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Plastics and their Properties

These icons indicate that detailed teacher’s notes or useful web addresses are available in the Notes Page.

This icon indicates the slide contains activities created in Flash. These activities are not editable.

For more detailed instructions, see the Getting Started presentation.


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Everyday plastics

Take a few minutes to look around the room and identify some everyday plastics.

Can you find the following objects and decide what type of plastic they are made from?

Polypropene

  • Chairs

  • Jumper

  • Comb

  • Carrier bag

  • Pencil case

Acrylic

Nylon

Polyethene

Neoprene



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Categories of plastics

Plastics can be broken down into two categories:

thermoplastics and thermosets.

  • Soften when heated

  • Can bereshaped

  • More commonly used in schools

Thermoplastics

  • Initially set byheat

  • Cannot be reshaped once set

  • Extremely stronganddurable

Thermosets


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Uses of plastics (thermoplastics)

Plastics have an extremely wide range of uses. Here are some common products made from thermoplastics.

Polystyrene

High Density

Polyethene

ABS

Low Density

Polyethene

Polypropene

Acrylic


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Uses of plastics (thermosets)

Thermosets have different qualities to thermoplastics. Here are some uses for thermosets.

Epoxy

resin

Urea

formaldehyde

GRP

Melamine formaldehyde

Phenol formaldehyde





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Working with plastics – other processes

Plastics can also be worked in other ways.

Hot wire

strip heater

Oven

Scroll Saw

Drill

Buffer


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Working with plastics – industrial processes

When plastic is used to make a large number of identicalproducts, industrial processes are used. Specialized machines are used to mass produce products. Press play to see a video of the vacuum forming process.


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Working with plastics – industrial processes

The injection moulding process involves heating plastic granules to their melting point and then injecting them at high pressure through a nozzle into a mould. When the plastic cools the mould is opened and the newly formed plastic part can be removed.

Injection moulded

polyethene wheel

What similarities and differences can you identify between the vacuum forming and injection moulding processes?


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Joining plastics

Materials can be joined temporarily or permanently. Three methods of joining plastic are shown below.

Riveting

Adhesive

Nut, bolt and

washer


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Working with plastics – finishing techniques

Plastics have excellent surface qualities. As they are self-finishing, plastics require little or no surface finish. However, when designers want a specific colour or texture, spray paints can be used.

  • Use wet and drypaper (wet) to smooth the surface down and create a ‘key’ for the primer to grip to.

  • Primer is used to create an undercoat to protect the plastic and provide a good surface finish for the top coat. The primer should be rubbed down using wet and dry paper between coats.

  • Top coat is applied once the primer has completely hardened. There are different surface textures: gloss, matt and metallic being the most common. Top coat is applied in several layers to build up a thick, tough surface layer on the top of the primer.