How Paper Towels Absorb Water | A Moment of Science | PBS

Scientific concepts, discoveries, or nature phenomena

Mechanism of liquid absorption by paper towels

• Paper towels are made mostly of cellulose fibers, which have a porous structure with tiny spaces.
• Water fills the pores within the cellulose fibers.
• Polarity interactions drive binding:
  • Sugar molecules (associated with cellulose) have an opposite polarity to water.
  • The positive ends of water molecules attract the negative ends of the sugar molecules—similar to how sugar dissolves in coffee.
• Effect on fiber strength and structure
  • When sugar molecules bind with water (instead of water binding strongly to itself), the cellulose fiber network becomes weaker against ripping.

Difference between absorbing water vs. oil

• If the liquid doesn’t bind strongly to the cellulose/sugar sites (example given: oil):
  • The towel may become wet, but it won’t rip apart as easily as with water.
• Demonstration concept:
  • Water absorption can prevent paper towels from supporting a load (e.g., marbles).

Capillary action (water wicking)

• Capillary action is described as how water is pulled upward into the paper towel.
• It occurs because water molecules are more attracted to cellulose than to each other.
• This effect is likened to plants pulling water up from the ground.

Biological digestion note

• Humans lack enzymes needed to digest the sugar/cellulose components the way cows and goats can.

Researchers or sources featured

• Mandy Strife (host/presenter)
• PBS (broadcaster; via the “A Moment of Science” program)
• amomentofscience.org (website mentioned for more science facts)