IV| Engineering Materials ----Polymers and Nano Materials · IV| Engineering Materials ----Polymers and Nano Materials 3 | P a g e BUNA-S BS RUBBER: Random copolymer of butadiene

IV| Engineering Materials ----Polymers and Nano Materials

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1. Classification of polymers Based on polymerization reaction

i). Addition polymers • polymers formed by chain wise addition reaction.

An addition reaction is, two or more molecules combine to form large

molecule with no elimination of small molecules. Molecules needs a

double or triple bond. Total molecular weight of polymer chain segment is

an exact integer multiple of molecular weight of monomers.

ii). Condensation polymers • polymers formed by step wise condensation

reaction. A condensation reaction is, two or more molecules combine to

form large molecule with elimination of small molecules like water,

ammonia etc.

Addition Polymerization Vs Condensation Polymerization

Ans. i). Addition or chain polymerization » » Repeated addition of monomers to yield long chain. >> No elimination of small molecules like water or HCl etc during the progress of reaction. » It takes place only with compounds having double or triple bonds such as ethylene, vinyl chloride etc. » Total molecular weight of polymer chain segment is an exact integer multiple of molecular weight of monomers.

ii). Condensation or Step polymerization »

» Step by step condensation of monomers to yield long chain. >> The reaction is accompanied by elimination of small molecules like water or HCl etc. >> Total molecular weight of polymer chain segment is not an exact integer multiple of molecular weight of monomers. >> It takes place when condensing functional group pairs are present like -OH and -COOH or -NH2 and -COOH etc


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Co– polymerization »

» Two or more different types of monomers undergo polymerization together to give

co– polymer.

Example BuNa-S (Addition Co-polymer)

Example Kevlar (Condensation Co-polymer)


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BUNA-S BS RUBBER: Random copolymer of butadiene and styrene. BuNa-s is a trade name. Bu stands for butadiene, Na stands for sodium(Na) initiator, S for

styrene. It was initially synthesised using sodium initiator. Other trade names are GR-S (Govt. Rubber

styrene) SBR (styrene butadiene rubber).

Synthesis: Formed by addition co-polymerization between Butadiene (75 %) and styrene (25%) By

emulsion polymerization of butadiene and styrene using peroxide initiator and a temperature of

about 5⁰C. Therefore it is also called cold rubber.

Properties and applications BuNa-S

Prop: It is a synthetic replacement of natural rubber (it is not a chemically synthesised natural

rubber).

Prop: It is vulcanizable with sulphur (but requires only little amount).

Application:

Replacement for Natural Rubber Make light duty tyres.

Making Gaskets, foot wares, shoe soles, conveyor belts etc Prop: It has good adhesive properties and water repellent nature

Application:

Used as a binder in adhesives

Used for making tank lining.

Prop: It is sensitive to ozone. (degrade in presence of ozone)

Prop: It is electrically non-conducting but does not have fire retardant nature .


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ABS Acrylonitrile Butadiene Styrene Plastic

It is formed by addition polymerization. It is a ter-polymer of Acrylonitrile, butadiene

and styrene

.

Properties and applications of ABS Plastic

High Impact Strength (Making Automotive parts)

Electroplatable (metallic finish can be obtained -- Shower heads, door handles etc)

Scratch and wear resistant (TV cabin, radio casing, Key board caps, musical

instrument casing etc)

Electrically non-conducting


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ADVANCED POLYMER - KEVLAR (invented by Stephanie Kwolek)

Kevlar is a condensation copolymer of 1,4-phenylene-diamine and terephthaloyl

chloride. It is a poly-Aromatic-Amide (Aramides). It is a super strong plastic.

Wet spinning of the synthesized Kevlar will result in fibre.

Fibers are long thread like material having high tensile strength. The polymer chain

segments are held together by very strong intermolecular interactions (Hydrogen

bonding and aromatic pi – pi interaction.

Property 1: High strength to weight ratio than steel {stronger than steel and light

weight)

Application: Body armour, Military helmet, bulletproof vest, Formula 1 car body

parts.

Property 2: Heat resistant, does not melt and fire retardant

Application: Fire proof Clothing, Formula 1 car petrol tanks

Property 3: Difficult to cut and drill,


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Applications: Cut resistant lathe gloves, In order to protect from puncture

cycle tyres are lined with Kevlar. Shark like chewing on undersea internet cables so

Google wraps them in Kevlar (to protect from shark bites).

What is Wet Spinning?

Wet Spinning is a manufacturing process for creating polymer fibres. The polymer is

converted into visco-fluid state by heating, then the molten polymer is passed through a

spinneret and allowed to cool. The liquid-to-fibre formation process is similar to the

production process for cotton candy (Panji Muttai)


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ADVANCED POLYMER - POLYBUTADIENE (PBD) RUBBER

A synthetic rubber Homo polymer made monomer 1,3-butadiene by addition polymerization. 1,3-butadiene can polymerize in 3 different ways,

Depending on the percentage of each fragment on the polymer chain the properties changes. High cis-polybutadiene: Ziegler-Natta polymerization yields high cis variety. Catalyst is combination of transition metal halide + organometallic compound. Neodymium metal halide gives 99% cis and straight chained polymer, where as copper catalyst highly branched structure. Organo-lithium catalyst gives a mixed product with 40 % cis, 50 % trans and 10 % vinyl Vinyl content increases the Tg and plasticity. Transition Metal catalyst gives high trans polymer. But it is a plastic material.

Properties: High cis variety is an elastomer.

It has better green resistance (it is resistant to deformation and fracture before

vulcanization)

It has cut growth resistance (Tear and crack wont propagate during dynamic operation.

It has high elasticity and resilience and good abrasion resistance.

Applications of PBD Manufacture of tyres (tyre treads and side walls) Vulcanized PBD is used to make bouncy balls Golf ball inner core is made using PBD.


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ADVANCED POLYMER - SILICONE POLYMER

Silicone polymers have Siloxane bonds (-Si-O-Si-O-Si-O-Si-) . Siloxane bonds are highly

stable than -C-C- bonds. Therefore silicon polymers have higher heat resistance, better

electrical insulation property and high chemical stability

Synthesis/preparation

.

:

Functionality of monomers


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Depending on the degree of polymerization and percentage of above fragments in a

polymer chain, silicon polymers can be in liquid, semisolid, rubber like or hard material.

Silicone polymers on vulcanization/curing (linking) give silicone rubber.

Vulcanization/Curing methods to produce silicone rubber:

Method 1: Peroxide Curing:

Vinyl terminated silicone poymers on treatment with a peroxide gives silicone rubber.


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Method: Addition Curing: H-Terminated silicone polymer adds to a Vinyl

terminated silicone polymer in 1,2-addition.

Method : Condensation Curing: Acetate [CH3-COO-] terminated silicone polymer

condenses with OH terminated silicone polymer with the elimination of acetic acid.

Properties and application of silicone rubber:

Elastic rubber like nature --- Used to make air craft tyres.

They have adhesive properties, water repellent nature -- Used as sealants for

bathroom fittings, fish tanks etc.

They have excellent heat resistance – Used to make pastry brush.


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They have high chemical stability and bio compatible– Used to make baby teether,

artificial heart valves etc

They are used as drying oil in paints to get protection against weather changes.


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Conducting polymers

» Polymeric materials that conduct electricity.

The conducting polymers are of two basic types,

‡ Intrinsically conducting polymers – Where the polymer material itself conducts. The

conductivity can be semiconducting or metallic like conducting.

‡ Extrinsically conducting polymers – Here polymeric material is non-conducting. Polymer on

which conductivity is induced by adding graphite or aluminium powder or a conducting polymer.

‡ Intrinsically conducting polymers – Where the polymer material itself conducts. Two types

A. Conjugated π-electron conducting polymers: Polymers having large number of conjugated

double bonds (alternating single and double bond). The band gap of these polymers is in

between 1 to 2 eV. So they are semiconducting in nature.

B. Doped Conducting Polymers: By removing electrons (creating holes) by oxidation or

inserting electrons by reduction into the material makes the band gap smaller and enhances

the conductivity. This process is called doping. By doping conductivity can be improved up to

metallic regime.

Types of doping

p-doping : Some electrons are removed from the semiconducting polymer chain by oxidation.

The radical cation produced is called polaron. If two radical centres are created then it is a bipolaron.

The polarons are mobile and can move along the polymer chain by resonance delocalization. Hence

the polymer becomes conducting.

The oxidation process can be brought about by chemically by allowing the polymer to react with

Lewis acids FeCl3 or with oxidizing agents like (I2, Br2, AsF6 etc)


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n-doping : Some electrons are inserted to the semiconducting polymer chain by reduction. The

reduction can be brought by an electrode process or treating the semiconducting polymer with

Lewis bases like sodiumnaphthalide or alkali metals.

Factors affecting conductivity

1. Band gap : Band gap increases conductivity decreases.

2. Density of charge carriers. : Polaron density increases conductivity also increases.

3 . Temperature : The conductivity of a conducting polymer decreases with decrease in

temperature in contrast to the conductivities of metals which increases with decrease in

temperature

Advantages of conducting polymers.

1. Low cost fabrication

2. Flexible

3. Polymers are easy to process.

4. Tuning of properties can be achieved by substitution.

5. Light weight.


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Applications of Conducting polymers.

1. Can be used as antistatic coating material.

By coating with a very thin layer of conducting polymer it is possible to prevent the build up

of static electricity. This is particularly important where such a discharge may be dangerous

in an environment with flammable gases.

2. Artificial nerves.

Due to the biocompatibility of some conducting polymers it can be used to transport small

electrical signals through the body. Ie they can act as artificial nerves.

3. Electroluminescent devices.

Electroluminescent means light emission stimulated by electric current. Electroluminescent

polymers can be used as display screens.

4. Photovoltaic cells.

Conducting polymers can be used to harvest light and convert it to electricity.

5. Electrochromic Screens. Fully oxidized form, partially oxidized form, fully reduced form and

partially reduced forms of conducting polymer have different colours. They can be used for

electro chromic screens.

6. Super Capacitors: rapid charge-discharge cycles and high capacitance.

Polyaniline conducting polymer PANI.

Chemical Synthesis

- is conducting

Amine monomer and oxidant is dissolved in 1M HCl and mixed. The reaction is highly exothermic.

Electrochemical Synthesis

Reactor vessel is equipped with 3 electrode assembly.

A working electrode (anode) on which the polymer is formed by oxidative polymerization.

Other two electrodes are a Pt electrode and reference Saturated Calomel Electrode.

Electrochemcial solution contains the monomer, supporting electrolyte and a solvent.


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Synthesis can be carried out either potentio-statically (constant voltage) or galvano-statically

(constant current). Potentio-static condition will give thin filims. Galvano-static condition will give

thick film.

Advantages of electrochemical Synthesis

Simple, Less expensive, no need of catalyst etc.

Properties and Applications of PANI

Light weight, Flexible, low cost etc.

By doping conductivity can be changed.

Has electrochromic properties.

Chemcial sensors, Electrochromic displays, Antistatic coating material, flexible electrodes,

Super capacitor etc

Polypyrole conducting polymer PA

Chemical synthesis by oxidative polymerization

Monomer pyrrole and an oxidant ammonium persulphate is mixed well at room temperature in a

suitable solvent.

Polypyrrol can be doped to increase their conductance by oxidation or reduction.

Electrochemical Synthesis

Reactor vessel is equipped with 3 electrode assembly.

A working electrode (anode) on which the polymer is formed by oxidative polymerization.

Other two electrodes are a Pt electrode and reference Saturated Calomel Electrode.

Electrochemcial solution contains the monomer, supporting electrolyte and a solvent.

Synthesis can be carried out either potentio-statically (constant voltage) or galvano-statically

(constant current). Potentio-static condition will give thin filims. Galvano-static condition will give

thick film.


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Advantages of electrochemical Synthesis

Simple, Less expensive, no need of catalyst etc.

Properties of PPY (Polypyrrole)

Light weight, Flexible, low cost etc.

By doping conductivity can be changed.

Has electrochromic properties.

Biocompatible

Applications of PPY

Catalyst support for fuel cells

Artificial muscles and nerves

Solar cells

Polymer LEDS

OLED Organic Light Emitting Devices/Diodes

Works on the principle of electroluminescence

Certain materials can emit light in response to an electric current passing through it.

Basic Architecture of OLED


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Mechanism

Hole and Electron recombine in the EML to produce light.

If all the layers are made of small organic molecules then we call it as Small Molecule OLED

If any of the layers is a conducting polymer then we call it as Polymer LED (PLED).

The device architecture can be simplified to a bilayer device if the EML material has either electron

transporting property or hole transporting property.

If the EML material has both hole transporting and electron transporting property then the device

will be single layered one.

Advantages of OLED: Light weight. Very Small thickness. Flexible. Less Power required. Higher Brightness No need of back light when compared with LCD

Applications of OLED:

Full Colour Display Screens

White OLEDs for Solid state white lighting

Roll-up displays – OLED printed in fabrics, flexible displays etc.


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Nanomaterials.

Materials with at least one external dimension in the size range 1 to 100 nm (nano-scale). Examples DNA strand (width of DNA strand is approximately 2 nm), Fullerene (n nano size carbon allotrope), nano gold etc

Classification of nanomaterials.

Based on dimension: Zero dimension – All three dimensions are in nano-scale (example nano-particles). One Dimension – One dimension is outside the nano-scale (example nanorod, nanowire, nanotube). Two Dimension – Two of the dimensions are not confined to nano-scale (example nanosheet, nanolayer, nanocoating). Three Dimension - They are bulk nanomaterials. Example aggregates of nanocrystals to form a bulk structure or a bundle of nanowires. Based on the material: Carbon based nanomaterial – It contains only carbon. Examples are carbon nanotube, fullerene, graphene sheet. Metal based nanomaterial – Contains metals. Examples are mono-metallic nano particles like nano-gold, nano-silver etc, mixed metal nano particles like CdTe and GaAs semiconductors, metal oxide semiconductor electrodes like TiO2 and ZnO nano particles.

Biological nanomaterials – Materials in biology. Examples are DNA strand, protein strand etc. These materials can sense, grow, replicate, heal etc, so they are smart materials. Understanding these materials helps to develop new smart materials. Therefore study of biological nanomaterials is very interesting one. Nanopolymers – Polymers in nanoscale. Example dendrimers – tree like polymers, they have well defined cavities which find application as drug carriers in medicine. Nanocomposites - Nanomaterials have high strength to weight ratio. Composites made of nanomaterials as reinforcing agents are having light weight with good strength.


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Properties and applications of nanomaterials.

In catalysis: Nanoparticles have high surface to volume ratio. Hence they act as efficient catalyst. High Technology application: Nanomaterials have interesting semiconducting and optical properties. Therefore they find applications is solar cells, semiconductor devices, Non-linear optical devices etc. Nanocomposites: Nanomaterials have high strength to weight ratio. Therefore they are used as a reinforcing material to prepare nanocomposites having light weight and good strength. In medical application: Biocompatible nanomaterials tagged drugs created the possibility of diagnosing and treatment of cancer like diseases. Nanotechnolgy can be used for delivering drugs to specific cells using nanoparticles. Thus overall drug consumption and side effects can be significantly lowered. In textiles: Adding nanoparticles enables anti odour functioning, wrinkle free functioning and stain resistant functioning.

Chemical Methods for preparation of nanomaterials.

Hydrolysis (Hydrothermal and Sol-gel methods)

Hydrothermal / Thermal Hydrolysis (For preparation of Metal Oxides nano particles)

Nanomaterials are synthesis under high Temperature and Pressure in water medium.

Precursor materials are insoluble at ordinary temperatures and pressures, but solubility

increases at higher temperature.

Synthesis is carried out in autoclaves (sealed steel cylinder) that can withstand high

temperature and pressure.

Precursor material along with mineraliser (to increase solubility) is placed in the bottom of

autoclave and is heated. The precursor material will dissolve.

The temperature in the dissolving region is relatively higher than the temperature at

crystallizing zone.


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This temperature gradient results in a natural movement. The bottom warm solution is

less dense so moves upward to the crystallizing zone. The cooler temperature in the crystallizing

zone leads to super-saturation of solution. Nano sized materials precipitates out. The cool dense

fluid sinks to the dissolving region and the cycle continues.

Aqueous sol-gel process. (For preparation of Metal Oxides nano particles)

In aqueous sol-gel process a precursor solution is converted into nano-sized inorganic solid

via polymerization reaction induced by water.

Common precursor materials are metal alkoxide or any metal salts.

Steps involved, a. Preparation of a homogeneous solution of precursor material in water. b. Conversion of the homogeneous solution into a sol by treatment with water

(Hydrolysis). c. Further polycondensation results in a gel (interconnected, rigid and porous inorganic

networks enclosed in liquid phase). d. Dry the gel. Removal of solvent in the gel by evaporation results in the shrinking of

pore volume of the gel structure and results in XEROGEL. If the solvent in the gel is removed at super critical condition, the network structure is retained and results in AEROGEL.

Advantage of sol-gel process:

Shape the material into any desired forms such as films, fibres, mono-sized

powders etc.


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Reduction (Another Chemical Methods for preparation of nanomaterials) Chemical Reduction (For preparation of Metal nano particles – Silver nano particles)

Metal salt solution is reduced by adding reducing agents such as Sodium borohydride,

glucose, hydrazine etc.

Steps:


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Electrochemical reduction:

Similar to electro plating an electrolysis cell is constructed

Steps:

The anode is the bulk metal copper for copper nano particle production. Oxidative dissolution

take place at anode. Cu Cu2+ + 2e

Migration of Cu2+ towards cathode.

Reductive formation of Cu metal at the cathode Cu2+ + 2e Cu

Aggregation of Cu to form Copper nano particles.

Arrest the growth and stabilize the nano particle by adding surface protecting ligands.

Advantages of electro Chemical reduction

Low cost, simple, pure product etc.


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Carbon nano tube (CNT).

It is a carbon based nano tube. All carbon atoms are sp2 hybridized. All carbon atoms are in hexagonal framework. The shape is like a graphene sheet rolled up into a seamless cylinder. Open ends and closed ends are available. CNT with many radii can be found. Two types single walled CNT (one atom thick sheet of graphene rolled into a cylinder) and multi walled CNT (contains many concentric cylinder).

Based on lattice folding, three types of CNT (Chiral, Armchair and ZigZag) Properties of CNT Their tensile strength is greater than steel of same dimension. Youngs modulus is greater than steel. They have high thermal conductivity more than silver. They have light weight, density about 1/4th of steel. Some of them conduct electricity better than metals. Applications of CNT: Nanoelectronics: Depending on the size and structural variations their electrical conductivity differs. Hence some are semiconductors and some are conductors of electricity. Therefore used in semiconductor technology, display devices etc. Strengtheners: CNT has the highest strength to weight ratio. So it can be used to make nanocomposites to build light weight materials with good strength. Medical Applications: CNT is helpful in diagnosing and treatment of cancer like diseases. They are used for drug delivery. The overall drug consumption and side effects can be considerably reduced. Chemical and Bio-Sensors: CNT is chemically modified to obtain selectivity towards a particular material. When this material makes an interaction with CNT, its electrical or optical property changes. so we can identify the presence of that material. Good Adsorbing Material: CNT has high surface to volume ratio and carbon has adsorbing ability, so these materials are good adsorbent materials. Probe tips for Surface Scanning Techniques: High resolution is obtained when using CNT as probe tips.


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Carbon Fullerene

Fullerene is a nanosize allotrope of carbon. Carbon atoms are linked together in hexagonal or

pentagonal framework. Examples are C60, C70, C76, C80.

In C60 fullerene there are 60 carbon atoms, all are in sp2 hybridization. There are twelve pentagons

and 20 heaxagons in C60 fullerene. Each pentagon is surrounded by five hexagons. Pentagons does

not touch each other.

Properties: Thermally stable upto 400 ⁰C Excellent photo-stability Are electron acceptors Applications Super Conductor: Alkali metal doped fullerene behave like super conductor Medical Application: Fullerene have antiviral activity. Chemically modified fullerene can inhibit HIV. Photodynamic Therapy: They can act as Photo-sensitizer, therefore used in photodynamic therapy for the creation of singlet oxygen. Good Adsorbing Material: CNT has high surface to volume ratio and carbon has adsorbing ability, so these materials are good adsorbent materials. Solar Cells: They have high electron affinity. They have electron transporting ability. Fullerenes are used as electron acceptors in Bulk-hetero Junction solar cells. Hydrogen gas storage:

Fullerene can reversibly store 18 molecules of hydrogen.

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IV| Engineering Materials ----Polymers and Nano Materials · IV| Engineering Materials ----Polymers and Nano Materials 3 | P a g e BUNA-S BS RUBBER: Random copolymer of butadiene