So this is not really a 'modern' experiment of mine. A couple of years ago I got interested in making soap from lye and various oils. I used a calculator for soap based on which oils and how much of what, etc. I made quite a few batches of different types, and most are still around today, such as this one:
They are still around for a few reasons:
1) I made a LOT of it.
2) It is fairly dense, not being full of injected air like Dial and other commercial brands. A bar lasts a long time.
3) Nobody else trusted my "lye" ingredient, so I am mostly the only user. Never mind that Dial has lye in their process too. They list the ingredient formed with lye such as 'sodium palmate' or similar. That is essentially lye and palm oil combined. They lye!
4) I made some pretty ones that serve as decoration in various homes of friends and family.
Anyway, I will not discuss the process or recipes in great detail. Like bread making, this is an art form unto itself. It might be months before I come out the other side. Most of my formulations work really well, so it isn't that hard to make good soap. I tried just about every oil and combination thereof. I trust my soap more than Dial for keeping the 'Rona away.
So this post will be more about the general chemistry.
We start with the ever-useful NaOH, sodium hydroxide. As we know by now, it dissolves in water easily to form Na+ and OH- ions.
But you know what doesn't mix with water? Oils. They are hydrophobic as they are not polarized. Remember water itself has H+ and OH- ions floating around, both with charges.
This creates a problem. We form oils on our body, but can't wash them off with water because they don't mix. Oils are nonpolar. We need an oil to wash away the oils, but that sounds like a contradiction in terms. It kind of is except for the process known as saponification. It bonds fats and oils and lipids with an aqueous alkali such as NaOH. Heat speeds up the reaction. The result has polar metal ions (so it can dissolve into water) and also the fatty acid that can bond with other oils and grease and dirt particles that don't want to wash off in water. At a high level, think of soap as a peacemaker between oil and water.
This can be done with KOH, for example, although I never tried it. Actually this is known as sailor's soap, as the K+ ions work better in saturated saltwater than more Na+. Just about every form of metallic 1+ ion and oil/fat/lipid have been tried. Whale blubber used to be used for soap making. Lye was extracted from wood ash. Presumably they all work, with varying properties such as how sudsy they are.
Now you also know why NaOH has a soapy or greasy feel to it. It is literally forming small amounts of soap on your skin as it bonds to our body oils.
Thanks for reading,
Paul
p.s. Soap can also act as a surfactant to get water and things that don't dissolve it in to mix. We did this in an earlier blog post when the sulfur did not mix with water - so we added some soap and it mixed happily. Now you know the water was attracted to a metal ion and the sulfur was bonded to fatty acids. When we heated the mixture enough for the reaction, between Ca(OH)2 and S, the soap just boiled off and/or remained as a harmless bystander in our solution for further reaction between one of the products and copper.
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