Why Do Newspapers Turn Yellow Over Time? - Science | HowStuffWorks

Home » Why Does Newspaper Turn Yellow » Why Do Newspapers Turn Yellow Over Time? - Science | HowStuffWorks

Maybe your like

Updated: Apr 16, 2024
  • Share Content on Facebook
  • Share Content on LinkedIn
  • Share Content on Flipboard
  • Share Content on Reddit
  • Share Content via Email
Lignin makes wood stiff and trees stand upright. It eventually turns paper yellow because of oxidation. Hitoshi Nishimura/Getty Images

Key Takeaways

  • Newspapers turn yellow over time due to the presence of lignin in the paper, which reacts with air and sunlight, causing oxidation and a change in color.
  • Newsprint contains more lignin than finer papers because it's cheaper to produce, leading to its quick yellowing when you expose it to sunlight and air.
  • Fine white paper is made by removing lignin through a chemical process, resulting in paper that resists yellowing over time.

Paper is made from wood, which is made up mainly of white cellulose. Wood also has a lot of a dark substance in it called lignin, which ends up in the paper, too, along with the cellulose. The exposure of lignin to air and sunlight is what turns paper yellow.

­ Lignin makes wood stiff and trees stand upright. You could say it acts as a glue to bind the cellulose fibers together. It is a polymer, a substance that is formed by the joining of simpler molecules into giant molecules that act differently than the smaller molecules did. Dr. Hou-Min Chang, a professor of wood and paper science at N.C. State University in Raleigh, N.C., compares lignin to the concrete used in buildings, with cellulose as the steel frame. Without lignin, Chang says, a tree could only grow to be about 6 feet tall. Lignin also helps protect the wood from pests and other damage.

Advertisement

Newsprint, which must be produced as economically as possible, has more lignin in it than finer papers. At the mill, the wood that will be turned into newsprint is ground up, lignin and all.

Paper manufacturers utilize the benefits of lignin in some types of paper, though. Brown kraft paper, the dark brown paper used in grocery store bags, and cardboard are stiff and sturdy because they have more lignin in them, and because those kinds of paper aren't treated with bleaching chemicals. It doesn't matter how dark they are because the printing on them is limited.

To make a fine white paper, the mill puts the wood through a chemical solvent process, which separates and discards the lignin. Pure cellulose is white, and the paper made from it will be white and will resist yellowing.

Lignin eventually turns paper yellow because of oxidation. That is, the lignin molecules, when exposed to oxygen in the air, begin to change and become less stable. The lignin will absorb more light, giving off a darker color. Chang says that if newsprint were kept completely out of sunlight and air, it would remain white. After only a few hours of sunlight and oxygen, however, it will start to change color.

Advertisement

Frequently Asked Questions

Can you prevent or reverse the yellowing of paper?
Preventing paper from yellowing involves minimizing its exposure to light and air, particularly UV light, and using acid-free paper which contains fewer lignin. Reversing yellowing is difficult and usually involves chemical treatment, which may further damage the paper.
Why is newspaper recycling important in relation to lignin?
Recycling newspapers helps reduce the demand for fresh wood pulp, which in turn lessens the environmental impact associated with lignin extraction and paper production, contributing to more sustainable paper usage.

Lots More Information

Related HowStuffWorks Articles

  • How many sheets of paper can be produced from a single tree?
  • Why doesn't paper money disintegrate when it gets washed in the washing machine?
  • How Newspapers Work
  • How much does 20-pound bond paper weigh?
  • How Freelance Magazine Writing Works

More Great Links

  • The Department of Wood and Paper Science at N.C. State University
  • About alkaline paper
  • Encyclopaedia Britannica on lignin
  • Bowater Corp.
  • Greenpeace
Cite This!

Please copy/paste the following text to properly cite this HowStuffWorks.com article:

Copy "Why do newspapers turn yellow over time?" 8 September 2000.HowStuffWorks.com. <https://science.howstuffworks.com/question463.htm> 19 January 2026 Close Citation More Awesome Stuff

Advertisement

Advertisement

Loading...

Tag » Why Does Newspaper Turn Yellow