Method for dyeing flame-retardant Lyocell fibers by using reactive dye taking isohexadecane as medium

Abstract

The invention relates to a method for dyeing flame-retardant Lyocell fibers by using an active dye taking isohexadecane as a medium. The method comprises the following steps: S1, in a non-aqueous chromosome system taking isohexadecane as a main medium, carrying out dyeing treatment on the flame-retardant Lyocell fiber, so that the reactive dye is adsorbed on the fiber; and S2, after the dyeing step is completed, directly adding aqueous alkali liquor into the non-aqueous dyeing system, and carrying out color fixation treatment, so that the reactive dye and the fiber form covalent bonding. The whole process is carried out in a non-aqueous medium, dissolution and damage of a flame retardant caused by a large amount of water, salt and alkali in traditional water bath dyeing are avoided, and the flame retardant property of the dyed fiber is greatly reserved.

Description

Technical Field

[0001] This invention belongs to the field of textile chemistry and dyeing and finishing engineering, and relates to a method for dyeing flame-retardant Lyocell fibers with reactive dyes using isohexadecane as a medium. Background Technology

[0002] Flame-retardant Lyocell fiber is a high-performance, environmentally friendly fiber that combines the excellent comfort, biodegradability, and special flame-retardant properties of Lyocell fiber. It has broad application prospects in protective clothing and home textiles in fields such as fire protection, metallurgy, and power. Reactive dyes, due to their complete color spectrum, bright colors, and excellent wet fastness, are the preferred dyes for dyeing cellulose fibers.

[0003] However, applying traditional reactive dye water bath dyeing processes to flame-retardant Lyocell fibers faces a series of insurmountable technical bottlenecks. First, traditional water bath dyeing requires high temperature, high electrolyte (such as sodium sulfate), and strong alkali (such as sodium carbonate) conditions. This harsh chemical environment severely damages the flame retardants (usually phosphorus- or nitrogen-containing compounds) added to the fiber, leading to a significant decrease or even loss of the fiber's flame-retardant properties. Second, the presence of flame retardants often increases the fiber's hydrophobicity, hindering the penetration of aqueous dye liquor into the fiber interior, easily causing uneven dyeing problems such as color spots and discoloration. Furthermore, traditional water bath dyeing generates large amounts of high-salt, high-alkali, and high-color dyeing wastewater, placing enormous pressure on the environment and incurring high treatment costs.

[0004] To address the aforementioned issues, non-aqueous dyeing technologies offer a potential solution. For example, while supercritical carbon dioxide dyeing is environmentally friendly, its high equipment investment, high operating pressure, and narrow process window hinder large-scale industrial application. Using organic solvents as dyeing media, however, is more practical. Isohexadecane, as a non-polar, chemically stable, low-toxicity, and easily recyclable organic solvent, is one of the ideal non-aqueous dyeing media. However, in existing technologies, how to effectively dye polar fibers like flame-retardant Lyocell using reactive dyes in non-polar media such as isohexadecane remains an unresolved problem. The main challenges are: 1) reactive dyes are almost insoluble in non-polar solvents, making effective transfer to the fibers difficult; 2) the covalent bonding reaction (fixation) between reactive dyes and cellulose fibers depends on an alkali and a certain water molecule environment, which contradicts the nature of non-aqueous systems.

[0005] Therefore, there is an urgent need in this field to develop a new process that can maintain the flame-retardant properties of fibers while achieving efficient, uniform, and environmentally friendly dyeing, so as to promote the widespread application of flame-retardant Lyocell fibers. Summary of the Invention

[0006] This invention aims to solve the technical problems caused by the decline in flame retardant properties, uneven dyeing, and large amounts of wastewater pollution when existing reactive dye water bath dyeing processes are applied to flame retardant Lyocell fibers. This invention provides a method for dyeing flame retardant Lyocell fibers with reactive dyes using isohexadecane as a medium, so as to achieve efficient, uniform, and environmentally friendly dyeing of flame retardant Lyocell fibers.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] A method for dyeing flame-retardant Lyocell fibers with reactive dyes using isohexadecane as a medium, the method comprising the following steps:

[0009] S1. Dyeing step: The flame-retardant Lyocell fiber is dyed in a non-aqueous dyeing system with isohexadecane as the main medium, so that the active dye is adsorbed onto the fiber.

[0010] S2. Fixing step: After completing the dyeing step, add an aqueous alkaline solution directly to the non-aqueous dyeing system for fixing treatment, so that the reactive dye forms a covalent bond with the fiber.

[0011] In this invention, a co-solvent is used to assist in the dispersion of the reactive dye in isohexadecane.

[0012] In this invention, during dyeing, the dye is adsorbed onto the fiber surface due to the hydrophobic effect of the medium and diffuses into the amorphous region of the fiber. During fixation, the fiber swells moderately and activates the reactive groups of the dye, and the dye forms covalent bonds (Dye-O-Cell) with the hydroxyl groups of the fiber to complete the fixation.

[0013] The core of the technical solution of this invention lies in its unique two-step process design: First, by utilizing the huge polarity difference between the non-polar isohexadecane medium and the polar flame-retardant Lyocell fiber, the reactive dye particles are physically "displaced" and driven to be directionally adsorbed onto the fiber surface; then, while maintaining the macroscopic non-aqueous properties of the entire system, a "trace amount" of aqueous alkaline solution is introduced to create a local, microscopic reaction environment on / inside the fiber surface. This environment is sufficient to cause the fiber to swell slightly and activate the dye, thereby achieving covalent bonding and color fixation between the dye and the fiber.

[0014] Preferably, the non-aqueous dyeing system comprises a reactive dye, isohexadecane, and a co-solvent. The amount of reactive dye is 0.5-5% owf, and the amount of co-solvent is 10-30% of the mass of isohexadecane. In the best case, the amount of co-solvent is 15-25% of the mass of isohexadecane. Preferably, the amount of reactive dye is 2-3% owf.

[0015] Preferably, the bath ratio of flame-retardant Lyocell fiber to isohexadecane is 1:10 to 1:50. More preferably, it is 1:30 to 1:40.

[0016] Preferably, in step S2, the amount of the added aqueous alkaline solution is 1-25% of the total mass of isohexadecane and co-solvent. More preferably, it is 5%-25%. This technical parameter is key to achieving the beneficial effects of this invention; it ensures that the necessary reaction conditions are provided without compromising the non-aqueous properties of the system, thereby maximizing the protection of the flame-retardant properties of the fibers.

[0017] Preferably, the alkali in the aqueous alkaline solution is sodium carbonate, sodium bicarbonate, trisodium phosphate, sodium hydroxide, or a combination thereof, and the concentration of the alkaline solution is 1-5 g / L. More preferably, the concentration of the alkaline solution is 1-2 g / L. This concentration achieves a good color-fixing effect while effectively reducing the amount of water used.

[0018] Preferably, the non-aqueous dyeing system for 1.0 g of flame-retardant Lyocell fiber contains: 30 mL-40 mL of isohexadecane, 6 mL-10 mL of co-solvent (preferably methyl oleate), and an aqueous alkali solution (sodium carbonate solution) at a concentration of 5%-25% of the total mass of isohexadecane and co-solvent. The concentration of the aqueous alkali solution is 1-2 g / L.

[0019] Preferably, the dyeing step in step S1 is performed at a temperature of 60-120℃ for 10-200 min; the color-fixing step in step S2 is performed at a temperature of 60-110℃ for 10-150 min. In this dyeing process, dyeing performance is good when the dyeing temperature is within the range of 80℃–90℃ and the dyeing time is within the range of 60-80 min.

[0020] Preferably, the method further includes a soaping step after step S2, wherein the soaping temperature is 40-60°C and the time is 10-30 min. This removes excess dye, yielding dyed flame-retardant Lyocell fibers.

[0021] Preferably, the soaping solution consists of 2 g / L standard soap flakes and 2 g / L sodium carbonate.

[0022] Preferably, the reactive dyes are selected from one or more of Reactive Yellow S-3R, Reactive Red 3BS, and Reactive Yellow 145; the cosolvents are selected from one or more of oleic acid, methyl oleate, benzyl benzoate, and sorbic acid fatty acid esters.

[0023] Preferably, the co-solvent is methyl oleate.

[0024] Preferably, the non-aqueous dyeing system and flame-retardant Lyocell fibers are placed in the dye cup of an adjustable sampler; the adjustable sampler raises the temperature to the dyeing temperature at a constant rate and holds it during the dyeing and fixing process, while stirring at a constant rate to ensure that the dye is evenly applied to the flame-retardant Lyocell fibers.

[0025] The beneficial effects of this invention are:

[0026] 1. The entire process of this invention is carried out in a non-aqueous medium, which avoids the dissolution and destruction of flame retardants by large amounts of water, salt and alkali in traditional water bath dyeing, and the flame retardant properties of the dyed fibers are largely preserved.

[0027] 2. This invention overcomes the limitations of traditional water bath dyeing for flame-retardant Lyocell fibers through a two-step method of "non-aqueous adsorption + micro-aqueous fixation." It utilizes the polarity difference between the non-polar medium of isohexadecane and the fiber to achieve efficient directional transfer of reactive dyes, resulting in highly efficient dyeing and fixation. The K / S value of the dyed products can reach over 33, with rich and vibrant colors. More importantly, due to the uniform distribution of the dye during the transfer process, the product exhibits excellent levelness, with a non-uniformity value controlled below 3.0, far superior to traditional water dyeing processes, effectively avoiding defects such as color spots and uneven dyeing.

[0028] 3. This invention uses an alkaline solution activation system containing trace amounts of water, which promotes fiber swelling and dye activation while maintaining a non-aqueous medium environment. The covalent bond binding rate reaches over 90%, and the color fastness reaches grade 4-5.

[0029] 4. This invention uses recyclable isohexadecane instead of water as the main medium, eliminating the generation of dyeing wastewater at its source and greatly reducing water consumption and environmental pollution. Simultaneously, the process eliminates the need for large amounts of dyeing-promoting salts, further reducing chemical consumption and subsequent treatment costs, aligning with the trend of green manufacturing.

[0030] Furthermore, the process principles and methods proposed in this invention are not only applicable to flame-retardant Lyocell fibers, but also provide a new technical route for reactive dyeing of other functional cellulose fibers that are sensitive to water and alkali (such as antibacterial fibers, UV-resistant fibers, etc.). Attached Figure Description

[0031] Figure 1 This is a sample image of flame-retardant Lyocell fibers after being dyed with reactive dyes in isohexadecane medium, as shown in Example 1 of this invention.

[0032] Figure 2 This is an example of SEM images of flame-retardant Lyocell fibers before and after dyeing with reactive dyes in isohexadecane medium, as shown in Example 1 of this invention. Figure 2 a is undyed flame-retardant Lyocell fiber. Figure 2 b represents flame-retardant Lyocell fibers dyed in a non-aqueous medium;

[0033] Figure 3 This is a picture of a sample of flame-retardant Lyocell fiber dyed with reactive dye in an aqueous medium, as shown in Comparative Example 1 of this invention.

[0034] Figure 4 This is a picture of the dyed sample of flame-retardant Lyocell fiber after fixation in alkaline solution, which is Comparative Example 2 of this invention. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below through specific embodiments. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0036] In this invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0037] Unless otherwise specified, the reagents used in the following examples can be purchased from a regular biochemical reagent store.

[0038] Reactive Yellow S-3R dye was purchased from Zhejiang Shaoxing Longsheng Dyestuff & Chemical Co., Ltd.

[0039] Isohexadecane medium, purchased from Guangzhou Chengyi Chemical Co., Ltd., China;

[0040] Methyl oleate was purchased from Aladdin Biochemical Technology Co., Ltd., Shanghai, China.

[0041] Flame-retardant Lyocell fiber, purchased from the China Textile Research Institute.

[0042] Example 1 (Best Practice):

[0043] This embodiment provides a method for dyeing flame-retardant Lyocell fibers with reactive dyes using isohexadecane as a medium. The steps are as follows:

[0044] (1) Dyeing working solution: Place 0.02 g of reactive yellow S-3R dye in 32 mL of isohexadecane medium and add 8 mL of methyl oleate. Stir thoroughly to disperse the dye evenly in the medium.

[0045] (2) Dyeing: Immerse 1.0 g of flame-retardant Lyocell fiber in the dyeing suspension in step (1) and dye for 60 min at a temperature of 90℃;

[0046] (3) Fixing: Add 8 mL of 1 g / L sodium carbonate solution to the staining cup after step (2) and fix the color for 30 min at a temperature of 90℃.

[0047] (4) Cleaning: After color fixing in step (3), the flame-retardant Lyocell fiber is placed in 20 mL of soaping solution (2 g / L standard soap flakes and 2 g / L sodium carbonate) and cleaned at 50°C for 30 min.

[0048] (5) Testing: The flame-retardant Lyocell fiber samples after washing were tested. The K / S value and levelness were the main indicators for evaluating the dyeing effect. The test methods are as follows:

[0049] After dyeing, the flame-retardant Lyocell fibers were dried and re-moistened, then flattened and pressed onto translucent apertures. The K / S values ​​at the maximum absorption wavelengths at 10 different locations were measured using a colorimeter, and the average value was recorded. The standard deviation of the dyed fabric was calculated from the measured K / S values, and the unevenness of the dyed fabric was calculated using the following formula. ,

[0050] In the formula: S λ λ represents the standard deviation; λ is the maximum absorption wavelength of the corresponding dye, in nm; n is the number of sampling points. The smaller the non-uniformity, the better the leveling performance; the larger the non-uniformity, the worse the leveling performance.

[0051] The relevant test results for Example 1 are shown below. Figure 1 , Figure 2 And Table 1.

[0052] Comparative Example 1

[0053] The difference from Example 1 is:

[0054] This embodiment uses a traditional water bath staining process, and its staining method is basically the same as that described in Example 1. The difference is that in step (1) of this embodiment, isohexadecane and methyl oleate are replaced with an aqueous solution, and the amount used is 40 mL. The test results of this embodiment are as follows: Figure 3 As shown in Table 1.

[0055] Comparative Example 2

[0056] The difference from Example 1 is:

[0057] This embodiment uses a traditional water bath color-fixing process, and its color-fixing method is basically the same as that described in Example 1. The difference is that in this embodiment, after step (2), the dyed fabric is placed in a 2 g / L aqueous alkaline solution, with a dosage of 20 mL. The test results of this embodiment are as follows: Figure 4 As shown in Table 1.

[0058] Table 1. Staining effect of flame-retardant Lyocell in different systems

[0059]

[0060] As shown in Table 1, compared with traditional water-based dyeing (Comparative Example 1), the method of the present invention (Example 1) can achieve extremely high dyeing depth (K / S value) while maintaining excellent levelness (uniformity value is generally below 3.0), which is difficult to achieve with existing technologies. The average K / S value of the dyed fabric is 34.356, and the levelness (uniformity value) is 2.533, which is similar to Comparative Example 2, proving the feasibility of the micro-alkali fixation method in isoalkanes. Wash fastness tests show that the color fastness is all in the range of 4-5. After dyeing with isohexadecane, the limiting oxygen index of flame-retardant Lyocell is 32.46%, while it is 30.15% after water dyeing, proving that isohexadecane has little effect on the flame-retardant properties of flame-retardant Lyocell.

[0061] also, Figure 1 The flame-retardant Lyocell fiber was showcased, which, after dyeing, exhibits a bright orange color with even color distribution. Figure 2 a is undyed flame-retardant Lyocell fiber and Figure 2 Image b shows a scanning electron microscope (SEM) image of flame-retardant Lyocell fibers dyed in a non-aqueous medium. The image indicates that the surface of the Lyocell fibers was relatively rough before dyeing, with obvious grooves and irregular textures. After dyeing, the surface became smoother, and the grooves and textures were reduced. This is likely because the dye filled the pores and grooves on the fiber surface during the dyeing process, resulting in a more uniform surface. In summary, the isohexadecane non-aqueous dyeing system has a certain impact on the surface morphology of flame-retardant Lyocell fibers, making the surface smoother. This effect may be due to the interaction between the dye and the fiber surface during the dyeing process, but it does not affect the fiber itself or its flame-retardant properties.

[0062] Comparative Example 3

[0063] Referring to Example 1, the effect of different dye dosages on the dyeing effect in the dyeing working solution of step (1) is discussed. Other dyeing methods and process conditions are the same as in Example 1. The test results of this comparative example are shown in Table 2.

[0064] Table 2. Effects of different dye dosages on the dyeing of flame-retardant Lyocell fibers with isohexadecane.

[0065]

[0066] With increasing dye dosage, the coloring effect on the fiber surface is significantly enhanced, as evidenced by a continuous increase in the K / S value. This is mainly due to the increased dye concentration on the fiber surface. The K / S value is positively correlated with the dye concentration on the fiber surface; increased dye dosage encourages more dye molecules to adsorb onto the fiber surface, thereby improving the apparent color depth. On the other hand, at lower dye dosages, dye molecules diffuse more easily into the fiber interior, achieving through-dyeing. However, with increasing dosage, the proportion of dye adsorbed on the surface increases, potentially leading to more dye accumulation on the fiber surface, further increasing the K / S value. However, increasing dye dosage can also lead to decreased leveling properties, manifested as localized color spots on the fiber surface. This is because excessive dye is difficult to distribute evenly on the fiber surface. Based on a comprehensive evaluation of coloring effect and leveling performance, this invention determines 2% (owf) as the optimal dye dosage, which can achieve a high K / S value while maintaining good leveling properties. The preferred range for reactive dye dosage is 2-3% owf.

[0067] Comparative Example 4:

[0068] Referring to Example 1, this study discusses the effect of different amounts of isohexadecane in the staining working solution of step (1) on the staining effect. Other staining methods and process conditions are the same as in Example 1. The test results of this comparative example are shown in Table 3.

[0069] Table 3. Effects of different amounts of isohexadecane on the dyeing of flame-retardant Lyocell fibers with isohexadecane.

[0070]

[0071] With increasing hexadecane dosage, the apparent color yield (K / S value) of the fiber increases accordingly, and the levelness is also improved. This is mainly because, under low liquor ratio conditions, hexadecane has limited ability to promote the flow of the dye bath, resulting in insufficient effective contact between the dye and the fiber. Appropriately increasing the dosage of hexadecane helps to enhance the fluidity of the dye liquor, promote the uniform adsorption and diffusion of dye molecules on the fiber surface, thereby significantly improving the color yield and levelness. However, when the dosage of hexadecane continues to increase, although the levelness still improves to some extent, the rate of improvement tends to plateau.

[0072] Based on the above results, a non-aqueous dyeing system containing 30-40 mL of isohexadecane in a 1.0 g flame-retardant Lyocell fiber dyeing system yields better dyeing results. Considering both dyeing effect and energy-saving and environmental protection requirements, the optimal amount of isohexadecane is 32 mL.

[0073] Comparative Example 5:

[0074] Referring to Example 1, this study discusses the effect of different amounts of co-solvent (methyl oleate) in the dyeing working solution of step (1) on the dyeing effect. Other dyeing methods and process conditions are the same as in Example 1. The test results of this comparative example are shown in Table 4.

[0075] Table 4. Effects of different methyl oleate dosages on the dyeing of flame-retardant Lyocell fibers with isohexadecane.

[0076]

[0077] The amount of co-solvent has a significant impact on the dyeing effect. Adding an appropriate amount of co-solvent can effectively promote the dissolution and dispersion of dyes in the dye bath, enhance the dye's affinity and penetration into the fiber, thereby improving the dyeing depth and uniformity. When the amount of co-solvent is too low, the dye dissolves insufficiently, easily leading to uneven dyeing; while excessive amounts may cause excessive swelling or aggregation of the dye, which is detrimental to the directional adsorption and fixation of the dye, and increases production costs and environmental impact. Therefore, considering both dyeing performance and economic and environmental factors, this invention determines that the preferred range of co-solvent is 6 mL-10 mL, with the optimal amount being 8 mL.

[0078] Comparative Example 6:

[0079] Referring to Example 1, this study discusses the effect of different dyeing temperatures on the dyeing effect in step (2) of the dyeing process. Other dyeing methods and process conditions are the same as in Example 1. The test results of this comparative example are shown in Table 5.

[0080]

[0081]

[0082] Temperature is a key factor affecting the fixation reaction of reactive dyes. Its effect is closely related to the active functional groups and overall structure of the dye molecule. Therefore, different types of reactive dyes require dyeing within a specific temperature range. Too low a temperature leads to insufficient dye reactivity, affecting fixation efficiency; too high a temperature easily causes dye hydrolysis, reducing color fastness and color yield. Reactive Yellow S-3R dye exhibits good dyeing performance in the range of 80℃–90℃. From a molecular thermodynamics perspective, appropriately increasing the temperature can enhance the kinetic energy of dye molecules, promoting their diffusion in the dye bath, thereby increasing the effective collision probability with the fiber and facilitating the formation of covalent bonds between the dye and fiber. This process not only helps to increase the apparent color yield (K / S value) but also improves the evenness of dyeing.

[0083] Comparative Example 7:

[0084] Referring to Example 1, this study discusses the effect of different dyeing times on the dyeing effect in step (2) of the dyeing process. Other dyeing methods and process conditions are the same as in Example 1. The test results of this comparative example are shown in Table 6.

[0085] Table 6. Effects of different dyeing times on the dyeing of flame-retardant Lyocell fibers with isohexadecane.

[0086] Staining time (min) 20 40 60 80 100 120 K / S 29.985 32.034 34.356 33.153 32.047 33.065 level dyeing 2.105 2.123 2.533 2.134 2.136 2.142

[0087] Under optimal dyeing temperature conditions, the apparent color yield (K / S value) of the fiber gradually increases with increasing dyeing time, and the levelness of dyeing also improves accordingly. When the dyeing time is too short, the dye molecules fail to fully adsorb onto the fiber surface and diffuse inwards, resulting in insufficient migration and poor levelness. Appropriately extending the dyeing time helps promote the uniform distribution of dye on the fiber surface and its migration inwards, thereby simultaneously improving both color depth and dyeing uniformity. Considering both apparent color depth and levelness, a dyeing time within the range of 60-80 minutes yields better results, with 60 minutes being the optimal dyeing time.

[0088] Comparative Example 8:

[0089] Referring to Example 1, this study discusses the effect of sodium carbonate solution concentration on the dyeing effect in step (3) of the color-fixing process. Other dyeing methods and process conditions are the same as in Example 1. The test results of this comparative example are shown in Table 7.

[0090] Table 7. Effects of different sodium carbonate concentrations on the dyeing of flame-retardant Lyocell fibers with isohexadecane.

[0091]

[0092] The addition of Na₂CO₃ promotes dye dissolution and causes fiber swelling, thereby facilitating dye diffusion into the fiber interior. During this process, Na₂CO₃ not only provides an alkaline environment to promote covalent bonding between the dye and fiber for color fixation, but also enhances dye adsorption by neutralizing the negative charge on the fiber surface, thus increasing the apparent color yield (K / S value). An appropriate amount of soda ash can effectively promote the dye-fiber reaction and inhibit dye hydrolysis, thereby improving color fixation efficiency. Experimental results show that a soda ash concentration of 1-2 g / L results in better dyeing. When the soda ash concentration is 1 g / L, the color yield and leveling properties of the fiber reach an optimal balance. Further increasing the amount of soda ash can further promote the color fixation reaction, but it leads to a decrease in dye migration performance and a deterioration in leveling properties. This is because an excessively high soda ash concentration results in an excessively fast color fixation reaction rate, limiting the migration and rearrangement of the dye on the fiber surface; simultaneously, the intensified dye hydrolysis side reaction also adversely affects the dyeing effect.

[0093] Comparative Example 9:

[0094] Referring to Example 1, this study discusses the effect of the amount of sodium carbonate solution used on the dyeing effect in step (3) of the color-fixing process. Other dyeing methods and process conditions are the same as in Example 1. The test results of this comparative example are shown in Table 8.

[0095] Table 8. Effects of different sodium carbonate dosages on the dyeing of flame-retardant Lyocell fibers with isohexadecane.

[0096]

[0097] With increasing alkali dosage, the apparent color yield (K / S value) and levelness of the fiber are significantly improved. Water, as a solvent, effectively promotes dye dissolution and uptake in this system, thereby enhancing dye adsorption and coverage on the fiber surface and increasing dyeing depth. Even under low water dosage conditions, this dyeing system can still maintain good levelness performance.

[0098] As shown in Table 8, the dyeing effect is good when the sodium carbonate solution dosage is between 2 mL and 10 mL (5%-25% of the total mass of isohexadecane and co-solvent). Considering the dye yield, levelness, and water conservation requirements, this invention determines the optimal alkali solution dosage to be 8 mL (20% of the total mass of isohexadecane and co-solvent), which can achieve excellent dyeing results while meeting the needs of green production. Comparative Examples 3-9 demonstrate that dyeing temperature, dyeing time, dye dosage, and alkali dosage have a significant impact on the dyeing effect of flame-retardant Lyocell fibers. With the increase of temperature in the non-aqueous medium of isohexadecane, the K / S value of the dyed flame-retardant Lyocell fibers increases significantly and exhibits good levelness. These data strongly demonstrate the significant advantages of this invention in dyeing performance.

Claims

1. A method for dyeing flame-retardant Lyocell fibers with reactive dyes using isohexadecane as a medium, characterized in that, The method includes the following steps: S1. Dyeing step: The flame-retardant Lyocell fiber is dyed in a non-aqueous dyeing system with isohexadecane as the main medium, so that the active dye is adsorbed onto the fiber. S2. Fixing step: After completing the dyeing step, add an aqueous alkaline solution directly to the non-aqueous dyeing system for fixing treatment, so that the reactive dye forms a covalent bond with the fiber.

2. The staining method according to claim 1, characterized in that: The non-aqueous dyeing system includes reactive dye, isohexadecane, and co-solvent. The amount of reactive dye is 0.5-5% owf, and the amount of co-solvent is 10-30% of the mass of isohexadecane.

3. The staining method according to claim 1, characterized in that: In step S2, the amount of aqueous alkaline solution added is 1 to 25% of the total mass of isohexadecane and cosolvent.

4. The staining method according to claim 1, characterized in that: The alkali in the aqueous alkaline solution is sodium carbonate, sodium bicarbonate, trisodium phosphate, sodium hydroxide, or a combination thereof, and the concentration of the alkaline solution is 1-5 g / L.

5. The staining method according to claim 1, characterized in that: The temperature for the staining step in step S1 is 60-120℃ and the time is 10-200 min; the temperature for the color-fixing step in step S2 is 60-110℃ and the time is 10-150 min.

6. The staining method according to claim 1, characterized in that: The method further includes a soaping step after step S2, wherein the soaping temperature is 40~60 ℃ and the time is 10-30 min.

7. The staining method according to claim 6, characterized in that: The soap solution consists of 2 g / L standard soap flakes and 2 g / L sodium carbonate.

8. The staining method according to claim 2, characterized in that: The reactive dyes are selected from one or more of Reactive Yellow S-3R, Reactive Red 3BS, and Reactive Yellow 145; the cosolvents are selected from one or more of oleic acid, methyl oleate, benzyl benzoate, and sorbic acid fatty acid esters.

9. The staining method according to claim 2, characterized in that: The co-solvent is methyl oleate.

10. The staining method according to claim 1, characterized in that: The flame-retardant Lyocell fibers obtained by this method have a uniformity value of less than 3.0 in their dyeing properties.

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