Question

Compare the molecular structures of cotton and polypropylene, the two major components of thermal underwear. One of these gets wet easily and holds the water in contact with the skin. The other one does not get wet, but wicks the water away from the skin and feels relatively dry to the touch. Explain the difference in how these two fabrics respond to moisture.

Short answer

Cotton is made up of cellulose molecules while polypropylene is made up of large number of isopropanes. Cotton becomes wet easily since it has a large number of hydroxide groups. However, polypropylene is practically a hydrocarbon and is considered to be hydrophobic. Hence, it feels relatively dry to touch.

Step-by-step solution

Cellulose (cotton)

It is a polymer of beta glucose. It is the chief structural material of the plants and is obtained from wood and cotton. About 50 % of wood is cellulose. Cellulose contains about 90-95% cellulose. Cellulose is an example of natural polymer.

Polypropylene

This type of polymer is formed by the successive addition of monomer units to the growing chain carrying a reactive intermediate such as a free-radical. The most commonly used radical initiator is benzoyl peroxide. Polypropylene is a type of chain-growth polymers (addition polymers).

Explanation

Cotton is made up of cellulose molecules while polypropylene is made up of large number of isopropanes. Cotton becomes wet easily since it has a large number of hydroxide groups. However, polypropylene is practically a hydrocarbon and is considered to be hydrophobic. Hence, it feels relatively dry to touch.