Speaker 1: Welcome to brain Stuff from house stuff Works dot com
Speaker 1: where smart happens. Hiem Marcia Brain with today's question why
Speaker 1: do newspapers turn yellow over time? Paper is made from wood,
Speaker 1: which is made up mainly of white cellulos. In the
Speaker 1: ideal case, paper would contain nothing but white cellulos, But
Speaker 1: wood also has a lot of a dark substance in
Speaker 1: it called lignant, which ends up in the paper despite
Speaker 1: the best efforts to keep it out. The exposure of
Speaker 1: this lignant to air and sunlight is what turns paper yellow.
Speaker 1: Lignin makes wood stiff and helps trees to stand upright.
Speaker 1: You could say that it acts like a glue to
Speaker 1: bind the cellulose fibers together. Lignant is a polymer, a
Speaker 1: substance that's formed by joining together simple molecules into giant
Speaker 1: molecules that act differently than the simple molecules would. According
Speaker 1: to Dr Who Men Chang, a professor of wood and
Speaker 1: paper science at NC State University, a tree could only
Speaker 1: grow about six ft tall if it didn't have lignant.
Speaker 1: Lignant also helps to protect the wood from pests and
Speaker 1: other damage. Newsprint, which must be produced as economically as possible,
Speaker 1: has more lignant in it than finer papers. At the mill,
Speaker 1: the wood that will be turned into newsprint is ground
Speaker 1: up lignant and all. That's not uncommon because paper manufacturers
Speaker 1: use the benefits of lignant in some types of paper.
Speaker 1: For example, brown craft paper, which is the dark brown
Speaker 1: paper used in grocery store bags, and cardboard are stiff
Speaker 1: and sturdy because they have more lignant in them, and
Speaker 1: because those kinds of paper aren't treated with bleaching chemicals.
Speaker 1: It doesn't matter how dark they are because the printing
Speaker 1: on them is limited. To make a fine white paper,
Speaker 1: the mill puts the wood through a chemical solvent process
Speaker 1: which separates and discards the lignant. Pure cellulose is white,
Speaker 1: and the paper made from it will be white and
Speaker 1: it will resist yellowing. Lignant eventually turns paper yellow because
Speaker 1: of oxidation. That is, the lignant molecules, when exposed to
Speaker 1: oxygen in the air, begin to change and become less stable.
Speaker 1: The lignant will absorb more light, giving off a darker color.
Speaker 1: Chang says that if newsprint were kept completely out of
Speaker 1: sunlight and air, it would remain white. After only a
Speaker 1: few hours of sunlight and ocygen, however, it will start
Speaker 1: to change color. Be sure to check out our new
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