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Plastics (Manufacturing process (The transformation of these raw materials…
Plastics
Manufacturing process
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During the manufacturing process, we can add materials such as flbreglass, textile fibres, paper, silica and sawdust to reduce production costs, and to develop certain characteristics.
We can incorporate chemical additives to increase flexibility and to strengthen the polymers, and we can add pigments to give colour to the plastics.
Types
Natural plastics
They are obtained directly from raw vegetable materials.
For example: cellulose or latex, or from animal proteins.
Synthetic plastic
They are made from compounds extracted from petroleum, natural gas and carbon.
The mayority of plastics belong
to this group.
Classification
Thermoplastics
We manufacture thermoplastics from compounds acquired from
petroleum.
They are formed by strongly-linked chains running in different directions .
When heated, they become soft and can be shaped. When cooled, they cannot be remoulded by applying heat.
Elastomers
Made by vulcanisation mixing sulphur and rubber, and heating to 160ºC.
They are hard, resistant and very elastic, stretching easily under force.
Theyare formed by chains linked laterally and the folded over themselves, like a ball of wool pr string.
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Characteristics
Strength, elasticity, rigidity and flexibility
Properties
Mechanical, acoustic, electrical, thermal, low, density and impermeability
Recycling processes
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Energetic recycling
We can incinerate plastics and the energy that
is produced is used tn industry, for heating or producing electnctty.
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Formation techniques
Extrusion
- We put thermoplastic, in granular form, Into a previously heated
cylinder.
2.We apply pressure by means of a large, rotatting screw, whitch forces
the melted material out, through a nuzzle.
- We cool the shaped material slowly in a refngerated water bath until
lt's solid.
- Finally, we collect the pieces of plastic through a feeder system.
Lamination
Thermoplastic produced by the extrusion method is passed through a series of hot cylinders to produce sheets of varying thickness.
With this technique, we can produce different finishes, for example, glossy, matt or textured. this depends on the outer coating applied by the final cylinder.
Vacuum forming
- We put thermoplastic into a mould.
2.We then use a heater to heat the mould and soften the plastic.
- We extract the air below the sheet so that the plastic is pulled against the inside walls of the shaped mould, and the desired form is created.
- We leave the mould to cool, then remove the obiect.
Moulding
Blow moulding
- We put a tubular-shaped piece of plastic into a hollow mould which has the same shape as the oblject that we want to make.
- We close the mould and blow pressurised air into it, so that the plastic adheres to the sides of the mould and takes its shape.
- When the object is cold, we remove it from the mould.
Injection moulding
- We inject melted thermoplastic into a mould.
- When the material has cooled and solidified, we extract it from the mould.
Compression
- We put thermostable plastic, which can be in granular form, into the base of a cavity mould.
- The outer part of the cavity mould, shaped the same, is closed to compress the material inside. We then heat it and it becomes soft and malleabie.
- The plastic adapts to the shape of the cavity between the two parts of the mould.
- We extract the object when the plastic has cooled and solidified
Plastics are materials formed by polymers. The polymers in plastics are
made from long chains of carbon atoms.