3. Thermoplastics GCSE AQA Graphics

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  • Biodegradeable: a material based on animal/vegetable matter which can be broken down by other living organisms into harmless waste.
  • However, 95%of all plastics are made from non-renewable, non-environmentally friendly material-oil.
  • Fortunately, recent technological advances mean that 5% of all plastics are biodegradeable, like plastics made from cellulose or starch found in plants-these are bioplastics.
  • Why are plastics used for packaging?
    • They are tough; they protect.
    • Lightweight
    • Clear; can see the product
    • Economical; easy to make, easily available.
    • Aesthetically useful; can be made to look good and can be printed on.
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Types and properties of plastics

  • Bioplastic - biodegradeablle, based on plants, can be clear or coloured - food packaging.
  • Cellulose Acetate - partially biodegradeable, based on plants, has added chemicals, it is clear, but it isn't tough - photocopiable clear film and film for cameras.
  • Acrylic - stiff but brittle, can shape and polish edges to high gloss, can have a wide range of colours - Point of sale stands, available as rods, tubes and sheets.
  • PET (polyethylene terephthalate) - tough, very good at retaining 'fizz' - fizzy drinks bottles.
  • PS (polystyrene) - not tough, can be vacuum formed -  shell forms for packaging, CD jewel cases, yoghurt pots.
  • Expanded polystyrene - very light, impact absorbing - protective packaging, block modelling.
  • PVC (polyvinyl chloride) - tough, scratch-resistant - blister packs, games pieces
  • PP (polypropylene) - flexible - crop packets
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Shaping and Forming plastics-Vacuum Forming

  • Vacuum Forming -makes uncomplicated hollow shapes by '****ing' a heat plastic like PVC over a mould-blister packaging, chocolate trays.
    • 1- Mould is made with draft angles and rounded edges and 'air' holes to **** air out.
    • 2- Mould is put into the vacuum former, and the plastic is heated up until it softens. Don't touch the heating elements.
    • 3- The mould is raised into the heated and soft plastic, and the air is ****ed out so plastic takes the shape of the mould.
    • 4- The plastic cools so it becomes rigid again.
    • 5- the mould is lowered so the polystyrene impression is removed and 'flashing; or excess material is cut off.
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Shaping and Forming Plastics-Injection Moulding

  • Injection Moulding-most common in shaping many different thermoplastics. Involves heating up solid granules of a thermoplastic into liquid form, then placed in a strong metal mould, allowing it to cool and solidify, and the shaped item is ejected.
    • 1- Expensive steel mould is made.
    • 2- granules of the plastic is placed into the hopper.
    • 3- Heaters melt the plastic into a thick liquid which is pushed towards the mould by an Archimedean Screw.
    • 4- A hydraulic ram forces the plastic under huge pressure into the mould.
    • 5- the mould is cooled and the object released.
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Shaping and Forming Plastics-Blow Moulding

  • Blow moulding-heating up a thermoplastic, putting it into a mould. Air is blown into the hot plastic, expanding it into the shape of the mould-makes bottles, fizzy drinks/plastic milk containers.
    • 1- Using a machine very similar to the injection moulding machine, thermoplastic is heated to produce a hot tube of plastic.
    • 2- the mould is wrapped around this hot tube.
    • 3- Compressed air is forced into the mould, making the plastic expand into the mould.
    • 4- The mould is cooled and the product is released.
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Shaping and Forming Plastics-Line Bending

  • Line Bending- bending straight lines in a thermoplastic-can be done with acrylic. Can be done easily at school with a strip heater and acrylic.
    • 1- Mark a line on the thermoplastic using a non-permanent pen.
    • 2- Heat plastic evenly on both sides until soft. Do not touch the heating elements.
    • 3- Bend the plastic using a jig or mould.
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