Photo: Erik Moreno (Flickr)
Open an older book and you may find the paper yellowed around the edges. Even older books fall apart as you turn the pages. But you might be surprised to learn that the pages in some of the oldest books are still white and turn easily without cracking.
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.