Why Does Paper Turn Yellow Over Time?

History has always fascinated me; the way our world has evolved over the years is simply amazing – unbelievable even! Thanks to all the historians and authors who wrote down all the important events in the history books, we can better understand who we are and how we developed as a global society. Personally, my grandfather is the reason why I became so addicted to history. He has many books about world history and he never gets tired of showing me these sacred tomes and talking about all the fascinating aspects of history.

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Through my grandfather’s books, I was able to travel through time. It truly intrigued me how life on earth had evolved over the time and the changes that the world has gone through over the years. Something else also intrigued me, however… the way my grandfather’s books also changed over time. No! The history contained in them obviously remained the same, but the papers gradually turned from white to yellow in his books. The words had even become difficult to read at times.

Why does paper turn yellow from white, and how can we protect books against this?

Paper: The Process of Creation and the Curious Case of Lignin

Paper is made from types of wood. Wood mainly contains two polymers: cellulose and lignin. It is the lignin that causes paper to turn yellow. Lignin has a naturally dark color, which is what makes wood hard and stiff. Lignin undergoes oxidation when exposed to sunlight and air, and it breaks down into many phenolic acids that are yellow in color.

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How to Stop Yellowing and Make Books Last:

Nowadays, papers are made acid-free, and to achieve this, lignin is removed from the wood. This makes modern paper last longer, as compared to older types of paper made with lignin. An additional chemical process is required for removing the lignin from wood and this process is more expensive than making paper with lignin still in it.

This is the reason why newspapers turn yellow over time, as they are produced in bulk and more importance is placed on their economical cost of printing, rather than the length of time they remain in good condition.

As far as old history books and documents (which were made using lignin) are concerned, they can be protected from further damage by keeping them in a stable, acid-free environment, namely one that is dry, dark and free of any insects.

These types of historical papers can still be seen at history museums, where they are kept at ideal temperatures so that our history remains safe for future generations.

References:

  1. Why Does Paper Yellow? – Smithsonian Institution
  2. How Stuff Works
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About the Author:

Ashwin Vinod has a B.Tech in Electronics and Communications from APJ Abdul Kalam Technological University, Trivandrum (India). He likes to watch movies, reading fiction novels and surf the internet.

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