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Miscellaneous: Saponification

Soap is a mixture of sodium or potassium salts of various fatty acids. They are usually produced by the hydrolysis of fats and oils. This process is also known as saponification. During the mentioned process, fats and oils are broken down. As a result, glycerin and salts of various fatty acids are formed (which actually form soap):

saponification

While the industrial production of soap involves more complicated and continuous processes, smaller amounts of soap can be obtained by some of the traditional methods, which can be divided into: 1) the cold process, in which saponification is done at room temperature; 2) the hot process, in which saponofication is done at a higher temperature. In this case, the soap has been produced by implementing the cold process, whereby the glycerin stays in the soap. The saponification in the cold process can take up to several weeks. After that period, the soap attains its final properties.

saponification

One can use many combinations of oils and fats, which can produce soaps of different properties. The combination of oils used in this experiment is not necessarily the best one, but it was chosen since the oils used, are easily available in most stores. For this experiment, 225 grams of olive oil, 25 grams of sunflower oil and a solution of sodium hydroxide (32.1 grams of sodium hydroxide dissolved in 95 grams of water) have been prepared. By using the mentioned values, there was a slight excess of oil (about 10%) which is usually allowed when implementing the cold process because it ensures that all of the sodium hydroxide gets used up. The excess of the oil is not a problem, and it gives the soap, for most people, desirable properties. The approximate composition of the used oil mixture is shown in the table below:

fatty acid mass fraction, %
oleic acid 64
linoleic acid 18
palmitic acid 13
stearic acid 3
linolenic acid 1

Along with the oil mixture and the solution of sodium hydroxide, a hand blender, a small pot, an aroma, a mould, and some kind of cutting tool have also been prepared. As for the aroma, in this case, a mixture of food flavorants (blackberry, lemon and other types of fruit flavorants) has been used. The result was a pleasant and undefined fruity smell, which seemed right for the application described here.

saponification

The oils were first mixed in a small pot, and after that, the sodium hydroxide solution has slowly been added. Already at the start, a small amount of precipitate formed at the bottom of the pot, but most of the mixture was still transparent. When the mixing started, the mixture became yellow colored (above image, to the left). Although the aroma had a dark blue color, when added to the mixture, it formed a brick red color (above image, to the right).

saponification

The reaction mixture has been mixed with a hand blender for about five minutes. After the mentioned period of time, the mixture became thicker and started to look like pudding. The mixture was then poured in the mould and left at room temperature for about 48 hours.

saponification

After the mentioned period of time, the mould, together with the soap, has been placed in the freezer for about half an hour, so that the soap could be separated more easily from the mould. In this case, a few cans placed one on another, have been used to break out the soap from the mould. Afterwards, the soap has been cut into smaller pieces, about 2 centimeters high. Such smaller pieces were then left for the next 1-2 weeks in an airy place, to allow the completion of the saponification process. After that period, the soap was ready to be used.

After the saponification, the aroma was still present. Therefore, food flavorants can be used relatively efficiently, although better results would probably be achieved by using aromas that were specifically designed to be added to soap. During the whole process, the color of the soap changed several times. In the end, a pale brick red color was formed. By using colorants specifically designed to be added to soap, one could probably achieve a more lasting color.

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