ENMAT101A Engineering Materials and Processes
Associate Degree of Applied Engineering
(Renewable Energy Technologies)
Lecture 19 – Plastics materials and rubbers
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Plastics materials and rubbers
Reference Text
Section
Higgins RA & Bolton, 2010. Materials for Engineers and Technicians,
5th ed, Butterworth Heinemann
Ch 19
Reference Text
Section
Callister, W. Jr. and Rethwisch, D., 2010, Materials Science and
Engineering: An Introduction, 8th Ed, Wiley, New York.
Ch 4
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Plastics materials and rubbers
Note: This lecture closely follows text (Higgins Ch19)
Geomembrane liner: http://www.fabtech.com.au
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19.2 Types of plastics (Higgins 19.2)
READ HIGGINS Ch19.2
Thermoplastic materials, Thermosetting materials, Elastomers
19.2.1 Raw materials
19.2.2 Composition of plastics
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19.2 Types of plastics (Higgins 19.2)
(i) Linear polymers: These are polymers in which monomeric units are
linked together to form linear chain. Tend to pack well and have high
intermolecular forces of attraction, giving high densities, high tensile
strength and high melting points. Some common example of linear
polymers are HDPE, nylon, polyester, PVC, PAN, PS, PMMA. PTFE etc.
(ii) Branched chain polymers: These are polymers with side chains or
branches of different lengths. These cause irregular packing and
therefore, they have low tensile strength, low density, boiling point and
melting points than comparable linear polymers. Examples include low
density polythene, modified linear polymers.
http://www.lbl.gov/MicroWorlds/Kevlar/KevClue1Act1.html
http://courses.chem.psu.edu/chem112/materials/polymers.html
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Alkanes
Covalent bonding of C atoms
with H atoms.
The most basic type of hydrocarbon, usually derived from
fossil fuels (esp crude oil). They
all burn with oxygen to produce
C02 + water.
Bio-fuel (ethanol) is an alcohol,
so it has oxygen in it.
http://www.3rd1000.com
Ethanol above
Oil refinery right
Wikipedia
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CH4
C2H6
C3H8
C4H10
Boiling point
[°C]
-162
-89
-42
0
Melting point
[°C]
-182
-183
-188
-138
Density [g·cm3]
(at 20 °C)
gas
gas
gas
gas
Pentane
C5H12
36
-130
0.626 (liquid)
Hexane
C6H14
69
-95
0.659 (liquid)
Heptane
C7H16
98
-91
0.684 (liquid)
Octane
C8H18
126
-57
0.703 (liquid)
Nonane
C9H20
151
-54
0.718 (liquid)
Decane
C10H22
174
-30
0.730 (liquid)
Undecane
C11H24
196
-26
0.740 (liquid)
Dodecane
C12H26
216
-10
0.749 (liquid)
Icosane
C20H42
343
37
solid
Triacontane
C30H62
450
66
solid
Tetracontane
C40H82
525
82
solid
Pentacontane
C50H102
575
91
solid
Hexacontane
C60H122
625
100
solid
Alkanes
Alkane
Formula
Increasing
molecule
size.
Methane
Ethane
Propane
Butane
Gas has 1
to 4 C.
Petrol
contains 5
to 12 C.
Wikipedia
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Alkanes
Increasing molecule size
increases boiling point
and viscosity (thickness or
resistance to flow).
Eventually you get wax at
a few hundred C atoms.
Then, at about 1200 C
atoms, you have plastic:
Polyethylene.
Composition of
carbon chains
Boiling range
(oC)
Percent of
crude oil
Natural Gas
C1 to C4
Below 20
10%
Petroleum ether
(solvent)
C5 to C6
30 to 60
10%
Naphtha
(solvent)
C7 to C8
60 to 90
10%
Gasoline
C6 to C12
75 to 200
40%
Kerosene
C12 to C15
200 to 300
10%
Fuel oils,
mineral oil
C15 to C18
300 to 400
30%
Lubricating oil,
petroleum jelly,
greases,
paraffin wax,
asphalt
C16 to C24
Over 400
10%
Fraction
http://www.3rd1000.com
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Plastics
Unlike metals where the outer-shell electrons can travel freely, the outer-shell
electrons in covalently bonded substances (like plastics) are securely held to
the atoms and cannot move away. So they make great electric insulators.
Polyethene was first used as an electrical insulator in electronics
equipment used in radar during the Second World War.
Higgins 1.4.4 Fig 1.7
Why is it called Polyethylene?
Poly-mer means “Many”– “mers”. In the case of Polyethylene, the mer (or base unit) looks like methane.
The original name given in 1898 was polymethylene.
However, it is made from polymerization of ethylene –
which is a gas.
HDPE bin
bcsplastics.com.au
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Van der Waals Forces
Why do the alkanes get stiffer as the molecules get longer until eventually
becoming a solid? The molecules are held together by weak electrical
imbalances in adjacent molecules (caused by electron distribution).
These forces are too weak to hold short molecules together, but when there
are hundreds of Carbon atoms in the chains, the Van der Waal molecular
forces increase.
This is why HDPE (garbage bin)
is harder than LDPE (squeeze
bottle).
LDPE bottle
promotionsonly.com.au
HDPE bin
bcsplastics.com.au
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Gecko feet
Biomimicry is when engineers
copy ideas from nature.
Velcro was copied from seed
burrs in 1948.
Today we are trying to copy the
feet of the gecko because they
stick to anything – even glass,
but not by suction.
The gecko can stick to any
smooth surface and also friable
sandstone.
A gecko can hold it’s entire
weight on one toe.
http://www.sfu.ca
No hooks, no slime, no suction.
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Gecko feet. Van der Waals Forces!
The secret of the Gecko’s grip is Van der Waal’s
forces. The forces are weak, but with enough
surface area they become substantial.
Wikipedia/CC BY 1.0
The surface area is
achieved by splitting the
toes into smaller and
smaller hairs – until there
is about a billion hairs of
nanometer size.
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Copying Gecko feet. Velcro to Anything!
Researchers have developed a
robot that can climb vertical
surfaces.
Other teams are making gecko tape
that sticks like 1 sided Velcro.
http://www.sfu.ca
Gecko Tape: http://news.sciencemag.org
Sticky gecko feet
Space Age Reptiles
BBC animals
2:25 min
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19.2 Types of plastics (Higgins 19.2)
READ HIGGINS Ch19.2
Thermoplastic materials, Thermosetting materials, Elastomers
19.2.1 Raw materials
19.2.2 Composition of plastics
19.2.3 General properties of plastics materials
Resist atmospheric corrosion
Lightweight
http://www.dotmar.com.au
Reasonably tough and strong
Cannot handle much heat
Good finish, colours, some transparent
Easy to process
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19.3 Thermoplastics (Higgins 19.3)
READ HIGGINS Ch19.3
19.3.1
Plasticisers
Plasticised PVC cable: www.diytrade.com
Rigid PVC pipe: Wikipedia
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19.4 Thermoplastic materials (Higgins 19.4)
READ HIGGINS Ch19.4
19.4.1 Vinyl plastics
Polyethylene (PE)
Polyvinyl chloride (PVC)
Polyvinyl acetate (PVA)
Polyvinyl acetate/chloride copolymers
Polyethylene-vinyl acetate (EVA)
Polypropylene (PP)
Polypropylene-ethylene copolymers
Polystyrene (PS)
Acrylonitrile-butadiene-styrene (ABS)
PVC boat: Wikipedia
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19.4 Thermoplastic materials (Higgins 19.4)
READ HIGGINS Ch19.4
19.4.2 Fluorocarbons
19.4.3 Cellulose-base plastics (cellulose esters)
19.4.4 Polyamides (PA)
19.4.5 Polyesters
http://www.dotmar.com.au
19.4.6 Polyacetals
19.4.7 Acrylics
19.4.8 High-temperature thermoplastics
Polyimides, Polysulphones, Polyether ether ketone (PEEK),
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19.5 Thermosets (Higgins 19.5)
READ HIGGINS Ch19.5
Headlamp Housing
http://www.withermoset.com
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19.6 Thermoset Materials (Higgins 19.6)
READ HIGGINS Ch19.6
19.6.1 Phenolics
Phenol formaldehyde (PF)
Urea formaldehyde (UF)
Melamine formaldehyde (MF)
http://en.wikipedia.org/wiki/Silicone
19.6.2 Polyester resins
19.6.3 Polyurethanes
19.6.4 Epoxy resins
19.6.5 Polyimides
19.6.6 Silicones
http://www.glowpaint.com.au
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19.7 Elastomers (Higgins 19.7)
READ HIGGINS Ch19.7
19.7.1 Long chain molecules in rubber
19.7.2 Vulcanisation
19.7.3 Engineering elastomers
Natural rubber (NR) and polyisoprene (IR)
Styrene-butadiene rubber (SBR)
Butadiene rubber (BR)
Polychloroprene rubber (CR)
Acrylonitrile-butadiene rubbers (NBR)
Butyl rubber (IIR)
Ethylene-propylene rubber (EPM)
Silicone rubbers (SI)
news.alibaba.com
news.alibaba.com
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Recycling of plastics
Plastic recycling
Only thermoplastics can be re-melted.
Identification is needed to prevent mixing.
Food grade must be virgin (new) – not recycled material.
Common plastics can be collected (PET), but specialist polymers are too rare.
Product must be simple enough to sort.
Recycling Misconceptions: http://www.ecologycenter.org/ptf/misconceptions.html
PET: wikipedia
Recycled Polyethylene: http://www.replas.com.au
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Recycling of plastics
Plastic recycling
http://learneasy.info/MDME/MEMmods/MEM30007A/polymers/polymers.html
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Resources.
Polymers
Wikipedia: Plastic
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Online Resources.
http://www.dotmar.com.au/engineered-plastics-products.html
http://www.adelaideplastics.com.au/glossary.htm
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Glossary
Polymer
Monomer
Polymerisation
Thermoplastic
Thermosetting
Elastomer
Copolymer
Cross linking
Vulcanisation
Branched polymer
Mer
Molecular weight
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QUESTIONS
Higgins Ch19: Callister Ch4
Moodle XML: Some questions in 10104 Polymers
1. Define all glossary terms.
2. Attempt relevant questions from Quiz 10104 Polymers
3. Which elastomer is used for car tyres? What are the strong and weak points of this
polymer?
4. Explain the different uses of the terms vulcanisation and cross-linking.
5. Using their molecular features, explain the physical differences in the range of
polyethylenes. What type of molecular force is responsible for this change?
6. Make comparisons of thermoplastic and thermosetting polymers (a) on the basis of
mechanical characteristics upon heating, and (b) according to possible molecular
structures.
7. Some of the polyesters may be either thermoplastic or thermosetting. Suggest one
reason for this.
8. (a) Is it possible to grind up and reuse phenol- formaldehyde? Why or why not? (b)
Is it possible to grind up and reuse polypropylene? Why or why not?
9. Compare the general properties of the four classes of polymeric structures: Linear,
branched, cross-linked and network. Gives 2 examples in each type.
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