The first soaps were from the sap of plants that people called soap plant and soapberry. They later learned to make soap by combining fats with ashes, which are highly alkaline. The resulting chemical reaction produced stearate, the basic constituent of soap. Today we still manufacture soap by combining fats and oils with some kind of alkaline material to form a stearate. The addition of a number of other ingredients improves the properties of the finished soap.
Fats
The starting point for the manufacture of soap can be any of a number of plant oils or animal fats. Commonly used vegetable oils come from coconut, palm, olive, soybean and canola. Castile is a mild soft soap made from olive oil. More often soaps contain animal fats in the form of beef tallow or pork lard. (ref 1)
Alkalines
The addition of an alkaline material results in a chemical reaction with the fat components. Often the alkaline is lye, or sodium hydroxide, but other basic chemicals like ammonium hydroxide and sodium carbonate work as well. The reaction forms a soapy compound like sodium or possasium stearate, depending on the specific alkaline used. To make sure all the alkaline material fully reacts with the fat and no traces remain in the finished soap, an extra amount of fat is usually used.
Glycerin
Glycerin is a byproduct of the reaction of the fat and the alkaline. It is a natural skin softener and may be left in the soap mixture or added back in later. Ironically, if removed, it often ends up in products that counteract the skin-drying effect of soaps.
Anti-bacterial Agents
Anti-bacterial soaps contain additives to kill germs. These may include the chemicals triclosan and triclocarban, pine oil, or an ammonium compound.
Abrasives
Some soaps contain abrasive particles that assist in the cleaning process. Usually these are calcite, feldspar, quartz or sand. Lava heavy duty hand soap is an example of a product containing such an abrasive, in this case volcanic pumice.
Preservatives
Stearates, the basic constituents of soap, are organic compounds and they need preservatives to prevent them from breaking down. These additives also keep any leftover fats or oils from becoming rancid. Many soaps contain Butylated Hydroxytoluene, but other compounds like ethylene diamine, tetraacetic acid, or glutaraldehyde may be used instead.
Cosmetic Additives
Many other types of additives give the soap a pleasing appearance or fragrance. These include dyes, colorants, scents, and opacifiers, which mask the clear or translucent appearance of stearates. The white color of many soap products is due to the addition of titanium dioxide.
Member Comments