Polymers - thermoplastics and thermosets

Question 1

What are the properties of thermoplastic polymers?

Answer 1

• low stiffness
• low density
• stretchy

Question 2

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

Answer 2

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

Question 3

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

Answer 3

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

Question 4

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

Answer 4

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

Question 5

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

Answer 5

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

Question 6

What are the two forms of polyvinylchloride (PVC)?

Answer 6

• plasticised (flexible)
• unplastericised (rigid)

Question 7

What are the benefits to polyvinylchloride (PVC)?

Answer 7

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

Question 8

How can polyvinylchloride (PVC) be used?

Answer 8

used as sheets, window profiles, pipes and interior items

Question 9

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

Answer 9

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

Question 10

What are the properities of polycarbonate (PC)?

Answer 10

• tougher than PMMA
• imoact areas, roof etc

Question 11

What are the properites of polymethylmethacrylate (PMMA)?

Answer 11

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

Question 12

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

Answer 12

lightweight, good insulation, good moisture, resistance

Question 13

What are polystyrene foams used in?

Answer 13

• roof insulation
• wall insulation
• ceiling and attic insulation
• geotechnical insulation
• composite panels

Question 14

What are the polyamides (PA; nylon)?

Answer 14

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

Question 15

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

Answer 15

easy to form fibres
resistant to damp, vibration or grinding

Question 16

What are nylon fibres used for?

Answer 16

nylon fibres for geotextiles and geogrids

Question 17

What is Bitumen?

Answer 17

naturally occuring high molecular weight hydrocarbons

Question 18

How is Bitumen usually obtained?

Answer 18

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

Question 19

Where is Bitumen used?

Answer 19

used in paving and roofing applications

Question 20

What are the examples of thermosetting polymers?

Answer 20

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

Question 21

What are some applications of thermosetting polymers?

Answer 21

• adhesives
• coatings
• laminates
• sports good
• moulded components

Question 22

Whar are the two stages of fabrication of thermosets?

Answer 22

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)

Question 23

What are epoxies?

Answer 23

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

Question 24

What can epoxies be used for?

Answer 24

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

Question 25

Epoxies have a very strong adhesion to many substrates what may be added to durability?

Answer 25

Very strong adhesion to many substrates
- silane additions may be required for long term bond durability

Question 26

What can unsaturated polyester/vinyl ester be used for?

Answer 26

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

Question 27

Where can vinyl ester be used?

Answer 27

vinyl ester can be used in marine applications
- goof corrosion resistance
- resists water absorption
NB: some polyesters are thermoplastic

Question 28

What is polyurethane used for?

Answer 28

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

Question 29

What are phenolics?

Answer 29

good resistance to chemicals, water and temperature
excellent fire performance
used in roofing, cavity board, wall and floor insulation

Question 30

What are the uses for urea formaldehyde?

Answer 30

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

Question 31

What thermoplastics are used in structural engineering?

Answer 31

PE, PP, PVC, PC, PMMA and acrylics, Polyamides (nylon), Polystyrene (PS), Bitumen (not strictly a polymer)

Question 32

What are some thermoset polymers?

Answer 32

Epoxies, unsaturated polyester, vinyl ester, polyurethane (foams), phenolic (foams), urea formaldehyde (foams), silicone rubber