In the textile printing and dyeing industry, "environmental protection" and "efficiency" are no longer optional, but mandatory. In recent years, Sodium Formate has rapidly become a popular "new alternative" to traditional dyeing auxiliaries – it not only reduces high-salt wastewater discharge but also improves dyeing results. However, many industry professionals have encountered the same problem: the same Sodium Formate yields vastly different results when used with different dyes. Below, we will analyze the compatibility logic of Sodium Formate with various mainstream dyes, along with practical tips to help you avoid ineffective dyeing pitfalls.
Key Understanding: Why is Sodium Formate a "golden partner" for dyes?
Before discussing compatibility, let's understand the "strengths" of Sodium Formate. The reason it can replace traditional auxiliaries such as sodium sulfate and sodium sulfide lies in three key characteristics: First, its mild dyeing promotion: its formate ions have a better dyeing promotion effect than chloride ions, helping dyes adhere more evenly to the fibers while avoiding the color unevenness caused by traditional inorganic salts; second, stable pH control: the pH of its aqueous solution remains stable at around 7.3 and is unaffected by temperature, providing a stable environment for dye reactions; third, environmental advantages: it is biodegradable, and the wastewater salt content from dyeing with it is reduced by more than 52%, significantly reducing subsequent treatment costs.
However, these advantages do not apply to all dyes; the key is whether the chemical characteristics of the dye match the mechanism of action of Sodium Formate.
Compatibility 1: Reactive Dyes – A good example of an environmentally friendly alternative
Reactive dyes are commonly used for cellulose fibers such as cotton and linen. Traditional dyeing requires a large amount of sodium sulfate for dyeing promotion, resulting in serious wastewater salt pollution. Sodium Formate and reactive dyes are a perfect match, mainly in two dimensions:
From the perspective of dyeing promotion effect, the sodium ions of Sodium Formate can effectively reduce the Zeta potential of the fiber surface, improving the dye exhaustion rate. Experiments show that when sodium formate is combined with sodium sulfate in a specific ratio (total amount 24g/L), the dye fixation rate can reach 89.56%. Although slightly lower than the pure sodium sulfate system, the salt usage is directly halved, and the dyeing wastewater can be recycled and reused more than three times without affecting the results. It is particularly suitable for KN-type reactive dyes, allowing for dye fixation under near-neutral conditions without the need for additional strong alkalis.
From an environmental perspective, sodium formate significantly improves the photocatalytic degradation efficiency of dyeing wastewater. When sodium formate is combined with sodium sulfate at a ratio of 1:2, the degradation rate constant of Reactive Red 3BS dye solution is 120 times that of the pure sodium sulfate system, reducing the difficulty of wastewater treatment.
Practical tips: When using sodium formate alone, it is recommended to control the dosage at 30-40g/L. If a high dye fixation rate is desired, it can be combined with 5-10g/L of sodium sulfate; the dyeing temperature should be maintained at 60-80℃, and the pH value should be kept stable between 7-8.
Top 2 compatibility: Sulfur dyes – a safe alternative to toxic gases
Sulfur dyes are commonly used for dyeing dark colors in cotton fabrics, but traditional sodium sulfide reducing agents release highly toxic hydrogen sulfide gas, resulting in extremely high sulfur content in wastewater. The emergence of sodium formate completely solves this problem. It acts as a mild reducing agent, reducing the sulfur element in sulfur dyes to a soluble state while avoiding the generation of pollutants.
Orthogonal experiments have proven that in liquid sulfur black dyeing, when the sodium formate dosage is 44g/L and sodium hydroxide is 42g/L, the K/S value (color depth) and soap washing color fastness of the dyed yarn are comparable to the sodium sulfide system, and the wastewater COD value is reduced by more than 30%, completely eliminating hydrogen sulfide release. This combination is particularly suitable for denim, workwear fabrics, and other applications requiring high color fastness, ensuring both quality and compliance with new environmental regulations. Practical Tips: The reaction between Sodium Formate and sulfur dyes requires an alkaline environment, so it must be used in conjunction with sodium hydroxide, with a ratio of approximately 1:1. When dyeing, add Sodium Formate and the alkali agent first, then raise the temperature to 40℃ before adding the dye to prevent premature reduction and inactivation of the dye.
Moderate Compatibility: Disperse Dyes – A "Stabilizer" for High-Temperature Dyeing
Disperse dyes are mainly used for synthetic fibers such as polyester, and the dyeing temperature often reaches above 120℃, making the dyes prone to hydrolysis, leading to uneven color. The key role of Sodium Formate here is not to promote dyeing, but to "stabilize dyeing" and "protect color."
It has extremely strong thermal stability, not decomposing below 400℃. In high-temperature dye baths, it can form low-melting eutectic mixtures, lowering the melting point of the dye and promoting the diffusion of the dye into the fiber. At the same time, Sodium Formate can inhibit dye hydrolysis, reduce floating color, and make the color distribution more even. Especially in the one-bath one-step dyeing of polyester-cotton blended fabrics, Sodium Formate can be used with both disperse dyes and reactive dyes simultaneously, simplifying the process while avoiding interference between the two dyes.
However, it should be noted that Sodium Formate has a weak dyeing-promoting effect on disperse dyes, and using it alone may lead to a low dyeing rate. It is recommended to use it in combination with a dispersant, with a dosage of 20-30g/L.
Lower Compatibility: Acid Dyes – A "Supporting Role" for Careful Use
Acid dyes are mostly used for protein fibers such as wool and silk, and dyeing needs to be carried out under acidic conditions. However, the aqueous solution of Sodium Formate is weakly alkaline, and direct use will reduce the dyeing rate, so the compatibility is relatively low. However, this does not mean it cannot be used at all; Sodium Formate can play a "supporting role" as a pH regulator.
In wool dyeing, the initial pH of the acid dye solution is usually 4-5. Adding 5-10g/L of Sodium Formate can buffer the acidity changes and prevent fiber damage due to excessive acidity. Experiments show that this combination can increase the breaking strength retention rate of wool fabrics by more than 15%, while maintaining a color fastness rate of around 85%. However, excessive use should be avoided, as it can lead to a darker color.
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