Polymers - thermoplastics and thermosets Flashcards
Lecture 17
What are the properties of thermoplastic polymers?
- low stiffness
- low density
- stretchy
How are polyethylene (PE)/polypropylene (PP) used?
used in membranes, sheeting, pipes, damp proof course etc
How are polyethylene (PE)/polypropylene (PP) recycled?
recycled to form:
- roadside furniture
- railway sleepers
- embankment reinforcements etc
What is the difference between low desnity polyethylene (LDPE) and high density polyethylene
low density polyethylene (LDPE) - more chain branching
high density polyethylene (HDPE) - essentially linear chains
What is a ultra-high molecular weight polyethylene (UHMWPE)?
greater chain linearity
greater chain length hence molecular weight improved physical and mechanical properties
greater crystallinity possible
What are the two forms of polyvinylchloride (PVC)?
- plasticised (flexible)
- unplastericised (rigid)
What are the benefits to polyvinylchloride (PVC)?
resistant to weathering with low maintenance requirements, durable, good thermal insulation
How can polyvinylchloride (PVC) be used?
used as sheets, window profiles, pipes and interior items
How can polycarbonate (PC)/polymethylmethacrylate (PMMA) be used?
mainly used as sheets for decorative or glazing purposes however both are transparent but can be coloured
What are the properities of polycarbonate (PC)?
- tougher than PMMA
- imoact areas, roof etc
What are the properites of polymethylmethacrylate (PMMA)?
aquaria, sinage etc
also known as perspex
part of the acrylic family
roofing tiles, cladding adhesives and scalants coatings and paints, interior items
What are some properties of polystyrene foams (polystrene, styrofoam)?
lightweight, good insulation, good moisture, resistance
What are polystyrene foams used in?
- roof insulation
- wall insulation
- ceiling and attic insulation
- geotechnical insulation
- composite panels
What are the polyamides (PA; nylon)?
Most commo as a fibre, although available as moulded parts and sheets
What are the mechanical properties of polyamides (PA; nylon)?
easy to form fibres
resistant to damp, vibration or grinding
What are nylon fibres used for?
nylon fibres for geotextiles and geogrids
What is Bitumen?
naturally occuring high molecular weight hydrocarbons
How is Bitumen usually obtained?
Generally obtained from cracking of oil or coal as the residue when most of the “useful” fractions have been removed
Where is Bitumen used?
used in paving and roofing applications
What are the examples of thermosetting polymers?
- Epoxies
- unsaturated polyester
- vinyl ester
- polyurethane (foams)
- phemolic (foams)
- urea formaldehyde (foams)
- silicone rubber
What are some applications of thermosetting polymers?
- adhesives
- coatings
- laminates
- sports good
- moulded components
Whar are the two stages of fabrication of thermosets?
- form a linear polymer
- typically a liquid
- relatively low molecular weight
- 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)
What are epoxies?
often available as a resin and a hardener, which cure (set) when mixed - this is the polymerisation process
What can epoxies be used for?
adhesives, points, grouts, etc
The polymer matrix in composites
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
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
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
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
What are phenolics?
good resistance to chemicals, water and temperature
excellent fire performance
used in roofing, cavity board, wall and floor insulation
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
What thermoplastics are used in structural engineering?
PE, PP, PVC, PC, PMMA and acrylics, Polyamides (nylon), Polystyrene (PS), Bitumen (not strictly a polymer)
What are some thermoset polymers?
Epoxies, unsaturated polyester, vinyl ester, polyurethane (foams), phenolic (foams), urea formaldehyde (foams), silicone rubber
