Most plastics are made from organic materials found in the natural environment and can include plants, minerals and fossil fuels. The base material in much of the plastic we use today is an unrefined petroleum created by the remains of dead plants and animals, referred to as crude oil. This oil is essential in creating various compounds that contain the hydrocarbons necessary to make an identical chain of molecules called monomers. The production of plastics begins with a process called “cracking”, which refines oil and separates heavier molecules into groups called fractions. Once sorted, the monomers go through one of two major processes, either being polymerisation or polycondensation.
In both cases, the hydrocarbons from each fraction are chemically combined with specific catalysts to create larger molecules. As these processes occur in a reactor, the heat allows the monomers to link together to form long polymer chains. The result of these reactions are polymer resins, which are collected and further processed by adding plasticisers, dyes and flame-retardant chemicals (Freudenrich, 2007) if necessary. The resins, now in the form of pellets, are able to complete the last stage by being heated, combined and cooled through specific processes depending on the type of plastic product being produced. Some examples of methods are extrusion, injection moulding and blow moulding.