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Thermoplastics : Introduction,classification,Processing & applications
The document discusses advanced manufacturing techniques using plastics and thermoplastics. It begins by describing some limitations of conventional materials and how plastics offer benefits like ease of manufacturing and versatility. It then classifies plastics into thermoplastics, thermosets and elastomers. The bulk of the document focuses on thermoplastics, describing their properties including glass transition temperature, behavior under temperature conditions, orientation, and water absorption. Examples of commonly used thermoplastics are provided along with applications and potential future developments in the field.
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Thermoplastics : Introduction,classification,Processing & applications
- 1. Pratik Chaudhari MIS- 111210015 TYMechanical div-1 Subject – Advanced manufacturing techniques
- 2. Conventional materials Conventionalmaterials 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 Elastomersthermosets Thermoplastics
- 5. Thermoplastics Polymers whichmoulds above Glass transition temperature and returns to normal state upon cooling
- 6. Thermoplastics Most commonlyused 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 Amorphouspolymers 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 Whenheated 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 onpage 569
- 12. Orientation When thermoplasticsare 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 & stresswhitening 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 Thisis 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
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- 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 Moleculesform 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
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- 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
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- 23. Thermoplastic Polyester General FamilyCharacteristics • 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
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- 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, LongFiber 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 versusFiber 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
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- 31. Current Composite Materialsand 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 ClampingPressing Press (in two modes) Finished Part
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- 34. Injection Molding MachineBasics 34
- 35. 35 Blow Molding Extruded Parison- Mold Open MoldClosed and Bottle Blown Finished Bottle Removed from Mold Plastic
- 36. Plastic Materials andPocesses 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
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- 39. Applications For High-Performance Thermoplastics •Aerospaceand 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 ? • Thermoplasticspolymers 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.
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Editor's Notes
- #4 Plastics can comprise both linear chains and also branched and crosslinked chains. The chain length and the branches define not only the composition but also the main characteristics of the individual materials.