Q.1043: Why do newspaper turns yellow when exposed to sunlight?
Ans. Newsprint is generally made from wood. Wood is mainly consist of cellulose fiber, which is white in color and lignin, which is brown in color. For finer grades of paper lignin is removed during pulping and or bleaching, but to make newsprint as economical as practical, lignin is retained during pulping and only modified (not removed) during bleaching.
It is this lignin, which eventually turns paper yellow due to oxidation. The lignin molecules, when exposed to oxygen in the air, begin to change and become less stable. The lignin will absorb more light, giving off a darker color. If newspaper is kept completely out of sunlight and air, it would remain white. After only a few hours of sunlight and oxygen, however, it will start to change color.