Engineering Materials and ProcessesLecture 19 – Plastics materials and rubbers

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Plastics materials and rubbers

Engineering Materials and Processes

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

Plastics materials and rubbers

Engineering Materials and Processes

Note: This lecture closely follows text (Higgins Ch19)

Geomembrane liner: http://www.fabtech.com.au

19.2 Types of plastics (Higgins 19.2)

Engineering Materials and Processes

READ HIGGINS Ch19.2Thermoplastic materials, Thermosetting materials, Elastomers19.2.1 Raw materials19.2.2 Composition of plastics

19.2 Types of plastics (Higgins 19.2)

Engineering Materials and Processes

(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.htmlhttp://courses.chem.psu.edu/chem112/materials/polymers.html

AlkanesCovalent 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.

Engineering Materials and Processes

Ethanol aboveOil refinery right

Wikipedia

http://www.3rd1000.com

AlkanesIncreasingmolecule size.

Gas has 1 to 4 C.

Petrol contains 5 to 12 C.

Engineering Materials and Processes

Wikipedia

Alkane Formula Boiling point [°C]

Melting point [°C]

Density [g·cm3] (at 20 °C)

Methane CH4 -162 -182 gasEthane C2H6 -89 -183 gas

Propane C3H8 -42 -188 gasButane C4H10 0 -138 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 solidTriacontane C30H62 450 66 solid

Tetracontane C40H82 525 82 solidPentacontane C50H102 575 91 solidHexacontane C60H122 625 100 solid

AlkanesIncreasing 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.

Engineering Materials and Processes

http://www.3rd1000.com

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 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%

PlasticsUnlike 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 electronicsequipment used in radar during the Second World War.

Engineering Materials and Processes

Higgins 1.4.4 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. HDPE bin

bcsplastics.com.au

Van der Waals ForcesWhy 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.

Engineering Materials and Processes

LDPE bottlepromotionsonly.com.au

HDPE binbcsplastics.com.au

This is why HDPE (garbage bin) is harder than LDPE (squeeze bottle).

Gecko feet

Engineering Materials and Processes

http://www.sfu.ca

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.

No hooks, no slime, no suction.

Gecko feet. Van der Waals Forces!

Engineering Materials and Processes

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.

The surface area is achieved by splitting the toes into smaller and smaller hairs – until there is about a billion hairs of nanometer size.

Wikipedia/CC BY 1.0

Copying Gecko feet. Velcro to Anything!

Engineering Materials and Processes

http://www.sfu.ca

Researchers have developed a robot that can climb vertical surfaces.

Other teams are making gecko tape that sticks like 1 sided Velcro.

Gecko Tape: http://news.sciencemag.org

Sticky gecko feet Space Age ReptilesBBC animals2:25 min

19.2 Types of plastics (Higgins 19.2)

Engineering Materials and Processes

READ HIGGINS Ch19.2

Thermoplastic materials, Thermosetting materials, Elastomers19.2.1 Raw materials19.2.2 Composition of plastics19.2.3 General properties of plastics materialsResist atmospheric corrosion LightweightReasonably tough and strongCannot handle much heatGood finish, colours, some transparentEasy to process

http://www.dotmar.com.au

19.3 Thermoplastics (Higgins 19.3)

Engineering Materials and Processes

READ HIGGINS Ch19.3

19.3.1 Plasticisers

Rigid PVC pipe: WikipediaPlasticised PVC cable: www.diytrade.com

19.4 Thermoplastic materials (Higgins 19.4)

Engineering Materials and Processes

READ HIGGINS Ch19.4

19.4.1 Vinyl plasticsPolyethylene (PE)Polyvinyl chloride (PVC)Polyvinyl acetate (PVA)Polyvinyl acetate/chloride copolymersPolyethylene-vinyl acetate (EVA)Polypropylene (PP)Polypropylene-ethylene copolymersPolystyrene (PS)Acrylonitrile-butadiene-styrene (ABS)

PVC boat: Wikipedia

19.4 Thermoplastic materials (Higgins 19.4)

Engineering Materials and Processes

READ HIGGINS Ch19.4

19.4.2 Fluorocarbons19.4.3 Cellulose-base plastics (cellulose esters)19.4.4 Polyamides (PA)19.4.5 Polyesters19.4.6 Polyacetals19.4.7 Acrylics19.4.8 High-temperature thermoplasticsPolyimides, Polysulphones, Polyether ether ketone (PEEK),

http://www.dotmar.com.au

19.5 Thermosets (Higgins 19.5)

Engineering Materials and Processes

Headlamp Housinghttp://www.withermoset.com

READ HIGGINS Ch19.5

19.6 Thermoset Materials (Higgins 19.6)

Engineering Materials and Processes

READ HIGGINS Ch19.6

19.6.1 PhenolicsPhenol formaldehyde (PF)Urea formaldehyde (UF)Melamine formaldehyde (MF)

19.6.2 Polyester resins19.6.3 Polyurethanes19.6.4 Epoxy resins19.6.5 Polyimides19.6.6 Silicones

http://www.glowpaint.com.au

http://en.wikipedia.org/wiki/Silicone

19.7 Elastomers (Higgins 19.7)

Engineering Materials and Processes

READ HIGGINS Ch19.7

19.7.1 Long chain molecules in rubber19.7.2 Vulcanisation19.7.3 Engineering elastomersNatural 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

Recycling of plastics

Engineering Materials and Processes

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

Recycled Polyethylene: http://www.replas.com.auPET: wikipedia

Plastic recycling

Recycling problems with Plastics

Engineering Materials and Processes

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.

Recycling plant fire in Melbourne 2017:

Plastic recycling

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 of plastics

Engineering Materials and Processes

http://learneasy.info/MDME/MEMmods/MEM30007A/polymers/polymers.html

Plastic recycling

Engineering Materials and Processes

Wikipedia: Plastic

Resources.

Polymers

Engineering Materials and Processes

Online Resources.

http://www.dotmar.com.au/engineered-plastics-products.html

http://www.adelaideplastics.com.au/glossary.htm

Glossary

Engineering Materials and Processes

PolymerMonomerPolymerisationThermoplasticThermosettingElastomerCopolymerCross linkingVulcanisationBranched polymerMerMolecular weight

QUESTIONSHiggins Ch19: Callister Ch4Moodle XML: Some questions in 10104 Polymers

1. Define all glossary terms. 2. Attempt relevant questions from Quiz 10104 Polymers3. 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.

Engineering Materials and Processes