[eli5] Why does the lignum has to be removed from wood in the process of paper making?

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[eli5] Why does the lignum has to be removed from wood in the process of paper making?

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Lignum is the natural glue that keep the wood fibers together. At first though that would be desired in the making of paper, but seems it isn’t. Why?

Lignin is removed from the wood (lignum).

from Wikipedia:

Lignin is an impediment to papermaking as it is colored, it yellows in air, and its presence weakens the paper.

The primary constituents of wood fibers are cellulose, lignin, and hemicellulose. As has been said in one of the comments lignin is essentially what allows wood fibers to maintain its rigidity while still part of a tree. Paper derives it’s strength (and many other favorable properties ) largely from cellulose, while lignin contributes to several unfavorable paper properties (discoloration) and the abundance of lignin in paper product means you have less cellulose i.e. less abundance of good stuff. The “strength” of wood fibers is not analogous to the strength of paper, as the latter relates to bonds made between fibers during the papermaking process and length of fiber

As others have said, it makes the paper yellow over time..

Newspaper contains high amounts of lignin, which is why it yellows so quickly in comparison to other paper.

Lignin can also essentially leech into other materials pressed against it, which is why you’ll find professional framing shops advertising ‘acid and lignin free’ materials.