Thermoplastics: Introduction,classification,processing & applications

1
Thermoplastics

• Pratik Chaudhari
• MIS- 111210015
• TY Mechanical div-1
• Subject Advanced manufacturing techniques

2
Conventional materials

• Conventional materials are shows more
  crystallinity. Shows deflection under service
  load
• More crystallinity , harder, stiffer and less
  ductile
• Structure sensitive
• Problems with sophastication, machinability,tolera
  nce, etc.
• Changed by small changes in chemical composition
  

3
Plastics

• Material of New age
• Its basic constituent is prepared synthetically
  or semi-synthetically from monomer.
• Easily machined , cast and joined
• Ease of manufacturing and versatility
• hardness, elasticity, breaking strength,
  temperature resistance, thermal dimensional
  stability, chemical resistance 

4
Plastics - Classification
thermosets
Elastomers
Thermoplastics
5
Thermoplastics

• Polymers which moulds above Glass transition
  temperature and returns to normal state upon
  cooling

6
Thermoplastics

• Most commonly used engineering thermoplastics as
  matrices
• Nylon
• Polycarbonate (PC)
• Polyethylene terephthalate (PET)
• Polypropylene (PP)
• Stronger and stiffer but lower toughness
• Have engineering as well as advanced applications

7
Glass transition temperature
Amorphous polymers do not have a specific melting
point. At low temp., they are hard, brittle,
rigid and glassy and at a high temp. rubbery and
leathery. The temperature at which this
transition occurs is called Glass transition
temperature (Tg).
8
Effect of temperature

• Above glass-transition temp. polymers become
  leathery and then rubbery
• At higher temperatures, polymers become a viscous
  fluid, with viscosity decreasing with increasing
  temperture.

9
Behaviour under temperature conditions

• Below temperature Tg, plastic polymers are glassy
  ,rigid, hard or brittle and behave as a elastic
  body.
• If the load exceeds the certain critical value,
  it fractures as a piece of glass
• 1. Elastic deformation
• 2. Viscous deformation
• 3. Maxwell Model of Viscoelastic deformation
• 4. Voigt or Kelvin Model of Viscoelastic
  deformation

10
Viscoelastic behavior

• When heated above Tg , It becomes leathery first
  and then rubbery with increasing temperature
• If we increase above Tm (melting point ), it
  becomes viscous and viscosity goes on decreasing
  with increase in temperature and strain rate
• As viscosity is not constant, thermoplastic shows
  visco-elastic behavior

11

• Draw diagrams on page 569

12
Orientation

• When thermoplastics are permanently deformed by
  stretching, long chain molecules align in general
  direction of elongation. This is known as
  orientation.
• The polymer becomes stiffer and stronger in the
  elongation direction as compared to transverse
  direction
• This technique is used to enhance the strength
  and toughness of polymers

13
Crazing stress whitening

• Some thermoplastics such as polystyrene develop
  localized,wedge shaped narrow regions of highly
  deformed material when subjected to high tensile
  stresses or bending
• Presence of various additives, solvents, water
  vapour favours crazing
• Stress whitening - When polymer subjected to
  tensile stresses such as by folding or bending,
  the plastic becomes lighter in color due to
  formation of micro-voids in the material.

14
Water absorption

• This is limitation of thermoplastics
• Water acts as plasticizing agent. Thus, it makes
  polymer more plastic
• It lowers the glass transition temperature, yield
  stress and elastic modulus of polymer
• Sometimes,Undesired dimensional changes occur

15
Classification
16
Amorphous thermoplastic polymers

• Molecule chains are completely chaotically
  arranged and tangled with each other like the
  threads of a cotton wool pad
• amorphous structure means that these materials
  cannot be subjected to loads above the glass
  transition point
• Properties
• Low tendency to creep
• Good dimensional stability
• Tendency to brittleness
• Sensitive to stress cracking

17
Semi-crystalline thermoplastics

• Molecules form crystalline structure
• Due to the crystalline areas, the materials are
  extremely tough (strong intermolecular forces)
  and are capable of withstanding mechanical loads
• Properties
• Opaque
• Good fatigue resistance
• Tendency to toughness
• Good chemical resistance
• Wear resistance

18
Some examples
19
Polyamides or Nylons (PA)
20
Acetals or Polyoxymethylenes (POM)
21
Acetals or Polyoxymethylenes (POM) and Polyamides
characteristics

• Mechanicaldo not embrittle, good impact strength
• Moisturevery little (shower heads)
• Chemical resistancevery high, resists
  stains, sensitive to strong acids and bases
• Electrical resistance - good
• Machininglike cutting brass
• Adhesionepoxy glues

22
Thermoplastic Polyesters (PET/PBT)
23
Thermoplastic Polyester General Family
Characteristics

• PET
• Higher mechanical stiffness
• Strength by orienting chains not by H-bonding
• Get 50 crystallinity
• forced by mechanical stretching
• PBT
• crystallizes rapidly
• processes faster
• lower overall properties

24
Polycarbonate
25
Flouropolymers
26
Other aspects
27
Cost challenge
28
Short fiber, Long Fiber and Continuous Fiber
Composites
Typical short fiber thermoplastic
material, granules with fiber length of approx. 2
to 4 mm, resulting fiber length in a part of
approx. 0.4 mm
Long fiber thermoplastic material, pellets of ½
and 1 fiber length, resulting fiber length in a
part of approx. 4-6 mm in injection molding and
approx. 20 mm in compression molding
Continuous reinforced thermoplastic material,
tape used for woven sheets (thermoforming),
filament winding or pultrusion
29
Composite Performance versus Fiber Length
30
Processing
31
Current Composite Materials and Processes
32
Thermoplastic - Thermoforming
Press (in two modes)
Blanks
Clamp
Finished Part
Oven
Pressing
Clamping
33
Extrusion
34
Injection Molding Machine Basics
35
Blow Molding
36
Compression Molding
37
Applications
38
(No Transcript)
39
Applications For High-Performance Thermoplastics

• Aerospace and defense
• Radomes, wing and fuselage sextions,
  anti-ballistics
• Infrastructure and Construction
• Window profiles, rebar, beams, structures,
  composite bolts
• Consumer / recreational
• Orthotics, safety shoes, sporting goods, helmets,
  personal injury protextion, speaker cones,
  enclosures, bed suspension slats
• Auto and truck
• Bumper beams, skid plates, load floor, seat
  structures
• Transportation
• Railcar structure, body structure and closures
• Energy production and storage
• Oil and gas structura tube, wind turbines

40
Future ?

• Thermoplastics polymers go to more structural
  applications using different technical
  thermoplastics in combination with glass, carbon
  and synthetic fibers.
• Thermoplastics will replace metal applications
  and reduce weight.
• Improved processing methods will be developed and
  applied.

41
Thank you