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THE CHEMISTRY OF IRONING

Lorch, Mark. American Scientist; Research Triangle Park Vol. 105, Iss. 3,  (May/Jun 2017): 142.

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I hate ironing; I'll do more or less anything to avoid it. I started to wonder why those shirts emerged from the clothes dryer looking like a tangled bag of rags.

It turns out that the wrinkles in my shirts come down to the chemistry of plant-based fabrics. Cotton, linen, hemp, and so on are predominantly made of cellulose, a polymer that consists of thousands of glucose molecules joined together to form linear chains. Each glucose subunit is "sticky" because it can bind to neighboring cellulose molecules via hydrogen bonds. Individually, these bonds are very weak, but together they form a network that gives the fabric its strength.

These hydrogen bonds are forever breaking and then rapidly reforming. As a result, clothes start taking on the shape that they are left in. As they sit there in a pile, the bonds break and reform, the clothes take up the new shape of the fabric, and the creases are set in place.

Things get even worse when water enters the equation (as it does in the washing machine). Water molecules insert themselves between the cellulose molecules, break up the hydrogen bonds, and act as a lubricant, allowing the cellulose molecules to slide over one another. Then, when the fabric dries, the cotton keeps its now-wrinkled shape.

This is where the hot, steaming iron comes in. The combination of heat and moisture quickly breaks the hydrogen bonds. As I apply these with a bit of pressure, all the cellulose molecules are forced to lie parallel with one another, thereby flattening the cloth.

But what if I want to avoid doing the ironing? I could go with the age-old practice of starching my clothes to keep them crease free. This works because starch is also a polymer made from glucose, so it too...