Capillary Action and the Absorbancy of Diifferent Kinds of Paper Towels

What You Need to Know

Absorb means to soak up. Porous means to have many small holes. Capillary action is the movement of a liquid, such as water, through a very small space due to adhesion and surface tension. Surface tension is the attraction between molecules at the surface of a liquid. This attraction is due to cohesion, which is the bonding force between like particles.

How Does Capillary Action Work?

Capillary action occurs when a liquid, such as water, is in a narrow vessel. Adhesion of water molecules to the walls of the vessel causes an upward force on the liquid at the edges and results in these molecules moving up the walls. The surface tension, which acts much like a skin across the water's surface, holds the water molecules together. So instead of just the edges of the water moving upward, the whole liquid surface is dragged upward, creating a curved surface as shown in the diagram

Fun Fact

Cotton can absorb up to 27 times its own weight in water. This is why bath towels are generally made of cotton. The most absorbent towels are made with looped strands of cotton on both sides of the towel because the loops act like very small sponges. Loosely twisted loops are softer and more absorbent than tightly twisted loops, which produce a rougher fabric.

The height to which capillary action will lift water depends on the weight of water that the surface tension can lift. As shown in the diagram below, the narrower the tube the higher capillary action can lift the water.

The fibers in paper towels are surrounded by different-sized spaces that are interconnected. The spaces between the fibers are small enough that the effects of capillary action can take place when the paper towel is placed on a liquid. The more narrow the space between the fibers the farther the liquid moves.

Real-Life Science Challenge

Disposable paper diapers absorb better now because of NASA. This is because extra-absorbent diapers were needed for astronauts. It was discovered that adding sodium polyacrylate to the paper fibers in a diaper produced a safe superabsorbent diaper.

Experiment

Now, start experimenting with the absorbency of different kinds of paper towels.

Hints

• Cut paper towels into equal-size strips.
• Make a testing apparatus to dip the strips in equal amounts of water.
• Determine how to measure the absorbency of the paper.

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