Negotiations on a treaty to limit plastic pollution takes place in Nairobi until November 19. How is plastic made? Mostly from crude oil, as this videographic explains. VIDEOGRAPHIC
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00:00Most plastics come from crude oil. It is first heated to a high temperature in a
00:11refinery and then sent to a distillation tower to separate various components. The
00:17heaviest products settle at the bottom of the tower, while the lighter ones rise
00:22to the top. One of these products is naphtha, which is a liquid used in most
00:27plastics. In petrochemical plants, naphtha undergoes a treatment known as
00:32steam cracking. The liquid is diluted with steam and heated to 800 degrees
00:37Celsius, then cooled to 400 degrees. Naphtha is transformed into gases such
00:44as ethylene and propylene, which then undergo a chemical reaction called
00:49polymerization to create plastic. The substance leaves the plant in powder or
00:54granulated form. To shape it, manufacturers use extruders. Granules are
01:02heated and mixed by a twin screw, then shaped using a mold that fits the final
01:07product.