Why doesn't paper money disintegrate when it gets washed in the washing machine?
Normal paper -- including notebook paper, newspaper, construction paper -- is all made out of cellulose, which comes from trees. The trees are chemically broken down into their individual wood fibers, and the cellulose fibers are chosen and formed into very thin sheets to create paper.

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Paper money can survive the washing machine because it's made of rags, not cellulose.
It turns out that rag fibers bond together much more firmly than fibers in regular paper. Rag fibers are basically unaffected by water, whereas cellulose fibers absorb water and come apart when they get wet. So paper money comes through the washer just fine, while cellulose paper comes unglued.
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