Re: What makes wet paper coil when dried?

Thanks for the question, Jeanne. The scientific explanation for the project is pretty simple. My explanation may be slightly long-winded, but I hope it gives you enough information to satisfy the curiosity of the third graders.

Paper is made up of wood fibers that are released from trees during the pulping process. These fibers range from a couple millimeters to about a centimeter in length; you can see them if you tear the paper and look at the edge. Once the fibers are released from the tree, they are mixed with water and sprayed on a moving screen. While on the screen, much of the water will drain through the screen, leaving the fibers arranged in a thin film that is now paper. The rest of the process involves pressing and drying to remove the remaining water from the paper.

The strength of paper comes from the bonds that develop among the fibers while they are dried (these bonds take several forms and are definitely too complicated for this discussion). The bonds hold the fibers together in much the same way tape will hold things together.

When you wet paper, the water interrupts the bonds that hold the fibers together (remember that the bonds formed when the paper dried). If the wet paper is reshaped and held until it dries, it will remain coiled because new bonds have formed between the fibers that will hold the paper in its coiled shape.

It is just like having two things taped together, removing the tape, rearranging the objects, and taping them together again in a different configuration. The ability, with the help of water, of paper to regenerate bonds over and over again makes recycling paper possible. It also has some negative consequences, for example a cardboard box will collapse when it gets wet. Paper manufactures combat this by using additives called sizing agents (see 985384231.Ot and 973636573.Ch. Therefore, the activity mentioned in the question will not work as well with highly sized paper such as milk and juice cartons or brown paper bags.

I hope this helps you with providing background for the project. Good luck, I hope everything turns out well.