Plastics - PowerPoint PPT Presentation

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Plastics

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... Individual strands Change behavioral regimes when heated Thermosets Polymers are cross-linked Can t melt Vulcanization: cross-linking of a thermoplastic ... – PowerPoint PPT presentation

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Title: Plastics


1
Plastics
2
Question
  • Which is more effective at cleaning your hair a
    thick, viscous shampoo or a thin, freely flowing
    shampoo, or are they probably about equal?

3
Observations About Plastics
  • Some plastics are clear, others translucent
  • Some plastics are stiff, others are flexible
  • Some plastics stretch, others dont
  • Some plastics melt, others dont
  • Some plastics smell, particularly when hot
  • Some glues dry, others harden without drying

4
Plastic
  • Polymers enormous chain or tree like molecules

5
Chemical bonds
  • Metallic bond
  • electrons shared between many atoms
  • Ionic bond
  • atoms become oppositely charged ions
  • Covalent bond
  • atoms share a pair of electrons

6
Polymerization
  • Plastics employ covalent bonds
  • Individual monomer molecules are joined
  • This polymerization forms giant molecules
  • Some molecules are linear chains
  • Some are branched tree-like structures
  • Some are networked together completely

7
Plastic structure
  • Amorphous
  • random mess of polymers
  • Crystalline
  • neatly oriented polymers

8
Regimes
  • Glassy hard, brittle solid
  • Glass-rubber transition leathery
  • Rubbery plateau flexible and elastic
  • Rubbery flow viscous flow but elastic
  • Reptation chains slide along their length
  • Liquid flow viscous liquid

9
Changing regimes
  • Temperature
  • Plasticizers
  • Chemical dissolved in a polymer to soften it
  • Shift a polymers behavior to a different regime

10
Question
  • Which is more effective at cleaning your hair a
    thick, viscous shampoo or a thin, freely flowing
    shampoo, or are they probably about equal?

11
Thermoplastics
  • Individual strands
  • Change behavioral regimes when heated

12
Thermosets
  • Polymers are cross-linked
  • Cant melt
  • Vulcanization cross-linking of a thermoplastic

13
Glues are Plastics
  • White Glue (Water-Soluble Plastic)
  • Model Cement (Solvent-Soluble Plastic)
  • Heat Melting Glue (Glue Gun Glue)
  • UV-Hardening Acrylic Glues (Acrylates)
  • Superglues (Cyanoacrylates)
  • Mix-Hardening Glues (Epoxies)

14
Oriented Plastics
  • Kevlar (Liquid Crystal Plastics)
  • Spectra (Draw-Ordered Plastics)
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