PLASTICS

Topics

• Definition of plastics and engineering plastics

• Types

• Merits and Limitations

• Preparation, Properties of a few important plastics

DEFINITIONSociety of Plastics Industry

“Any one of a large and varied group of materials consisting wholly or in part

of combinations of carbon with oxygen, nitrogen, hydrogen, and

other organic or inorganic elements which, while solid in the finished

state, at some stage in its manufacture is made liquid, and thus capable of being formed into various shapes, most usually through the

application, either singly or together, of heat and pressure.”

Plastic is an organic composite which can be moulded to required shape by the application of heat and

pressure

Types

Based on Applications

�Engineering

�Commodity

Based on Thermal properties

�Thermoforming (TP)

�Thermosetting (TS)

Engineering Plastics(Industrial / Structural)

• Plastics that have very well defined mechanical properties, usually very tough and high strength,

Examples : Acetal, Polycarbonate, Nylon and Polyesters etc

Commodity Plastics(House hold / Domestic)

Plastics that are used for consumable

items that do not require high strength

and hardness

Examples

Polyethylene, Polystyrene and

Polypropylene etc

Boon

i. LOW THERMAL CONDUCTIVITY(ABS, PC, NYLON, PVC, BAKALITE, etc )

ii. GOOD FLAME RETARDANT ( PVC , PPO)

iii. LOW SPECIFIC GRAVITY (1/2 of Al and 1/6th of steel – PE , PS, PVA etc)

iv. LOW COEFFICIENT OF FRICTION ( hence used in gears - TEFLON, ACETAL and NYLON are classic examples)

v. EXCELLENT TRANSPARENCY (contact lenses, or camera lenses , wind shields – PVA , PC etc.,)

vi. WATER RESISTANCE (Polyester and Polyamides)

vii. CHEMICAL RESISTANCEMost plastics resist chemicals on a selective basis. Some are resistant to almost all chemicals.

viii. Bio –compatible (no allergic reactions – PC)

ix. COLOR : Easy to colour ( does not fade)

x. EASE OF MASS PRODUCTION

Bane

i.HIGH COEFFICIENT OF THERMAL EXPANSION (on comparison with other materials of same strength)

ii. Low Thermal Stability : Some gives out poisonous gas on heating

iii. High Weathering

iv. NON BIODEGRADABLE

General Method of preparationof Homopolymers

CHX =CHY ----------► [-CHX – CHY-]n

TeflonX,Y = F

2H = F

PVCX=H

Y=Cl

PEX and Y =H

Poly

Vinyl Chloride

PREPARATION

Raw materials : Acetylene and HCl

Catalyst : Metal Chloride

Temperature : 60 – 80 oC

Pressure : 1 to 1.5 atm.

Polymerisation in presence of benzyl peroxide or H2O2 in an autoclave

nHC≡CH +nHCl →nCH2=CHCl ▬►[CH2- CHCl]nVC PVC

PROPERTIES

• Non flammable,

• Chemically inert,

• resistant to atmospheric oxygen light and inorganic acids and alkalis

• soluble in chlorinated hydrocarbons (ethyl chloride)

• Rigid and brittle.

• High Softening point (148oC)

USES

Rigid PVC / Un-plasticised PVC

• Sheets for tank lining

• Electrical Fittings

• Safety Helmets

• Fridge Components

• Tyres

• Cycle and Motor Cycle Mud gaurds

Plasticised PVC

• Table Cloth

• Rain Coats

• Electrical insulation Cables and Tapes

• Packing Material

• Radio Components

• Plastic Coated Textile

• Thermal insulating foams for aeroplanes

• Coal mine conveyer belts

Teflon/Fluon

PREPARATION

Polymerisation of tetrafluoroethylene in presence of benzoylperoxide in an autoclave

nCF2=CF2 ▬► [CF2- CF2]n

PROPERTIES

• Very Tough

• High Softening point (350oC)

• Good Chemical resistance

• High density (2.1g/cm3)

• Very Low Co-efficient of friction

• Good Electrical and mechanical properties

USES

• Non stick kitchen ware

• Insulating material for motors

• cables wires

• Gaskets,

• chemical carrying pipes

• Tank linings

• Coating glass and asbestos fibres

• Self lubricating bearings and stop cocks (burettes)

Poly Carbonate/Lexan /Merlon

PREPARATION

Raw Materials: diphenyl carbonate and bisphenol-A

n [C6H5-O]2CO+ n HOC6H4-C(Me)2-C6H4OH

↓

[-O-C-O-C6H4-C(Me)2-C6H4-O-]n||

O + 2nHOC6H5

PROPERTIES

• High impact strength

• High tensile strength

• High thermal stability

• Soluble in organic solvents and alkalies (due to the presence of phenolic OH)

• Transparent

• Good dimensional stability

• Rigid

• Admirable biocompatibility

USES

• Domestic cook ware (Micro wave safe)

• Electrical insulator

• Used in making camera and binocular bodies

• Solar collectors

• Lenses and photographic films

• It finds application as dental and ocular implants due to its exceptional strength and bio compatibility

Poly Urethane (or) Perlon-U (or) Spandex

PREPARATION

Raw materials : 1,4-butane diol and hexane methylene 1,6- di-isocynate

HO(CH2)4OH+O=C=N-(CH2)6-N=C=O

↓↓↓↓-[O(CH2)4O-C-HN-(CH2)6-NH-C]n-

ǁ ǁO O

PROPERTIES

• Low thermal stability

• Excellent abrasion resistance

• Insoluble in solvents

• Good impact resistance

• Tough

• Flexible

USES

• Used as adhesives

• Foamed poly urethane is used as packing material(Thermocole)

• Compounded poly urethane foams (coirfoam)are used as mattress and door mat

• Used as a substitute to leather (rexine).

• Used to make gaskets and seals

Nylon 6:6

PREPARATION

Raw Materials: Adipic Acid and Hexamethylene diamine

HOOC(CH2)4COOH + H2N(CH2)6 NH2

↓↓↓↓- [OC(CH2)4CON(CH2)6 NH]n-

l

H

PROPERTIES

• High Melting point (255oC)

• Translucent

• Good Thermal Stability

• Good Abrasion resistance

• Insoluble in common organic solvents

• Soluble in organic acids and phenol

• High Impact strength

• Self Lubricating

USES

Nylon 6:6 fibres are used for making

• Socks

• Carpets

• Dresses

• Upholstery

• Tooth brush bristles

• Due to self lubricating property, used in making bearings and gears

PET

Poly Ethylene Terephthalate (or)

Terlene (or) Dacron (or) Diolen (or) Trevira

PREPARATION

Raw Materials: Ethylene glycol and

Terephthalic acid

nHOCH2–CH2OH+n HOOC –C6H4-COOH

↓↓↓↓-[OCH2–CH2O-OC –C6H4-CO-]n

PROPERTIES

• High Melting point (250oC)

• Very light Weight

• Good Chemical resistance

• Good transparency

• Good Impact resistance

• Good Tensile strength

USES

• Used to make synthetic fibres like terlene

• Blended with wool to provide wrinkle resistance

• Due to its transparency used inaseye shield in helmets, aircraft etc.,

• Used to store water , soft drinks etc