BP 2025 (Ph. Eur. 11.6 update)
Action and use
Non-ionic surfactant.
DEFINITION
Mixture of monoesters and diesters of mainly stearic (octadecanoic) acid and/or palmitic (hexadecanoic) acid and macrogols. It may be obtained by ethoxylation or by esterification of macrogols with stearic acid 50 (type I) or stearic acid 95 (type II) (see Stearic acid (1474)). It may contain free macrogols. The average polymer length is equivalent to 6 to 100 ethylene oxide units per molecule (nominal value).
CHARACTERS
Appearance
White or slightly yellowish, waxy mass.
Solubility
Soluble in ethanol (96 per cent) and in 2-propanol. Macrogol stearate corresponding to a product with 6-9 units of ethylene oxide per molecule is practically insoluble, but freely dispersible in water and miscible with fatty oils and with waxes. Macrogol stearate corresponding to a product with 20-100 units of ethylene oxide per molecule is soluble in water and practically insoluble in fatty oils and in waxes.
IDENTIFICATION
A. Saponification value (see Tests).
B. Composition of fatty acids (see Tests).
TESTS
Alkalinity
Dissolve 2.0 g in ethanol (96 per cent) R and dilute to 20 mL with the same solvent. To 2 mL of this solution add 0.05 mL of phenol red solution R. The solution is not red.
Melting point (2.2.15)
See Table 1234.-1.
Melt about 10 g at 80-90 °C. Introduce a sufficient amount of the substance into the tube by capillary action to form a column of the prescribed height. Allow to stand at 0 °C for 2 h.
Acid value (2.5.1)
Maximum 4.0, determined on 2.0 g.
Hydroxyl value (2.5.3, Method A)
See Table 1234.-1.
Iodine value (2.5.4)
Maximum 2.0.
Saponification value (2.5.6)
See Table 1234.-1.
Table 1234.-1
| Ethylene oxide units per molecule (nominal value) |
Melting point (°C) |
Hydroxyl value | Saponification value |
| 6 | 26 – 37 | 80 – 110 | 85 – 115 |
| 8-9 | 26 – 35 | 80 – 105 | 88 – 100 |
| 20 | 33 – 40 | 50 – 62 | 46 – 56 |
| 32 | 46 – 50 | 20 – 40 | 30 – 45 |
| 40-50 | 38 – 52 | 23 – 40 | 20 – 35 |
| 100 | 48 – 60 | 15 – 30 | 5 – 20 |
Composition of fatty acids
Gas chromatography (2.4.22, Method C).
Composition of the fatty acid fraction of the substance:
| Type of fatty acid used |
Composition of fatty acids | |
| Macrogol stearate type I | Stearic acid 50 | Stearic acid: 40.0 per cent to 60.0 per cent, Sum of the contents of palmitic and stearic acids: not less than 90.0 per cent. |
| Macrogol stearate type II |
Stearic acid 95 | Stearic acid: 90.0 per cent to 99.0 per cent, Sum of the contents of palmitic and stearic acids: not less than 96.0 per cent. |
Ethylene oxide and dioxan (2.4.25)
Maximum 1 ppm of ethylene oxide and 10 ppm of dioxan.
Water (2.5.12)
Maximum 3.0 per cent, determined on 0.50 g. Use as the solvent a mixture of equal volumes of anhydrous methanol R and methylene chloride R.
Total ash (2.4.16)
Maximum 0.3 per cent, determined on 1.0 g.
STORAGE
In an airtight container.
LABELLING
The label states:
— the number of ethylene oxide units per molecule (nominal value);
— the type of macrogol stearate.
