Thermoplastics : Introduction,classification,Processing & applications

1. 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,tolerance, 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
Elastomers thermosets
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. •Mechanical—do not embrittle, good impact
strength
•Moisture—very little (shower heads)
•Chemical resistance—very high, resists
stains, sensitive to strong acids and
bases
•Electrical resistance - good
•Machining—like cutting brass
•Adhesion—epoxy glues
Acetals or Polyoxymethylenes (POM)
and Polyamides characteristics

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. Costsin$/lb
Automotive Structures
$1 - $3/lb
Innovative Materials and
Processes
$5 - $20/lb
Typical Aerospace Structure
$50 - $100/lb
and more
Materials:
Glass Fiber / Polypropylene, SMC/BMC
Processes:
Compression Molding, Injection Molding
Materials:
Thermoplastic Woven Sheets, Glass,
Carbon and Kevlar Fiber, Engineering
Polymers
Processes:
Co-Compression Molding, Co-
Injection Molding, Thermoforming
Materials:
Carbon Fiber / Epoxy, Carbon
Fiber / BMI, Carbon Fiber /
PEEK
Processes:
Hand Lay Up
Apply Materials and
Processing Techniques
being Developed for
Automotive Applications to
Aerospace Applications
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
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.1 1 10 100
Length (mm)
RelativePropertyLevel
Modulus
Strength
Impact
Processibility

30. Processing…

31. Current Composite Materials and
Processes
Process Type of Application
Injection Molding
Compression
Molding
Thermoforming
Hand Lay Up /
Vacuum Bag /
Autoclave
Low-Structural
Components
Semi-Structural
Components
Structural Components

32. Thermoplastic − Thermoforming
Blanks
Oven
Clamp
Clamping Pressing
Press (in two modes)
Finished
Part

33. Extrusion

34. Injection Molding Machine Basics
34

35. 35
Blow Molding
Extruded
Parison-
Mold Open
Mold Closed and
Bottle Blown
Finished Bottle
Removed from
Mold
Plastic

36. Plastic Materials and Pocesses 36
Compression Molding
Platen
Mold
Plunger
Guide
Pins
Mold
Cavity
Platen
Hydraulic
Plunger
Heat
and
Cooling
Heat
and
Cooling
Hydraulic
Pressure
Compound to be molded

37. Applications…

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…