Where does paper come from, and where does it go when we throw it away?

In numbers

• AD 105the year Cai Lun improved papermaking
• 40–50%of wood is cellulose

In five stops

1. 1

   Where were its atoms born?

   Paper is made mainly of cellulose: carbon, hydrogen and oxygen. Its hydrogen comes from the Big Bang, its carbon and oxygen from stars. These atoms entered the tree from carbon dioxide in the air and water in the soil.

2. 2

   How did nature prepare it?

   Trees turn the glucose they make by photosynthesis into cellulose fibres and build their trunks from these fibres, glued together by a substance called lignin. Wood is about 40–50% cellulose.

3. 3

   What did people do?

   Papermaking developed in China: in AD 105 Cai Lun, an official of the Han court, greatly improved the method of making paper from tree bark, hemp waste, old rags and fishing nets; even older paper-like fragments have been found. By the late 8th century paper was being made in Baghdad, and in the 13th century it spread to Europe. Since the 1840s paper has mostly been made from wood pulp: wood chips are broken into fibres, the watery pulp is spread on a screen, drained, pressed and dried.

4. 4

   What happens when we use it?

   When you write, the ink soaks in between the fibres. The fibres hold on to one another to keep the sheet together; when paper gets wet that grip weakens and it tears easily.

5. 5

   Where does it go next?

   Collected paper is broken down in water into pulp, the ink is removed and it becomes paper again. Because the fibres get shorter each time, eventually they can no longer make new paper, so fresh fibre is added to the pulp. Paper sent to landfill releases methane and carbon dioxide as it rots without air; if it is burned, its carbon returns to the air at once.