Fat and oil
Fat and oil consist of a compound of fatty acids and glycerine, a trihydric alcohol. During saponification, fat and oil is split into its components, alcohol (glycerine) and acid (fatty acid). The difference between fat and oil lies in the composition of fatty acids. Fat contains many long chains and unsaturated fatty acids, while oil contains a larger proportion of shorter and unsaturated fatty acids.

Fatty acid
Fatty acids consist of a chain of carbon atoms carrying an acid group at the end of the chain. The chain or tail of the molecule is lipophilic (water-repellent), the head of the acid group is hydrophilic (fat-repellent). This ambivalent constellation enables fatty acids and especially their sodium and potassium salts to act as detergents.

Biodegradability
Basic soap stock consists of the sodium salts of fatty acids, as well as water, glycerine and common salt. Due to the production process which starts with the feed in of natural fat and oil, the fatty acids in the basic soap stock show a range of different chain lengths (Table 1).

C 8:0	1–2 %	C 14:0	3–6 %	C 18:1	30–36 %
C 10:0	1–1,5 %	C 16:0	28–34 %	C 18:2	5–11 %
C 12:0	8–11 %	C 18:0	2,5–7 %	C 18:3	0–1 %

Table 1:

Typical C-chain distribution in basic soap stock for toilet soap on the basis of natural fat and oil. For describing fatty acids, a system of letters (C for carbon) and two numbers separated by a colon is used frequently. The first number denotes the number of carbon atoms in the fatty acid. The second number denotes the number of double bonds in the fatty acid. So C 8:0 is a fatty acid with 8 carbon atoms and no double bonds. C 18:1 is a fatty acid with 18 carbon atoms and 1 double bond.

Fatty acids and their derivates are common in nature. They are essential for building membranes and for storing energy in procaryotes (creatures without a cell nucleus, such as bacteria) and in eucaryotes (creatures with a cell nucleus, such as amoeba, animals, humans).
The degradation of fatty acids can be aerobic or anaerobic. Fatty acids form a hardly soluble compound with calcium from the elements constituting the temper structure in water. That is why fatty acids are mainly degraded in sewage sludge . Here, fatty acids are degenerated by ß-oxidation (Ill.1) and subsequent metabolisation of the acetic acid derivates, resulting in methane and carbon dioxide. The aerobic oxidation in activated sludge takes place in the same way, via ß-oxidation and subsequent metabolization of acetic acid derivates to carbon dioxide .
Ill. 2 shows the elimination of fatty acids by biological degradation in an OECD 301 E test. Within 28 days, the rate of elimination is 98% for basic soap stock 80/20 and 96 % for vegetable-based soap stock. Thus they are classified as “readily biodegradable” according to the OECD guidelines.
Ill. 2 shows that, according to OECD test guidelines 301, there is no significant difference between basic soap stock on the basis of palm oil / coconut oil (vegetable soap stock) and basic soap stock on the basis of tallow / coconut oil. A test according to OECD 301 B shows that basic soap stock on the basis of palm oil, coconut oil and rape seed oil shows a degradation of fatty acids = 60 % after 7 days (13 days for higher test concentrations; not shown). Therefore this basic soap stock is classified as “inherently biodegradable” according to OECD 301 B.



Ill. 1: Biodegradation of fatty acids by ß-oxidation

The biodegradability according to OECD 301 B for soap on the basis of tallow shows a degradation of fatty acids = 60 % after 13 days (22 days for higher test concentrations; not shown). This basic soap stock is thus classified as “biodegradable” according to OECD 301 B.
The difference between the rates of biodegradability according to OECD 301 B between basic soap stock on the basis of palm oil, coconut oil and rape seed oil, and basic soap stock on the basis of tallow and coconut oil is probably due to the reduced biological availability of fatty acid salts from tallow. Fatty acids from tallow have longer C-chains leading to a reduced solubility of fatty acid anions. The average molar weight of fatty acids from tallow is Mr = 278 g/mol, the average molar weight of a mixture of palm oil, coconut oil and rape seed oil is Mr = 258 g/mol.


Ill. 2: Biodegradability of basic soap stock according to OECD 301 E


Ill. 3: Biodegradability of basic soap stock according to OECD 301 Biii

Syndet soap
The word syndet is made up of synthetic and detergent. Synthetic detergents are mainly products of fatty acids whose acid group has been chemically modified.

Combo soap
Combo soap is a mixture of synthetic detergents (syndet) and natural soaps. The pH value of combo soap is between that of alkaline soap (pH 9.5 to 11) and that of syndet soap (pH 3.5 to 6).

Tallow
Tallow is an important raw material for the production of industrial intermediate products such as fatty acids and fatty alcohols and soaps. Tallow is also used is the food industry, e.g. for the production of margarine and puff pasty. Tallow, which is won from slaughter fat such as the kidney fat of beef, is white to slightly yellow in colour and melts between 40 °C and 45 °C.

Olive oil
Olive oil is won by pressing olives. Olives are mainly grown in the Mediterranean region.

Palm oil and palm kernel oil
The two vegetable oils palm oil and palm kernel oil are won from the fruit oil palms. This plant, which is cultivated in plantations in Malaysia and Indonesia, grows up to 30 m and bears fruit the size of walnuts, whose pulp contains 60 – 70% palm oil. The pulp surrounds the kernel, from which palm kernel oil is won.

Coconut oil
Coconut palms are the most important source for vegetable oils. They grow in the Philippines and Sri Lanka and bear up to 400 coconuts a year. Coconut oil is won from the pulp of coconuts. The fruit is stripped of the brown coconut fibre, boiled and opened. The meat, which is also called copra, is dried in the sun. It contains between 60 and 70% coconut oil. Once dried, the copra is taken to oil mills to extract the oil.

Curd soap
Curd soap is a product of the reaction of fats and oils with caustic soda or caustic potash solution. They consist of anions of fatty acids and their cations, sodium or potassium. They also contain glycerine, a product of the reaction, and small amounts of common salt.

Soap flakes
Soap flakes are sodium soaps with a very low content of moisture. The soap is rolled into a thin film and cut into small flakes. Due to their large surface, the flakes dissolve quickly in water.

Toilet soap
Toilet soap is made of high quality soap stocks. Toilet soaps contains further more ingredients such as perfume oil, moisturizers and dyes.

Transparent soap
Transparent soap, or glycerine soap, is made by adding glycerine and ethanol. Unlike translucent soap it is cast in moulds.

Translucent soap
Translucent soap is made by adding polyvalent alcohols. Translucent soap is slightly less see-through than transparent soap. In contrast to transparent soap, translucent soap can be produced much more economically using stamping technologies.

Aluminium soap
Aluminium soap comes from adding abrasives such as prepared chalk, magnesia, kieselgur, kaolin, etc. to soap.

Sand soap
Sand soap is used for cleaning the skin of hard-to-remove dirt such as bitumen, tar or oil. It is produced by adding abrasives such as siliceous chalk or pumice to soap.

Ox gaul soap
Ox gaul soap consists of soap and ox gaul, and is used for removing stains from textiles.

Tooth soap
Tooth soap, the predecessor of today’s toothpaste, was made from 50% curd soap (detergent basis and carrier for abrasives), 40% calcium carbonate, and 10% chalk (abrasive).

Medical soap
Medical soap consists of soap (detergent basis) as a carrier for the active component and the actual agents. The alkaline reaction in the soap leads to the upper layer of the skin to swell, which improves the absorption and deep-cleansing action. There is a distinction between soft and hard medical soaps.
Soft soaps are often based on potassium soap. The medical agents are disinfectants, tacamahac, tar, sulphur, phenole, shale oil, salicylic acid, resorcin, etc.
Hard medical soaps are produced by adding selected oils (in the Middle East 10% laurel oil for irritation of the skin, eczema and dandruff, or in the Far East 2-5% sandalwood oil for irritated skin and eczema) to the basic soap stock during the saponification process.

Shaving soap
Solid shaving soap and shaving paste are produced by mixed saponification (use of caustic potash solution and caustic soda) of fats and oils (tallow, palm oil and/or coconut oil).

Marseille soap
Marseille soap is made by the saponification of olive oil (sometimes cotton oil). This soap, which is used for cleaning hands and textiles, is considerably softer than curd soap.

Floating soap
Curd soap and toilet soap have a density higher than 1,000 kg/m³, which makes them sink in water. By expanding the soap with air during production, the density is reduced to below 1,000 kg/m³, which makes it float in the bathwater.

Soft soap
Soft soap or potassium soap is produced by saponification of fats and oils with caustic potash solution instead of caustic soda. This leads to a paste-like soap, which is used for cleaning surfaces.Soft soap or potassium soap is produced by saponification of fats and oils with caustic potash solution instead of caustic soda. This leads to a paste-like soap, which is used for cleaning surfaces.

sand-free, sandy
Basic soap stock, the main ingredient of soap, is produced by spray drying wet soap. During this process, over-dry particles may form, which appear as small, sandy particles when rinsing with cold water. Such particles often dissolve in lukewarm water.