Supercritical CO2 dyeing
Supercritical CO2 dyeing is an anhydrous dyeing technology invented by E. Schollmeyer, Northwest Textile Research Center, Germany in 1989.
This technology uses supercritical CO2 as the dyeing medium to dissolve the dye into the fiber pores, so that the dye can be dyed on the fabric quickly and evenly. After the dyeing is completed, the CO2 can be fully separated from the dye, without the need for cleaning, drying and other operations. Unused dyes can be recycled.
Supercritical CO2 dyeing process
The CO2 is heated and pressurized to a supercritical fluid state that is neither gas nor liquid, and the circulation pump is used to continuously circulate between the dye tank and the dye tank. The supercritical CO2 fluid dissolves the dye while dyeing the fabric.
The dyeing conditions are 20~30MPa, 80~160 ℃, and the dyeing time is about 1 h. After dyeing, the remaining dye and CO2 can be recovered and recycled.
Supercritical CO2 dyeing technology has many advantages such as energy saving and emission reduction, lower production costs, and strong applicability. At present, researches in various countries around the world are trying to push it to practical and industrialization.
Research content of supercritical CO2 dyeing technology
Dyeing process conditions, dyeing mechanism, disperse dye screening, dyeing thermodynamics and diffusion kinetics research, applicable fiber or fabric research, etc., but most of them are concentrated on the dyeing research of hydrophobic synthetic fibers with disperse dyes.
Advantages of supercritical CO2 dyeing
- No water, no waste water pollution, textile companies no longer have to pay huge waste water treatment costs, it is an environmentally friendly dyeing and finishing process;
- After the dyeing is finished, the pressure is reduced, and the CO2 is quickly gasified, so post-dying drying is not required, which not only shortens the process flow, but also saves the energy required for drying;
- Fast dyeing speed, good level dyeing and penetration performance, and excellent dyeing reproducibility;
- CO2 itself is non-toxic, odorless, non-flammable, and can be reused; (5) Dyes can be reused, without adding any dispersants, leveling agents, buffers and other additives during dyeing, which reduces production costs and reduces pollution;
- It is applicable to a wide variety of fibers, and some synthetic fibers that are difficult to dye (such as polypropylene, aramid, etc.) can also be dyed normally.
Research on Dyeing Process Conditions
The process parameters such as temperature, pressure and time during dyeing have a great influence on dyeing performance.
Case Study One
Lin Chunmian, School of Biological and Environmental Engineering, Zhejiang University of Technology, and others used Disperse Red E-4B to dye polyester fabrics. They believe that temperature, pressure and time have a significant effect on the dyeing effect of polyester fabrics. Under the conditions of 120 ℃ and 16~18 MPa ，Dyeing for 10~15 min, can get a more ideal dyeing effect.
Research case two
Li Zhiyi and others from Dalian University of Technology used Disperse Blue 60 to perform supercritical fluid dyeing experiments on polyester. They investigated the variation of dye uptake and dyeing depth K/S value with operating pressure, temperature and time, and determined the most suitable process conditions as follows: ：The pressure is 28 MPa, the temperature is 120 ℃ and the dyeing time is 80 min.
Case Study Three
Researchers such as Hou Aiqin of Donghua University discussed the effects of different temperatures and pressures on the structure and properties of the dye aggregates during supercritical dyeing, as well as the effects on fiber morphology and properties under the same conditions.
Case Study Four
Yu Zhicheng of Zhejiang Sci-Tech University and others studied the effect of supercritical CO2 dyeing on the structure and properties of polyester, and found that supercritical CO2 has plasticizing and swelling effects on polyester, which reduces the glass transition temperature of the fiber.
Disperse dye research
Research on Dyeing with Single Dyes
Disperse dyes are generally used to dye synthetic fibers, such as polyester fibers, polyamide fibers and polypropylene fibers. The application performance of the dye is closely related to its structure. There have been studies on the effect of different groups on the dye molecule on the dye uptake and dye fastness of different fibers in supercritical CO2 dyeing, but it is still difficult to be affirmed in theory. As a result, they are still at the stage of summarizing and sorting out experimental data.
In order to find suitable disperse dyes in supercritical CO2 fluids for supply, the original Ciba company specially developed dyes for supercritical CO2 dyeing of polyester fibers. There are now more than 15 available dyes.
Volker Rossbach et al. developed reactive disperse dyes containing sulfonyl azide groups, which can form covalent bonds with fibers. At present, this dye has been used to dye polyester fibers, polyamide 66 and wool in supercritical fluids, with good color fastness and color yield.
The disperse-reactive dyes (containing vinylsulfone groups) synthesized by SKLiao and other laboratories have been successfully applied to the supercritical CO2 dyeing of nylon 66.
Research on Color Matching Dyeing of Mixed Dyes
For the supercritical CO2 dyeing process, if it is to be truly industrialized, it is also necessary to study the color matching dyeing in supercritical CO2. At present, there are few reports on the research of color matching dyeing of mixed dyes at home and abroad.
Tamura et al. measured the solubility of Disperse Blue 134, Disperse Yellow 16 and their mixtures in supercritical CO2. Lin Chunmian’s research team used Disperse Red 343 and Disperse Blue 366 on a self-developed supercritical CO2 dyeing device to perform one-bath (two dyes dyeing at the same time) and two-bath method (two dyes dyeing sequentially) color matching dyeing of polyester filaments. In the experiment, the dyeing temperature range is 70~130℃, and the pressure is 16~24MPa.
Dyeing thermodynamics and kinetics research
Study on the solubility of dyes in supercritical CO2
Scholars at home and abroad have measured the solubility of some disperse dyes in supercritical CO2, and investigated the factors that affect their solubility, but they are limited to the measurement and correlation of solubility data.
Draper S L et al. used an autoclave to study the dissolution status of more than 20 disperse dyes with similar structures under the conditions of 20-40 MPa and 50-100 ℃, and explored the relationship between dye structure and functional groups and solubility.
Guzel et al. measured the dissolution status of disperse yellow, disperse orange, coal dyed brown, coal dyed red and other dyes in supercritical CO 2. Xu Fei et al. measured the solubility of Disperse Red 343, Disperse Blue 366 and Disperse Orange 29 in supercritical CO2, and used Chrastil and MT two classical empirical models and their improved models for correlaThe dyeing research of polyester fiber in supercritical CO2 was the earliest and most comprehensive, and very good results have been achieved. Aramid fibers and some high-performance fibers that are not suitable for conventional dyeing by dip dyeing can also be dyed in supercritical CO2 at a temperature above 200 ℃ to achieve good level dyeing properties. Polyester fabrics can be dyed under the same conditions to obtain better color depth and uniformity than polyester, and nylon 6 and nylon 66 dyeing effects are also better.
Research on the Distribution of Dyestuffs between Fiber and Supercritical CO2
In order to achieve the optimization of process conditions and dye uptake, it is necessary to study the distribution of dyes between supercritical CO2 and fabrics.
At present, there are few studies on the distribution of dyes. Kazarian et al. determined that the distribution coefficient of Disperse Red 1 in polymethyl methacrylate film and supercritical CO2 is close to 1 × 104.
Shim et al. measured two disperse dyes (CIDis-perse Red 60 and CIDisperse Blue 60) in the range of 308.2~423.2 K and 5.0~33 MPa in 4 kinds of synthetic fibers (polystyrene, polymethacrylate). 6) Absorption and distribution coefficient on methyl ester, polyethylene terephthalate and nylon. Lin Chunmian’s research team investigated the distribution coefficient of Disperse Yellow 119 between supercritical CO2 and fabric.
Study on the Dye’s Diffusion Behavior in Fiber
Schnitzler JV et al. studied the dyeing status of two different dyes on polyester fibers under different temperature and pressure conditions, combined with the time relationship to study the diffusion coefficient of disperse dyes in the supercritical state, and believed that the mass transfer resistance is mainly caused by the dye in the fiber pores. The diffusion process is determined, that is, the speed of diffusion depends on the structure of the dye. The study also found that CO2 will adsorb and swell the fiber, which helps to reduce the diffusion resistance of the dye.
Sicardi S et al. studied the dye uptake in water dyeing, and then calculated the diffusion coefficient based on the diffusion distance, and found that the diffusion rate of Disperse Red 324 in supercritical CO2 was 2 orders of magnitude higher than that in the water phase. At the same time, it is believed that the “scroll method” can also be used to study the diffusion of dyes in the fiber under supercritical conditions.
Dai Jinjin’s research group studied the dye diffusion kinetics in the fiber, and compared it with the traditional water-medium dyeing, and obtained the diffusion coefficient of the dye on polyester under different temperature conditions.
Suitable for dyeing object research
Supercritical CO2 anhydrous dyeing technology is suitable for the anhydrous dyeing of knitted grey fabrics, hemp/cotton, pure cotton and various fiber products. At present, there are reports on the development of supercritical CO2 dyeing technology for acetate, nylon, acrylic, wool, silk, cotton and polypropylene which is difficult to dye in traditional water baths.
It has been reported in the literature that supercritical CO2 dyeing is particularly suitable for various synthetic fibers (polyester, polyamide, elastic, polyethylene, polypropylene, etc.). For synthetic fibers that cannot be dyed by traditional methods, supercritical CO2 can basically be achieved.
The dyeing research of polyester fiber in supercritical CO2 was the earliest and most comprehensive, and very good results have been achieved. Aramid fibers and some high-performance fibers that are not suitable for conventional dyeing by dip dyeing can also be dyed in supercritical CO2 at a temperature above 200 ℃ to achieve good level dyeing properties. Polyester fabrics can be dyed under the same conditions to obtain better color depth and uniformity than polyester, and nylon 6 and nylon 66 dyeing effects are also better.
Supercritical CO2 is still difficult to apply to the dyeing of natural fibers such as cotton and wool. As the share of natural fibers and their blended products in the textile market is increasing year by year, in recent years, researchers have been involved in the feasibility study of natural fiber supercritical CO2 fluid dyeing.
Since natural fibers are hydrophilic fibers, commonly used reactive dyes, direct dyes and acid dyes are almost insoluble in supercritical CO2. In the dyeing test of all natural fibers so far, because of the need for pretreatment, sometimes the fibers need to be washed in water or solvent after dyeing to remove the fibers.
The surface is pre-impregnated, so it loses the main advantages of anhydrous supercritical CO2 dyeing.
In addition, additional energy-consuming treatment and fiber drying steps are required, which are unnecessary in traditional water-based dyeing. Therefore, the research on supercritical CO2 dyeing of natural fibers at home and abroad is still not ideal. It has been reported that the supercritical CO2 dyeing of natural fibers can be achieved in three ways: pretreatment (or modification) of the fiber, adding a co-solvent to change the polarity of the liquid or modifying the dye.
Change the properties of the fiber
Natural fibers can be dyed with supercritical CO2 by impregnating a swelling agent or pretreatment with a crosslinking agent.
German DTNW Research Center Schollmeyer et al. conducted a study on dyeing natural fibers with disperse dyes under supercritical CO2. The wool fabric was pretreated with swelling and GlyezinC D before dyeing. The results showed that dyeing in supercritical CO2 is feasible, but After washing, the color fastness is relatively poor, and the color yield is not ideal.
The British Clifford A A et al. and the Italian Beltrame PL et al. soaked cotton fibers with benzoyl chloride, polyvinyl alcohol, benzamide, etc., and then used disperse dyes for supercritical CO2 dyeing experiments, and achieved good color yields. And elution fastness.
Dalian Institute of Light Industry and others used plasma method to modify the wool fabric, and then investigated the effect of supercritical CO2 dyeing. Shaanxi Normal University used different methods to modify the ramie fiber, optimize the structure of the ramie fiber, introduce functional groups and modify, denature, etc. The dyeing results showed that the alkali-benzoyl chloride modified ramie fiber has the best dyeing effect.
Change the polarity of the liquid
By adding a co-solvent, the polarity and solubility of CO2 are improved, thereby increasing the dye uptake. Gebert B et al. added methanol to supercritical CO2 to increase the polarity of the solvent, thereby improving the binding ability of disperse dyes with cotton fibers and wool Although the experiment has achieved good dyeing results, the dyed dyes are easily eluted in water. Saus et al. used water, alcohol, surfactants and other substances together with CO2 to form a co-solvent to improve the solubility of water-soluble dyes in supercritical CO 2 during natural fiber dyeing, and achieved certain results.
Modification of dyes
Modify the dye, introduce hydrophobic groups and use them to react with the fiber to form chemical bonds, improve the affinity of the dye to the fiber, and improve the dyeing effect.
Rossbach, S K Liao, etc. respectively dye wool, rabbit hair and cotton fiber with colored vinyl sulfone and acrylamide modified dyes in supercritical CO2, and the deep dyeing effect can be obtained at 100~120℃.
Development of Supercritical CO 2 Dyeing Equipment
Since Schollmeyer and others in Germany developed the first laboratory supercritical CO2 dyeing device in 1989, a large number of researches on supercritical CO2 dyeing devices have been carried out in China, which promoted the process of supercritical CO2 dyeing technology from laboratory scale to industrialization.
However, due to the high confidentiality of these technologies and little exchange of information, the current development of supercritical CO2 dyeing equipment is still in the laboratory and pilot stage, and has not yet been truly industrialized.
Josef Jasper Gmbh
In 1991, the German machine manufacturer Josef Jasper Gmbh and the Northwest Textile Research Center (DTNW) developed the first semi-industrial supercritical CO 2 dyeing machine with a dyeing tank volume of 67L, which can dye up to 4 bobbins (2 kg/piece), the equipment is equipped with a stirring device and does not have the function of circulating supercritical CO2 fluid. In recent years, a supercritical CO2 dyeing device with an equipment volume of 80L has also been introduced, and it has been put into trial use in a German factory.
In 1994, the German Amann & Sohne company used Jasper’s supercritical CO2 dyeing equipment for dyeing polyester sewing threads, but because the equipment cannot circulate the dyeing liquor and the dyeing efficiency is low, Jasper has given up on continuing development and research in this area.
Uhde High Voltage Technology Co., Ltd.
In 1995, German Uhde High Pressure Technology Co., Ltd., based on the research of DTNW, manufactured a supercritical CO2 dyeing pilot plant equipped with a 30 L autoclave, which can dye up to 2 cheeses or fabrics wound on the warp beam, and has Dye liquor circulation function. This machine was exhibited at ITMA 1995 in Milan, Italy and OTEMAS in Osaka, Japan in 1997. In 1997, North Carolina State University and Unifi Corporation began to cooperate in the development of industrial-scale supercritical CO2 dyeing equipment.
Development of Supercritical CO2 Dyeing Equipment in China
BIT supercritical CO2 fluid dyeing machine
In the late 1990s, Donghua University and our company developed China’s first self-designed supercritical CO2 fluid dyeing small prototype and the first supercritical CO2 fluid disperse dye solubility measuring device. In 2002, the country’s first one was developed. The supercritical CO2 dyeing experimental equipment with industrialization potential has laid the foundation for China to conduct systematic research on this new technology.
In 2008, the supercritical CO2 dyeing prototype (30 L) jointly developed by the school and the Shanghai Textile Energy Conservation and Environmental Protection Center was identified by an expert group organized by the Shanghai Economic Commission to reach the international advanced level.
Meichen High-tech Separation Technology Co., Ltd.
Guangzhou Meichen High-tech Separation Technology Co., Ltd. has developed the largest industrialized (150 L×2) supercritical CO2 dyeing equipment in China, which has been successfully debugged and put into operation. This set of equipment has simple operation and fast dyeing speed, which is 5-10 times that of the traditional water dyeing process. It has good level dyeing and translucent dyeing properties, and the dyeing rate is over 98%.
The Hong Kong Productivity Council, the Hong Kong Futian Group and the Hong Kong Textile and Garment Research and Development Center have jointly developed a water-free dyeing system with a capacity of 30 kg of fabric (yarn) each time. The dyeing quality of chemical fiber varieties has met the requirements.
The cost of dyeing per pound is HK$0.46, which is similar to the traditional process, and the dyeing cycle is only 15-30 minutes, zero emission, and the remaining dyes can be recycled, and various indicators are better than foreign standards. In addition, Dalian University of Technology, Bright Chemical Research and Design Institute, and Industrial Technology Research Center in Hsinchu, Taiwan have all developed their own supercritical CO2 dyeing devices.