Plastics

Plastics

1. Origin

   • A plastic is made of polymers
   • They can be
     • Natural
       • Obtained from natural substances
     • Artificial
       • Obtained from petroleum hydrocarbons
       • They are the majority
   • Obtaining process
     • The oil is extracted from the wells
       • In the refineries we obtain the hydrocarbon
         • It is stirred in a reactor with the aditives
           • The polymer is obtained in granules
           • Some aditives are incorporated to increase the flexibility and the resistance to the polymer

2. Types

   • Thermoplastics
     • Linear internal structure
     • Melt easily
     • Ideal for recycling
     • Very cheap
     • Easy to model
     • Deform with high temperatures
     • Examples
       • 1. PET
       • 2. HDPE
       • 3. PVC
       • 4. LDPE
       • 5. PP
       • 6. PS
       • 7. Others
       • 1, 2, 4 and 5 are SAFE to reuse
   • Thermosets
     • Strong bonds
     • Heating can give them shape
       • A second heating will decompose them
     • Not recyclable
   • Elastomers
     • More or less linear chains
       • Great flexibility and elasticity
     • Easily degraged by heat

3. Environmental problems

   • They take many years to decompose
     • They don't dissapear, they transform in microplastics
       • They end up in fish, meat, fruits, etc
   • They create pollution
     • Big trash islands in the sea
   • Animals eat them and they die

4. Bioplastics

   • Biodegradable
     • Plastics that can be used for microorganisms as food
     • They are reincorporated as an organic material
   • Compostable
     • Plastics that decompose and transform into organic compost in a similar speed to organic materials

5. Plastic forming

   • Injection molding
     • Melted plastic pushed in a mold
       • When it colds, the piece is removed from the mold
     • Pieces of complicated shapes
   • Extrusion
     • Molten plastic pushed through a nozzle
     • Tubes and pipes
   • Blow molding
     • A preform is introduced into a mold
       • Hot air is introduced to shape it
     • Bottles
   • Vacuum molding
     • A plastic sheet attached to a mold
       • Extract the air
     • Large surfaces