Making Soap

Soap Fabrication


Introduction [1]

The main uses of soap include bathing, washing, cleaning and other types of housekeeping.Soap acts as surfactant because it has surface active properties. When Soaps are dissolved in water, they can break dirt from the surfaces and emulsify oils. Moreover, in industry,soaps are important components of lubricants and sometimes used in textile spinning. Chemically, soap is a water-soluble sodium or potassium salts of long chain fatty acids. When triglycerides in fat/oil react with aqueous NaOH or KOH, they are converted into soap. The formation of soap is called the Saponification.

2. Raw Material [2]

The major raw materials of manufacturing soaps include fat and lye.

Fat:

Animal fat are lipid materials derived from animals and are composed of triglycerides. Physically, animal fats are solid. In the past, people can directly obtain the animal fat from a slaughterhouse. However, modern soapmakers use fat which has been processed into fatty acids. This new “fat” eliminates many impurities, and the byproduct will be water instead of glycerin. In addition to the animal fat, many vegetable fats, including coconut oil, palm kernel oil and olive oil are also used in soap making process today.

Lye:

Lye, or alkali are necessary components of soaps. The reaction between the lye and the fat is what we call saponification. Once the saponification (the reaction between the lye and the fat) is completed, all lye will convert into soap. The finished soap bar doesn’t contain any lye. There are two types of lye, sodium hydroxide and potassium hydroxide. Sodium hydroxide is used for making solid soap. Potassium-based soap is called soft soap since it is a more water-soluble product than sodium-based soap. The combination of soft and solid soap is commonly used in shaving products or to make cream soaps.

Others:
Without dye, soap will be dull grey or brown. Modern manufacturers will add additives, abrasives, fragrances to enhance the color, texture, and scent of soap, making the soap more enticing to the consumer.

3. The Manufacturing Process [2]

The processes of soap manufacturing are various, including kettle boiling and continuous saponification. Today, some small soap manufacturers still use the kettle process which takes around four to eleven days to complete and can result in the quality of each batch being quite inconsistent due to the different kinds of oils. Engineers and scientists developed a more efficient method called the continuous process in 1940. This method is commonly used by large soap manufacturers all over the world nowadays. Soaps are made continuously rather than one batch each time in the continuous process. There are several improvements. Firstly, it just takes around six hours to complete one batch of soaps which is much quicker than the kettle process. Secondly, the technicians can easily do the quality control of all the finished goods.

3.1 The Ketal Process:

Boiling:

A kettle is a steel tank which can stand as high as three stories, holding several thousand pounds of material simultaneous. Steam coils within the kettle heat the batch and then boil them. After boiling, the fat reacts with the alkali to produce soap and glycerin.

Salting:

The purpose of the salting is to divide the soap and glycerin. The mixture of soap and glycerin is treated with soap. As a result, the soap will rise to the top and the glycerin will settle to the very bottom. Then extracting the glycerin from the bottom of the kettle.

Strong Change:
The strong caustic solution is added into the kettle in order to remove the small amounts of unsaponified fat. Then boiling the saponified fat again. The manufacturer could either do the salt treatment at this time or proceed to the next step.

Pitching:
 The last step is called “pitching”. Firstly, the left soap in the kettle will be boiled for one more time with water. The semi-finished products will separate into two different layers. The top layer contains about 70% of soap and 30% water. We call it “neat soap”. The lower layer which is called “nigre” is almost the impurities including dirt, salt and water. The neat soap is taken off and cooled in the end. The finishing process is the same for both kettle and continuous process.

3.2 Continuous Process

Splitting:
The first step is to split natural fat into fatty acids and glycerin. The equipment is called hydrolyzer which is vertical stainless steel column with barrel. The height may up to 80 feet(24 meter). Pumps and meters attached to the column help to do the precise measurement.

Molten fat is pumped into one end of the steel column, meanwhile, at the other end, boiled water (266°F [130°C]) and pressure are introduced. This large container splits the fat into two different components, fatty acids and glycerin. During the process, there are continuous fatty acids and glycerin being pumped out as more fat and water enter. Then the fatty acids are distilled for purification.

Mixing:

Mixing the purified fatty acids with precise amount of alkali to form soap. The soapmakers can mix other ingredients such as fragrance and abrasives simultaneously to make attractive scent. The hot liquid soap can then incorporate with air.

Cooling and Finishing:
The soap may be poured into modes or large slabs and can be cooled in special freezers. The slabs will then be cut into smaller bar sized pieces. The entire continuous process, from splitting to finishing, can be accomplished just in couple hours.

4. Soap Mill and Refining Process [3]

Addition to the basic process, most soap will undergo milling. Soapmakers use a three roll mill to refine the soap. Refining grinds all the particles into small sizes. Three roll mill is used to improve the fineness and homogeneity of the one product. As a result, the milled bars will have finer consistency and thus lather up better than the non-milled ones. The cooled soap is then crushed and kneaded after being fed through three roll mill. During the milling, fragrances and abrasives can be better incorporated since volatile oils don’t evaporate in the cold mixture. After the soap emerges from three roll mill, it becomes more smooth and extrudes. Then cutting the extruded soap into bar size. The last step is to stamp and wrap the finished goods. The most significant parameter of a three roll mill is the gap between the last two rolls. The advisable gap should be 0.15 or 0.20mm. The increasing or decreasing of the gap may lead to the difference of production rate.

References:
1. Saponification-The process of Making Soap, http://amrita.olabs.edu.in/?sub=73&brch=3&sim=119&cnt=1 
2. http://www.madehow.com/Volume-2/Soap.html

3. http://www.soapworld.biz/soap-roll-mill.html