Tuesday, May 15, 2007

Why Does Newspaper Turn Yellow?

There are various paper products that we use in our everyday lives including paper plates, construction paper, tissues, brown paper grocery bags, printing paper, and newspaper. Have you ever wondered where all this paper comes from? These paper products are all made from wood, which is primarily made up of two polymer substances called cellulose and lignin. Polymers are formed from simpler molecules that are joined into large molecules that behave differently than the smaller molecules alone. Cellulose is made up of simple molecules that are linked together like chains, while lignin is made up of more complex molecules that are linked like circles or rings. The cellulose chains are easy to break apart, but the lignin rings are difficult to break apart because lignin acts like glue to make wood stiff so that trees can grow and stand upright.

Cellulose and lignin are usually separated from each other when wood is being processed to make paper. Cellulose is white in color, while lignin is dark in color. Most paper products are required to be white or very light in color like printing paper and paper plates, and these products are primarily made from cellulose. However, sometimes the visual quality of the final paper product does not need to be very light in color, so these paper products are made from both cellulose and lignin. These products include newspaper and brown paper grocery bags.

Lignin can turn yellow in color when it is exposed to oxygen or air especially in the presence of sunlight. The molecules in lignin will change and the circular links will become less stable. Since there is more lignin present in newspaper than most paper products, the newspaper will also eventually turn a yellow or brown color over time as it is exposed to air and sunlight. On the other hand, cellulose does not turn dark in color in the presence of air and sunlight.

For more information about how paper is made, see the website of the Energy Information Association.

Little Lion Experiment:

Items Needed:

  • 1 sheet of newspaper that is only a day or two old
  • 1 piece of printing paper (this paper can be used)
  • 2 freezer bags
  • Access to sunlight
  • Access to an area where no sunlight shines, which could be a cupboard, closet, or drawer


  1. Cut the newspaper into two pieces.
  2. Place one piece onto a window sill or tape it to a window where sunlight shines.
  3. Place the other piece into the freezer bag and shut it so no air can get inside.
  4. Put the freezer bag with the newspaper in it into the area where no sunlight shines.
  5. Repeat steps 1-4 for the printing paper.
  6. Leave the pieces of newspaper and printing paper alone for 1 day and then visually compare all the pieces of paper. Continue the experiment and examine the different pieces of paper after 2, 3, 4, and 5 days to see if the paper changes much over time.


  • How do the different pieces of paper visually compare with each other?
  • Are the ones exposed to air and sunlight darker in color than those pieces of paper that were not? How do the pieces of newspaper visually compare with each other?
  • How do the pieces of printing paper compare with each other?
  • Are there any visual changes between the same types of paper?