Polymers - thermoplastics and thermosets Flashcards

Lecture 17

1
Q

What are the properties of thermoplastic polymers?

A
  • low stiffness
  • low density
  • stretchy
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2
Q

How are polyethylene (PE)/polypropylene (PP) used?

A

used in membranes, sheeting, pipes, damp proof course etc

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3
Q

How are polyethylene (PE)/polypropylene (PP) recycled?

A

recycled to form:
- roadside furniture
- railway sleepers
- embankment reinforcements etc

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4
Q

What is the difference between low desnity polyethylene (LDPE) and high density polyethylene

A

low density polyethylene (LDPE) - more chain branching
high density polyethylene (HDPE) - essentially linear chains

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5
Q

What is a ultra-high molecular weight polyethylene (UHMWPE)?

A

greater chain linearity
greater chain length hence molecular weight improved physical and mechanical properties
greater crystallinity possible

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6
Q

What are the two forms of polyvinylchloride (PVC)?

A
  • plasticised (flexible)
  • unplastericised (rigid)
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7
Q

What are the benefits to polyvinylchloride (PVC)?

A

resistant to weathering with low maintenance requirements, durable, good thermal insulation

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8
Q

How can polyvinylchloride (PVC) be used?

A

used as sheets, window profiles, pipes and interior items

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9
Q

How can polycarbonate (PC)/polymethylmethacrylate (PMMA) be used?

A

mainly used as sheets for decorative or glazing purposes however both are transparent but can be coloured

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10
Q

What are the properities of polycarbonate (PC)?

A
  • tougher than PMMA
  • imoact areas, roof etc
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11
Q

What are the properites of polymethylmethacrylate (PMMA)?

A

aquaria, sinage etc
also known as perspex
part of the acrylic family
roofing tiles, cladding adhesives and scalants coatings and paints, interior items

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12
Q

What are some properties of polystyrene foams (polystrene, styrofoam)?

A

lightweight, good insulation, good moisture, resistance

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13
Q

What are polystyrene foams used in?

A
  • roof insulation
  • wall insulation
  • ceiling and attic insulation
  • geotechnical insulation
  • composite panels
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14
Q

What are the polyamides (PA; nylon)?

A

Most commo as a fibre, although available as moulded parts and sheets

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15
Q

What are the mechanical properties of polyamides (PA; nylon)?

A

easy to form fibres
resistant to damp, vibration or grinding

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16
Q

What are nylon fibres used for?

A

nylon fibres for geotextiles and geogrids

17
Q

What is Bitumen?

A

naturally occuring high molecular weight hydrocarbons

18
Q

How is Bitumen usually obtained?

A

Generally obtained from cracking of oil or coal as the residue when most of the “useful” fractions have been removed

19
Q

Where is Bitumen used?

A

used in paving and roofing applications

20
Q

What are the examples of thermosetting polymers?

A
  • Epoxies
  • unsaturated polyester
  • vinyl ester
  • polyurethane (foams)
  • phemolic (foams)
  • urea formaldehyde (foams)
  • silicone rubber
21
Q

What are some applications of thermosetting polymers?

A
  • adhesives
  • coatings
  • laminates
  • sports good
  • moulded components
22
Q

Whar are the two stages of fabrication of thermosets?

A
  1. form a linear polymer
    • typically a liquid
    • relatively low molecular weight
  2. curing and cross-linking
    • create bonds between chains
    • may be accelerated by temperature and pressure
    • reactions are irreversible
    • after curing materials are demensionally stable
    • can be removed from molds whilst hot (200 - 300 C)
23
Q

What are epoxies?

A

often available as a resin and a hardener, which cure (set) when mixed - this is the polymerisation process

24
Q

What can epoxies be used for?

A

adhesives, points, grouts, etc
The polymer matrix in composites

25
Epoxies have a very strong adhesion to many substrates what may be added to durability?
Very strong adhesion to many substrates - silane additions may be required for long term bond durability
26
What can unsaturated polyester/vinyl ester be used for?
many similar applications to epoxy -> but not really used as an adhesive Polyester cheaper, vinyl ester strong -> properties of vinyl esters essentially lie between those of epoxy resins and polyesters however both widely used in composite applications
27
Where can vinyl ester be used?
vinyl ester can be used in marine applications - goof corrosion resistance - resists water absorption NB: some polyesters are thermoplastic
28
What is polyurethane used for?
Most PU is used as foam: - flexible and rigid foam - good insulation, used for walls, floors and roofing, as will as upholstery packaging etc Polyurethane also has good adhesion - used as coatings and adhesives NB: some polyurethanes are thermoplastics
29
What are phenolics?
good resistance to chemicals, water and temperature excellent fire performance used in roofing, cavity board, wall and floor insulation
30
What are the uses for urea formaldehyde?
extensively used in the 1970s for insulation mixed with raw materials and can be easily injected with a hose commonly used in existing homes in areas such as in existing cavity walls
31
What thermoplastics are used in structural engineering?
PE, PP, PVC, PC, PMMA and acrylics, Polyamides (nylon), Polystyrene (PS), Bitumen (not strictly a polymer)
32
What are some thermoset polymers?
Epoxies, unsaturated polyester, vinyl ester, polyurethane (foams), phenolic (foams), urea formaldehyde (foams), silicone rubber