Chemisty of Stain Removal

I am just returning home from the 95th Canadian Society for Chemistry conference, which was hosted in Calgary, Alberta this year. One of the great things about going to Calgary for me (aside from visiting the zoo) is that my sister lives there. Instead of staying in one of the over-priced hotels near the conference centre, I was able to stay in one of the over-priced downtown apartments near the conference centre. This was great! And sure, the accommodation may not have had the most comfortable bed, it did come with free internet, home cooked meals, and a couple of cats to snuggle with. Oh, and family that I love. In this time though, my sister found that having a free-loading chemist as a house guest isn't all that bad. Not only will she leave her fabulous shoes for you to wear, she can apply her knowledge to help you remove a baked-in oil stain from one of your favourite sweaters.

The stain: in an expensive and great lululemon zip-up hoodie, an oil stain that was very visible was set in the pockets. The sweater had been machine washed and dried. Its distraught owner was quite sure nothing further could be done for the sweater. It was to fall victim to this villainous stain. 

Our heros: a chemist, canola oil, and dishsoap. The canola oil was rubbed into the stained areas. Then dishsoap was poured on top and also rubbed in. The sweater was then thrown back into the washing machine.

The outcome: one stain-free sweater, good as new.

That's right, we used oil to remove oil. Magic right? Not so. Here's the chemistry: because the oil had been washed and dried, it was now trapped in the fibers of the fabric and therefore  not accessible to soap when further washing would take place. This is because water and oil, as the saying goes, don't mix. This creates a barrier between the oil in the fibers and the soap. In order to get the oil out then, we need to find a medium that it does mix with. This is where the chemistry phrase "like dissolves like" comes in. Oils are soluble in other oils. Any oil will do: canola, olive, WD40, take your pick. By rubbing the oil onto the stain, it is able to dissolve the oil that is set into the fabric fibers. Once it has, you pour on the dishsoap, and the soap does what soap is designed to do, and form what are called "micelles" around the oil particles that can now be washed away in water. The result is a stain-free fabric. 

I talk a little bit more about some of the factors involved in my blog about water. The terms hydrophobic, hydrophilic all play a role in this chemistry. Oil is hydrophobic: water-hating. Soap is what is called "amphiphilic", meaning that one part of it likes water, while the other part doesn't. When placed in water it will arrange itself in the small spheres (micelles) with the hydrophilic (water-loving) part facing out into the water, the hydrophobic part facing in. Because oil is also hydrophobic, it ends up on the inside of these micelles, away from the water.    

So there you have, practical chemistry to save your clothing from destruction!