Title: Thermoplastics: Introduction,classification,processing & applications
1Thermoplastics
- Pratik Chaudhari
- MIS- 111210015
- TY Mechanical div-1
- Subject Advanced manufacturing techniques
2Conventional 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
3Plastics
- 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 resistanceĀ
4Plastics - Classification
thermosets
Elastomers
Thermoplastics
5Thermoplastics
- Polymers which moulds above Glass transition
temperature and returns to normal state upon
cooling
6Thermoplastics
- 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
7Glass 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).
8Effect 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.
9Behaviour 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
10Viscoelastic 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
12Orientation
- 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
13Crazing 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.
14Water 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
15Classification
16Amorphous 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
17Semi-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
18Some examples
19Polyamides or Nylons (PA)
20Acetals or Polyoxymethylenes (POM)
21Acetals 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
22Thermoplastic Polyesters (PET/PBT)
23Thermoplastic 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
24Polycarbonate
25Flouropolymers
26Other aspects
27Cost challenge
28Short 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 Ā½
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
29Composite Performance versus Fiber Length
30Processing
31Current Composite Materials and Processes
32Thermoplastic - Thermoforming
Press (in two modes)
Blanks
Clamp
Finished Part
Oven
Pressing
Clamping
33Extrusion
34Injection Molding Machine Basics
35Blow Molding
36Compression Molding
37Applications
38(No Transcript)
39Applications 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
40Future ?
- 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.
41Thank you