WEBVTT - Why do newspapers turn yellow over time?

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<v Speaker 1>Welcome to brain Stuff from house stuff Works dot com

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<v Speaker 1>where smart happens. Hiem Marcia Brain with today's question why

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<v Speaker 1>do newspapers turn yellow over time? Paper is made from wood,

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<v Speaker 1>which is made up mainly of white cellulos. In the

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<v Speaker 1>ideal case, paper would contain nothing but white cellulos, But

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<v Speaker 1>wood also has a lot of a dark substance in

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<v Speaker 1>it called lignant, which ends up in the paper despite

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<v Speaker 1>the best efforts to keep it out. The exposure of

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<v Speaker 1>this lignant to air and sunlight is what turns paper yellow.

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<v Speaker 1>Lignin makes wood stiff and helps trees to stand upright.

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<v Speaker 1>You could say that it acts like a glue to

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<v Speaker 1>bind the cellulose fibers together. Lignant is a polymer, a

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<v Speaker 1>substance that's formed by joining together simple molecules into giant

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<v Speaker 1>molecules that act differently than the simple molecules would. According

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<v Speaker 1>to Dr Who Men Chang, a professor of wood and

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<v Speaker 1>paper science at NC State University, a tree could only

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<v Speaker 1>grow about six ft tall if it didn't have lignant.

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<v Speaker 1>Lignant also helps to protect the wood from pests and

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<v Speaker 1>other damage. Newsprint, which must be produced as economically as possible,

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<v Speaker 1>has more lignant in it than finer papers. At the mill,

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<v Speaker 1>the wood that will be turned into newsprint is ground

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<v Speaker 1>up lignant and all. That's not uncommon because paper manufacturers

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<v Speaker 1>use the benefits of lignant in some types of paper.

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<v Speaker 1>For example, brown craft paper, which is the dark brown

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<v Speaker 1>paper used in grocery store bags, and cardboard are stiff

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<v Speaker 1>and sturdy because they have more lignant in them, and

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<v Speaker 1>because those kinds of paper aren't treated with bleaching chemicals.

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<v Speaker 1>It doesn't matter how dark they are because the printing

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<v Speaker 1>on them is limited. To make a fine white paper,

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<v Speaker 1>the mill puts the wood through a chemical solvent process

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<v Speaker 1>which separates and discards the lignant. Pure cellulose is white,

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<v Speaker 1>and the paper made from it will be white and

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<v Speaker 1>it will resist yellowing. Lignant eventually turns paper yellow because

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<v Speaker 1>of oxidation. That is, the lignant molecules, when exposed to

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<v Speaker 1>oxygen in the air, begin to change and become less stable.

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<v Speaker 1>The lignant will absorb more light, giving off a darker color.

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<v Speaker 1>Chang says that if newsprint were kept completely out of

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<v Speaker 1>sunlight and air, it would remain white. After only a

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<v Speaker 1>few hours of sunlight and ocygen, however, it will start

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<v Speaker 1>to change color. Be sure to check out our new

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<v Speaker 1>down at it today on items