material can be used as a single
piece. Ex Fevicol.
The surfaces may be metals , glasses, plastics, papers etc.
-Process of binding two surface is known as bonding.
-surfaces joined are called Adherents.
Classification:
1. Composition of principal components:
a) Natural ( gum, glue, starch, natural rubber) –low bond strength
b) Synthetic( PF, UF, Epoxy resins, etc.)-Superior Strength
2. Classification based on Mechanism of adhesion
a) Solvent responsive adhesives:
- Flow of the adhesives during application and adherence during bonding is
caused by volatile liquid carrier. These adhesives are used in the form of
solution ,pastes, gels and dispersions. Ex. Vegetable gums, starch,
natural rubber. Engineering Chemistry

• b) Heat sealing adhesives: These adhesives solid at room
temperature ,but they become sticky and undergoes fusion
by the application heat and then they applied on the
bonding surfaces. These adhesives are tougher , flexible,
resistance to moisture ,solvent and chemicals.
Ex. Waxes, cellulose , esters, polyvinyl alcohol, resins etc.
C) Pressure sensitive adhesives: Used as adhesives tapes,
- should be capable of providing instanteous adhesion
when applied with light pressure.
-they should be capable of being removed from the surface
with a very pull if not required.
Ex- butyl rubber , neoprene , acrylic polymers , alkyl resins
etc.

Application
• 1. epoxy resins used to join glass, metals, wood.
• 2. Used in Industrial flooring , skid resistance, highways surfacing,
patching materials.
• 3. used as laminating materials in electrical equipments.
• 4. Molds made from epoxy resins are used in the production of
aircraft and automobiles components.
• 5. Used as matrix in fiber reinforced plastics.

Ken Youssefi Mechanical Engineering Dept. 99
What is a composite Material?
A broad definition of composite is: Composites is a material formed
by combining two or more chemically distinct materials (insoluble in
each other and retain their individual identities). Composites has
improved properties over it’s individual materials, it could be natural
or synthetic.
Wood is a good example of a natural composite, combination of cellulose fiber and
lignin. The cellulose fiber provides strength and the lignin is the "glue" that bonds
and stabilizes the fiber.
A common example of a synthetic composite is concrete. It consists of a binder (cement) and a reinforcement
(gravel).Adding another reinforcement(rebar)transformsconcreteinto athree-phase composite
Composite Material

Composites
Modern technology require such as aircraft application –low density, high
strength, good corrosion resistance, good abrasion and impact resistance .
-Not possible by single use of any metal, alloys, ceramic.
-Search of particle leads to composite.
-Two different materials combine to form a material suitable for structure
application as refer as composites.
A composite is a combined material formed by the assembly of two or more
components, such as fillers or reinforcing agents and a compatible matrix binder
in order to obtain specific characteristic properties.
Made up of two phases- matrix (continuous part or binder of composite
materials and dispersed phase constructed by reinforcing particulates and
fillers.
Classification:
1. On the basis of Matrix constituent: OMCs, MMCs, CMCs
2. On the basis of Reinforcement form: Fiber reinforced composites,
laminar composites, particulate composites Engineering Chemistry

©2002 John Wiley & Sons, Inc.
M P Groover, “Fundamentals of
Modern Manufacturing 2/e”
On the basis of Matrix
constituent
1. Metal Matrix Composites (MMCs) -
2. Ceramic Matrix Composites (CMCs) - especially in
high temperature applications
– The least common composite matrix
3. Organic (can be Polymer or carbon) Matrix
Composites (OMCs) - thermosetting resins are widely
used in OMCs and PMCs

Functions of the Matrix Material
• Provides the bulk form of the part or product
made of the composite material
• Holds the imbedded phase in place, usually
enclosing and often concealing it
• When a load is applied, the matrix shares the
load with the secondary phase, in some cases
deforming so that the stress is essentially born
by the reinforcing agent

On the basis of Reinforcement
form
• Fiber reinforced composites,
• laminar composites,
• particulate composites
• Function is to reinforce (To strengthen by adding
extra support or material) the primary phase
• Imbedded phase is most commonly one of the
following shapes:
– Fibers
– Particles
– Flakes

Figure 9.1 - Possible physical shapes of imbedded phases in composite
materials: (a) fiber, (b) particle, and (c) flake
(a) fiber (b) particle (c) flake

Ken Youssefi Mechanical Engineering Dept. 106
Reinforcement: fibers
Glass
Carbon
Organic
Boron
Ceramic
Metallic
Matrix materials
Polymers
Metals
Ceramics
Interface
Bonding
surface
Components of composite materials

Continuous vs. Discontinuous
Fibers
• Continuous fibers - very long; in theory, they
offer a continuous path by which a load can be
carried by the composite part
• Discontinuous fibers (chopped sections of
continuous fibers)

Fiber in composite materials:
(a) continuous fibers; (b) continuous fibers; and (c) random, discontinuous
fibers

2. Laminar Composite
Two or more layers bonded together in an
integral piece
3. particulate Composite
Particles may be flakes,
powder, and wood particles

Fiber-Reinforced Polymers (FRPs)
• A PMC consisting of a polymer matrix
imbedded with high-strength fibers
• Polymer matrix materials:
– Usually a thermosetting (TS) plastic such as
unsaturated polyester or epoxy
– Can also be thermoplastic (TP), such as nylons
(polyamides), polycarbonate, polystyrene, and
polyvinylchloride
– Fiber reinforcement is widely used in rubber
products such as tires and conveyor belts

-Components of a composite do not dissolve or merge
completely into each other but act together while retaining their
individual properties.
Matrix constituent: OMCs (Organic matrix composites), MMCs
(metal matrix composites), CMCs( ceramics matrix composites)
Term organic matrix composites include –polymer matrix
composites and carbon matrix composites.(Carbon-carbon
composites)
-Second classification – refer to reinforcement form,

Laminar Composites
-Long with sandwich structure belong to the class of
structural composites.
-Composed of thin layers held together by matrix.
-Sheets or panels of constituting materials are stacked and
glued together with different orientation that yield material
with high isotropic strength.
-Materials used in fabrication- include sheets, papers, glass
fibers are embedded in plastic matrix.

Fiber reinforced plastics (FRP)
-Composed of fibers and polymer matrix.
-Fibres are the reinforcement and main source of strength .
--polymer matrix glues up all the fiber together in shape and
transfer stress between reinforcing fibers.
-Fillers or modifier are added to smoothen the manufacturing
process ,impart special properties .
-Common fiber reinforcing agents include –Aluminum and its
oxide, aluminum silica , abestos, beryllium carbide, carbon
graphite , glass molybdenum, polyesters, quartz etc.
-Polymer matrix include thermoplasticmaterials like acetals,
acryronitrile, butadiene, styrene, nylon,PE,PP etc.
-Thermoset resin matrix include polyesters(widely used),
vinyl,epoxy( higher adhesion) ,phenolic resins.
-Polyester widely used because of low cost.

Uses of FRP
• - Light weight- used in making aircraft, cars
• High strength(graphite epoxy) –used in making bridges
• Resistance to corrosion- fiber glass used in making cars and
boats.
• Elastic in nature – used in car leaf springs.
• High strength and insulation – used in making armors.
• Fiber glass Used in thermal and sound absorption.
• Non conductive nature , ladders made with fiberglass (power
line)

117
Conductive polymers or, more precisely, intrinsically conducting polymers (ICPs) are
organic polymers that conduct electricity. Such compounds may have metallic conductivity
or can be semiconductors

Conducting polymers
-Before 1960 organic polymers used as insulators.
-In 1960 Chemist Shirakawa ,Plastic research lab. BASF, Germany, accidentally
added a catalyst 1000 times more than the required during polymerization of
acetylene ,which result in conducting polyacetylene.
Organic polymers having electrical conductance of the order of conductors are
called conducting polymers.
Classification:
1. Extrinsically conducting polymers (conductivity due to mixing conducting
fillers like metal fibers, metaloxide, carbon black with insulating materials)
- Also called as Conductive element filled polymers.
- Insulation material formed the continuous phase and the added filler form
the conducting networks.
- Minimum concentration of conducting filler has to be added so that
polymers start conducting.
- Conductance is not due to matrix is due to fillers.

Intrinsically conducting polymers (for example, poly (p-
phenylene), polyacetylene, polyaniline)
-Conductivity is due to organic polymers themselves.
They conduct electricity when doped with Oxidizing ,reducing
agents or protonic acids

Conducting polymers with conjugated pi- electrons
• -due to high delocalized Pi- electron systems organic polymer has
conductance in the range of conductor are called as inherently or
intrinsically conducting polymers or synthetic metals.
• EX-
• 1. Poly (p- phenylene)
• 2. polyaniline
• 3. polyacetylene
• These conjugated polymers in their pure state are insulators or
semiconductor. (pi- electron are localized)
• These electron are delocalize on doping and conduct electricity..
• Dopant are oxidizing (p-doping) , reducing( n-doping), protonic acid (H-
doping)
• Redox doping of organic conductor s is similar to doping of silicon
semiconductor.

Discuss in terms of VB and CB
1. When Pi- bond is formed VB( Valence band) and CB
(conduction band) are created.
2. Before doping sufficient gap between in VB and CB. Electron
remains in VB.
3. Upon doping Polaron and solitons are formed which results in
formation of new localized electronic states that fills the energy
gap between VB and CB.
4. Sufficient solitons are formed , a new mid gap band formed
which overlaps the CB and VB allowing the electron to follow.

Liquid crystals (LCs) are matter in a state that has properties between those of
conventional liquid and those of solid crystal. For instance, an LC may flow like a
liquid, but its molecules may be oriented in a crystal-like way.
The nematic liquid crystal phase is characterized by molecules that have no positional order but tend to point in the same
direction. Inthe following diagram, notice that the molecules point vertically but arearrangedwithnoparticular order
Liquid Crystals
Nematic liquid crystal
Nematic liquid crystal

In the nematic phase the molecules of a liquid crystal are rod shaped and pack next to
each other. In the smectic phase basically the molecules are placed in layers that can
slide past each other.
The smectic phases, which are found at lower temperatures than the nematic, form well-defined layers that can slide over one
another in a manner similar to that of soap. In the smectic state, the molecules not only maintain the general orientational
orderofnematics, but alsotend to align themselvesin layersorplanes.
Smecticphases
Smecticphases

Directional order: Yes
Positional order: No
Directional order: Yes
Positional order: Yes

Liquid crystals
.Liquid crystals are substances that exhibit a phase of matter that has
properties between those of a conventional liquid, and those of a solid
crystal. For instance, a liquid crystal (LC) may flow like a liquid,
but have the molecules in the liquid arranged and/or oriented in a
crystal-like way.
-Molecules posses charterstics order in orientation in order like
solid but randomness in their position like liquid phase.
-
- Most of LC compound exhibits polymorphism. (more than one
phase is observed in crystalline state) .Subphases of LC materials is
called Mesophases. All this formed due to different ordering in the
sample.

Compound shows liquid crystal Properties
• 1 methyoxybenzilidenebutylanaline (MBBA)
• 2. p-Azoxyanisole
• 3. p-Azoxyphenetole
• 4. Phentyl-p-cyanobiphenyl (PCB)

Classification of liquid crystal
• Thermotropic liquid crystals :Thermotropic phases are those that
occur in a certain temperature range. If the temperature is raised too
high, thermal motion will destroy the delicate cooperative ordering
of the LC phase, pushing the material into a conventional isotropic
liquid phase. too low a temperature, most LC materials will form a
conventional (though anisotropic) crystal. Many thermotropic LCs
exhibit a variety of phases as temperature is changed. For instance, a
particular mesogen may exhibit various smectic and nematic (and
finally isotropic) phases as temperature is increased.
Lyotropic liquid crystals :A lyotropic liquid crystal consists of two or
more components that exhibit liquid-crystalline properties in
certain concentration ranges. In the lyotropic phases, solvent
molecules fill the space around the compounds to provide fluidity to
the system. In contrast to thermotropic liquid crystals, these lyotropics
have another degree of freedom of concentration that enables them to
induce a variety of different phases.

Types of Mesophases
1. Nematic Liquid crystal: One of the most common LC phases is the
nematic , where the molecules have no positional order, but they do
have long-range orientational order. the molecules flow and their centre
of mass positions are randomly distributed as in a liquid, but they all
point in the same direction (within each domain).
2. Liquid crystals are a phase of matter whose order is intermediate
between that of a liquid and that of a crystal. The molecules are
typically rod-shaped organic moieties about 25 angstroms (2.5
nanometers) in length and their ordering is a function of temperature.
3. The nematic phase, for example, is characterized by the orientational
order of the constituent molecules. The molecular orientation (and
hence the material's optical properties) can be controlled with applied
electric fields. Nematics are (still) the most commonly used phase in
liquid crystal displays (LCDs), with many such devices using the
twisted nematic geometry.

• These nematic crystal are thread like when seen from polarized
light. (Nematos- Greek word means thread).
• These LCs flow like liquid and hence no positional order but on the
average arranged parallel.
• Uniform Alignment with respect to their long axis.
• The average direction along which the molecules orient themselves
are (n).
• Easily aligned in external magnetic or magnetic field.
• Used in LCDs.

• Nematic phase of a chiral substance is called Cholestric because it
observed like cholestrol derivatives.
• Only Chiral molecules and optically active molecule can give rise to
such phase.
• Intramolecular forces between chiral molecules favor alignment at a
small angle to the adjacent group of molecules. Direction in each
layer is twisted with respect to the layers above and below it.
• Such that the director takes a helical pathway as travel through LCs.

-Cholestric mesophases is charterized by an important property called
pitch , which is defined as the distance it takes for director to rotate
on full turn in the heliex .
- Chiral Nematic crystal has ability to reflect light whose wavelength
is equal to pitch length.
- Pitch length depends upon temperature . (temperature increases
pitch length shorter) because greater thermal energy increases the
angle at which the director changes. , thus tightening the pitch.

Sematic liquid crystals
• The word "smectic" is derived from the Greek word for soap. This
seemingly ambiguous origin is explained by the fact that the thick,
slippery substance often found at the bottom of a soap dish is
actually a type of smectic liquid crystal.
• Molecules in this phase show a degree of translational order not
present in the nematic. In the smectic state, the molecules maintain
the general orientational order of nematics, but also tend to align
themselves in layers or planes. Motion is restricted to within these
planes, and separate planes are observed to flow past each other. The
increased order means that the smectic state is more "solid-like"
than the nematic.
Sematic A and C are arises – when the molecules are oriented along
the layers normalor.

Picture of the smectic C phase
Picture of the smectic A phase
Photo of the smectic A phase
(using polarizing microscope)
Photo of the smectic C phase
(using polarizing microscope)

Applications of liquid crystals
• 1. LCs used to detect Tumor, since tumor cell are at higher
temperature than normal cell, these indicated by color change.
• 2. Used in electronic industry , a break in circuit increases the
temperature , which is detected by change in color of LCs.
• 3. Used in thermostrips and disposable thermometers to read body
temperature.
• 4. Used in Optical imaging and recording .
• 5. Used to detect radiation and pollution in atmosphere.
• 6. LCD screen used in watches ,calculator, laptops, television, sigh
board.
• 7. used in non-destructive testing of materials under stress.
• 8. low molecular mass LCs used in erasable optical disks and light
modulator for color electronic imaging.

Bark is the outer most skin of the tree.
Processing of Latex (for rubber formation)

Recovering the Rubber
• The preferred method of recovering rubber from latex
involves coagulation - adding an acid such as formic acid
(HCOOH); coagulation takes about 12 hours
coagulation of rubber latex

The coagulum, now soft solid slabs, is then squeezed through a series of rolls which
driveoutmostofthewaterandreducethicknesstoabout3mm(1/8in)

The sheets are then dried in smokehouses. Several days are normally required to
completethedryingprocess

Polymers

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