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close this bookHow to Make? An Improved Soap .. Not just for more Foam (GTZ, 1993, 71 p.)
close this folderA. Basic elements for making improved soap
View the documentA.I. Raw materials
View the documentA.II. Technology of improved soaps making

A.I. Raw materials

The raw material needed for making soap are fats (oil, grease or butter), alkaline, water and secondary products (salt, additive colors, scents etc.).

A.I.1. Fats

A.I.1.1 Nature and chemical characteristics

The natural fats used for soap making are triglycerol, which is an ester from an alcohol triple, glycerol with linear carbonic acid chains (fatty acid). According to their solidity at ordinary temperature, fats divide into oils (liquid at usual ambient temperatures) and butters (solid).

Some fats are extracted from plants while others are animals origin. On the chemical point of view, all are appropriate for saponification. However more or less fundamental differences exist between the proprieties of each of them. In the practice the number of fats used for soap production is limited. The main reasons for this limitation are economic and technical proprieties of fats and of the soaps generated from them, availability and price.

There exists two (2) main chemical parameters to characterize the appropriateness of triglycerol for saponification: Iodine Number and Saponification Value.

The Iodine Number of a fat expresses the weight of iodine in grams which can be fixed from 100 g of them. It indicates the presence of double links, thus the degree of insaturation of the carbonic chain.

Its value varies between 10 to 200. Note that the butters and greases, which are solid under normal conditions , have an Iodine Number inferior or equal to 70. Moreover the soap made from a high Iodine Number fat has the tendency to be soft. The Saponification Value of a fat is the quantity of caustic potassium (KOH) in mg needed to transform 1 g of it in soap. For most of the natural triglycerol, this index is situated at about 190-200. The important exceptions concern palmist, copra and cowbutters with value reaching 240-250. A high Saponification Value indicates an easier transformation of the fat into soap.

In soap making process iodine number and saponification value play an important role in a sense that their values allow to predict some important proprieties of the soap obtained from the fats (or the mixture of fat).

The INS Factor (Iodine Number-Saponification Value), which represents the difference between these indexes, is an essential parameter enabling to characterize as well the (mixture of) fats as the soap obtained from the latter.

With increasing values of this factor, the following proprieties can be observed:

1. The fat tends to be solid;
2. The soaps made are tough (rough);
3. The bleaching and foam forming proprieties tend to decrease
4. The solubility of soaps tend to decrease;
5. The soaps tends sharply to become rancid.

Copra and palmist fats constitute the exceptions to the above stated rules.

Table I. indicates the values of iodine and saponification indexes of the main fats used in soap making in tropical areas.

The majority of these fats are plant origin and are extracted from cultivated plants. However in certain rural areas, a high proportion of fatty materials used in traditional soapmaking are extracted from fruits of wild plants.

In Sahel and Savanna Zones, the following wild species are used in soap making: Balanites aegyptiaca, Karitea (shea) (Byturospermum parkii), Cailcedra (Khaya senegalesis), Manan (Lophira lanceolota), Baobab (Adansonia digitata) etc.

Some essential using proprieties of an improved soap strongly depend on the nature of the fat being used for its composition.

Table II. indicates some important characteristics of soaps from selected fats

Table I. Iodine number and saponification values, INS Fac of principal fats used in soap making in tropical zone; weight of caustic soda to saponify 1 kg

FATS

SAPONIFICATION VALUE

IODINE NIMBER

INS FACTOR

CAUSTIC SODA NEEDED TO SAPONIFY 1 kg (in g)

Butters/Fats





Cocoa

195

38

157

1339,03

Coprah

256

8

248

1882,53

Karitea

187

61

126

1333,33

Fat (pork)

198

70

128

141,17

Tallow (cow)

197

40

157

140,46

Tallow (mutton)

195

39

156

139,03

Oils





Peanuts

190

95

95

1335,47

Baobab

206

27

179

1446,88

Cotton

194

109

85

1338,32

Kobi

195

71

124

1339,03

Kapok

193

83

110

1337,61

Manan

191

70

121

1336,18

Neem

196

69

127

1339,73

Palm

200

51

149

1442,60

Palmist

248

17

231

1776,82

Physic oil

196

92

104

139,75

Castor oil

182

85

97

127,77

Sesam

190

111

79

1335,47

Soja

192

128

64

1336,90

Sunflower

190

135

55

1335,47

Baobab (Adansonia sp.), Kobi (Carapa sp.), Kapok (Eriodendron s and Manan (Lophira sp.), are wild species of humid and semiarid tropical zones.

Table II. Characteristics of sodium soaps from the main soap making fats in tropical zone

Soap from

Colour

Consistency

Foaming capacity
Foam characteristics

Bleaching effect

Effect on the skin

Usage

Butters/Fats







Coprah

Pale yellow to white

Very hard Crumbly

Strong, quick, foam less stable

Very good even at cold

Rough

Washing

Karitea

White

Hard

Slow

Middle

Very soft

Body hygiene, Washing

Fat

White

Hard

Strong, quick stable foam

Good

Very soft

Body higiene

Tallows

White to yellow pale

Very hard

Weak, slow, stable foam

Good

Very soft

Body hygiene, Washing

Oils







Peanut

Tan

Quite hard

Weak, slow

Middle

Very soft

Body hygiene, Washing

Cotton

Grey-yellow

Soft

Middle, stable foam

Good

Smooth

Washing

Manan

Tan

Hard

Strong, stable foam

Good

Smooth

Washing, body hygiene

Neem

Dirty yellow

Hard

Strong, quick, stable foam

Very good

Smooth, antiseptic

Washing, body hygiene

Palm

Yellow pale

Hard

Strong, slow foaming, stable foam

Very good

Very smooth

Body hygiene, Washing

Palmist

Yellow pale

Very hard (Crumbly)

Strong, quick, foam less stable

Very good even at cold

Rough

Washing

Pourghere

White pale

Soft

Strong, quick, foam stable

Good

Smooth, antiseptic

Washing, body hygiene

Castor-oil

White

Very hard

Weak, foam stable

Good

Smooth

Washing, body hygiene

Sesam

Brown-clear

Soft

Strong, slow, foam stable

Good

Smooth

Washing

A.I.1.2 Pretreatment

The usual techniques for extraction generate fat products containing impurities. Moreover these fats present sometimes, at raw state, strong odors and more or less intense colorations. Soaps produced from such raw materials are least quality.

To obtain a good appearance and better usage quality soap from such materials, the precedent refining and bleaching are consequently necessary. To achieve this, there are some simple methods.

A simple method of refining (purification and deodorisation) consists in boiling the fat in mixture with water during 5 h at least (one volume of fat for 1/2 a volume of water).

The addition of some natural products can considerably improve the performances of this method, for instance that of a mixture from okra powder (hibiscus esculentus). At the end of the operation, the impurities pass into the watery phase and the purified oil floods above.

A modification of this techniques consists in boiling the fat with 25% of its weight from a solution of 10% salt in water during 30 minutes.

The bleaching (decoloration) is also necessary as pretreatment method of some soap making fat with initial strong coloration.

Palm-oil, and in a less measure, that of cotton, should go through this stage before their saponification. The simple bleaching methods we can consider are as follows:

- Thermic treatment (oxidation at hot air);
- Bleaching by adsorption on special muds targile, kaolin) or/and activated charcoal;
- Chemical bleaching with strong oxides.

Thermic bleaching is achieved by boiling the fat body to 200-250 °C in a basin opened during 5 to 6 hours. The operation is carried until a white paper dipped into the oil doesn't show any more coloration.

As for bleaching by adsorption, the fat is boiled at 90 - 100 °C; you then add around 5% of its weight in adsorbent muds (and eventually 1 to 2% of active charcoal). The product is mixed during 15 to 20 minutes.

The chemical bleaching is made with potassium bichromate (1 to 2 %) in presence of a strong mineral acid (H2SO4 or diluted HCl). The temperature of the mixture should be maintained under 52 °C.

So this operation is thus somewhat more delicate than the two precited others.

A.I.2. Alkali

For direct saponification of neutral fats (triglycerols) we need to put a strong basic solution (alkali) in the water. Caustic soda and caustic potasch are the most frequently used for this goal. The soaps obtained from these two bases are however different in some characteristics such as consistency, foam formation, solubility etc.

A.I.2.1. Caustic soda (NaOH)

This is the most alkali used for saponification of neutral fat. The soaps obtained (sodium soaps) are harder and less soluble than those obtained from potassium. Moreover they are less able to retain the humidity of the air.

The caustic soda is a chemical basic product used in various fields of crafts: tanning, dying etc. So it is easily available on the market, even in developing countries.

At pure natural stage, it is a white crystallin substance, which is easily soluble in water with heat production. The concentrated caustic soda solutions are harmful to the skin and can cause serious burns. They should consequently be handled cautiously.

The caustic soda solution quickly retains the carbondioxid from the air, which leads to a change in the initial concentration. For this reason, usage of the densimeter enabling the determination of exact concentration of the alkaline solution available for saponification, is necessary.

To prepare the caustic soda solution by using the solid product from the market, you dibite the quantity of soda in the same weight of water (add small portions of the product to water by stirring well). Be cautious by wearing protecting glasses and gloves.

FOR SECURITY REASON, NEVER PRACTICE THE ABOVE MENTIONED OPERATION IN THE ADVERSE SENSE, BY POURING WATER ON CAUSTIC SODA !

The basic solution so obtained can be easily diluted by water addition and usage of a densimeter to control progression of the dilution. You so obtain the concentrated solution required for the chosen saponification process.

A simple and approximate method to determine the concentration of an alkaline solution consists in putting into it an egg of chicken. When this just floats over the surface, the solution contains respective:

180 g of caustic soda (NaOH)
230 g of caustic potassium (KOH)

for each liter.

Table III. gives the density and corresponding concentration levels of caustic soda and potassium solutions.

Table III: Density and concentration in free alcali of caustic soda (NaOH) and potassium (KOH) solutions

Degre Baume (°Be)

Density at 15°C

1L of solution contains:

1Kg of solution contains:



(g NaoH)

(g KOH)

(g NaOH)

(g KOH)

1

1,007

6

9

6,,100

9

2

1,014

12

17

122,000

17

3

1,022

21

26

200,000

26

4

1,029

28

36

277,100

35

5

1,036

35

46

333,500

45

6

1,045

42

58

400,000

56

7

1,052

49

67

466,400

64

8

1,060

56

78

522,900

74

9

1,067

63

88

588,700

82

10

1,075

70

99

655,500

92

11

1,083

79

109

733,100

101

12

1,091

87

119

800,000

109

13

1,100

95

132

866,800

120

14

1,108

104

143

944,200

129

15

1,116

112

153

1000,600

138

16

1,125

123

167

1009,700

148

17

1,134

134

178

1118,400

157

18

1,142

144

188

1226,400

165

19

1,152

156

203

1335,500

176

20

1,162

167

216

1443,700

186

21

1,171

177

228

1551,300

195

22

1,180

188

242

1559,100

205

23

1,190

200

255

1667,700

214

24

1,200

212

269

1776,700

224

25

1,210

225

282

1885,800

233

26

1,220

239

295

1995,800

242

27

1,231

253

309

2005,900

251

28

1,241

266

324

2114,200

261

29

1,252

283

338

2226,400

270

30

1,263

299

353

2336,700

280

31

1,274

316

368

2448,100

289

32

1,285

332

385

2558,000

298

33

1,297

348

398

2668,300

307

34

1,308

364

416

2778,000

318

35

1,320

384

432

2888,300

327

36

1,332

399

449

2999,300

337

37

1,345

420

469

3112,200

349

38

1,357

441

487

3224,700

359

39

1,370

462

506

3336,900

369

40

1,383

483

522

3449,600

378

41

1,397

506

543

3662,500

389

42

1,410

528

563

3774,700

399

43

1,424

553

582

3888,000

409

44

1,438

575

605

3999,900

421

45

1,453

602

631

4114,100

434

46

1,468

629

655

4228,300

446

47

1,483

658

679

4443,800

458

48

1,498

691

706

4661,500

471

49

1,514

721

731

4766,000

483

50

1,530

750

756

4900,200

494

In general, 13 to 15% of the weight of the fat are necessary for saponification with caustic soda. The concentration of the alkaline solution to be used can vary between 8 and 50% according to the preparation method which is used.

Examples showing how to calculate the quantity of caustic soda solution needed for saponification by using the saponification value and the Baune-densimeter.

The among of caustic soda necessary for complete saponification of a fat is obtained by using the following formula:

(Weight of fat (Kg) X saponification value X 0,713) / 1000

where

0.713 = ratio of molar masses of caustics soda and potassium (40 g: 50,1 g = 0.713) and
1000 = conversation factor from grams into kilograms.

To saponify for instance 5 Kg of peanut oil, you need:

For a mixture of fat, the easiest method consists in calculating the respective quantities for complete saponification of each component.

The addition of these values finally gives the total quantity of soda for saponification of the mixture.

Example: 100 Kg of a fat mixture composed of:

cotton oil

30 Kg

palm oil

30 Kg

karitea (shea) butter

40 Kg

For saponification of the various component, the following quantities of caustic soda are needed:

Cotton oil:

Palm oil

Karitea butter:

Total = 13,76 KG

When you use an alkaline solution, the quantity needed for saponification is obtained as follows:

The exact concentration of the alkaline solution is obtained by measuring the density of the liquid with a Baume aerometer.

Knowing the degree of the solution and based on indications in Table III, you can determine the quantity of pure caustic soda contained in 1 Kg (or in 1 l).

Example:

The precedent mixture of 100 Kg needed, as noticed, 13,76 Kg of pure caustic soda for a complete saponification.

By using a solution at 24 °Be, the total quantity of that solution for a complete saponification will be:

A.I.2.2 Caustic potassium (KOH)

It is a strong base, which like caustic soda, allows direct saponification of neutral fats. As the latter, the concentrated solutions can cause serious burns on the skin. Caustic potasse is less currently used at home level than soda. So it's less available on the market.

However the home-soap-making uses it most exclusively as alkaline source in rural zones. For this purpose you treat vegetable ashes with water. Potassium made soaps are quite soluble in water and present a bright ability to adsorb it (hydroscopy). They are thus of soft consistency and even liquid.

A.I.3. Water

The reaction environment for saponification is an emulsion between fat and water, in which the needed alkali is diluted. Appropriate water for soap making is soft water (rainwater for instance), as hardness elements of water, the magnesium and calcium ions present the propriety of deleting the washing action of soaps.

An easiest method for softening a hard water consists in adding concentrated alkaline solution, mixing it well and left still for 1 to 2 days. The Mg and Ca ions will then form in water insoluble byproduct that deposit at the bottom of the container

A.I.4. Secondary products

The secondary products used for making improved soap are: salt, additives (clay, kaolin,starch, silicate, carbonate etc). Usage of these products is not strictly necessary for soap making, but they can present some technical and trading advantages(improvement of usage qualities, decrease in production costs for instance).

A.I.4.1. Salt

Addition of salt to soda soap leads to achievement of very hard soaps. This practice is based on the fact that soap is not soluble in salted water. Glycerine which is soluble in water is than eliminated with other impurities of the raw materials. Soaps obtained from some fat like copra, palmist or castor oils can incorporate high quantities of salt without being greened out. In this case salt can be used as filling material.

The quantity of salt to be added for greening out varies according to the nature of the fat and is about 10 g of salt for each 100 g of original fat material. The main advantage of greening out is that it gives purified soap.

A.I.4.2 Additives

These products are added to soap in order to either increase the quantity or to give it a hard consistency. To that aim you can use clay or kaolin or starch or silicates of soda or potassium etc. The later can contribute to improvement of washing qualities of the soaps containing it and protect them also form becoming rancid. Other types of additives like alcohol, sugar and glycerine are used to produce transparent soaps. Kaolin can be added to an optimal rate of about 5% of the mass of the initial fat to be saponified.

A.I.4.3 Colors

The color of the product may be important for good selling. To achieve this, the home level soap maker may use some natural colors. Among them you can use the extracts from niebe leaves (vigna sp) for the green color and extracts from red sorgho (Sorghum sp) for colors going form red-brown to orange.

The extraction of these colors is made with diluted alkaline solutions. The process consists in putting mashed leaves in maceration in alkaline solution until you achieve the color you wish. The obtained liquid can be used after filtering.

Non bleached palm oil also can be used (after being filtered) for colorations from light-yellow to orange.

According to local availability, other natural colors can be used. They should how ever be stable to alkaline and oxidation.

The above mentioned extracts should be incorporated to the hot mass of soap at the rate of 0,l to 5% of the initial fat weight.

A.I.4.4 Scents

In order to give a scent to the soap, the soap maker may use extracts from local plants containing perfumes (etheric oils). Extracts from citronel and lemongrass (Cymbopogon sp.), Eucalyptus (Eucalyptus sp) etc. are appropriate.

The extraction itself is a simple process which is done with steam according to the following scheme:


Installation of steam distillation of etheric oils

- Putting water into containers I and II (metallic containers of 50 1 for example);
- Heating intensively container I and moderately container II;
- After bringing containers I to boil, put the smashed vegetable material in container II;
- Put in place a vase to recuperate the liquid of condensation, connect the tube for condensation and close hermetically the container II;
- Then connect I and II, close I hermetically and go on heating it intensively during about 15 minutes;
- After 15 minutes, stop the operation and recuperate the cloudy water of condensation.

The so achieved extract is incorporated into the soap by mixing it at rate of 1 to 100 g for 100 kg of raw fats.

A.I.4.5 Skin protecting agents

Soaps obtained from some fats are damageable to skin. These harsh side-effects are particularly valid for palmist and copra butter based soaps. For this reason addition of skin protecting agents to such soaps is necessary.

Among the natural products which can play this role by improved soaps you may consider: the portion of insaponifiable in the fat, a light surplus of non saponified fat (to be added for instance at the end of the operation) and addition of natural wax (about 3 - 5 % of beeswax for example).