Unit No- 03 Engineering Materials

A-Specialty Polymer Engineering Thermoplastic Bio-degradable Polymer Conducting Polymer Electroluminescent Polymer Polymer Composites

B – Nanomaterial

Important application of Nanomaterial Classification of Nanomaterial Important properties of Nanomaterial Graphene Carbon Nanotubes Quantum Dots

1: Engineering Thermoplastics:

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

Advantages of Engineering Thermoplastics –

High thermal stability High tensile strength High mechanical strength Readily mouldable into complicated shapes Excellent Chemical resistance High dimension stability Engineering Thermoplastics - Polycarbonate

Polycarbonate is obtained by interacting Bisphenol A with Diphenyl carbonate

Properties:

High tensile strength Transparent refractive index 1.58 Dissolves in organic solvent and alkali, not resistant to UV. Resistant to water and many organic solvent. Good heat resistance

Application:

As a bullet proof material vests ,for windows of vehicle, tough cabinets ,cover etc

Moulded domestic ware , helmets, cover of vehicle light Data storage – CD and DVD As insulator in electronics. Handles of screw driver, for pliers etc.

2: Biodegradable Polymer:

Biodegradation is the process of converting polymer material into harmless simple gaseous products, by action of enzymes of micro-organism and water.

Factors responsible for biodegradation of polymer –

a) Microorganism – Naturally occurring microorganism such as bacteria, fungi and algae are responsible for biodegradation of polymers, by breaking C-C bond. Process takes place at slower rate.

b) Environment – For the survival, action of microorganism and for biodegradation process to function suitable condition like temperature, moisture, light , oxygen, pressure are important .

c) Nature of polymer –For biodegradation, nature of polymer should be favorable. Biodegradation process proceeds by hydrolysis and oxidation.

Classification of biodegradable polymer:

i) Natural biopolymer : Originating from plant or animal resource .e.g. cellulose, starch, protein etc

ii) Biosynthetic biopolymer : Produced by fermentation process by microorganism .e.g.polyhydroxy alkonate

iii) Synthetic biopolymer: Polymer produced synthetically .e.g. polylactic acid, polycaprolactone.

Application of biodegradable polymer:

1: As packing material: used for disposable plastic packaging material, food packaging, foam for industrial packaging, film wrapping etc.

2: Medical application: used in controlled drug delivery, absorbable surgical implants, cell transplantation etc

3: Agricultural application: used as time released coating for fertilizers and pesticides. Making film for moisture and heat retention.

Biodegradable polymer – Polyhydroxybutyrate –hydroxyvalerate (PHB-HV)

Properties –

The resistance of PHBV to oil is very good. Highly crystalline, optically active. Soluble in chloroform. Polymer is moisture resistant and impermeable.

Application:

Used for moulded article, film for packaging and lamination. Useful for medical and veterinary application. Used for sustained release of fertilizers, medicines, growth hormones for

plant. Useful for surgical, organic transplant and orthopedic operations.

3 : Conducting Polymer :

Organic polymers are bad conductors of electricity because of non availability of free electrons.

Type:

1: Extrinsically conducting polymer: An extrinsically conducting polymer material is one which is filled with metal powder, metal filaments or graphite powder to make it conducting.

2: Intrinsically conducting polymer: An intrinsically conducting polymer material is he one which conduct electricity by its own.

Structural Requirement:

The polymer chain contains conjugation (alternate sigma and pi bond) throughout chain o that there are resonating or mobile electrons for conduction.

Polymer is highly crystalline and there is high planarity in structure. Presence of aromatic ring in the chain with continuous resonance.

Polymer should have linear chain.

Doping of polymers:

The conductivity of polymer chains with conjugation can be increased to the extents of metal on doping.

In doping process, the polymer is either oxidized (removal of electrons) or reduced (addition of electrons), so the polymer chain carries the resonating charge.

Important doing reaction for Polyacetylene:

a) Oxidative or p-doping: The oxidizing reagents for p-doping are like iodine vapours, I2 dissolved in CCl4 , HClO4 , Br2 etc.

(CH)n 3/2 I2 (CH)n+I3

-

Polyacetylene Polyacetylene chain with positive charge

The positive charge resonance throughout the polymer chain and can be transferred to the neighboring chains through I-

2 .

b) Reductive or n-doping: The reducing agents for n-doping are like Na metal, FeCl2, lithium metal, sodium naphthalide etc.

(CH)n Na (CH)-Na+

Polyacetylene Polyacetylene chain with negative charge.

The negative charge resonates throughout the chain and transferred to neighboring chains, through Na+ during conduction.

Polyacetylene:

Structure:

Properties:

Bulk density 0.4 g/cm3. Insoluble in solvents, making it difficult to process the material. Films containing the cis form are coppery while the trans form is silvery. High thermal stability but exposure to air causes a large decrease in the

flexibility.

Application:

Rechargeable batteries – because of high charge carrier concentration, they are used as charge storage material.

As antistatic material: To avoid static electricity in plastic, carpet in offices, theaters doped polymers can used.

Optical filters: Radiation from computer screen, other electrical devices can be absorbed by conducting polymer by coating on screen .

In electronics: can be used for photodiodes, light emitting wall papers, LED, and data storage .

4: Electroluminescent polymer:

The property in which a material produces bright light of different colours when stimulated electronically is known as electroluminescence. The material which shows electroluminescence is known as electroluminescent polymer.

Polyparaphenylene Vinylene (PPV) :

Properties:

PPV is diamagnetic material It gives bright yellow-green fluorescence on application of electric field. Very low intrinsic electrical conductivity. PPV is insoluble but its precursors can be manipulated in aqueous solution.

Application:

In the form of thin film for information displays. Automotive instrument backlighting Electroluminescent night lamps. Light strips for decorating building and vehicle safety precautions. Photovoltaic cell.

A basic polymer LED based on PPV:

A typical polymer LED is composed of a layer of electroluminescent polymer (like PPV) situated between two electrodes, the transparent anode (ITO) band cathode (Al , Ca, Mg) all deposited on glass/polymer substrate . An applied electric field leads to injection of holes (Positive charge)and electrons in to the light emitting polymer film from the two electrode contacts.

Recombination of an electron hole pair within the polymer may result in the emission of photons (light) since holes migrate much more easily through PPV than the electrons; electron-hole recombination takes place in the vicinity of cathode.

5: Polymer Composites:

A polymer and a reinforcing material as a two phase mixture with interface between them ,is known as Polymer composites.

The polymer phase is called as matrix phase and the composite used for making is known as Dispersed phase. The boundaries between the matrix and dispersed phase are known as interface.

Function of matrix in polymer composite:

To bind reinforcing particle/fibre strongly. It acts as medium for distribution of applied load to the dispersed phase. It keeps the reinforcing fibers in proper orientation for the high strength

development. It prevents propagation of cracks due to its plasticity.

Classification of Composites:

A: Particle reinforced composites

B: Fibre reinforced Composites

C: structural composites

A: Particle reinforced composites: They are composed of particles distributed 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 shows improvement in tensile strength , toughness and abrasion resistance are used manufacturing automobile tyres.

B : Fibre reinforced Composites : These are composed of fibers embedded in the matrix material.

These are further divided into three categories. Continuous aligned composites, discontinuous aligned and discontinuous randomly oriented fibre composites. In case of discontinuous aligned composites ,its properties vary with fibre length whereas in case of continuous fibre composites the length of fibre if increases does not alter properties like elastic modulus.

C: Structural Composites: Properties of structural composites on constituent of materials and geometrical design of formation.

a) Laminar Composites: A laminar composites made of lamellar sheets that high strength in particular direction (along the direction of alignment of fibers) such as wood.

b) Sandwich panels: Sandwich panels consist of two strong outer faces separated by a layer of less core. Face material is generally fibre reinforced plastic and core material can be synthetic rubber, foamed polymer etc. These type of material is used in air craft wings, Boat hulls, floors, walls etc.

Properties of Composites:

High tensile strength. High thermal stability. High oxidation resistance. High abrasion resistance. Low thermal expansion.

Application of Composites:

i) In automobile body and parts, turbine engines, pumps, valve etc.ii) In fabrication of roofs and floors , furniture iii) In manufacturing sports goods, toys , musical instruments iv) In components of rockets, aircrafts ,helicopters etcv) In communication antenna , electronic circuits boards (PCB).

Types of Fibre reinforced composites:

I) Glass fibre reinforce polymer composites : They use glass fibre reinforced in polymer composites containing nylons , polyesters etc

Advantages:

High tensile strength and impact resistance. Lower densities Excellent resistance to corrosion and chemicals.

Limitations:

Polymer matrix deteriorates or flow at high temperature. Material does not have stiffness and rigidity, cannot be employed as

structural components.

Application: used in automobile parts, storage tank, industrial flooring, plastic pipes etc.

II) Carbon fibre reinforce polymer composites: They use carbon reinforced in polymer matrix like epoxy or polyester resin. Carbon fibers are obtained by pyrolysis of cellulose or acrylonitrile in inert atmosphere.

Advantage:

Excellent resistance to corrosion High elastic modulus Low density High temperature resistance.

Application: Used as structural components (like wings, body, stabilizers) of aircrafts and helicopters, making sports goods, laptops, musical instruments etc.

B – Nanomaterial

Important application of Nanomaterial Classification of Nanomaterial Important properties of Nanomaterial Graphene Carbon Nanotubes Quantum Dots

Nanomaterial is very small size in the range of 1-100 nm. Nanomaterial can be metals, ceramics, polymeric materials or composite materials. Nanomaterial have created interest in recent years because of its unusual mechanical, electrical, optical and magnetic properties.

Classification of Nanomaterial : Nanomaterial are classified as

1: Zero dimensional nanomaterial: have all dimensions within nanoscale range and larger than 100nm. E.g. Particle, quantum dots, hollow spheres etc..

2: One dimensional nanomaterial: nanomaterial having grown along one dimension beyond nanoscale. e.g. Nanowires, nanorods, nanobelts, nanofilms etc

3: Two dimensional nanomaterial : have two dimensions out of scale. e.g. Carbon nanotubes, nanoplates, naosheets , nanoprism , nanowalls etc.

4: Three dimensional nanomaterial: are the bulk nanomaterial which are not confined to nanoscale in any dimension. e.g. fullerene , bundles of Nanowires, bundles of nanotubes etc.

Nanomaterial Features0 D All dimensions at nanoscale 1 D Two dimensions at nanoscale and one dimension at macro scale2 D One dimension at nanoscale and one dimension at macro scale3 D No dimension at nanoscale and one dimension at macro scale

Important properties of Nanomaterial : 1 : Optical properties: of nanomaterial depend on parameter such as size,

shape, surface characteristics and other variable including doping and interaction with surrounding environment. Optical properties of nanomaterial include its use in optical detector, laser, sensor, solar cell, photo electrochemistry and biomedicine.

2 : Electrical properties: of nanomaterial are different than their bulk materials. In electrically conducting carbon nanotubes only one electron wave mode is observed which transport the electrical current.

3 : Mechanical properties: of metallic and ceramic nanomaterial are influenced by porosity, grain size and filler used . Filling polymers with nanoparticle and nanotubes leads to significant improvement in their mechanical properties.

4 4 : Magnetic Properties : Bulk gold and pt are non-magnetic but at nano size they are magnetic. Magnetic nanoparticle of pd ,pt and Au are obtained from non magnetic bulk materials .

Graphene:

Two dimensional graphene molecules – SP2 carbon has three hybrid orbital’s at 1200 angle in one plane (forming sigma bonds with three such carbon) and one unhybridised orbital having one electron at right angle to the plane .

Hexagonal arranged network sheet of carbon atom is formed by joining of each SP3 carbon by pi –bonds. This way of joining the carbons, results in forming huge and flat molecules, with millions of carbon atoms in the plane .There is an unhybridised orbital on each carbon parallel with such orbital’s on the neighboring carbons. Due to resonance phenomenon , the annular rings of the delocalized or mobile electrons are formed . All the annular rings are joined to form region of electrons of all the carbon in the flat molecule, above and below the plane of carbon. These regions contain the freely, mobile or resonating electrons and hence graphene is good conductor of electricity. The C-C bond length is 1.42A0 .The valance and conduction bands are overlapped and there is no energy gap. The two sheets like graphene molecules are at the distance of 3.4 A0 .

Properties:

About 200 times stronger than strongest steel Efficiently conduct heat and electricity and is nearly transparent. Shows large and non linear diamagnetism. It is only form of carbon in which every atom is available for chemical

reaction from two sides.

Application:

Used in solar panels , LEDs, touch panels , smart phone Capacitors , batteries , 3D printer materials Its powder can be used in making polymer composites As transistors for integrated circuits As sensors for gas detection

Carbon Nanotubes (CNT) :

The carbon nanotubes can be considered as the cylinders made of graphite sheets, mostly closed at the ends with hemispherical fullerene or just like as graphite sheet cap.

A carbon nanotubes can be imagined to be formed by folding of graphite sheet just like rolling of paper into a cylindrical form. If rolling of graphite sheet imagined then some lattice strain is due to curvature is expected in the carbon hexagon.

There are two types of CNT- Single walled carbon nanotubes (SWCNT) and Multiwall carbon nanotubes (MWCNT).

There are three types of SWCNT i.e. zigzag, armchair and helical carbon nanotubes. Helical CNT is chiral tube i.e its mirror image is not similar to original structure. Zigzag and armchair CNT are achiral

.

Properties:

CNT have low density for a solid of 1.3 to 1.4 g/cm3 . Moderate chemical stability, high electrical conductivity and extra ordinary

thermal conductivity. Useful absorption, photoluminescence properties. CNT has one dimensional structure. The carbon atoms in CNT are SP2

hybridized. CNT can be made conducting by making its compounds with alkali metals.

Application :

Filtration - CNT can be used to separate particles of size greater than diameter of CNT, during filtration through CNT.

CNT as Nanocylinders –A gas like H2 , for energy battery or vehicle can be safely stored inside the CNT and problem of H2 storage hazards can be solved .

Drug delivery system. Body parts implants Catalysts for certain reaction. Masks, coating etc.

Quantum Dots :

Quantum dots are semiconductor nanoparticle that glow a particular colour after being illuminated by light .

Types of quantum dots :

i) III – V – semiconductor quantum dots – They are made up of elements from Gr. III of periodic table of element (boron, aluminum ,gallium , indium ) and from Gr. V (nitrogen, phosphorous, arsenic antimony )

e.g. Gallium arsenide (GaAs) used as light source in optical data processing.

ii) ii) II – VI – Semiconductor quantum dots : They are made up of elements from Gr. II of periodic table of element ie transition metal (Zinc, cadmium ) and from Gr. VI (oxygen , sulphur, selerium, tellurium) e.g. cadmium selenide ,cadmium telluride , zinc oxide is used in electronics , photovoltaic and biomedicine .

iii) Silicon Quantum dots : They are made up of elements silicon ,which is standard material of semiconductor and chip industry . Silicon quantum dots to be used as a component of optical chip, optical sensors etc.

Properties:

Properties intermediate between bulk semiconductor and discrete atom or molecule.

Properties of quantum dots are determined by size, shape, composition and structure – optoelectronics properties

Fluorescence properties Shows color glow when illuminated by UV light.

Application :

1: Optical application- Light emitting diode, solid state lighting, display and photovoltaic, photo detectors etc.

2: They are widely used in the study of intercellular processes, tumor targeting, diagnostic and cellular imaging at high resolution.

3: Quantum dots being used to produce miniature lasers for use in communication device.

4: Quantum dots can be used in TV or computer displays.

5: Quantum dots can be used to treat antibiotic resistant infection.