The majority of plastics are still made from petroleum products. But it can be obtained from cellulose, starch or even natural gas.
Naphtha, the basic ingredient of plastic
Naphtha is a liquid from petroleum refining that condenses between 40 and 180°C. It is the raw material for plastics. Before being used by plastics processors, naphtha must undergo a cracking operation.
Cracking
Under the effect of heating (800°C) then sudden cooling (400°C), the large molecules of hydrocarbons that constitute naphtha are fragmented into molecules that are more easily exploitable.
Polymerization
The monomers obtained after cracking contain between 2 and 7 carbon atoms each. Thanks to so-called addition reactions (chain of identical monomers) or condensation (chain of different monomers), they bind together to form polymers.
Formatting
On leaving the refinery, the polymers come in the form of granules, liquids or powders. The various plastic materials known to us are obtained through the addition of adjuvants and additives. They are then shaped by molding, extrusion, injection or thermoforming.
Plastic waste recycling
After use and collection, plastic waste is sent to treatment plants to be pre-washed and sorted. They are then ground into flakes, washed, rinsed, wrung out, dried, sieved and regenerated into granules. It should be noted that the calorific value of plastic is equivalent to that of coal or oil. Thus, a significant portion of plastic waste currently follows an energy recovery process.
