Paper made from mechanical pulp contains significant amounts of <answer>lignin</answer>, a major component in wood. In the presence of light and oxygen, <answer>lignin</answer> reacts to give yellow materials, which is why newsprint and other mechanical paper yellows with age. Paper made from bleached kraft or sulfite pulps does not contain significant amounts of <answer>lignin</answer> and is therefore better suited for books, documents and other applications where whiteness of the paper is essential.
A book is likely made with paper that has low amounts of what component of wood?
lignin