Too Hot Cotton

Imogen asks “What happens if the iron becomes too hot for a cotton fabric?”

Cotton is made from cellulose, a compound found in all plant cells, but in cotton has special characteristics which make it strong, durable and absorbant. Cellulose is composed of beta-glucose, basically a regular glucose sugar with a hydrogen and hydroxyl group swapped on the first carbon clockwise from the oxygen (called the primary carbon, or carbon 1). This has the effect of causing each beta glucose to be flipped upside down compared to the last, giving it a fibrous, strong structure, and can also form hydrogen bonds between layers, increasing it’s strength.

It is these hydrogen bonds (see the article on ice http://www.ask-me-anything.info/2007/10/06/why-is-ice-lighter-than-water/) that cause all the trouble when you leave the iron on it accidentally, or set it on fire. Because cellulose contains a large volume of water, this gets evaporated out, allowing the fibres to become closer. When this happens, the hydrogen bonds become better aligned, and when enough heat is added a chemical reaction called a condensation occurs. At temperatures upto 110*C, the water simply evaporates out, but when the temperatures head above 220*C the hydrogen and hydroxide react to form water, and a chemical bridge forms between the cellulose which is a bond proper (a hydrogen bond is not quite classified as a true bond.) This bond is a lot stronger than the normal hydrogen bond, and this pulls the cellulose strings together, forming a film. This is why heat damaged cotton goes hard and shiny, and cannot be reformed.

Hope this helps

Triga@ask-me-anything