The textile industry is the pillar industry of the national economy, and it is also an industry with serious pollution. The state attaches great importance to energy conservation and emission reduction in the textile industry. In the textile industry's pollutant discharge and energy consumption, the printing and dyeing industry, especially pre-treatment of printing and dyeing, also accounts for an important proportion. China's unit fabric energy consumption is 2.4 times the world average, of which the dyeing and finishing industry accounts for 60% of the textile industry. Among the wastewater discharged from the textile industry, the large amount and serious pollution are mainly printing and dyeing wastewater, accounting for 80%.
In the printing and dyeing industry's energy consumption and pollutant discharge, the printing and dyeing of cotton fabrics, especially the pretreatment of cotton fabrics, also account for an important proportion. Because cotton fabrics are still widely used in PVA slurry sizing with poor desizing performance and difficult to biodegrade, high temperature and strong alkali desizing process are required, resulting in high CODcr value, high viscosity, high pH value and poor biodegradability of desizing wastewater. Energy consumption, water consumption and wastewater discharge are also large. In the scouring, bleaching and dyeing of cotton fabrics, high energy consumption is also produced.
At present, Jiangnan University has made certain progress in the five integrated technologies of environmentally friendly slurry, biological enzyme treatment, low temperature bleaching, ultrasonic water washing, and ultra-fine coating dyeing. These technologies can realize "low temperature printing and dyeing of cotton fabrics" and make "end treatment". The transition to “source control†has truly achieved the goal of energy saving and emission reduction in the printing and dyeing industry.
The new treatment process of “Cotton Fabric Low Temperature Printing and Dyeing†developed by Jiangnan University presents the following advantages: the use of high-performance modified starch instead of PVA slurry sizing can use a-amylase desizing, which will significantly reduce the difficulty of desizing wastewater treatment and improve desizing Quality; scouring process through the action of cutinase, alkaline pectinase, can be steamed at 50 ~ 60 ° C or at room temperature, to achieve energy, water and emissions reduction; bleaching agent with bleach activator, at 50 At °C, it can achieve energy saving and consumption reduction; the dyeing process can be carried out at room temperature by using ultra-fine coating and cationization treatment of cotton fiber, so as to save energy, and the dyeing process does not need to add salt, and the utilization rate of the coating is high. Ultrasonic washing can penetrate the whole process of desizing, scouring, bleaching and dyeing to achieve energy saving and water saving.
Environmentally friendly slurry replaces PVA
PVA slurry has good sizing performance and wide application, and there is no good substitute product at present. However, PVA is difficult to desizing, and the desiccant wastewater has high COD content and is difficult to biodegrade. In 1997, China Cotton Textile Industry Association proposed “less use and no PVAâ€. It has achieved remarkable results in more than ten years. Some varieties have achieved no PVA sizing, but in some high-difficult varieties, PVA slurry sizing is not needed at all, its overall technology Development still has a long way to go.
To solve the problem of PVA slurry desizing and environmental pollution, there are two technical routes: First, the use of PVA enzyme, but its cost is high, and PVA decomposing enzyme is not yet industrialized; the second is to develop a slurry to replace PVA, which The method is now more realistic. Jiangnan University has developed a multi-denatured starch slurry with a combination of cationic and acetate groups. It has made good progress in replacing PVA slurry and improving sizing effect, and laid a foundation for bio-enzyme desizing.
In the future, it is important to strengthen the development of high-performance multi-depth modified starch, ternary and multi-polyacrylate slurry, combined slurry synergistic mechanism, high toughening and high plasticizing slurry additives to achieve complete replacement of PVA slurry.
Biological enzyme pretreatment technology
Cotton fabric bio-enzyme pretreatment has the following advantages: saving a large amount of process water, energy consumption, chemical raw materials, etc., while reducing the cost of wastewater treatment, so the comprehensive production cost is not higher than the traditional process; greatly reducing waste water discharge and discharging waste water The content of salt, AOX, dyes, chemical agents, etc., the COD value of wastewater is significantly reduced; the fabric has good hand, appearance, physical and mechanical properties and dyeing properties, etc. due to avoiding damage to the fibers by chemical agents such as strong alkalis and oxidants. Significantly improved.
The traditional high temperature and strong alkali dyeing and finishing process of cotton fabric has the following problems. Water consumption: 10,000 meters of cotton fabric treatment consumes 300 tons of water; high energy consumption: processing temperature 95~100 °C, accounting for 45% of the total process energy; wastewater treatment is difficult: pH>11, COD>3000mg/L, BOD/COD<0.2; fiber damage; equipment is easily damaged.
Industrial application obstacles: PVA-containing pulp fabrics hinder the application of amylase desizing, and low-quality cotton (such as carded cotton) has too high impurity content, especially cottonseed hulls, which have a long production time.
In the future, further research is needed: PVA instead of slurry sizing fabric enzyme desizing process; high-efficiency complex enzyme preparation technology based on multi-enzyme function compounding; cottonseed shell enzymatic removal technology; enzymatic de-cooking cold reactor technology and medium-temperature continuous steaming Technology; promotion of bio-enzyme pretreatment technology focusing on industrial applications.
The bio-enzyme pretreatment technology has remarkable effects on energy saving and emission reduction: taking traditional fiber (cotton fabric) dyeing and finishing as an example, the biological pretreatment is compared with the traditional chemical treatment process: the wastewater discharge is reduced by 50% to 60%, and the wastewater COD value is decreased. 1/3~1/2, the pH value of wastewater reaches the direct discharge requirement, saving 1/2 of dyeing time, 2/3 of steam consumption, 1/2 of power consumption, and 1/3~1 /2 of comprehensive cost.
Low temperature bleaching technology
Conventional bleaching of cotton fabrics is carried out at 98-100 ° C, with high energy consumption during processing and high fiber damage. Low temperature bleaching has now been carried out down to 80 °C.
Low-temperature bleaching technology of natural fiber based on cationic bleach activator developed by Jiangnan University: the activator has good water solubility and can react rapidly with hydrogen peroxide to form a cationic activated hydrogen peroxide system. It has good directness to cellulose and can be neutral. Bleaching (pH7), no need to wash a lot of water after rinsing, no special treatment is required after effluent discharge, especially the bleaching temperature can be reduced to 50 °C, which is energy-saving and has no obvious damage to cotton fiber.
Ultrasonic low temperature water washing technology
Washing is a necessary process for printing and dyeing. Water-saving and water-saving washing equipment has always been the focus of research in this industry. Textile printing and dyeing processing requires a large amount of heat (steam) and water, of which the washing process accounts for a considerable proportion, whether it is desizing, scouring, bleaching, mercerizing in the pre-treatment, or removing the floating color and impurities after dyeing or printing. All must be washed with high temperature to ensure the quality of the final product. The water consumption and steam energy consumption in the water washing process account for 60% and 40% of the total printing and dyeing water and energy consumption, respectively.
Ultrasonic low-temperature water cleaning principle developed by Jiangnan University: The high-frequency oscillation signal (sound wave with frequency >20000 Hz) emitted by the ultrasonic generator is transmitted to the medium by the transducer to be converted into high-frequency mechanical oscillation, so that the water cleaning liquid flows and Produce tens of thousands of tiny bubbles. The tiny bubbles existing in the liquid vibrate under the action of the sound field. When the sound pressure reaches a certain value, the bubbles grow rapidly, then suddenly close, and the shock wave is generated when the bubble is closed, and thousands of atmospheric pressures are generated around it (cavitation effect) ), destroying insoluble dirt and dispersing them in the cleaning solution to achieve the purpose of cleaning the surface of the material.
Ultrasonic dyeing and finishing washing machine developed by effectively combining ultrasonic equipment and printing and dyeing equipment is mainly used in various types of washing in dyeing and finishing: such as washing, boiling, washing after washing, washing after dyeing, washing after printing, and the like.
Jiangnan University, together with Jiangsu Hongqi Printing and Dyeing Machinery Co., Ltd. and Wuxi Southern Acoustics Engineering Co., Ltd. jointly developed the first ultrasonic printing and dyeing washing machine with independent intellectual property rights in China. It has three integrated technologies: “Intelligent multi-frequency constant power ultrasonic deviceâ€, “High-efficiency ultrasonic washing unit for printing and dyeing†and “Ultrasonic water washing processâ€.
From November 18th to December 20th, 2011, Shaoxing Haishen Printing and Dyeing Garment Co., Ltd. tried the ultrasonic printing and dyeing washing machine and tested the washing effect of ultrasonic washing. Compared with the conventional washing effect, the following conclusions were reached: 21 detected The washing effect of the batch printing products found that the ultrasonic washing of 95% of the batch products was comparable to or even improved by the conventional washing twice. Since June 2010, Changzhou Printing and Dyeing Machinery Testing Center (Changzhou Bayang Textile Co., Ltd.) has two sets of ultrasonic water washing devices for actual production. The results showed that the friction and soaping fastness of the fabric after ultrasonic washing were better than the conventional washing cloth, and the product quality was stable. Ultrasonic water washing eliminates steam heating and brings greater economic benefits.
Superfine coating dyeing technology
Conventional dyeing of textiles often needs to be carried out at a temperature of 50-100 ° C or even more than 100 ° C, and the dyeing bath ratio is large. A large amount of salt is needed as a dye-accelerating agent in the dye bath, the dye utilization rate is low, and the dyeing water is used. The wastewater discharge is large, the chroma is high, and the salt content is high. In particular, different fibers require different dyes and dyeing processes, the process is complicated, and the dyeing quality is difficult to control.
The ultra-fine coating preparation technology developed by Jiangnan University with a particle size of about 200 nm and the ultra-fine coating dyeing technology based on the pre/simultaneous modification of fiber cations. Compared with the conventional paint dyeing, the color strength, gloss and hiding power of the ultra-fine paint are significantly increased due to the ultra-fine pigmentation, and the K/S value of the fabric after the dyeing of the ultra-fine paint is significantly increased, and the fabric is darker in color, which can significantly save the coating amount. It is dyed with ultra-fine paint and only needs to be carried out at room temperature, saving energy, saving dyeing materials and water saving, and the process is simple, the process is short (1/3 of the time), and the dyeing quality is good. Compared with dyeing, ultra-fine coating dyeing has four major advantages: the universality of the fiber to be processed, the wide variety of chromatographic choices, the optimization of environmental pollution, and the economics of energy saving.
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