POLYMERS AND

COMPOSITES

Dr. SURENDRAN PARAMBADATH (M.Sc, M.Phil, M.Tech)

Formerly: Post Doctoral Research Associate,Nano-Information Materials Research Laboratory,

Pusan National University, Busan-South Korea

Currently: Assistant ProfessorGovt. Polytechnic College, Perinthalmanna

What is a polymer?

• A long molecule made up from lots of small molecule called monomers.

Poly = many, Mer = unit

Macromolecules: If the compound containing hundreds or thousands of atoms per molecule are called macromecules.

Eg: Starch, Cellulose, proteins, nucleic acids, rubber, silk etc.

The repeating unit in the molecule is called monomer.

Polymers consisting of a single type of monomer molecules are known as homopolymers.

The polymers obtained from monomers of different types are called copolymers.

Homopolymer

-A-A-A-A-A-A-A-A-Example: Polythene, nylone-6, Polystyrene, Polyvinyl chloride (PVC)

Formation of homopolymer………………

Copolymer

-A-B-A-B-A-B-A-B-A-B-Example: Nylone-6.6, Styrene-butadiene rubber (SBR), Buna-S, Bakelite.

Formation of Copolymer…………………

POLYMERIZATION

It is the process of chemical combination of two or more smaller and simpler molecules of similar or different types, with or without the elimination of small molecules like H2O, HCl or C2H5OH, resulting in the formation of new C-C or C-N linkages in the product.

Example: Polythene from etheneNylone-6 from caprolactumBuna-S from Butadiene and styrene Nylone-6,6 from Hexamethylene diamine and adipic acid with elimination of H2O.

Polymerization is of two types

1. Addition polymerization

2. Condensation polymerization

1. Addition polymerization

In this type of polymerization, the polymer formed in an exact multiple of monomer molecules and there is no elimination.

This polymerization may initiate by heat or pressure.

nCH2=CH2 -(-CH2-CH2-)-Ethylene Polyethylene

2. Condensation polymerization

In this type of polymerization, chain growth takes place together with elimination of small molecules like water, ammonia, alcohol etc.

This polymerization may initiate by heat or pressure.

HO-CH2-CH2-OH + HOOC-C6H4-COOH

-{-O-CH2-CH2O-CO-C6H4-CO-}-

-H2O

Ethylene Glycole 1,4-dibenzoic acid

Differentiate between Addition and Condensation

Polymerization

No Addition Polymerization Condensation Polymerization

1 Formed by the simple addition of monomers with out liberation of small molecules.

In this process two or more monomers will combine together with the liberation of some simple molecules.

2 Monomers usually contains double or triple bond

Monomers contain two functional groups.

3 The monomers and polymers having the same empirical formula.

The monomers and polymers having the different empirical formula.

4 Most of them asre formed by chain growth polymerization.

Most of them are formed by step growth polymerization.

Classifications Of

Polymers

1 Based upon source

Natural and synthetic polymers

2 Based upon synthesis

Addition and condensation polymers

3 Based upon elements

Inorganic and organic polymers

4 Based upon molecular forces.

Plastic: Intermolecular forces of attraction are intermediate between those of elastomers and fibers. Elastomers: Chains are held together by weak forcesFibers: Held together by strong inter molecular forces.

Elastomer

Plastic

Fibre

A plastic is a material which shows the property of plasticity ie, capacity to change to different forms under pressure.

Plastics may be defined as organic material of high molecular mass, which can be moulded into any desired shape, by subjecting to suitable heat and pressure conditions in presence of a catalysts.

Thermoplastics

• No cross links between chains.• Weak attractive forces between chains broken by warming.

• Change shape - can be remoulded.• Weak forces reform in new shape when cold.

Thermosetting Plastics

• Extensive cross-linking formed by covalent bonds.• Bonds prevent chains moving relative to each

other.

Thermoplastics Thermosetting Plastic

1 They have formed by addition polymerization and usually have linear structure

They have formed by condensation polymerization and usually have three dimensional extensive cross linking between the polymer chains.

2 They are soft, weak and less brittle and are soluble in organic solvents

They are more hard, strong brittle and insoluble in organic solvents.

3 Can be remoulded, recast reshaped, and reused by application of suitable pressure and temperature.

Cannot be remoulded or reshaped. Once set, it cannot be recast by any means.

4 On heating they soften and become fluid but on cooling become hard.

On heating, do not soften, rather they become hard and infusible, prolonged heating make them burn.

5 Eg. Cellulose acetate, PVC, Polythene, Polypropylene, Teflon etc.

Bakelite, polyester, terylene, resins, urea-formaldehyde polymer ect.

MERITS AND DEMERITS OF PLASTICS

1 Light weight, but tough very good tensile strength, high dimensional stability and high refractive index.

2 Low thermal and electrical conductance and high insulating power, low thermal expansion-coefficient, very good shock absorption capacity.

3 Resistance to corrosion and rust, to abrasion, to growth of fungus and insects, action of fumes, gases and corrosive substances.

4 Chemical inertness to acids, oils, dampness, light etc.

5 Capability of being made (a) hard or soft (b) rigid or pliable © tough or fragile (d) opaque or transparent (e) brittle or malleable or elastic (f) wearable, curvable or pourable.

6 Easy workability, ability to take variety of fast and appealing colors, shades. Shining glossy appearance etc.

7 Low fabrication cost and low maintenance cost.

1.Higher cost and combustibility2.Poor ductility3.Softness and deformation under load4.Brittleness at low temperature5.Low heat resistance6.Non biodegradable7.Not easy to dispose off.

Demerits

Elastomers

Elastomers include all those polymers, whose chains are held together by weak forces and hence can be stretched by pulling and on relieving the stress, can be made to regain their original shape.

Eg: Rubber

Natural Rubber

Destructive, distillation of rubber from the tree gives a hydrocarbon C5H8 isoprene-(2-methyl-1,3-butadiene) which is the repeating unit in rubber. Rubber contains 16000-20000 units in one string.

Vulcanization

It is the process of heating natural rubber with sulphur (3-5%), H2S, benzoyl chloride to a temperature range 110-140oC.

Merits of Vulcanization

1. It helps in preventing the slippage of chains on application of stress.

2. It makes rubber less sensitive to temperature changes.3. It increases elasticity, tensile strength and extensibility.4. It increases the resistance of rubber to oxidation, abrasion, wear

and tear, water and organic solvents. 5. Rubber becomes a better electrical insulator as a result of

vulcanization

Applications of Rubber

1. For making rubber bands, golf balls, mechanical rubber goods, rubber gaskets for sealing equipments like pressure cooker, refrigerators doors etc.

2. For making automobile and aeroplane tyres due to its abrasion resistance.

3. In telephone receivers, battery cases, electrical switch board panels etc.

4. Due to its remarkable resistance to electricity used for insulating coating on wires and cables.

5. In medicine, rubber is used for making heart valves, transfusion tubings, padding for plastic surgery etc.

6. It finds uses as an eraser and adhesive too.

Synthetic Rubber

These are man made, rubber like polymer………………

Eg: Buna-S, Thiokol, Buna-N

Name Uses

1 Buna-S Manufacture of motor tyres, floor tiles, gaskets, wire & cable insulation.

2 Buna-N Conveyer belts, high altitude air craft components, hoses printing rollers, automobile parts.

3 Neoprene Wire insulations, cable covering for conveyer belts and chemical apparatus, sponges etc.

4 Butyl Rubber Cycle and automobiles parts, tank linings

5 Thiokol Hoses, gaskets and covering for cables.

6 Silicon rubber Artificial heart valves, transfusion tubes and padding for plastic surgery, in lubricants, paints and protective coatings, shoes.

Fibre

Fibres are thread like bits of materials characterized by great tensile strength in the direction of the fibre. Cloths are making from fibres.

Types of Fibre……………..1.Natural fibre, obtained from natural sources

like cotton, jute, wool and silk.2.Semi synthetic fibres, obtained from natural

sources eg: cellulose, which is heated with special reagents to bring it to solution or dispersed state and then turned into filaments

Eg: Rayons.3.Synthetic fibres, obtained by addition or

condensation polymerization. Eg: Nylon, terylene, orlon etc.

A fibre may be defined as a flexible macroscopically homo-geneous body of high tensile strength, possessing a high ratio of length to thickness and a small cross section.

The main characteristics of a fibre forming polymer are,

1 Should be convertible to a dissolved form and then spun into fine fabric.

2 Should posses high tensile strength to produce stable fibre.

3 Should have sufficient resistance to light, heat and air-oxidation.

4 Should be able to take fast colours.

Some Important Synthetic Fibres

Nylon 6,6It is formed by the condensation polymerisation of adipic acid and hexamethylene diamine.It is a polyamide polymer.

n HOOC-(CH2)4-COOH

+ n H2N-(CH2)6-NH2

-[-OC-(CH2)4-C-NH-(CH2)6-NH-]n-

O

n H2O+

Nulon-6,6 is stronger than natural fibres. They are elastic, light weight, very strong and flexible, inert to chemicals and biological agents and are used in making fabrics, carpets, tyre cords, ropes etc.

Adipic acid Hexamethylene diamine

Nylon 6It is manufactured by prolonged heating of caprolactum at 260-270oC.It is another polyamide polymer.

260-270oC

CH2

CH2 C=O

HN

CH2CH2

CH2

Caprolactum

-[-C-NH-(CH2)5-]n-

O

Nylon 6

Terylene or Dacron

Condensation polymerization of terephthalic acid and ethylene glycol, in presence of a weak base results in the formation of the most important polyester fabric named Terylene.

COOHHOOC+

OH-CH2-CH2-OH

-[-OC-C6H4-CO-O-CH2-CH2-O-]n-

Teraphthalic acid Ethylene Glycol

Orlon

Polymerization of acrilonitrile (vinylcyanide) in presence of FeSO4 and H2O2, gives orlon.

It is water resistant quick drying, can be woven or knitted, can be blend with wool, used in making cloths, carpets, blankets etc.

n CH2=CHCN -[CH2-CH-]-

CN

Polymerization

Fe2SO4/H2O2

Composites

Composites are reinforced plastics.

Composites consists of two components,

1. Matrix phase and 2. Dispersed phase

1. Matrix Phase

Matrix phase is the main part of the composite.

Metal can give metal matrix composite,Ceramics can give ceramic matrix composite,Polymer can give polymer matrix composite.

Matrix should satisfy the following criteria,

2. It should be ductile3. The bounding between the matrix and the filler should be

strong.4. The fibre and matrix should be chemically compatible with

each other.

2. Dispersed phase

The reinforcing material should be strong and stiffer than the matrix to increase the strength of the matrix.

Wood floor, Asbestos, Clay, marble powder, mica, graphite, fibres of glass, cotton, carbon or ceramic may be used as dispersed phase.

Metallic oxides like ZnO, PbO or powders of metals like Si, Cu, or Pb are also used.

On the basis of the structures of the reinforcing material, the composites are classified as,

1. Fibre reinforced composite: In this type of composite, fibers are embedded in a suitable matrix.

2. Particulate composite: These contain particles of a wide range of size dispersed in a matrix.

3. Dispersion hardened composite: These contain very fine particles dispersed in a matrix.

Fibre reinforced composite

Glass Reinforced Plastics (GRP)

GRP are the most common example of fibre reinforced plastic. In this plastic acts as the matrix glass fibre as the dispersed phase. These have low density, high tensile strenghth, resistance to thermal and chemical corrosion.

GRP finds use in1. Plastic pipes2. Storage tanks3. Speed boats4. Flooring materials5. Automobile parts6. Battery boxes.

Thank You