Thermoplastics : Introduction,classification,Processing & applications

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,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 ( T g ).

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. 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 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 Pl astic

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…

38. 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

39. 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.

40. Thank you…