6'1 Main uses of thermosets

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6.1 Main uses of thermosets

• Phenolics molded electrical parts, circuit
  boards
• Melamine surface laminates to resist abrasion
  and high temperature, electrical parts
• Urea adhesives, additives in papers
• UP matrix resin for composites (e.g. fiber glass)

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6.2 Recycling symbols of plasticsDifficulties of
polymer recycling

• Thermosets are not recyclable
• Numerous grades for given type of plastic (e.g.
  PS)
• Different grades can not be mixed to give the
  required properties
• Color differences

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Recycling symbols of containers made of
thermoplastics
Recycling rates (1998) 25 of HDPE and PET
bottles
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6.3 Recycling of metals

• 45 of steels
• 60 of Al cans
• 65 of Pb
• 40 Ni
• 40 Cu
• 100 Au
• Driving force high energy content of metals

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6.4 Molecular structure of polymers
A macromolecule
Polymer material
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Molecular structure of polymersPolyethylene
n(C2H4)
Shackelford
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Inherent flexibility of the backbone
Shackelford
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Degree of polymerization and molecular weight

• Degree of polymerization n
• n is the average number of repeat units in a
  polymer molecule
• Example of PE
• mer C2H4
• Polymer (C2H4)n
• Typically, n102 to 103.
• Can be as high as 107 for UHMWPE.

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• Molecular weight M is the weight of one mole of
  polymer molecule. Unit g mol-1.
• MnM0, where M0 is the molar weight of the
  monomer.
• Example Polyethylene (C2H4)800, n800,
• M0(2?124?1)28 g.mol-1,
• MnM022,400 g.mol-1.

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6.5 Effect of M on properties
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Effect of M on viscosity
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Effect of M on properties

• Shorter chain, little entanglement. Easy chain
  realignment along force direction.
• Longer chain, greater entanglement. Greater
  resistance to flow.

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6.6 Subdivision by chain structure
Linear (Thermoplastic and elastomer)
Budinski
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Branching (Thermoplastic and elastomer)
Budinski
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Cross-linked (Thermosetting, cured rubber)
Budinski
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Effect of cross-linking on properties
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Effect of chain structure on properties

• Stiffness
• Linear lt Branching ltCross- linked.
• Softening temperature
• Linear lt Branching ltCross- linked.

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6.7 Crystallinity of polymers
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• Most thermoplastics are crystalline to varying
  degrees, up to 30.
• Greater crystallinity ?greater stiffness,
  strength and toughness.
• Kevlar (polyamide) has high degree of
  crystallinity, giving its high strength, is often
  used as strengthening fibers.

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Effect of crystallinity on properties