What Is Indigo?
Indigo, also known as Food Blue No. 1, Edible Cyan No. 2, Edible Blue, Acidic Indigo, Hardened Indigo, is a water-soluble non-azo colorant. Indigo pigments are one of the oldest pigments known to man, and are widely used in the food, medicine and printing and dyeing industries.
- Chinese name
- Indigo
- English name
- Indigo
- nickname
- CI Pigment Blue 66, etc.
- Chemical formula
- C16H10N2O2
- Molecular weight
- 262.2628
- CAS Registry Number
- 482-89-3
- EINECS registration number
- 207-586-9
- Indigo, also known as Food Blue No. 1, Edible Cyan No. 2, Edible Blue, Acidic Indigo, Hardened Indigo, is a water-soluble non-azo colorant. Indigo pigments are one of the oldest pigments known to man, and are widely used in the food, medicine and printing and dyeing industries.
Indigo Definition
- diàn lán, a blue color with purple in blue.
Indigo Basic Information
- Chinese alias: CI Pigment Blue 66; Indigo; Monolite Navy Blue BV; CI Reduced Blue 1; Indigo Powder; Indigo Powder; Reduced Indigo; Indigo;
- English alias: CI 73000; CI Vat Blue 1; 2- (1,3-Dihydro-3-oxo-2H-indol-2-ylidene) -1,2-dihydro-3H-indol-3-one; 2,2 '-Bis (2,3-dihydro-3-oxoindolylidene); Indigo blue; Vat Blue 1; 2,2'-biindole-3,3' (1H, 1'H) -dione; (delta (2,2 ' ) -biindoline) -3,3'-dione; (delta (sup2,2 ')-biindoline) -3,3'-dione; (delta2,2' (3H, 3'H) -Biindole) -3,3 '-dione; (delta2,2'-Biindoline) -3,3'-dione
- Indigo
- ChI = 1 / C16H10N2O2 / c19-15-9-5-1-3-7-11 (9) 17-13 (15) 14-16 (20) 10-6-2-4-8-12 (10) 18-14 / h1-8,17-18H / b14-13 + [1]
- Indigo pigments are one of the oldest pigments known to man, and are widely used in the food, medicine and printing and dyeing industries. The use of indigo as a fabric dye dates back to at least 2500 BC. Some of the clothing worn by ancient Egyptian mummy and the blue linen fabric unearthed from Mawangdui in China are dyed with indigo. One of the Yao people in China is named "Blue Indigo" because of its unique technology of producing and using indigo dyeing . In the food industry, indigo is used as a food coloring agent for its sodium sulfonate salt or its aluminized form, which is called "bright blue" and bright blue aluminum lake in China. It is called "indigocyanine" [2] .
Indigo physical and chemical properties
- Properties: Blue powder (may be dark blue), odorless.
- Solubility: Slightly soluble in water, ethanol, glycerin and propylene glycol, insoluble in oils. A 0.05% aqueous solution was dark blue. 1g can be dissolved in about 100ml of water at 25 ° C, and its solubility in water is lower than that of other edible synthetic pigments. A 0.05% aqueous solution is blue. Soluble in glycerol, propylene glycol, slightly soluble in ethanol, insoluble in oil. It appears dark blue when it is concentrated with sulfuric acid and blue when diluted. Its aqueous solution with sodium hydroxide is green to yellow-green. Indigo is easy to color, has a unique hue and is widely used. Heat resistance, light resistance, alkali resistance, oxidation resistance, salt resistance and bacterial resistance are all poor. Discoloration occurs during reduction, and if reduced with sodium hyposulfite or glucose, it becomes indigo. The maximum absorption wavelength is 610nm ± 2nm [3] .
- Stability: Poor light and heat resistance, unstable to citric acid, tartaric acid and alkali.
- Density: 1.417g / cm3
- Melting point: 390-392 ° C (dec.)
- Boiling point: 400.4 ° C at 760 mmHg
- Flash point: 158.2 ° C
- Vapor pressure: 1.27E-06mmHg at 25 ° C
Indigo storage and transportation characteristics
- Store in a cool, dry place. Store in a sealed place in a ventilated, dry place and avoid contact with other oxides. [4]
Indigo danger statement
- Danger code: Xn
- Danger level: R22- R36 / 37/38
- Security level: S26- S37 / 39
Indigo plant source
- Plant source
- Indigo is a vat dye with a history of more than 3,000 years. The ancient famous phrase "blue, blue is better than blue" in the Warring States Period originated from the blue dyeing technology at that time. Here "cyan" refers to cyan, and "blue" refers to blue grass from which indigo is made. Before the Qin and Han Dynasties, the application of indigo was quite common.
Indigo preparation process
- The indigo leaves are piled up and watered frequently to ferment them for 2 to 3 months and become a black soil mass. After being compacted with a mortar, it is called globular indigo, containing 2% to 10% of indigo pigment. Wood indigo is mixed with wood ash, lime and bran, mixed with water, heated to 30-40 ° C, and exposed to the air to become blue insoluble indigo.
Indigo cultivation technology
- In the long-term practice, the people of our country have gradually explored the key technology for making indigo, thus breaking the season limitation of bluegrass dyeing. The ancients' method of making indigo is as follows: first, indigo blue is erected in the pit, filtered with water, the filtrate is placed in the dipper, and lime is added in proportion, and then the water is sharply hit with a wooden stick to accelerate the dissolution of indigo in water and air oxygen. It is contacted to oxidize it to indigo. After precipitation, the water is removed. After the water of indigo is completely evaporated, it can be contained in a container to make indigo. This indigo-making and dyeing technology is completely consistent with the modern synthetic indigo dyeing mechanism.
- Like safflower, bluegrass can also be made into a solid dye: first, it is made into muddy indigo. When it is dyed, it is first fermented with distiller's grains. The hydrogen and carbon dioxide produced during the fermentation process can reduce indigo to indigo. The white cloth dyed with indigo white can be oxidized by air to show blue. This fermentation reduction technology of indigo has been used in the Spring and Autumn and Warring States Periods, and this ancient method is still in use today. Around 100 BC, indigo was made in India. Unlike the Chinese, they dyed blue with urine fermentation.
Indigo use
- It is mainly used for dyeing cotton yarn, cotton cloth, wool or silk. The pigment is an important pigmented product of vat dye indigo. It has excellent light fastness, weather fastness and heat stability. Preparation of liquid dispersion formulations, mainly used for viscose fiber pulp coloring and printing and dyeing. Used in biochemicals and indicators and dyeing of cotton yarn, cotton, wool or silk.
- Used as a food coloring agent, China's regulations can be used in red and green silk, the maximum amount of use is 0.02g / kg; in fruit juice (flavored) beverages, carbonated beverages, formulated wine, candy, cakes, tinned cherry cans (system For decoration), green plums, the maximum amount of use is 0.10g / kg; in dipping vegetables, the maximum amount is 0.01g / kg. [4]
Indigo preparation method
- (1) Indigo preparation. Edible indigo is actually disodium indigo disulfonate. The indigo is sulfonated with concentrated sulfuric acid, diluted with water after sulfonation, neutralized with soda ash, and finally salted out by adding sodium chloride, filtered, washed and dried to obtain the finished product. Each ton of product consumes 210kg of indigo powder (100%).
- (2) Preparation of indigo aluminum lake. Aluminum hydroxide is prepared from aluminum salts such as aluminum chloride and aluminum sulfate and alkalis such as sodium carbonate, and then added to an aqueous solution of indigo citrate to precipitate to obtain a product.
Indigo application areas
- According to China's "Sanitary Standards for the Use of Food Additives" (GB2760-1996), indigo can be used for pickled side dishes, fruit juice (flavored) beverages, carbonated beverages, formulated wines, candies, pastries, colored tinned cherries (for decoration ), Green plum, candy coating, the maximum usage is 0.1g / kg; red and green silk, the maximum usage is 0.2g / kg [3] .
- Used in the coloring of food, medicine and daily cosmetics. Edible indigo is an edible synthetic pigment. Food coloring is a class of additives used in food coloring, including synthetic and natural colorings, with a total of more than 60 types.