The document discusses high temperature polymers. It outlines that modern trends aim to develop materials that can withstand high temperatures without losing strength or properties. High temperature polymers can withstand over 200°C for 50,000 hours without deterioration. They include polyamides, polyarylene esters, polyphenylene sulphides, and liquid crystal polymers. Basic principles for increasing heat stability include using stronger bonds like Si-O instead of C-C, incorporating aromatic rings, and including rigid heterocyclic rings which decompose over 500°C.

1. High Temperature Polymers
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2. Outline
• Plastics as Engineering
Materials
• Applications showing
replacement of
conventional materials by
plastics
• High Temperature Polymers
• Basic Principles
• Conductive polymers
• Applications of conductive
polymers
• Photoconductive polymers
• Liquid Crystals
• What are liquid crystals?
• Classification of liquid
crystals
• Applications of Liquid
Crystals
• Liquid crystal display
devices (LCD)
• Typical uses of liquid crystal
polyesters
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3. Plastics as Engineering Materials
• Plastics and plastic based composites have become one of the most important
classes of advanced engineering materials today
• There is not a single sphere of human and economic activity today, which does
not require plastics
• This is equally true for developed as well as developing countries
• In recent years thermoplastics have been developed extensively;
– their good physical and mechanical properties making them superior to thermoset
in many cases.
– For instance, in polymer composites thermoplastics are replacing the well known
thermosets, namely,
• epoxies and polyester in many cases.
– In general, plastic materials are characterised by good mouldability and
exrudability.
• Their physical, chemical and mechanical properties can be easily altered and
enhanced to the extent that they can easily be substituted for many of the
conventional materials such as wood, paper, cement, ceramics and metals as
shown in Table in the next slide
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4. Applications showing replacement of conventional
materials by plastics
Applications Polymers used
Replaced conventional
materials
Packaging
Beverages PET Glass
Pharmaceuticals PVC, HOPE, PP Glass, Paper
Squeeze tubes
(toothpaste, ointment, etc)
HOPE, LLDPE, PP Metal
Fertilisers HOPE, LLDPE, PP Jute
Retail carry bags HOPE,LLDPE PP, Paper
Ropes NYLON, PET Jute, Cotton, Coir, Steel
Pallet wrap LDPE,LLDPE Heavy duty paper
Cement HOPE and PP woven sacks Jute
Minerals LDPE Jute
Storage Tanks
Water HOPE, LLDPE Cement, Mild steel
Agrochemicals HOPE Steel
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5. Applications showing replacement of conventional
materials by plastics
Applications Polymer used Replaced conventional material
Miscellaneous
Luggage High impact PP, ABS, FRP Wood, Steel
Carpet Acrylic, PP, Nylon Coir, Jute
Furniture PP structural foam, Phenolics laminate, HIPS, FRP Wood, Cane, Bamboo
Tubes and pipes
PVC, HOPE, LDPE, PP, FRP
Steel, Cast iron, Cement
Barrel for tube wells HOPE Steel
Window panes PC and Acrylic Glass
Door knobs and handles Acrylic Metal
Textile cone and bobbins PP, FRP Cardboard and metal
Buckets, tumblers HOPE, LLDPE Steel, Aluminium, Brass
Pipes for electric fittings PVC
Steel, Cast iron and Wooden strips
Tool handles Cellulose acetate Wood
Alcoholic bottles PET Glass
Quilt and mattresses Foam Cotton
Boat FRP Wood
Fan blade Glass filled acetals Steel
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6. Plastics as Engineering Materials
• Plastics are available in a variety of forms including
fibres, coatings, mouldings, castings, adhesives, films,
etc.
• other outstanding features justifying their widespread
use as engineering materials are :
– low in density and therefore capable of taking more loads. The consequent
effect is lot of energy saving
– aramid fibres and ultra high molecular weight polyethylene possess
outstanding specific strength and high specific stiffness.
– As a class, show excellent resistance against most of the corrosive media
except some organic solvents and therefore the frequency of replacement
needed is less
• cost is relatively low when compared with massive
metals.
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7. Plastics as Engineering Materials
• available in both transparent and translucent varieties
– refractive index of the transparent variety is quite high and in some cases, even higher
than that of glass
• show good design flexibility, (can be moulded to desirable shape)
• have good thermal insulating properties.
• As a class they are good insulators to electricity but can be made
electrically conductive to some extent by filling
• Inherently conductive varieties have also been produced
• show direct end usability, i.e. they do not need much finishing
after being moulded or cast
• can be shaded to a variety of colours
• are easily available
• Less energy is required for their conversion
• coefficient of friction is low
• damping properties are good
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8. Plastics as Engineering Materials
• For many of the applications there is no substitute for plastics
• Some of these applications include:
– films for projector, radiography, microphotography (optical, scanning and
transmission electron micrographs), and ordinary photography; electrical
switches and fittings; medicine packing, housings of a number of
electrical and electronic equipments, etc
• Various areas of their application include:
– agriculture; automobile and transportation; textile; aeronautical;
chemical; electrical and electronics; telecommunication; and computer
industries; naval engineering; building and furniture; biomedical field;
foot wear and domestic field
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9. Plastics as Engineering Materials
• In the transportation sector, the typical applications are:
– bumpers, fuel tanks, steering wheel assembly and other
components, for instrumentation meters and panels,
carburetors and components thereof, combination switches,
electric fittings, distributors, etc.
• In agriculture plastic films find use
– in canal, silage, nursery bags, low tunnel and in green houses.
• In minor irrigation systems and in the distribution and
supply of both potable and irrigation water, plastics are
being used considerably
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10. Plastics as Engineering Materials
• In electronics and telecommunication the typical applications
of plastics include:
– printed circuit board, fibre optic cables, housings and components
of electronic goods (both industrial and consumer), etc
• The possibility of making polymers conductive suggests their
futuristic uses involving:
– electromagnetic interference /radio frequency interference,
electrostatic dissipation shielding (required in the defense sector)
• Work is underway to replace silicon chip by semiconductive
plastic chip
• In electrical engineering plastics are widely used as insulating
materials
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11. Plastics as Engineering Materials
• In the biomedical field plastics offer their uses in
– Disposable syringes, catheter balloons & containers, handles of surgical
instruments, suction jars, instruments trays, respirator components,
artificial heart & pace makers
– As biodegradable materials, used as fracture plates, rods, pins inserted
in bones
• In aircraft industry used in composites form
• In textile, pulleys & bearings where lubrication is desired
• In process industry plastic are used:
– Packings, piping & tubing, material handling equipment, liner for
vibrators, thermal power stations, foundries etc
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12. High Temperature Polymers
• Modern trend to develop new materials which can
withstand high temp
– w/o loosing strength & other useful properties
– Must be processable to the desired shape with ease
• For e.g., construction of aircraft needs material that
– can withstand high surface temp
– Have low density
– Posses high dimensional stability
• In Electrical Engineering, motors can function more
efficiently at higher operating temp provided
– Material for insulation with greater thermal stability is
available
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13. High Temperature Polymers
• According to NASA, High Temperature Polymers are
those which can withstand service temp in excess of
200°C in air up to 50000 hrs without appreciable
deterioration of physical properties
• High Temperature Polymers can be grouped as:
– Polyamides of various types as condensation polyimides,
addition polyimides, acetylene terminated polyimides &
polyamideimide, polyester imide & bismaleimide
– Polyarylenes esters, polyphenylene sulphides, liquid crystals
polymers
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14. High Temperature Polymers
• Basic Principles
There are several ways by which the heat of stability of polymers
can be increased:
1. Bond Strength, which joins different groups in the main
polymer chain, i.e., polymer back-bone.
• For e.g., a polymer chain with Si-O bonds would be more
stable than one with C-C bond, because Si-O bond has higher
bond energy than C-C bond. i.e replacement of a C atom in
main polymer chain by inorganic atoms or grouping is one
way of producing structures with greater heat resistance
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15. Conti…. Basic Principles
Bond Strength
Bond Type Bond Energy, kJ mole-1
C-C
Si-O
Si-N
B-N
B-O
347
373
462
437
500
Bond Energies of different bonds
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16. Conti…. Basic Principles
2. Incorporation of aromatic ring structure
• Incorporation of aromatic
ring structure in the
polymer back bone
• Aromatic rings i.e., the
phenylene rings are
stiffer & more resistant
to deformation &
produce intrinsically
stronger bonds & hence
high temp resistance to
heat
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17. Conti…. Basic Principles
Incorporation of aromatic ring structure
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18. Conti…. Basic Principles
3. Incorporation of highly
stable & rigid
heterocyclic ring
system in polymer chain
also increases heat
resistance
• Structures formed by
incorporating heterocyclic
rings in the backbone are
generally not meltable and
decompose only above
500°C
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