Polymers and Emerging Materials Flashcards
Addition Polymerisation
- one carbon-carbon double bond add to another. monomers continue to react to form a chain.
- one carbon reacts to something to make a chain end and leave the other carbon reactive.
- reactive carbon reacts with another carbon double bond, forming longer chain.
- two active chain ends join together, or carbon reacts with another initiator to close chain
Condensation Polymerisation
molecules join together, forming and loosing small molecules like water as byproducts.
usually involves more than one monomer species
has small molecular weight
thermoplastic polymers
not chemically cross linked soften when heated -polyethylene PE -polypropylene PP -polyvinylchloride PVC - polycarbonate PC - acrylics -polynides (nylons) -polystyrene PS -Bitumen (not a polymer)
Thermosetting polymers
chemically crosslinked dont soften when heated need to be shaped before polymer is formed harder, more brittle, dimentionally stable -epoxies -unsaturated polyester -vinyl ester -polyethane -phenolic -urea formaldehyde -silicone rubber
crystalline
chains are aligned
stronger
amorphous
chains are not aligned
additives
used to modify properties
- fillers
- plasticizers
- stabilisers
- colourants
- flame retardants
fillers
can improve:- tensile and compressive strength
- abrasion resistance
- toughness
- dimensional strength
includes: - wood flour
- silica flour
- sand
- glass
- clay
- talc
- limestone
Fillers can reduce cost
plasticizers
improve strength and ductility reduce hardness and stiffness small molecules sit between large chains -increase inter chain distance -reduce inter molecular bonds large additions can lead to a liquid
stabilisers
uv and oxidation can lead to polymer degradation
help counteract the process
complex range of materials
colourants
dyes - dissolve into the polymer
pigments - remain as a phase in substance
can complicate recycling
v practical in application
polymers in structures
desirable properties :- low density, less mass used
-easy shaping
good adhesion
-good thermal and electrical insulation
low duty structural components :- surfaces
-membranes (moisture control)insulation foams
-adhesive
-pipes
-grouts
-geotextiles
polyethylene PE/ polypropylene PP
v similar polymers used in :- membranes -sheeting -pipes -damp proof courses recycles to form :- roadside furniture -railway sleepers -embankment reinforcement
types of polyethylene PE
low density polyethylene (ldpe) -chain branching high density polyethylene (hdpe) -linear branching ultra-high molecular weight polyethylene (uhmwpe) -greater chain linearity -greater chain length -improved physical and mech properties, more crystalline
polyvinylchloride (PVC)
plasticised (flexible) plasticised (rigid) resistant to weathering (slight discolouration) low maintenance requirements durable good thermal insulation used for :- sheets - pipes -window profiles -interior items
polycarbonate PC/polymethacrylade PMMA
mainly used as sheets for decorative or glazing purposes
transparent but can be coloured
PC - tougher but less transparent
- impact areas , roofs
PMMA - clearer
- aquaria, signage
part of acrylic fam
- roofing tiles
- cladding
- adhesive
- sealants
-coatings/paints
-interior itemsPolystyrene foams
lightweight, good insulation, good moisture resistance used in :- roof insulation - wall insulation -ceiling/attic insulation -geotechnical insulation -composite panels difficult to recycle
Polymides nylon
commonly a fibre
good mechanical properties: -easy to form fibres
-resistance to damp, vibration or grinding
used for : - getextiles and geogrids
used in composites as structural components
bitumen
naturally occurring high molecular weight hydrocarbon
residue fro oil and coal cracking
used in :- paving
- roofing applications
epoxies
avalible as a resin and a hardener which then cure (polymerisation) used as :- adhesive -paint -grouts -polymer matrix in composites v strong adhesion to many substrates
unsaturated polyester / vinyl ester
similar to epoxy, but not as adhesive
-polyester is cheaper, vinyl ester stronger
both used in composite applications
vinyl esters are used in marine applications - good corrosion resistance, resist water absorption.
polyurethane
used as a foam
- flexible and rigid forms
- good in insulation and upholstery packing
has good adhesion- used as coating and adhesive
flammable, flame retardants can help
not good uv radiation resistance
phenolic foam
good resistance to chemicals water and temperature excellent fire performance used in :- roofing -cavity board -wall and floor insulation
urea formaldehyde foam
used in the past for insulation
can be easily injected
used in hard to reach places in current homes
elastomers
rubber like elasticity (return to original shape )
unstressed chains are coiled and kinked, allowing for chains to straighten under stress.
cross linking is present
silicone rubber
elastometric material
good adhesion conforms well to surfaces. common sealant
