1. Material Science
POLYMERS

2. POLYMERS
Polymers are materials whose molecules are built up from a series of smaller units, and are based on the carbon atom.
Three types of polymers:
thermoplastics,
thermosets
Elastomers (rubber).

3. Thermoplastics

4. Thermoplastics
Thermoplastics soften when heated and become hard again when it is cooled
They are generally flexible and relatively soft.
Material can be recycled
Formed into the shape of final component by the use of moulds
The raw materials are usually in powder or granular form

5. Thermoplastics Commonly used thermoplastics: Polyethylene
Polypropylene
PVC
Polystyrene
PTFE
Nylon
Acrylics
ABS

6. Polyethylene Thermoplastics
Commonly called polythene
High resistance to corrosion caused by solvent or chemicals
Unaffected by food
Tough and flexible
Cheap to produce
Common uses:
Packing for food and sweet
Industrial and household container
Toys, cold water pipe and electrical insulation

7. Polypropylene Thermoplastics
More rigidity, strength and heat-resistance than polyethylene
Better resistance to corrosion caused by solvent or chemicals than polyethylene
Can be sterilized by steam
Withstand repeated bending without cracking
Widely used in:
Packaging
Electrical insulation
Automobile parts
Case and containers
Safety helmets

8. PVC Thermoplastics
Can be produced in either a rigid form or a flexible form
It is hard when solid and possesses both strength and toughness
Have exceptional resistance to acid and solvents
Excellent insulation properties
Common uses are:
Helmets
Bottles, handbags
Protective gloves and clothing
Garden hose, floor tiles, luggage
Electrical insulation, interiors of refrigerators

9. Polystyrene Thermoplastics
Can be produced in clear form with hard, glossy surface
Strong, flexible and light in weight but has low impact strength
Can be easily moulded in shape
High electrical resistance and good resistance to foods and household acids
Can be produced in form of foams
Common uses are:
Toys and refrigerator parts
Packaging for foodstuffs and fragile parts
Trays, pens and hull for some sailing boat
Thermal and sound insulation in house and factories

10. PTFE (Teflon) Thermoplastics
Unaffected by concentrated sulphuric acid which is capable of dissolving some metals
Can be used at temperature ranging from -200 to 300 0C
Most materials do not adhere to PTFE
Very low coefficient of friction
One of the most costly thermoplastics
It is produced in a fashion similar to metals in powder metallurgy
It is widely used for bearings, fuel hoses, gaskets, valve seat, pump parts and as a non-stick coating for pans and similar appliances

11. Nylon Thermoplastics Nylon is very strong, tough and light in weight
Good resistance to abrasion and low coefficient of friction
It is flexible ,has high impact strength and can be used without lubrication
Operation temperature about 150 0C
Uses of nylon include small gear, bearing, combs, ropes, fishing lines, tennis strings, casting and machine parts for domestic appliances, helmets, tubing, rollers pulleys and etc.

12. Acrylics Thermoplastics
Clear glass-like material, tough and lighter than glass, commonly called perspex
Hard and rigid with high impact and tensile strength
Its surface is easily scratched
Easily moulded into shape
Perspex is used for aircraft glazing, roofing panels, lenses, drawing instruments, telephone, baths, sinks, display signs, clock faces, handles and reflectors

13. ABS Thermoplastics
Have exceptional resistance to impact with good tensile strength
Resist to most acids, to many alkalis and to some solvents
Operation temperature of about 80 0C
Easily processed by a number of methods commonly used for thermoplastics
ABS is used for pipes, helmets, tool handles, toys, wheels, refrigerator parts, pump components, luggage, battery cases, widely used in the automobile industry for parts of bodywork ( may be chromium plated)

14. Thermosets

15. Thermosets
When thermoplastics are heated above their glass transition temperatures they can be reshaped
Thermosetting plastics undergo chemical change (curing) during moulding and can never again be softened by heating
Thermosets are stronger, more rigid and more brittle than thermoplastics

16. Thermosets Common used thermosets: Phenolics (bakelite)
Urea formaldehyde
Melamine formaldehyde
Polyurethane
Epoxy resins
Polyester resins

17. Phenolics (bakelite) Thermosets
Hard, strong and rigid and able to operate at about 200 0C
High electrical resistance, being used for electrical fittings
High chemical resistance and dimensional stability
Bakelite is used for electrical fittings, switchgear, handles, motor car parts, and parts for domestic appliances

18. Urea formaldehyde Thermosets
The basic resin is hard, brittle, rigid and scratch resistant
Like phenol formaldehyde it is never used alone but additives
It is resistant to most solvents and household detergents
It has good electrical insulation properties and being virtually colourless, it can be coloured by pigments to suit any decorative requirements
For this reason it is widely used for domestic electrical equipment (plugs, sockets and switches) and most domestic appliances, toys and buttons

19. Melamine formaldehyde Thermosets
This material is similar to urea formaldehyde, but is more resistant to heat and is less water absorbent.
This not only improves its electrical properties but makes it suitable for tableware.
This material also used for decorative panels (formica), electrical fittings, trays, light fixtures and handles

20. Polyurethanes Thermosets
One type is used in the manufacture of bottles and films
Many types are used as foams
The foams range from a hard and rigid material to a soft and flexible material
The rigid foams are generally used for heat insulation and for strengthening hollow structure
The soft and flexible foams used for upholstery and for item such as artificial sponges
They also used in adhesives (usually glass to metal) and base of paints

21. Epoxy resins Thermosets
The resins are usually combined with a hardener
The resulting properties of the material are:
High mechanical strength and toughness
Excellent adhesion to many other material
High resistance to chemicals and moisture
Epoxy resins are used for bonding glass fibre fillers. They are resistant to water and most reagents and have excellent electrical insulation properties.
Epoxy are also widely used as casting material for small components and material for sealing electrical equipment such as transformer and chokes
‘Araldite’ is a common epoxy resin glue

22. Polyester resins Thermosets
These materials have good heat resistance and excellent electrical insulation properties
They have good dimensional stability and are unaffected by water and most organic solvents
This makes them suitable for mouldings for high voltage insulators in television sets and for mouldings for the electrical equipment of road vehicles and aircraft
Alkyd resins are also used as the basis for the paint systems used on cars and domestic appliances
Their low water absorption and resistance to weathering make them an excellent binder for use with glass fibre reinforcement for mouldings ranging from domestic baths, chairs, to boat hulls

23. Elastomer

24. Elastomer
Elastomers (or rubbers) are polymers with considerable extensions which are reversible
Example: natural rubber and synthetic rubber
Synthetic rubbers are now used much more extensively and they are based on other polymers and produced from the distillation of oil.
Many components do not require great strength but they do require softness, flexibility and reversible elongation. Thus elastomers are ideal for such applications as resilient floor coverings, weather stripping, footwear, vehicle tyre, joint sealants, and anti-vibration mountings.

25. Application of Elastomer I
Vibration insulation and isolation
Shock absorbers
Anti-vibration machine and engine mountings
Sound insulation

26. Application of Elastomer II
Distortional systems
Correctives for misalignment: such as flexible couplings
Changing shapes: such as belts, flexible hose, covered rollers, and tyres
Seals and gaskets
Rubber hydraulics.

27. Application of Elastomer III
Protective systems
protection against abrasion
protection against corrosion
electrical insulation
protective clothing: gloves, aprons, boots.

28. Elastomer Commonly used elastomer: Acrylic rubbers Butyl rubbers
Nitrite rubbers
Polychloroprene rubbers
Polyisoprene (natural rubber)
Polysulphide rubbers
Rubber hydrochloride
Silicone rubbers

29. Acrylic rubbers Elastomer
These are derived from the same family of polymeric materials as ‘Perspex’
This group of rubbers has excellent resistance to oils, oxygen, and ultraviolet radiation, and they are used as the basis for the paints developed for motor vehicles.

30. Butyl rubbers Elastomer
This rubber is impervious to gases and is used as a vapour barrier and for hose linings
It is highly resistant to outdoor weathering and ultraviolet radiation and is used for construction industry sealant.

31. Nitrite rubbers Elastomer
This has excellent resistance to oils and solvents and can be readily bonded to metals
It is used for petrol and fuel oil hoses, hose linings, and aircraft fuel tank linings. It is also resistant to refrigerant gases.

32. Polychloroprene rubbers Elastomer
It has good resistance to oxidation, aging, and weathering
It is resistant to oils, solvents, abrasion and high temperatures
Because of its chlorine content it is fire resistant
It is used as a flexible electrical insulator and for gaskets, hoses, engine mounts, sealants, rubber cements and protective clothing.

33. Polyisoprene (natural rubber) Elastomer
This is derived from the sap of a tree
It has a relatively high tensile strength
Unfortunately solvents, petrol, mineral oils, and ozone readily attack it
It degrades rapidly in the presence of strong sunlight 
Modified by additives to give it increased strength and wear resistant properties
Natural rubber is used for vehicle tyres as it has excellent antiskid properties

34. Polysulphide rubbers Elastomer
Although this rubber has low mechanical strength, its resistance to solvents and its impermeability to gases are excellent and its weathering characteristics are outstanding
It also has good bonding properties and is widely used in the construction industries as a sealant. They are also used as fuels.

35. Rubber hydrochloride Elastomer
This material is better known as ‘Pliofilm’ and is used to form a transparent film for the vacuum packaging of foods
Its unusually high tensile strength and tear resistance easily identifies it.

36. Silicone rubbers Elastomer
Although silicone rubber has a relatively low tensile strength, it has an exceptionally wide working temperature range of -80°C to +235°C
It is also used in space vehicles and artificial satellites.