Have you ever noticed how paper turns yellow over time?

Piles and piles of old magazines and newspapers kept in some dusty corner of the house, when taken out during the annual maniac house cleaning, seem way yellower than before.I always wondered what caused that and turns out science has the answer.

Why Do Books Crumble?

During the last 500 years, the quantity of paper being produced has increased dramatically, but the chemical composition of modern paper causes it to turn yellow and crumble faster.

Cellulose To Paper

Paper can be made from almost any form of cellulose that can be shredded into tiny fibers and mixed into a watery pulp. Since cellulose is found in all plants, most plant matter can be used to make paper.

In the pulp, the cellulose fibers are partly dissolved so that when the sheet of paper is dried, the molecules of different fibers bond to each other.

 What Was Early Paper Made Of?

The earliest paper, made of white cotton rags beaten by hand consisted almost entirely of long cellulose fibers. As the demand for paper increased, paper makers used chlorine to bleach colored rags. Later, heavy machinery made it possible to turn wood into paper pulp.

But any chlorine bleach left in the paper eventually turns into hydrochloric acid. And so, too, does the lignin, which holds the cellulose fibers together in wood. Other acid-producing compounds were used to treat the paper, and even air pollution from coal-burning factories increased the acid-content of paper.

From White To Yellow... Why A Color Change?

All that acid breaks the chemical bonds between the cellulose molecules, making the paper brittle and turning it yellow. Today, many important documents are printed on acid-free paper, but in the meantime, library preservationists are working on ways to save millions of books before the acid in the paper turns them to dust.

All that acid breaks the chemical bonds between the cellulose molecules, making the paper brittle and turning it yellow. Today, many important documents are printed on acid-free paper, but in the meantime, library preservationists are working on ways to save millions of books before the acid in the paper turns them to dust.