Tearing

[kishtik]

Why is it easier to tear a wet piece of paper than a dry one?

[FZ+]

Hmm. My guess is that it is to do with the chemistry of the paper. Perhaps it is in a way water soluble?

[Mr. Robin Parsons]

Drying the paper out, was the last step in the paper making process, you are simply going backwards in the final process of solidification, hence it becomes less solid/coherant...

[turin]

This is just a guess:

Paper is a conglomerate of fibers. They are held together by friction and some sort of adhesive. When you tear the paper, wet or dry, you are essentially separating the fibers. If the paper is wet, you don't have to overcome the force of the (dried?) adhesive.

[kishtik]

Yes! A friend of mine said that water seperated fibres, weakening cohessive forces. Can this be true? I knew nothing about cohessive forces.

[turin]

I didn't think it was a cohesive issue, but I was just guessing anyway.

[Mr. Robin Parsons]

In the paper making process the 'stuff' starts out as a "slurry" which is a mixture of wood fibers and water, that is squeezed through rollers as to compress the fibers together, and to assist in pressing out the water. This is repeated till the fibers have been pressed together, interfiber surface area adhesion of the fibers that, dried out, and pressed, increases. Naturally, when you add water, to dried paper, it absorbs the water, expands, and thus breaks some of the interfiber surface area cohesion...the result is paper that is easier to tear....