1. Engineering Materials and Processes Lecture 19 – Plastics materials and rubbers
Prescribed Text:
Ref 1: Higgins RA & Bolton, Materials for Engineers and Technicians, 5th edition, Butterworth Heinemann. ISBN:
Readings:
Callister: Callister, W. Jr. and Rethwisch, D., 2010, Materials Science and Engineering: An Introduction, 8th Edition, Wiley, New York. ISBN
Ashby 1: Ashby, M. & Jones, D., 2011, Engineering Materials 1: An Introduction to Properties, Applications and Design, 4th edition, Butterworth-Heinemann, Oxford UK. IBSN:
Ashby 2: Ashby, M. & Jones, D., 2011, Engineering Materials 2: An Introduction to Microstructures and Processing, 4th edition, Butterworth-Heinemann, Oxford UK. IBSN:
Lecture (2 hrs):
Ref 1, Ch 1: Engineering materials;
Ref 1 Ch 2: Properties of materials.
Laboratory 1 (2 hrs): Hardness test
Callister: Ch 1, 2, 19-21
Ashby 1: Ch 1, 2
Ashby 2: Ch 1 1

2. Plastics materials and rubbers
Reference Text
Section
Higgins RA & Bolton, 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
Engineering Materials and Processes

3. Plastics materials and rubbers
Note: This lecture closely follows text (Higgins Ch19)
Geomembrane liner:
Engineering Materials and Processes

4. 19.2 Types of plastics (Higgins 19.2)
READ HIGGINS Ch19.2
Thermoplastic materials, Thermosetting materials, Elastomers
Raw materials
Composition of plastics
Engineering Materials and Processes

5. 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.
Engineering Materials and Processes

6. Alkanes Covalent bonding of C atoms with H atoms.
The most basic type of hydro-carbon, 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.
Alkanes
Ethanol above
Oil refinery right
Wikipedia
Engineering Materials and Processes

7. Alkanes Increasingmolecule size. Gas has 1 to 4 C.
Formula
Boiling point [°C]
Melting point [°C]
Density [g·cm3] (at 20 °C)
Methane
CH4
-162
-182
gas
Ethane
C2H6
-89
-183
Propane
C3H8
-42
-188
Butane
C4H10
-138
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
Tetracontane
C40H82
525 82
Pentacontane
C50H102
575 91
Hexacontane
C60H122
625
100
Alkanes
Increasingmolecule size.
Gas has 1 to 4 C.
Petrol contains 5 to 12 C.
Alkanes
Wikipedia
Engineering Materials and Processes

8. Composition of carbon chains
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.
Fraction
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
Naphtha (solvent)
C7 to C8
60 to 90
Gasoline
C6 to C12
75 to 200
40%
Kerosene
C12 to C15
200 to 300
Fuel oils, mineral oil
C15 to C18
300 to 400
30%
Lubricating oil, petroleum jelly, greases, paraffin wax, asphalt
C16 to C24
Over 400
Alkanes
Engineering Materials and Processes

9. Polyethene was first used as an electrical insulator in electronics
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 Fig 1.7
Why is it called Polyethylene?
Poly-mer means “Many”– “mers”. In the case of Poly-ethylene, 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.
Alkanes
HDPE bin
bcsplastics.com.au
Engineering Materials and Processes

10. 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).
Alkanes
LDPE bottle
promotionsonly.com.au
HDPE bin
bcsplastics.com.au
Engineering Materials and Processes

11. Gecko feet No hooks, no slime, no suction.
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.
Velcro
No hooks, no slime, no suction.
Engineering Materials and Processes

12. 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.
Engineering Materials and Processes

13. 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.
Alkanes
Sticky gecko feet
Space Age Reptiles
BBC animals
2:25 min
Gecko Tape:
Engineering Materials and Processes

14. 19.2 Types of plastics (Higgins 19.2)
READ HIGGINS Ch19.2
Thermoplastic materials, Thermosetting materials, Elastomers
Raw materials
Composition of plastics
General properties of plastics materials
Resist atmospheric corrosion
Lightweight
Reasonably tough and strong
Cannot handle much heat
Good finish, colours, some transparent
Easy to process
Engineering Materials and Processes

15. 19.3 Thermoplastics (Higgins 19.3)
READ HIGGINS Ch19.3
19.3.1
Plasticisers
Plasticised PVC cable:
Rigid PVC pipe: Wikipedia
Engineering Materials and Processes

16. 19.4 Thermoplastic materials (Higgins 19.4)
READ HIGGINS Ch19.4
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
Engineering Materials and Processes

17. 19.4 Thermoplastic materials (Higgins 19.4)
READ HIGGINS Ch19.4
Fluorocarbons
Cellulose-base plastics (cellulose esters)
Polyamides (PA)
Polyesters
Polyacetals
Acrylics
High-temperature thermoplastics
Polyimides, Polysulphones, Polyether ether ketone (PEEK),
Engineering Materials and Processes

18. 19.5 Thermosets (Higgins 19.5) READ HIGGINS Ch19.5
Headlamp Housing
Engineering Materials and Processes

19. 19.6 Thermoset Materials (Higgins 19.6)
READ HIGGINS Ch19.6
Phenolics
Phenol formaldehyde (PF)
Urea formaldehyde (UF)
Melamine formaldehyde (MF)
Polyester resins
Polyurethanes
Epoxy resins
Polyimides
Silicones
Engineering Materials and Processes

20. 19.7 Elastomers (Higgins 19.7) READ HIGGINS Ch19.7
Long chain molecules in rubber
Vulcanisation
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
Engineering Materials and Processes

21. Recycling of plastics Only thermoplastics can be re-melted.
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:
PET: wikipedia
Recycled Polyethylene:
Engineering Materials and Processes

22. Recycling problems with Plastics
Plastic recycling
Aluminium is the best-recycled material – around 70% is recycled and since it melts at 800 degrees, all the rubbish is burnt off. So it can be re-used for drink cans.
Plastic does not recycle anywhere near as well. Food is not allowed to come in contact with recycled plastic, and plastic degrades every time it is re-melted.
Which begs the question – why was there such a large pile of crushed PET bottles sitting in this industrial yard in the first place?
Shouldn’t it have been recycled into already, or is it just sitting there?
Recycling plant fire in Melbourne 2017:
Engineering Materials and Processes

23. Recycling of plastics Engineering Materials and Processes
Plastic recycling
Engineering Materials and Processes

24. Resources. Polymers Wikipedia: Plastic
h ttp://
S how this website on screen. Will be using this later.
Engineering Materials and Processes 24

25. Online Resources. Engineering Materials and Processes
h ttp://
S how this website on screen. Will be using this later.
Engineering Materials and Processes 25

26. Glossary Polymer Monomer Polymerisation Thermoplastic Thermosetting
Elastomer
Copolymer
Cross linking
Vulcanisation
Branched polymer
Mer
Molecular weight
Engineering Materials and Processes

27. Define all glossary terms.
QUESTIONS
Higgins Ch19: Callister Ch4
Moodle XML: Some questions in Polymers
Define all glossary terms.
Attempt relevant questions from Quiz Polymers
Which elastomer is used for car tyres? What are the strong and weak points of this polymer?
Explain the different uses of the terms vulcanisation and cross-linking.
Using their molecular features, explain the physical differences in the range of polyethylenes. What type of molecular force is responsible for this change?
Make comparisons of thermoplastic and thermosetting polymers (a) on the basis of mechanical characteristics upon heating, and (b) according to possible molecular structures.
Some of the polyesters may be either thermoplastic or thermosetting. Suggest one reason for this.
(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?
Compare the general properties of the four classes of polymeric structures: Linear, branched, cross-linked and network. Gives 2 examples in each type.
Engineering Materials and Processes 27