The soap manufacture is one of the oldest known chemical reaction. For centuries soapmaking was a homemade task using for it vegetable ashes and animal or vegetable fats. Thereafter ash was replaced by alkalis.
Its development is described with numerous recipes whose common denominator is:
Fat(or fat mixture) + caustic soda lye —> soap + glycerin
Unlike the industrial process, in the performance of handmade soap, glycerin is not removed, is part of the final product to moisture the skin.
The huge soap variety on the market can be explained by the wide variety of oils and fats that can be saponify and by the development process.
Natural fats are not pure substances, they are composed by different fatty acids in various proportions. This implies that if we want a soap with certain properties such as texture, hardness, solubility, easy to foam, etc., we will use a fat mixture.
If in the fat mixture predominate the saturated fatty acids, the originate soap will be hard and compact, whereas if there are predominantly unsaturated fatty acids the originate soap will be less compact and softer.
Saturated fatty acids
Saturated fatty acids are fatty acids without double links between carbons and tend to form extended chains. They look like as solid fats, commonly called “hard fats”.
- Lauric acid (dodecanoic acid) – Provides foaming and cleaning.
- Myristic acid (tetradecanoic acid) – Provides toughness, cleaning and foam.
- Palmitic acid (hexadecanoic acid) – Provides strength and persistence in the foam.
- Stearic acid (octadecanoic acid) – Provides strength and persistence in the foam.
Unsaturated fatty acids
Unsaturated fatty acids. They are fatty acids with double links between carbons. Each double link causes a “bend” that prevents forming fatty acid widespreaded chains, so macroscopically, they usually lare iquid at ambient temperature, which are called “oils”
- Oleic acid, cis-9 – Octadecenoic acid- It supplies conditioning
- Ricinoleic acid – It supplies cleanliness, foam and conditioning.
- Linoleic acid (cis, cis-9,12-Octadecadienoic acid) – It supplies conditioning
- Linolenic acid (cis-9,12, 15-Octadecatrienoic acid) – It supplies conditioning.
In the following chart are indicated the quantities of each of these acids contained in the various oils.
Why does soap clean?
What gives to the soap its unique ability to clean the clothes is that its molecules have a split personality: one side avoids the water -is hydrophobic- and tends to combine with fat, while the other side is hydrophilic, loves water.
Obviously the “pull” effect of the hydrophilic side must be higher to pull out the soiling from the fabrics. We help this reaction when we rub the garment. In the end remains a tiny droplet of dirtiness surrounded by an envelope of soap, a process which is favored in hot water.
Different processes involved in developing solid soap by saponifying
It consists in start from the initial cold reagents. They are developed with sodium hydroxide (caustic soda) and hard soaps are obtained. When the formulation includes hard fats, these are heated and mixed with liquid fats to obtain a mixtur with a lower melting point and therefore liquid at room temperature.
The soaps obtained by this procedure must have a curing process. This consists in letting them reposing for 4-8 weeks. During this time the saponification reaction is completed, so that the soap is acquiring a less basic pH. Apart from this, the soap also loses the excess water and hardens.
This name is given to the soap manufacturing process similar to the cold processing soap but that involves accelerating the saponification process by adding heat.
The soap, when it is well outlined, is subjected to a temperature of approximately 80 °, it is well stirred and reheated until the saponification process is completed (approx. 2 hours). In this moment we will add the chosen actives and essential oils.