Material Science

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Material Science

• POLYMERS

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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).

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Thermoplastics
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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

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Thermoplastics

• Commonly used thermoplastics
• Polyethylene
• Polypropylene
• PVC
• Polystyrene
• PTFE
• Nylon
• Acrylics
• ABS

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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

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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

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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

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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

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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
  

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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.

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AcrylicsThermoplastics

• 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

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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)

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Thermosets
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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

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Thermosets

• Common used thermosets
• Phenolics (bakelite)
• Urea formaldehyde
• Melamine formaldehyde
• Polyurethane
• Epoxy resins
• Polyester resins

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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

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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

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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

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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

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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

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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

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Elastomer
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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.

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Application of Elastomer I

• Vibration insulation and isolation
• Shock absorbers
• Anti-vibration machine and engine mountings
• Sound insulation

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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.

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Application of Elastomer III

• Protective systems
• protection against abrasion
• protection against corrosion
• electrical insulation
• protective clothing gloves, aprons, boots.

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Elastomer

• Commonly used elastomer
• Acrylic rubbers
• Butyl rubbers
• Nitrite rubbers
• Polychloroprene rubbers
• Polyisoprene (natural rubber)
• Polysulphide rubbers
• Rubber hydrochloride
• Silicone rubbers

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Acrylic rubbersElastomer

• 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.

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Butyl rubbersElastomer

• 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.

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Nitrite rubbersElastomer

• 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.

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Polychloroprene rubbersElastomer

• 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.

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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

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Polysulphide rubbersElastomer

• 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.

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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.

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Silicone rubbersElastomer

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