Sources and origins

Most polymers are obtained from crude oil often found deep within the Earth’s crust. They are called synthetic plastics and are chemically manufactured. They are often referred to as plastics as they exhibit plastic properties. The crude oil is accessed by drilling, which can be a costly and messy process.

Some polymers can be derived from natural sources, such as plants. The most common plant-based polymer used in schools is polylactic acid (PLA), which is commonly used in a 3D printer. PLA is obtained from corn starch - the corn is fermented to produce lactic acid, which is polymerised to produce polylactic acid.

Bioplastics are being continually developed to combat the environmental concerns related to the non-biodegradable properties of plastic polymers.

A stack of six coloured filament coils for 3D printing on a white backdrop.
PLA filaments for 3D printers

The process used to produce the common polymer polythene:

  1. crude oil is drilled and pumped to the surface of the Earth
  2. the oil is transferred to an oil tanker and shipped to an oil distillery
  3. the oil is heated to break it down and obtain different products through a process called fractional distillation
  4. a chemical called naphtha, a mix of hydrocarbons used for the production of many different plastic polymers, is vented off from the distillery column - a long vertical tube where the oil is separated into different components
  5. this then undergoes a process called cracking so that individual hydrocarbons, called monomers, are produced
  6. monomers undergo polymerisation, which links monomers together to make a polymer chain - the monomer ethene is polymerised to make polythene

When crude oil is heated, many different chemicals are vented off from the heating column. The thick and dense material bitumen, used for road surfacing, is vented off from the hottest part of the column at the base. Lighter, less-dense gas and petrol are vented at the cooler part of the column towards the top.

Using a fractionating column, crude oil is separated into fractionsThe distillery column

Polymerisation process

Some small molecules, called monomers, can join together to make very long molecules, called polymers - this process is called polymerisation. Many polymers are made from chemicals obtained from crude oil, eg molecules of ethane can join together to make polythene.

Ethene molecules make long polyethene molecules.Forming polythene from ethene

By polymerising other small molecules, a wide variety of different polymers can be made that have many uses.