1 Key to polymer acronyms used in this presentation: ABS poly(acrylonitrile-butadiene-styrene) EP poly(ethylene-propylene) EVA poly(ethylene-vinyl acetate) PAN poly(acrylonitrile) PBD poly(butadiene) PE poly(ethylene) PEEK poly(ether ether ketone) PEK poly(ether ketone) PET poly(ethylene terephthalate) PM poly(methylene) PMMA poly(methyl methacrylate) PP poly(propylene) PS poly(styrene) PTFE poly(tetra fluoro ethylene) PVC poly(vinyl-chloride) PVDC poly(vinylidene chloride) PVF poly(vinyl fluoride) PVDF poly(vinylidene fluoride) SAN poly(styrene-acrylonitrile) SBR poly(styrene-butadiene) poly THF poly(tetrahydrofuran) VAE poly(vinyl acetate-ethylene)
64
Embed
Key to polymer acronyms used in this presentation Plastics Materials, fifth ed. Brydson J. A. Butterworths 1989 . 7 Polymers consist of long chains of small repeat units (monomers).
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1
Key to polymer acronyms used in this presentation:
ABS poly(acrylonitrile-butadiene-styrene)
EP poly(ethylene-propylene)
EVA poly(ethylene-vinyl acetate)
PAN poly(acrylonitrile)
PBD poly(butadiene)
PE poly(ethylene)
PEEK poly(ether ether ketone)
PEK poly(ether ketone)
PET poly(ethylene terephthalate)
PM poly(methylene)
PMMA poly(methyl methacrylate)
PP poly(propylene)
PS poly(styrene)
PTFE poly(tetra fluoro ethylene)
PVC poly(vinyl-chloride)
PVDC poly(vinylidene chloride)
PVF poly(vinyl fluoride)
PVDF poly(vinylidene fluoride)
SAN poly(styrene-acrylonitrile)
SBR poly(styrene-butadiene)
poly THF poly(tetrahydrofuran)
VAE poly(vinyl acetate-ethylene)
2
Polymers are all pervasive in our world today. There is hardly an implement,
item of clothing, household furnishing, wall covering, mode of transport which
does not use polymers in one form or another.
The need for communication, control and power supply within the military field
has led to high performance wire insulation which is now used on cars and
civilian land transport. The wiring in trams and train carriages is now measured
in kilometres; the need to reduce weight, even on ships, has led to new products
- lighter, smaller, more robust (e.g 40 tons weight is saved on the wire insulation
alone in a frigate, mostly above the waterline).
Cars: high under-bonnet temperatures calls for airframe style wiring. ABS
brake sensor wiring require protection from heat, abrasion and solvents.
Probably the most important items, the tyres, are created using 4 or 5 different
polymers, all chosen for specific properties.
In all these environments, a predominant requirement now is to reduce fire and
toxicity hazards, whilst retaining the high performance characteristics which
allow the production of efficient systems and elegant design.
Specific properties are called for in each environment which often results in a
multiplicity of polymers being used - even the cheapest ball point pen uses up to
three or four different polymers.
The Alaska pipeline - 800 miles long (half of which is above ground), 48”
diameter, crosses 3 mountain ranges, 800 rivers and streams - is insulated with a
polymer coating. See: www.alyeska-pipe.com.
2
Creating an aircraft wiring loom
3
Under your feet and in your street – 1,200 pair telephone cables.
4
How not to do it!
5
6
A few details:
shellac - secretion of lac insects in SE Asia
amber - fossilised pine resin found in the Baltic
natural rubber - cis 1:4 polyisoprenefrom hevea brasiliensis tree
gutta percha - trans 1:4 polyisoprene from palaquium trees (SE Asia)
good dielectric - used for early undersea cables
other trans 1:4 polyisoprenes:
balata from mimosups balata - Caribbean - golf balls;
chicle from sapota achras - used for chewing gum
Reference: Plastics Materials, fifth ed. Brydson J. A. Butterworths 1989
7
Polymers consist of long chains of small repeat units (monomers). They can be
classified in a variety of ways: i) by source: natural products synthetic modified natural
ii) by properties e.g.:
elastic mod % elongation
elastomers (rubbers) 105 - 106 500 - 1000
plastics 107 - 108 100 - 200
Elastomers are extensible / deformable and revert very rapidly at room
temperature to their original dimensions.
Plastics deform but do not revert to their original dimensions on removal of the
applied stress.
Thermoplastics are capable of inelastic deformation at elevated temperatures,
i.e they can be re-processed indefinitely. Some elastomers exhibit thermoplastic
behaviour, but most thermoplastic polymers are not elastomers.
iii) by polymerisation mechanism (see slide below)
addition
condensation
polyaddition
iv) by microstructure (molecular structure & configuration)
semi-crystalline vs amorphous
random vs block copolymers
8
9
Addition and condensation are the two main polymerisation routes, and are
explained on the subsequent set of slides:
10
Polymerisation proceeds by the addition of subsequent monomer units with the
opening of double bonds - usually C=C, but not necessarily so. There are no
by-products formed in this process.
The three steps in polymerisation are detailed on the next slides.
11
The initiation step requires the formation of a radical a chemical moiety with
an unpaired valence electron (radicals are VERY chemically active), or ionic
species which attaches to a monomer unit, opening the double bond and
creating an active moiety which attacks a further monomer unit, leading to:
12
the propagation step.
The example chosen here is ethylene, and the original (radical formation)
process required high pressures and temperatures ( typically 20,000psi at
250degC ). Very spectacular when the process went awry! Traces of oxygen
are necessary to initiate the process. Other initiators used have been: peroxides,
hydroperoxides and azo compounds. This process gives highly branched
polymers of low density, low melting point (for PE) and low crystallinity.
Modern processes use a catalyst and aliphatic hydrocarbon solvent, with
pressures close to ambient and temperatures of about 60degC an ionic
mechanism of initiation is produced. This yields linear polyethylenes of higher
density, higher melting point and higher crystallinity than the high pressure
process example above.
13
Termination the various mechanisms result in a variety of differing main chain
lengths –
reaction with initiator radical: Init-(CH2-)n-CH2• + • Init Init-(CH2-)n-CH2-Init