- 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.
- 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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