PLASTICS:
Origin and transformation of plastics:
Natural plastics are obtained directly from raw vegetable materials (latex)
Synthetic plastics are made from compounds extracted from
petroleum, natural gas and carbon
The transformation of these raw materials and compounds into plastics
is called polymerisation:
During the manufacturing process, we can add matenals
We can incorporate chemical additives
Properties of plastics
Ecological properties
Strength, elasticity, rigidity, flexibility, mechanical, acoustic, electrical, thermal and other properties.
We can recycle plastics. There are three recycling processes:
Chemical recycling (we apply chemical processes)
Mechanical recycling: We make new products (1.Separation and crushing; 2.Floating; 3.Agglutination; 4.Extrusion; 5.Pelletising)
Energetic recycling (We can incinerate plastics and the energy that
is produced is used in industry)
The mallority of plastics are not yet biodegradable: 
Classification of plastics
Thermoplastics
We manufacture thermoplastics from compounds acquired from petroleum. They' re made up of weakly formed molecular chains.
Thermostable plastics
These plastics are made from compounds derived from petroleum. They are formed by strongly-linked chains running in different directions.
Elastomers
Made by vulcanisation: mixing sulphur and rubber, and heating to 160ºC. They are hard, resistant and very elastic.
Formation techniques:
Extrusion:
This technique has four stages:
1: We put thermoplastic; 2: We aplly pressure by means of a screw; 3: We cool the shaped material slowly; 4: We collect the pieces of plastic through a feeder system.
Lamination:
Thermoplastic produced by the extrusion method ls passed through a
senes of hot cylinders to produce sheets of varying thtckness
Vacuum forming:
Moulding:
We use plastic sheets with a large surface. It has four stages:
1: We put thermoplastic into a mould; 2:We then use a heater to heat the mould and soften the plastic; 3: We extract the air below the sheet; 4: We leave the mould to cool, then remove the object
There are three principal techniques
Injection
Compression
Blow moulding
It has two stages: 1:We inject melted thermoplastic into a mould; 2: When the material has cooled and solidified, we extract it from the mould
It has three stages: 1: We put a tubular-shaped piece of plastic into a hollow mould which the same shape of the object we will make; 2: We close the mould and blow pressurised air into it; 3: When the object is cold, we remove it from the mould.
It has four stages: 1: We put thermostable plastic in a base; 2: The outer part of the cavity mould is closed; 3: The plastic adapts to the shape of the cavity; 4: We take the object
Shaping and finishing techniques: There are differents forms of finishing plastics objects:
Cutting
Cutter, scissors, steel bit, fretsaw, etc.
Perforating: With a drill bit
Trimming and filing: With a file or a rasp
Joining plastics:
The joints can be permanent or temporary:
Temporary joints: We can join and then separate objects with mechanical fasteners
Mechanical fasteners: Nut and bolt; Standard screw; And double ended screw
Permanent joins: We use this type of join when we don't want to separate or dismantle the pieces. We can use adhesives or soldering.
Adhesives: Joining two surfaces permanently
Soldering: Joining thermoplastis using heat and pressure.
