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Plastics 
Properties of plastics.
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Ecological properties
We can recycle plastics.There are three recycling processes:chemical,mechanical and energetic.
Chemical recycling:We apply chemical processes to make new materials from the original components of plastics residues.
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Formation techniques
When we manufacture plastics objects in indstrys the plastics is available in three different form,powder,granules and resins.We can use different formations techniques depending on the type and use of plastics.
Extrusion
We apply pressure by means of a large,rotating.screw with forces the melted material out,trough a nuzzle.We put thermoplastics in granular form into a previusly heated cylinder.We cool slowly the shape material in a refrigetared water bath until its solid.Finally we collect the pieces of plastic trough a feeders system
Lamination
Thermoplastics produced by the method extrusion method is passed trough a scenes of hot cylinders to produce sheets of varying thickness.With this techinique we can produce different finishes,for example glossy, matt or textured.This depends of the outer coating applied by the final cylinder
Compression:
We put thermostable plastics,which can be in granular form, into the base of a cavity mould.The outer part of the cavity mould is shaped the same,is closed to compress the material inside.We heat it and it becomes soft and malleable.The plastics 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.
Vacuum Forming
We use plastics sheet with a large surface for this techniique.We put thermoplastics into a mould.We then use a heater to heat the mould and softhen 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 desire form is created.We leave the mould to cool,then we remove the object.
Moulding
Blow Moulding
We put a tubular shaped piece of plastic into a hollow mould which has the same shape as the object we want to make.
Compression
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.
Injection
We inject thermoplastics into a mould.When the material has cooled and solidified,we extract it from the mould.
Plastics plays a big part of our life.We all know they re used to make containers and packing.But we also use plastics in many economy and industrials sectors.Plastics are materials formed by polymers.The polymers in plastics are made from long chains of carbon atoms.
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Classifications of Plastic
Thermoplastics:
We manufacture thermoplastics from compounds acquired from petroleum.They are made up of weakly formed molecular chains.When we heat them,they become soft,which allows them to be formed into different shapes.The heating and cooling process can be repeated many times.
Thermostable Plastics:
These plastics are made from compounds derivied 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 cnnot be remoulded appling heat.
Elastormers:
Made by vulcanisation:mixing sulphur and rubber and heating to 160º.They are hard,resistant and very elastic.Streaching easily under force.They are formed by chains linked laterally and then folded over themselves,like a ball of wool or string.