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Why does folding/creasing loosen the fibre-fibre bonding in paper?

Creasing makes tearing paper easier because it weakens the fibre-fibre bonds or makes the strong fibres easier to tear, it is said. But why would the creasing make the bond easier to break? Some sources say that a certain elongation occurs at the sight while others mention about a deformation. Please explain.

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Paper consists of cellulose fibers held together with a small amount of binder (a glue-like substance). Creasing a piece of paper back and forth applies nonuniform shear and tensile forces to the fibers which tends to break the mechanical bonds between adjacent cellulose fibers. This then allows them to tear free of one another when you then unfold the paper and pull on it.

The strongest papers are those made from the longest fibers because they are more easily entangled with other fibers during the manufacturing process, and have the most binding agents. The weakest papers are those consisting of short fibers (and a minimum of binders).

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    $\begingroup$ Actually, the question asks as to why would creasing 'breaks the bonds'. $\endgroup$ – Zam Jun 12 at 8:45
  • $\begingroup$ answer edited. -NN $\endgroup$ – niels nielsen Jun 12 at 16:06

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