Plastics are derived from organic products. The materials used in the production of plastics are natural products such as cellulose, coal, natural gas, salt and, of course, crude oil.
Crude oil is a complex mixture of thousands of compounds. To become useful, it must be processed.
The production of plastic begins with a distillation process in an oil refinery
The distillation process involves the separation of heavy crude oil into lighter groups called fractions. Each fraction is a mixture of hydrocarbon chains (chemical compounds made up of carbon and hydrogen), which differ in terms of the size and structure of their molecules. One of these fractions, naphtha, is the crucial element for the production of plastics.
The two major processes used to produce plastics are called polymerisation and polycondensation, and they both require specific catalysts. In a polymerisation reactor, monomers like ethylene and propylene are linked together to form long polymers chains. Each polymer has its own properties, structure and size depending on the various types of basic monomers used.
There are many different types of plastics, and they can be grouped into two main polymer families:
- Thermoplastics (which soften on heating and then harden again on cooling)
- Thermosets (which never soften when they have been moulded)
Examples of Thermoplastics
Acrylonitrile butadiene styrene – ABS
Polycarbonate - PC
Polyethylene - PE
Polyethylene terephthalate - PET
Poly(vinyl chloride) - PVC
Poly(methyl methacrylate) - PMMA
Polypropylene - PP
Polystyrene - PS
Expanded Polystyrene - EPS
Examples of Thermosets
Polytetrafluoroethylene - PTFE
Unsaturated polyester resins (UP)