Unit 4. RESISTANT MATERIALS. PLASTICS.
1. HISTORY
The first plastics were made in about 1860, but it was the 1950's when plastic began to be used a lot, after the Second World War. Now, they are replacing traditional materials like wood and metal.
2. GENERAL PROPERTIES
· Waterproof
· Electrical and thermal insulators
· Lightweight
· Easy to work with
· Resist corrosion and oxidation
3. MAKING PLASTICS
Plastic is a synthetic material. It is made from chemicals found in crude oil. They are manufactured using a process known as polymerisation. Polymerisation occurs when monomers join together to form long chains of molecules called polymers.
4. TYPES OF PLASTIC
Plastics can be classified into three groups: thermoplastics, thermosetting plastics and elastomers.
A) Thermoplastics
Thermoplastics can be heated and shaped many times. Some common thermoplastics are PVC, Nylon (polyamide) and polystyrene.
Name / Properties / Principal uses /Polyamide (Nylon)
Methacrylate
(plexiglas)
Polystyrene
Polystyrene (expanded)
Low Density Polythene / .
High Density Polythene
PVC
PET
Polycarbonate
Teflon
B) Thermosetting plastics
Thermosetting plastics can only be heated and shaped once. The main thermosetting plastics are epoxy resin, melamine and polyester resin.
Name / Properties / Principal uses /Epoxy resin
Melamine
Polyester resin
Bakelite
C) Elastomers
An elastomer is a polymer with the property of elasticity.
Name / Properties / Principal usesSynthetic rubber
Neoprene
5. HOUSEHOLD RECYCLING GUIDE
6. ACTIVITIES
1. How much do you know about plastic recycling? Say which of the following products can be recycled and which cannot.
Sunglasses / / Bread bag / / Plastic dolls /Peanut butter jar / / Shampoo bottle / / Milk jug /
VHS cassettes / / Frozen vegetables bag / / Yogurt cup /
Reusable plastic food containers / / Water bottle / / Disposable cutlery /
Detergent jug / / Pill packaging / / Grocery bags /
2. Write 5 general properties of plastics.
3. Compare the three main categories of plastics.
4. Give one characteristic of the following plastics and describe a possible use for each one:
· Polythene:· Nylon:
· Metacrilate / · Epoxy resin:
· Melamine (formaldehyde):
· Polystyrene expanded:
5. The table contains the name of 5 plastic forming methods. Match descriptions A, B, C, D, E with the methods 1-5 in the table.
Plastic forming method / Description1. Vacuum forming / A. A thermosetting plastic powder slug is pressed into shape and heated in a mould.
2. Extrusion / B. A sheet of polystyrene is held in place, heated and then shaped to a former by sucking out the air between the plastic and the former.
3. Injection moulding / C. Nylon granules are melted and then forced through a die into a continuous stream to form a pipe.
4. Compression moulding / D. Polythene granules are fed into a heated chamber and then pushed into a sealed mould where the moulding takes place.
5. Blow moulding / E. Air is blown into an extruded section of plastic. The air expands and it forces plastic to the sides of the mould.
6. Name and describe the plastic manufacturing process shown below. Match terms A-F with parts 1-6.
A. Heater D. Motor,
B. Hopper E. Plastic powder/granules
C. Rotating screw F. Split mould.
7. Name and describe the plastic manufacturing processes shown below:
7. VOCABULARY
· Waterproof· Electrical and thermal insulators
· Lightweight
· Resist corrosion and oxidation
· Synthetic
· Polymerisation
· Polymer
· Thermoplastics
· Thermosetting plastics
· Elastomers
· Resist wear
· Chemicals
· Gears
· Casing
· Stiff
· Bath screen
· Headlight / tail light glass
· Razor
· Disposable plates
· Food containers
· Pipe
· Bucket / · Bowl
· Guttering
· Shoe sole
· Fizzy drink
· Bullet-proof glass
· Riot shield
· Non-stick
· Stain
· Saucepan handle
· Natural rubber
· Synthetic rubber
· Tyre
· Milk jug
· Yogurt cup
· Disposable cutlery
· Grocery bag
· Pill packaging
· Vacuum forming
· Extrusion
· Injection moulding
· Compression moulding
· Blow moulding
· Heater
· Hopper