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PLASTICS :!!: (Origin and transformation of plastics: (Natural plastics…

- - - - 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.
- - - - Acoustic: acoustic insulation
        
        Electrical: electrical insulation
        
        Thermal: thermal insulation.
        
        Other properties: low density, tempermeability
- - - - Separation and crushing. We separate the plastics according to type and then they' re crushed.
        
        Floating. We wash the plastics and then dry them by centrifugal
        force
        
        Agglutination. The material is compacted and then incorporated into other materials.
        
        Extrusion. We melt the material, and then tt's extruded into long
        filaments
        
        Pelletising. The filaments are then reduced to granules that we call pellets.
        
        Energetic recycling. We can incinerate plastics and the energy that
        is produced is used in industry, for heating or producing electricity.
    - - Plastics that decompose on contact with certain bacteria and
        biological agents
      - Plastics that dissolve in hot or cold water.
- - - - These plastics are made from compounds derived from petroleum. They are formed by Strong-Linked chains running in different directions. When heated, they can become soft and can be shaped. When cooled they cannot be remoulded by appling heat.
    - - Made by vulcanisation: mixing sulphur and rubber, and heating to 160ºC. They are hard, resistant and very elastic — stretching easily under
        force. They' re formed by chains linked laterally and then folded over
        themselves, like a ball of wool or string.
- - - - We apply pressure by means of a large, rotating screw, whtch forces
        the melted material out, through a nuzzle.
      - We put thermoplastic, in granular form, Into a previously heated cylinder.
      - We cool the shaped material slowly In a refrigerated water bath until
        lt's solid.
        
        Finally, we collect the pieces of plastic through a feeder system.
    - - Thermoplastic produced by the extrusion method is passed through a
        senes 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.
    - - We use plastic sheets with a large surface for this technique:
        
        We put thermoplasttc into a mould
        
        We then use a heater to heat the mould and soften the plasic
        
        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.
    - - There are three principal techniques:
        
        Injection.
        
        Blow moulding.
        
        Compression.
      - Injection Moulding:
        
        We inject melted thermoplastic into a mould
        
        When the material has cooled and solidified, we extract it from the
        mould
      - Blow Moulding:
        
        We put a tubular-shaped piece of plastic into a hollow mould which has the same shape as the object 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.
    - - 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 malleable.
        
        The plastic adapts to the shape of the cavity between the two parts of
        the mould.
        
        We extract the oblect when the plastic has cooled and solidified.