Supercritical CO2 fluid
Carbon dioxide is a colorless, odorless and non flammable, non-polar gas, with low boiling point and gas at room temperature.
If temperature and pressure exceed the critical temperature of carbon dioxide at 31. 1 C and critical pressure of 7. 39MPa, carbon dioxide is transformed into a supercritical fluid state if the temperature and pressure are higher than the critical temperature and pressure in the closed system.
Above the critical temperature, even if it is heated, he can not turn into gas. Similarly, even above the critical pressure, even pressure can not be changed into liquid and solid.
The background and the history of development
In 1988, the first patent for supercritical fluid dyeing of textiles was put forward.
In 1989, the Science Master Thesis of Ruhr University in Bochum, Germany, worked closely with Professor GMSchneider, using this new technology to carry out the first laboratory scale polyester dyeing.
Following the first successful test of the German northwest Textile Research Center (DTNW) of Germany Krefeld continued the work.
In 1991, based on the optimal laboratory scale of dyeing conditions, the German Velen Jasper company worked closely with the northwest Textile Research Center of Germany to produce the first semi industrial scale dyeing machine.
In 1994, one of the Jasper’s CO2 dyeing machines was installed in the Amann&Söhne company of Bŏnnigheim, Germany, for polyester sewing thread dyeing to test the possibility of the technology used in the textile industry.
At the beginning of 1995, the UHDEHochdrucktechnik company in Hagen, Germany, began a new discussion. The northwest Textile Research Center of Germany finally built a new CO2 dyeing test equipment.
Since 1995, the international interest in this technology has been increasing, initially in the United States and Asia, later in Europe.
Principle of the supercritical CO2 fluid dyeing technology
When dyeing, the dye with only molecular state can be dyed, with the dye fibers in the molecular state dye, the dye molecules in the micelles neutralize the grain will dissolve into the water until the dyeing end, and the dyeing speed is greatly limited at low temperature because of the low dye solubility.
Because most of the dyestuffs are in the presence of suspension, the dispersion stability of the dye is not high, it is easy to produce grain condensation, crystal transformation and grain growth, and the precipitation will occur in serious case, which causes dyed dyestuff or uneven.
The presence of dispersant improves the dispersion stability of the dye suspension, but it not only increases the production cost, but also pollutes the water quality, and some will reduce the dye balance.
Because of the low viscosity of carbon dioxide, the interaction between the dye and the dye molecules is small, and the dye diffuses faster in the supercritical carbon dioxide fluid, and the diffusion boundary layer near the surface of the fiber in this fluid is very thin, so the dye can quickly adsorb to the surface of the fiber.
Because of its strong plasticizing effect on fibers, it has fast dyeing speed, levelling and penetrating properties.
Process of the supercritical CO2 fluid dyeing technology
Supercritical CO2 staining can be dyed at 130, 24MPa and 10 minutes.
The dyeing rate is 5~10 times as high as that of the traditional process. The dyeing rate is more than 98%, and the dyeing rate is more than 98%.
The process of supercritical CO2 dyeing consists of 3 processes: isothermal compression, isothermal temperature rise and isothermal release.
Application of the supercritical CO2 fluid dyeing
Supercritical CO2 fluid dyeing technology is most suitable for polyester fiber at present.
The research in this field has been successful under laboratory conditions.
It is especially suitable for dyeing hydrophobic synthetic fibers with disperse dyes of low polarity.
Superfine polyester fiber
In addition, supercritical carbon dioxide fluid has made remarkable achievements in dyeing superfine polyester fiber.
Microfiber polyester fiber has small size and large specific surface area. Water bath dyeing often causes low color yield, poor color rendering and poor color fastness.
Supercritical carbon dioxide has great solubility in disperse dyes and gas characteristics that are easy to diffuse and move.
It is hopeful to solve the dyeing problem of superfine polyester fiber.
Supercritical carbon dioxide dyeing is also applicable to other kinds of synthetic fibers, such as polyester fiber, polypropylene fiber, polyamide fiber, polyacrylonitrile fiber and so on.
Dyeing with supercritical carbon dioxide can achieve good mechanical and fastness properties of dyed fabrics.
Polyester fibers are also less polar and easier to dye in carbon dioxide.
Surrent application of the technology
Studies have shown that the application of supercritical carbon dioxide dyeing in the dyeing of polyester and ultra-fine Polyester is the most successful.
It can obtain the same or even superior dyeing effect as conventional dyeing.
In the dyeing of synthetic fibers and natural fibers, domestic and foreign researchers have achieved initial success under laboratory conditions by modifying dyes or fibers.
However, the research on the influence of process parameters, modifier mechanism, suitable modification method and dyeing mechanism in this respect is still at a blank stage. Moreover, there are few reports on the actual industrial application of supercritical CO2 dyeing technology at home and abroad.
The technology is still in the stage of laboratory research. Therefore, the transfer of supercritical carbon dioxide from experimental equipment or semi-industrial equipment to industrial equipment still requires a lot of research work.
Advantages and disadvantages of the supercritical CO2 dyeing
- The real realization of anhydrous dyeing;
- No use of auxiliaries is needed;
- Carbon dioxide is easy to be obtained and safe. CO2 is non-toxic and easy to obtain, and CO2 can be recycled without bringing about “greenhouse effect”.
- The energy consumption is reduced and the heat consumption is only twenty percent of the conventional process.
- Dyeing effect is good, supercritical CO2 dyeing has higher dye uptake and good levelling.
- Dyes can be reused, and the residual dyes can be returned to powder and applied, so that the utilization rate of dyes is greatly improved.
- Dyeing time is short, and after dyeing, there is no need for reduction and cleaning. The production cycle is shortened and the production and operation mechanism of “quick response” can be realized.
- The use of high pressure, poor safety performance;
- High investment in equipment;
- Not suitable for natural fibers, such as cotton, wool, silk, etc.
Development prospect of the technology
Supercritical CO2 dyeing technology is a new dyeing technology with a good prospect, with CO2 as the medium, and the dyeing process does not produce pollutants, which fully embodies the concept of clean production.
The theoretical research and practice test of fiber modification and water free dyeing are strengthened, and the application of supercritical fluid in dyeing field is widely used, and the problem of environmental pollution in printing and dyeing industry is solved from the source, which is the main task of current research.