Composition And Formulation of Alkali Substitutes for Reactive Dyes

Introduction

Alkali substitutes for reactive dyes have the advantages of low dosage and low cost, significantly reducing the cost of alkali agents for reactive dyeing. They are now widely used in many dye factories. This article introduces the composition and formulation of conventional alkali substitutes. For educational purposes only.

I. Phosphate System

A representative product of the phosphate-based alkali substitute system is Alkaflo, developed by Sybron.  Morran's patent describes the specific method for preparing this alkali substitute system, using different raw materials to create alkaline solutions with varying pH values. The main components of the high-pH alkaline solution are tripotassium phosphate, potassium hydroxide, and sodium hydroxide (used in small amounts to improve the temperature stability of the alkaline solution; its inclusion is optional). The main components of the low-pH alkaline solution are sodium dihydrogen phosphate and phosphoric acid. By mixing the high and low-pH alkaline solutions in different proportions, a series of alkaline solutions with different pH values can be obtained. Adding borates and ethanolamines to the alkaline solution can improve the buffering capacity of the system. The ethanolamine can be monoethanolamine, diethanolamine, triethanolamine, or a mixture thereof.

When preparing the high-pH alkaline solution, the amount of tripotassium phosphate is 20%–50%, potassium hydroxide is 2.5%–20%, and if sodium hydroxide is added, the amount is 0.4%–7%, ethanolamine is 4%–8%, and borax pentahydrate is 4%–10%. When preparing the low-pH alkaline solution, sodium dihydrogen phosphate is 13%–40%, phosphoric acid is 0–30%, and ethanolamine is 1.9%–4%. The patent indicates that the amount of alkaline solution used in the dye bath is 0.1%–0.3%. The preparation formulas for 7 types of alkali substitutes are shown in the table below:

Formulation for phosphate-based systems

Alkaline solutions in phosphate systems show good dye fixation effects in reactive dyeing, but their use is now restricted due to their high phosphorus content.

2.Silicate System:

The substitute alkali sold under the trade name BEMOLFB is a product of the silicate system. The alkali solution formulated in the Aseervatham patent mainly consists of potassium hydroxide, potassium silicate, and a chelating agent. The chelating agent is added to remove metal ions and prevent them from negatively affecting the dyeing process. Commonly used chelating agents include sodium salts of ethylenediaminetetramethylenephosphonic acid, sodium salts of ethylenediaminetetraacetic acid, sodium salts of aminotriacetic acid, phosphonates, and sodium gluconate. In potassium silicate, the ratio of SiO2 to K2O is variable, with the best mass ratio being 1.43–2.09 (equivalent to a molar ratio of 2.24–3.28). A typical formula is shown in the table below, and its dosage in the dye bath is 2–2.5 g/L.

Typical formulations for silicate systems

The main components of the alkaline solution in Christie's patent are: potassium hydroxide, sodium silicate, and borate. The best composition is: 35% potassium hydroxide, 25% sodium silicate, 5% borate (such as sodium perborate, sodium metaborate, etc.), and 35% water. The resulting alkaline solution has both a sufficient pH value (to ensure the reaction between the dye and the fiber) and sufficient buffering capacity (to allow the reaction to proceed slowly). The amount of alkaline solution used in the dye bath is 2-10%. Although silicate-based substitute alkalis have good color-fixing effects, they can precipitate with metal ions, causing equipment blockage or forming spots on the fabric. This can be mitigated by adding chelating agents.

3. Carbonate System

The substitute alkali, marketed under the trade name Burco NP-QS alt, is a product of the carbonate system. Its main components are: sodium hydroxide, potassium hydroxide, sodium carbonate, citrate, and acrylate. It is a mixed alkali composed of inorganic and organic alkalis.

The main components of the substitute alkali given in the Moore patent are: potassium hydroxide, potassium carbonate, potassium citrate, and potassium polyacrylate. The citrate and polyacrylate act as crystallization inhibitors in the solution and also function as dispersants during the dyeing process. Potassium carbonate is prepared by reacting liquid carbon dioxide with a potassium hydroxide solution. The patent also defines total alkalinity and effective alkalinity. Total alkalinity refers to the amount of hydrochloric acid consumed when titrating to the endpoint using methyl orange as an indicator, while effective alkalinity refers to the amount of hydrochloric acid consumed when titrating to the endpoint using phenolphthalein as an indicator. The table below shows the total alkalinity, effective alkalinity, and pH value of 2% solutions of sodium carbonate, Alkaflo, and Burco NP-Q as measured in the patent.

Comparison of the alkalinity of different types of bases

The main components of the substitute alkali in the Bella patent are: alkali metal hydroxides, alkali metal carbonates, and chelating agents. The best formulation is: 6%–8% sodium hydroxide, 8%–30% potassium carbonate, and 4%–7% chelating agent (aminopolycarboxylic acid type). Potassium hydroxide can also be used instead of sodium hydroxide, with a dosage of 10%–12%. To ensure product stability, some stabilizers can be added, with a dosage of 0.12%–0.50%. The carbonate-based substitute alkali does not contain phosphates or silicates, and its effect is the same as that of sodium carbonate, making it of significant value.

Soda Substitute Sylic D2200 (CY-518)

Sylic has also launched ready-to-use alkaline products based on customer needs.

1. It is used as a fixing base for dyeing reactive dyes. It can be used as a substitute for caustic alkali, soda ash, trisodium phosphate and mixtures thereof.

2. The amount used in fixing is small, only 1/8-1/10 of the amount of soda ash.

3. Due to the synergistic effect of a variety of basic compounds, the ability to control the pH value of the dye bath is stronger, ensuring uniform dyeing, continuous dyeing, and controlling the dyeing speed. It is especially suitable for varieties such as emerald blue, grass green, and bean paste to reduce the rate of staining.

4. The fixing bath has low viscosity and can avoid the staining problem caused by the viscosity of the fixing bath. It can be used in various types of dyeing equipment, especially for low-bath dyeing of cheese yarn.

5. The residual alkali is easy to wash off, which can save two times of washing.

Light color 0.5-1g/L; medium color: 1.5-2g/L; dark color: 2-3g/L

The specific process should be adjusted by the user as appropriate.

Precautions

1. Soda Substitute Sylic D2200 is a highly alkaline and corrosive substance that should be disposed of with appropriate safety measures. Avoid direct contact with the skin and eyes. If it gets stuck, rinse immediately with plenty of water.

2. Before use, it should be turned into a solution and added in two to three times.

3. After the product is opened, it must be sealed immediately and not exposed to the air.

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