Stuff Matters: Exploring the Marvelous Materials That Shape Our Man-Made World

by Mark Miodownik

Most paper starts out life as a tree. A tree’s core strength derives from a microscopically small fiber called cellulose, which is bound together by an organic glue called lignin. This is an extremely hard and resilient composite structure that can last hundreds of years. Extracting the fibers of cellulose from the lignin is not easy. It is like trying to remove chewing gum from hair. Delignification of wood, as the process is called, involves crunching up the wood into tiny pieces and boiling them at high temperatures and pressures with a chemical cocktail that breaks down the bonds within the lignin and frees up the cellulose fibers. Once achieved, what is left is a tangle of fibers called wood pulp: in effect, liquid wood—at a microscopic scale it resembles spaghetti in a rather watery sauce. Laying this on to a flat surface and allowing it to dry yields paper. This basic type of paper is raw and brown. Making it white, sleek, and shiny requires a chemical bleach and the addition of a fine white powder such as calcium carbonate in the form of chalk dust. Other coatings are then added to stop any ink that is laid on top of the paper from being sucked too far into the cellulose mesh, which is what causes ink to bleed. Ideally the ink should penetrate a small amount into the surface of the note paper and then dry almost instantly, depositing its cargo of colored molecules, which sit there embedded in the cellulose mesh, creating a permanent mark on the paper.

The reason paper turns yellow is due to Lignin reacting with oxygen in the presence of light, chromophores is what's created as a result. Another neat thing is that the smell of old books that we've come to love is in fact the breakdown of chemical compounds... basically, we enjoy the smell of rotting paper. lol