speciality polymers

Rubbers also known as elastomers are linear polymers which exhibit elastic property distinctly.

Natural Rubber

Collection of latex

Processing of latex Coagulum Crepe rubber Smoked rubber Mastication

Isolation & Processing of Natural Rubber

Collection of latex:

Hevea brasiliensis(30-60 % rubber)

Processing of latex: Coagulum

Latex is filtered to remove any dirt present in it. This latex is then coagulated by using 1% acetic acid/formic acid solution.

A soft white mass is obtained called as coagulum.

Processing of latex Crepe rubber

Coagulated rubber is drained for about 2 hrs. and then passed through creping machine to obtain pale yellow crepe rubber.

Smoked rubber

Smoked rubber Latex is coagulated long times having vertical groves where

metal plates are fitted. Metal plates with groves are inserted in the tank after

coagulation. The tank is kept undisturbed for about 16 hrs. The tough slabs of rubber are obtained and passed through a

series of smooth rollers to get ribbon like pattern of thin rubber sheet.

These thin sheets are then hanged in smoke house for 4 days at 40-50oC.

The rubber so formed called as Smoked rubber.

Masticated rubber Crude rubber is masticated and compounded with chemicals

such as sulphur (vulcanization), accelerators & antioxidants and then converted into utility articles by suitable processing.

Mastication is the process of making rubber soft & gummy by subjecting it to several mechanical working.

During mastication, rubber is broken down into small particles by passing it through roller mill.

Mastication causes decrease in molecular weight of rubber due to oxidative degradation.

Natural Rubber is a polymer of Isoprene. To understand the structure of Rubber we shall concentrate on structure of Isoprene. Isoprene is a conjugated diene containing double bonds at alternate position.

Structure of Isoprene: Monomer of Natural Rubber

Structure of Rubber

Structure of Natural Rubber

Polymerization of Isoprene may follow either of the two pathways; either of cis-polymerization or trans-polymerization. The rubber formed from cis-polymerization is called cis-polyisoprene or Natural Rubber. Similarly, the rubber formed from trans-polymerization is called Synthetic Rubber.

Structure of Rubber

Gutta percha

It becomes soft at high temperature and too brittle at low temperature. Thus, it can be used in the range of 10 to 60oC only.

It is weak & its tensile strength is 200 kg/cm3.It has large absorption capacity.It can be attacked by non polar solvents like vegetables

and mineral oils, gasoline, benzene & carbon tetrachloride, etc

It perishes, due to oxidation in air.

Drawbacks of natural rubber:

It swells & gradually disintegrates in organic solvents.It possesses remarkable tackiness i.e. when two fresh raw

rubber surfaces are pressed together, they coalesce to form a single piece.

When stretched to high extent, it suffers permanent deformation.

Drawbacks of natural rubber:

Vulcanization of Natural Rubber

The process of compounding raw rubber with some chemicals (vulcanizing agents) like sulphur, hydrogen sulphide , benzoyl peroxide etc to improve the properties of rubber is called as vulcanization.

Vulcanization of Natural Rubber

Comparison of Natural and Vulcanized RubberNatural rubberUseful temp range is 10 to 60 oC Low tensile strength(200

kg/cm2)High water absorption capacityHigh tackiness Low resistance to oxidation in

air

Vulcanized Rubber -40 to 100o C

High tensile strength(2000 kg/cm2)

Low water absorption capacity Low tackiness High resistance to oxidation in

air

Styrene - Butadiene rubber (SBR)Government Styrene rubber

AmeripolBuna - S

Synthetic Rubber

It is prepared by copolymerization of 75% butadiene & 25% styrene by weight.

Cumene hydroperoxide is used as catalyst for polymerization.

It is a block copolymer, prepared by emulsion polymerization.

Preparation

Reaction nx CH2 CH CH CH2 + ny CHCH2

Copolymerization

CH2 CH CH CH2 CHCH2 AA

n

It possesses high abrasion resistance.It has load bearing capacity and resilience.It shows high resistance to heat.It swells in oils and solvents.It get readily oxidized by traces of ozone.It can be vulcanized by sulphur.

Properties:

Mainly used for making motor tires because of high abrasion resistance.

It is used for floor tiles, shoe soles, gaskets, electrical insulation, adhesives, carpet backing, conveyer belt etc.

Applications:

Speciality Polymers

Thermoplastic Polymers

Biodegradable Polymers

Conducting PolymersElectroluminescent

Polymers

Liquid Crystal Polymers

Polymer Composites

Engineering thermoplastics are group of materials obtained from high polymer resins which provide one or more outstanding properties when compared with the commodity thermoplastics such as polystyrene, polyethylene, polypropylene, etc


Advantages of Engineering Thermoplastics include,1.High thermal stability.2.Excellent chemical resistance.3.High tensile & impact strength.4.High flexibility.5.High mechanical strength.6.Light in weight.7.Readily mouldable into complicated shaped.8.High dimensional stability.

Thermoplastics: Applications


Polycarbonate Polysulphonates TeflonAcrylonitrile-

Butadiene-Styrene resin

Thermoplastic PolymersPolycarbonate (Lexan or Merlon)

O C

CH3

CH3

O C

O

AAn

It can be obtained by interaction of Bisphenol-A with diphenyl carbonate.

Polycarbonate

O C O

O

C

C C

C

CC

C

C

C

C

C C

C

CC

HH

H H

H H H

H H

H

H H

H

H

H H

( )n

Preparation of polycarbonate from bisphenol-A & Diphenyl carbonate

Thermoplastic Polymers: Polycarbonate (PC)

Physical Properties:1. High impact strength & tensile strength over wide range of temperature.2. Highly transparent plastic (higher light transmittance: 88%).3. It is resistance to water & many organic compounds, but soluble in number of

organic solvents & alkalis.4. It has a good resistance (up to 140oC), thermal stability, oxidative stability and

high melting point (265oC).It has a tendency to yellow with long term ultra violate exposureIt has good thermal & oxidative stability


Applications:1. Electrical and Electronic components Being good insulator, having heat resistant and flame resistant

properties, it is used in various products associated with electrical & telecommunication hardware.

They can be used for making electrical insulators, industrial plugs, sockets, switches, covers of cell phones, laptops, papers, etc

2. Data Storage The production of CD, DVD’s, and Blue ray Disc by injection moulding of polycarbonate.


Applications:3. Optical applications

It is used for (ultra-light) Sunglasses, Swimming & SCUBA glasses, safety glasses, visors in helmets, automotive head lamp lenses as it has high optical clarity. It is also used for widescreens for motorcycles, golf carts, small planes & helicopters.

It can also be used for electronic display for use In mobile and portable device for some LCD screens.


Applications:4. Security components

It can be laminated to make bullet-proof glass.

5. Other applications It is used as housing for machinery / apparatus such as hair drier bodies, camera & binocular bodies. It is used as transparent food containers, cooking utensils covers, blender jars, drinking bottles, glasses, toys, etc

Polycarbonate

BiodegradablePolymers

Biodegradable Polymer:

Definition:

Biodegradation of polymer is a process carried out by biological systems (usually bacteria or fungi) where in polymer chain is cleaved via enzymatic activity.

Biodegradable Polymer: Factors Responsible

1.Micro-organism• Naturally occurring micro-organisms such as bacteria,

fungi & algae are responsible for biodegradation of polymers by breaking C-C bond. The process takes place at very slow rate.

• For the survival, action of micro-organisms & for biodegradation process to function, suitable conditions like temperature, moisture, pH, oxygen, salts (concentration & type), pressure, light, etc are important.

• Polymer should have ability to biodegrade itself. So it needs such functional groups like amines, carboxylic that they absorb water, swell & degrade.

2. Environment

3. Nature of Polymer

Biodegradable Polymer: Features

1. Naturally occurring polymers are biodegradable.2. Synthetic addition polymers with only carbon atom main chain

are not biodegradable at molecular weight above 500.3. If polymer chain contains atom other than carbon in backbone it

may biodegrade depending on attached functional groups.4. Synthetic polycondensation polymers are generally

biodegradable to extent depending on functional groups involved ( ester > ether > amide ).

Biodegradable Polymer: Features

5. Amorphous polymers are more susceptible for biodegradation compared to crystalline polymers.

6. Generally lower molecular weight polymers undergo biodegradation easily compared to high molecular weight polymers.

7. Hydrophilic polymers degrade faster than hydrophobic polymers.

Biodegradable Polymers

1. Natural Biopolymerse.g. Cellulose, Starch, Protein

2. Biosynthetic Polymerse.g. Polyhydroxyalkanoates(Polyhydroxyvalarate, Polyhydroxybutarate, etc)

3. Synthetic Biopolymerse.g. Polycaprolactone, Polylactic acid, etc

Biodegradable Polymers: Applications1. As Packing Material: It can be used in food packing, foam for

industrial packaging, film rapping, disposable plastic packing material such as single serve cups, disposable food service items, etc.

2. Medical Applications: Polymers like HB-HV, Polylactic acids are used in controlled drug delivery because of biocompatibility & biodegradability. Cell transplantation using biodegradable polymers scaffolds offers possibility to create completely natural new tissues & replace organ function.

Biodegradable Polymers: Applications3. Agricultural Applications: These polymers are used as time

release coating for fertilizers & pesticides, making films for moisture & heat retention.

Biodegradable PolymersPolyhydroxybutarate (PHB)

Polyhydroxyvalarate (PHV)

Polyhydroxybutarate-hydroxyvalarate [PHB-HV / PHBV / Biopol]

Biodegradable PolymersPolyhydroxybutarate (PHB)

O CH

CH3

A CH2 C

O

An

It is produced by the fermentation of glucose by the bacterium Alcaligenes eutrophus

Biodegradable PolymersPolyhydroxyvalarate (PHV)

O CH

CH2

A CH2 C

O

A

CH3

n

It can be produced by fermentation of glucose A. eutrophus / P. oleovorans

Biodegradable PolymersPolyhydroxybutarate-hydroxyvalarate (PHBV)

O CH

CH3

A CH2 C

O

O CH

CH3

CH2 C

O

An

It can be produced by A. eutophus when grown in the presence of glucose & either propanoic or valeric acid

Biodegradable Polymers: PHBV

Physical Properties: The physical properties of biopol copolymer vary with hydroxyvalarate content of polymer.

1. As HV content increases in the range of 0.2 %, polymer flexibility, toughness, tensile strength, resistance.

2. Melting point reaches minimum at about 30 % mole hydroxyvalarate.

3. It is susceptible to hydrolysis above pH 9 and below pH 3, it can be dissolved in number of chlorinated solvents like chloroform & methylene chloride.

Biodegradation of PHBV:

PHBV shows complete biodegradation in both aerobic & anaerobic conditions.

Apart from small amounts of biological material, the final product of biodegradation are C02 & water for aerobic condition.

The final product of biodegradation are methane & some C02 for anaerobic condition.

The rate of degradation depends on moisture, nutrients supply, temperature, pH, etc

Biodegradable Polymers: Applications of PHBV

1. Medical Applications:PHBV are used for controlled drug delivery as

they are biocompatible & biodegradable. Also it is non-toxic.

2. Disposable Personal Hygiene:PHBV can be used as a sole structural material or

as a part of degradable composites.

3. Packaging:PHBV can be used for films, blow moulded bottles

& as a coating on paper.

ConductingPolymers

Conducting Polymer:

Definition:

Those polymers which has ability to conduct heat better than that of metals, are called as Conducting Polymers.

Polymers become conducting upon doping Polymer becomes electronically charged Polymer chains generate charge carriers Concentration of dopant causes certain electrons to become

unpaired Formation of polarons and bipolarons They have extended p-orbital system

Conductivity

Conducting Polymers: Classification

1. Intrinsically Conducting Polymers (ICP): Some polymers can conduct electricity of their own because of their structural features. Such polymers are known as ICP.

• These are linear have high planarity in structure & conjugation in the polymer chain.

• e.g. Trans-polyacetylene, Polyaniline, Polyparaphenylene, Polypyrrole, Polythiophene, etc

• Conjugated Π electrons conducting polymers are used in polymer light emitting diodes (PLED), photodiodes & in solar cells.

Intrinsically conducting Polymers (ICP)

CCC

CC

CC

CHAA

H

H

H

H

H

H

H

n

Trans-polyacetylene


A An

Polyphenylene


NH NH NHA An

Polyaniline


NH

NH

NH

NH

AAn

Polypyrrole

2. Doped Conducting Polymers: ICP posses low conductivity, but their conductivity can be improved by creating positive or negative charges on the polymer chain by oxidation or reduction. This technique is called as Doping.

a. P-doping

• It includes doping of ICP with a Lewis acid. Oxidation takes place & positive charge is developed on polymer chain increasing conductivity.

• Lewis acids like I2, Br2, FeCl3, PF6, AsF6 can be used as p-dopants.

• e.g. doping of FeCl3 in (C2H2)n to form (C2H2)n

+ FeCl4- + FeCl2. by

oxidation. b. N-doping

• It includes doping of ICP with a Lewis base. Reduction takes place & negative charge is developed on polymer chain increasing conductivity.

• Lewis acids like lithium, sodium metals, naphthyl amines can be used as n-dopants.

• e.g. doping of Sodium in (C2H2)n to form (C2H2)n

- Na+ by Reduction.

Doping in polyacetylene• Amount of dopant used is significantly higher• Doped polyacetylene is always in tans form• Neutral polyacetylene can be doped in two waysp type doping : oxidation with anions eg : ClO4(-)

n type doping : reduction with cations eg : Na(+)

- e+ ClO4(-) + ClO4(-)

+ e+ Na(+) (-)Na(+)

Doped Conducting Polymers

C2H2

n

+ FeCl32Oxidation

C2H2

n

+FeCl4

- + FeCl2

P-doping

C2H2

n

+Reduction

C2H2

n

-

Na Na+

N-doping

a. Conducting element filled polymer

• Metallic fibres, metal oxides, or carbon black can be mixed in the polymer during moulding process.

b. Blended conducting polymer

• It is obtained by blending conducting polymers with conventional polymer, physically or chemically.

3. Extrinsically Conducting Polymers: These are conducting polymers whose conductivity is achieved by adding external ingredients to them.

4. Coordination Conducting Polymers:

It is a charge transfer complex containing polymer, obtained by combining a metal atom with polydentate ligand.

So there is a formation of coordination bond between the polymer and metal which allow the transfer of electrons easily.

This there is a conduction takes place as energy gap between higher energy level and lower energy level decreases.

Conductivity in Conducting Polymers

Conjugated polymers like polyacetylene are organic semiconductors. They have a band gap. Conducting polymers have extended delocalized bonds that creates the band structure similar to that of silicon, but with delocalized state.

When charge carrier are introduced into the conduction or valence bands, the electrical conductivity increases dramatically.

Doping generates charge carriers which move in electric field. +ve charges (holes) & -ve charges (electrons) move to opposite electrodes. These movement of charge is responsible for electrical conductivity.

Conductivity in conducting polymers

In general, conductivity increases with decreasing band gap between the valence band & conduction band.

Conduction band

Valence band

Conduction band

Valence band

Conduction band

Valence band

Eg

ForbiddenEnergy gap

n-type

P-type

Polaron on localized band

Energy band structure Energy band structure of Si

Energy band structure of conducting polymer

Conducting Polymers: Applications1. In rechargeable light weight batteries, doped conducting

polymers are used.2. In electronic devices such as transistors, photodiodes & light

emitting diodes (LED).3. In optical display devices.4. In telecommunication system.5. In antistatic coatings for clothing.6. In solar cells.7. In drug delivery system for human body.8. In molecular wires & molecular switches.

Conducting Polymers: Limitations

Conjugated polymers have few large scale applications because of high cost, problems in processing (due to their insolubility, infusibility, brittleness) & long term instability.

Conducting Polymers: Polyacetylene

The polymer consist of a long chain carbon atoms with alternating single & double bonds between them. Each carbon posses one hydrogen atom. It can be in two forms: cis & trans (shown below) form.

Trans – polyacetylene (discovered by Prof. H. Shirkawa by using Ziegler- Natta catalyst)

A A

n

Conduction Mechanism in Polyacetylene:

1. An electrical conductive polymer is able to conduct electricity because of the conjugated Π-bond system.2. The conjugated double bonds permit easy electron mobility throughout the molecule because the electrons are delocalized.3. When the oxidative dopants such as I2 is added, it takes away an electron from the Π-backbone of the polyacetylene chain & creates a positive charge (hole) on one of the carbons. The other Π-electron resides on the other carbon making a radical cation known as polaron.


4.The lonely electron of the double bond from which electron was removed, can move easily. As a consequence the double bond moves along.

5.A bipolaron formed on further oxidation.

6.As the 2 electrons are removed, the chain will have 2 positive charges (holes). The chain as a whole is neutral, but the holes are mobile. When a potential is applied, they migrate from one carbon to another & accounts for conductivity.


7.When a Π-bond is introduced, valence band (VB)& conduction band (CB) are created. Before doping, there is sufficient energy gap between VB & CB, so the electrons remain in VB & polymer acts as an insulator.

8.Upon doping, polaron & solitons are formed which result in the formation of new localized electronic states that fill the energy gap between VB & CB.


9.When sufficient solitons are formed, a new mid-gap energy band is created which overlaps the VB & CB allowing electrons to flow.

10. The charged solitons are thus responsible for making polyacetylene a good conductor.

Conducting Polymers: Applications of Polyacetylene

1. Doped polyacetylene offer a particularly high electrical conductivity therefore used as electric wiring or electrode material in light weight rechargeable batteries.

2. Tri-iodide oxidized polyacetylene can be used as sensor to measure glucose concentration.

ElectroluminescentPolymers

Electroluminescent Polymer:Definition:

Electroluminescence is a phenomenon in which a material emits light in response to the passage of an electric current or strong electric field.

These are the polymers which emit light in response to the passage of an electric current or strong electric field.

They have potential applications in LED devices (Flat panel display for PC, TV, mobiles) and color pixels in ink jet printing.

Polymer Light Emitting Diode (PLED)

1. Semiconducting polymers, with Π electron system such as PPV (Polyphenylene-vinylene) exhibit electroluminescence. To generate light with these materials, a thin film of semiconducting polymers is sandwiched between two electrodes.

2. Indium Tin Oxide (ITO) is commonly used anode material. It is transparent electrode material which is deposited on glass / plastic substrate. Metals like Ca, Mg, Al are used for cathode.

Polymer Light Emitting Diode (PLED)

3.Electrons & holes are then injected from the cathode & anode respectively into polymer. Driven by the electric field, the charge carrier move through the polymer over certain distance & recombination takes place. The recombination of these charge carriers results in luminescence.

Electroluminescent PolymersPolyphenylene-vinylene (PPV)

Highly oriented PPV can be obtained by soluble polymeric precursor.

A

A

Electroluminescent Polymers: PPV

Physical Properties: (Bright yellow-green fluorescence on application of electric field)

1. It is diamagnetic in nature & has a very low thermal conductivity (10 – 13 S/ cm).

2. The electrical conductivity increases upon doping with iodine, ferric chloride, alkali metals or acids. However the stability of these doped materials are relatively low.

3. Alkoxy substituted PPV shows ease of oxidation & have much higher conductivities. Large side chain substitution lowers the conductivity.

4. It is water soluble, but its precursors can be manipulated in aq. Solution.

Electroluminescence Polymers: Applications of PPV

1. It is capable of electroluminescence. Due to its stability, processibility & electrical as well as optical properties, PPV is used in organic light emitting diode (OLED).

2. Devices based on PPV an emissive layer, emit bright yellow-green fluorescent light & derivatives of PPV are used when light of different color is required.

3. It is also used as electron donating material in organic solar cells.

Liquid CrystalPolymers

Liquid Crystal Phase:

Crystalline solids have sharp melting point. On heating, there is a sharp transition from solid crystalline phase (anisotropic) to liquid phase (isotropic).

However, certain crystalline solids do not show this sharp transitions from solid to liquid on heating. Intermediate stage can be identified called as liquid crystal phase or mesomorphic phase.

Liquid Crystal Polymer:

Solid phaseMesomorphic or

liquid crystal phase

Heat Liquid phase


Definition:

A polymer that under suitable conditions of temperature, pressure & concentration, exist as liquid crystal is known as liquid crystal polymer.

Polymers that form liquid crystal stage contain long, rigid units or disc shaped molecular structure called as mesogens

Liquid Crystal Polymers: Classification

1. Thermotropic Liquid Crystal Polymers:

• The polymers which have tendency to align their polymers chains (mesogens) over a large distance before their crystallization from the melt, is called as thermotropic liquid crystal polymers.

• e.g. Vectra, Victex, Xyder, etc

Liquid Crystal Polymers: Classification

2. Lyotropic Liquid Crystal Polymers:

• The polymers which have tendency to align their polymers chains (mesogens) over a large distance before their crystallization from the solution, is called as thermotropic liquid crystal polymers.

• e.g. Kevlar

Liquid Crystal Polymer: Classification

1.Smectic LCP• Polymer chains maintain orientational order , but also tend to align themselves in

layers i.e. mesogens are arranged in parallel & lateral order.• The polymer chains are arranged in parallel order but not in lateral order.• This is a modified nematic phase in which mesogens are oriented parallel to one

another but their directions vary from one layer to another.

2. Nematic LCP

3. Cholesteric LCP


1.Smectic LCP

2. Nematic LCP


3. Cholesteric LCP


When polymer exhibiting liquid crystalline properties are formed, they can be constructed with the mesogens with three forms as:

Main Chain LCP

Mesogens


Side Chain LCPMesogens

Polymer chain


Combined Chain LCPMesogens

Polymer chain

Liquid Crystal Polymers: Properties

They have good thermal stability, high dimensional stability, easily moulded, good electrical properties at high temperature, very low coefficient of thermal expansion, high chemical & solvent resistance and high crystallinity (Tg & Tm are high).

Liquid Crystal Polymers: Applications

In electronic & electrical equipments, data storage discs, fibre optic cables, chemical appliances, encapsulation of IC engine, housing for light wave conductors, aerospace applications, as filer for composite material, military communication.

Liquid Crystal PolymersKevlar (Poly paraphenylene terephthalamide)

NH NH C

O

C

O

AAn

The polymer has very high strength due to intermolecular hydrogen bond formed between carbonyl group and NH group.

Liquid Crystal Polymers: Kevlar

Physical Properties:1. It has outstanding high strength to weight ratio. It is 5 times stronger than

steel & 10 times stronger than aluminum on equal weight basis. It is light weight polymer with high strength.

2. It is thermally stable (M. P. > 500oC).3. It is very resistance to impact & abrasion damage.4. The Kevlar fibers can absorb moisture, so they are more sensitive to

environment than glass or graphite composites.5. Although tensile strength & modulus is high, compressive properties are

relatively poor.

Liquid Crystal Polymers: Applications of Kevlar

1. Kevlar is often combined with carbon fibers & embedded in epoxy resins to form hybrid composite that have the ability to withstand catastrophic impact.

2. It can also be used in light weight boat hulls, high performance race cars.3. It has outstanding high temperature resistance & high tensile strength,

therefore can be used for fire retardant fabric & tyre cord.4. It can be used as cables for mooring lines, offshore drilling platforms, for

parachute lines, fishing lines, mountaineering ropes & pulley ropes.5. It can be used in protective clothing & body armor.

PolymerComposites

Polymers Composites:

Definition:

Polymer composite is the material which is made up of polymer matrix & reinforcing materials being put together with a definite interface.

Polymers Composites: Constituents

1. Polymer matrix phase:

• It gives a continuous body constituent, surrounding the other phases & gives a bulk form to the composite.

• These may be thermoplastics (like polyolefins, polyimides, vinylic polymer, polyphenyles, etc) or thermosetting (like Epoxy resins, Phenolic resins, Polyesters, etc)

• Following are the functions of matrix phase:• It binds the dispersed phase/reinforcement together.• It helps in distributing externally applied load to the reinforcement.• It prevents the development of cracks due to plasticity & softness.• It protects the reinforcement /dispersed phase from chemical action & keeps

them properly oriented under the action of load.

Polymers Composites: Constituents

2. Reinforcement Phase:

• They are structural constituents like fibres, sheets, particles which are embedded in matrix phase and provide high strength, rigidity & enhance matrix properties.

• Fibres: Long thin filaments of glass, carbon, aramides are added to matrix to give high tensile strength, high stiffness & low density.

• Particulates: Small metallic or non-metallic particles can be added to the polymer matrix to increase surface hardness, abrasion, resistance & strength. They reduce shrinkage, friction & cost. Particles carry major portion of the load applied.

Polymers Composites: Classification

1. Particle reinforced composites:

• These are composed of particles distributed or embedded in the matrix body. Metallic or non-metallic particles can be added to polymer matrix to improve mechanical strength.

• e.g. carbon black reinforced rubber show improvement in tensile strength, toughness & abrasion resistance and are used in manufacturing automobile tyres.


2. Fibre reinforced composites:

• These are composed of fibres embedded in the matrix material. These can be further divided into three categories continuous aligned (a), discontinuous aligned (b) & discontinuous randomly oriented fibre (c) composites.

ab

c


3. Structural Composites:

• Laminar composites: A laminar composites are made up of lamellar sheets that have high strength in particular direction such as in wood or in continuous aligned reinforced plastics.

• Sandwich panels: Sandwich panels consists of two strong outer faces surfaces by a layer of dense core. Face material is generally fibre reinforced plastic whereas core material can be synthetic rubber, foamed polymer, etc. These type of materials are normally used in aircraft wings, boat hulls, roof, floors, walls, etc.

Polymers Composites: Properties

They have high thermal stability, high tensile strength, stiffness, chip & easily fabricable, low thermal expansion, high impact, oxidative & abrasion resistance.

Polymers Composites: Applications

•In automobile body & parts, turbine engines, pumps, valves, etc•In fabrication of roofs & floors, furniture.•In manufacturing sports goods like rackets, toys, musical instruments.•In marine applications – shafts, hulls, propellers, etc •In components of rockets, aircraft, helicopters, etc•In electronic applications – communication antenna, electronic circuit boards.

Polymer Composites: Fibre Reinforced Plastics

Fibre Reinforced Plastics (FRP):

Definition:

FRP is a composite material made of a polymer matrix reinforced with fibres.

The characteristic properties of FRP depends upon:a)Nature, orientation & distribution of fibresb)Nature of polymer matrixc)Strength of interfacial bonds between fibre phase & polymer

matrix phase.

FRP: Classification

1. Glass FRP:

• They use glass fibres reinforced in polymer matrix containing nylon, polyesters, etc. Glass fibres are obtained by forcing glass melt through spinnerate (having small holes) and rapidly pulling & cooling to get fibres.

• Advantages: They show improved properties as:• High tensile strength & impact resistance.• Lower densities• Excellent resistance to corrosion & chemicals.

FRP: Classification

1. Glass FRP:

• Limitations: • As Polymer matrix flows at high temperature, they show applications in

limited temperature range.• Since the material do not posses desired stiffness & rigidity, they cannot be

employed as structural components.• Applications:

• They are used in automobile parts, storage tanks, industrial flooring, plastic pipes, etc

• They are extensively used in automobiles to reduce vehicle weight & boost fuel efficiency.

FRP: Classification

2. Carbon FRP:

• They use carbon fibres reinforced in polymer matrix like epoxy or polyester resins. Carbon fibres are obtained by pyrolysis of cellulose / Acrylonitrile in an inert atmosphere. It has much higher elasticity modulus than glass fibres & show better resistance to temperature & corrosive chemicals. However, they are short fibres & are more expensive.

• Advantages: They show improved properties as:• High elastic modulus.• Low density.• Excellent resistance to corrosion.• High Temperature resistance.

FRP: Classification

2. Carbon FRP:

• Applications:• They are used as structural components (like wings, body, stabilizers, etc) of

aircrafts & helicopters.• They are used in making sports goods (rackets, archery, racing bicycles, etc),

laptops, fishing rods, musical instruments, etc

FRP: Classification

3. Aramid FRP:

• They use carbon fibres reinforced in polymer matrix like epoxy or polyester resins. Carbon fibres are obtained by pyrolysis of cellulose / Acrylonitrile in an inert atmosphere. It has much higher elasticity modulus than glass fibres & show better resistance to temperature & corrosive chemicals. However, they are short fibres & are more expensive.

• Advantages: They show improved properties as:• High elastic modulus.• Low density.• Excellent resistance to corrosion.• High Temperature resistance.

FRP: Classification

3. Aramid FRP:

• They are divided into two types• Short Fibres - reinforced composites: Short fibres give high surface area,

toughness, strength, heat stability, wear resistance & effective reinforcement.• Applications: Used in automobile brakes & clutches.• Long Fibres - reinforced composites: Aramid fibres are capable of absorbing

energy to show very high compressive strength & ductility.• Applications: Used as structural & advanced engineering material for aircrafts &

helicopter parts, as protective clothes, etc

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speciality polymers

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classificationliquid

high dimensional

liquid crystal

high tensile

liquid crystal

high thermal

strong electric

doped conducting