(
In the new American POP exhibit here at The Children’s Museum of Indianapolis, we have a ton of awesome artifacts from throughout the history of pop culture. We have toys, comic books, lunchboxes, and all sorts of other neat stuff. One thing we have a lot of that you might not think of as necessarily being related to pop culture is clothing. We have an entire section of the gallery dedicated to fashion. I mean, when you think about it, you can look at certain clothes and know exactly what time period they came from. If that doesn’t say pop culture then I don’t know what does.
One thing about fashion, though, is that it’s not always practical. One of our artifacts is a paper dress. For a brief period in the 1960s, designers and fashionistas tried to sell America on the idea that disposable paper clothes were the wave of the future. They didn’t last long, and one of the reasons why is the subject of today’s Saturday Science.
Materials:
- 2 pieces of paper towel
- 2 pieces of regular white copy paper
- 2 pieces of corrugated cardboard (just cut them out of one of the million Amazon boxes everyone has lying around these days)
- 2 washcloths or kitchen towels
- 1 cup of water
- 1 eyedropper (optional)
- 1 kitchen
Process:
- Lay out all of your material samples on your kitchen counter. We’re using the counter because things are going to get wet and the counter was designed to get wet without getting damaged.
- Our first task is a control test. We’re stress-testing our materials today when they get wet, so to know the difference between wet and dry, we have to stress-test our dry materials first. Attempt to tear one of each of your materials. How easily do they tear? Do any of them not tear?
- Form a hypothesis: what effect do you think water will have on the tearability of your samples?
- Take your cup of water and pour a decent amount onto each of the samples you didn’t attempt to tear.
- Make some early observations. What does the water do to both kinds of paper, the cardboard, and the cloth?
- Let the water sit for 3 or 4 minutes, then come back to your samples. It’s time for our second stress test.
- Pick up your wet materials, one after the other, and attempt to tear them. Did the water change any of them? How? Which ones do you think would make for poor clothing materials? Why?
Summary:
I bet you figured out pretty quickly why paper clothes didn’t last very long. Paper is easily tearable when it’s dry, and if you went out into a rainstorm in your paper dress you’d be wearing shreds inside a few minutes. Not exactly practical for everyday use. Even if you made your clothes out of cardboard, enough moisture would still have you tearing through your knickers like, well, like wet paper. Cloth is hard to tear when it’s dry, and making it wet doesn’t change that. Definitely a better plan for all your fashion needs.
So what’s the difference here? It comes down to what the different materials are made out of. Paper, in all its forms (including cardboard) is made up of a chemical called cellulose. Cellulose, like everything else in the universe, is made of tiny pieces called molecules, and those molecules are made of even tinier pieces called atoms. The molecular structure of cellulose is what makes it get weak when it’s wet.
Here’s a picture of two molecules of cellulose connected by the “O” in the middle.
See all of those OH groups around the outside of the molecule? Those are called hydroxyl groups. They’re a combination of a single atom each of hydrogen and oxygen. One of the reasons that dry paper is tougher than wet paper is that those hydroxyl groups form something called hydrogen bonds with each other. Basically, when they get close enough, they’re attracted to each other a bit and that attraction holds the molecules tight and makes the cellulose stable.
Introducing water messes all that up. See, water is H2O, two atoms of hydrogen and one of oxygen. Another way to think of water, then, is HOH: a hydrogen attached to a hydroxyl group. The water starts forming its own hydrogen bonds with the OHs in the cellulose, and suddenly the cellulose molecules aren’t attached to each other as strongly as they were before. This makes them structurally weak, and you can tear through wet paper with the greatest of ease.
Cloth isn’t made of cellulose. Depending on what type of cloth it is it can be made from wool, cotton, or synthetics materials like nylon, which is basically tiny, tiny strings of plastic woven together. The molecular structure of all of those materials isn’t bound together with hydrogen bonds, so the water ends up just making it wet, but it’s still tough and tear-resistant.
Try a follow-up experiment: wet some paper and cardboard samples, but this time let them dry out completely before you try to tear them. Given what you now know about cellulose, water, and hydrogen bonds, can you explain the results?
