The textile industry is a pillar industry of the national economy, and it is also an industry with serious pollution. The state attaches great importance to the energy saving and emission reduction of the textile industry. In the emission of pollutants and energy consumption in the textile industry, the Printing and dyeing industry, especially pre-printing and dyeing, accounted for an important proportion. China's energy consumption per unit of fabric is 2.4 times the world average, of which, the energy consumption of the dyeing and finishing industry accounts for 60% of the textile industry. Among the waste water discharged from the textile industry, a large amount and a serious pollution are mainly printing and dyeing wastewater, accounting for 80%.
In the energy consumption and pollutant emissions of the printing and dyeing industry, the printing and dyeing of cotton fabrics, especially the pre-treatment of cotton fabrics, account for an important proportion. Because the current cotton fabrics also use a large number of PVA slurries with poor desizing performance and are difficult to biodegrade, high-temperature and strong-base desizing processes are required, resulting in high CODcr value, high viscosity, high pH, ​​and poor biodegradability of the 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 some progress in five major integrated technologies such as environmental protection slurry, biological enzyme treatment, low-temperature bleaching, ultrasonic washing, and ultrafine coating dyeing. These technologies can achieve “low-temperature dyeing of cotton fabrics†and “end-controlâ€. The change to "source control" has truly reached the goal of energy saving and emission reduction in the printing and dyeing industry.
The new process of “low-temperature printing and dyeing of cotton fabrics†developed by Jiangnan University has the following advantages: The use of high-performance modified starch instead of PVA slurry sizing can be achieved by a-amylase desizing, which can significantly reduce the difficulty of desizing wastewater treatment and improve desizing. Quality; scouring process through the role of cutinase, alkaline pectinase, can be steamed at 50~60°C or at room temperature to achieve cold storage, to achieve the purpose of energy saving, water saving and emission reduction; bleaching link with bleach activator, at 50 Under the condition of °C, energy saving and consumption reduction can be achieved; the dyeing process can be carried out at room temperature by using ultra-fine coating and cationizing treatment of cotton fiber, so as to achieve the purpose of energy saving, and no salt is added in the dyeing process, and the utilization rate of the coating is high. Ultrasonic washing can run through the whole process of desizing, scouring, bleaching and dyeing to achieve the purpose of energy saving and water saving.
Green Paste Replaces PVA
PVA slurry sizing performance is good, widely used, there is no good alternative products. However, PVA desizing is difficult, desizing wastewater has high COD content and is difficult to biodegrade. In 1997, the China Cotton Textile Industry Association proposed the “less or no use of PVAâ€. Over the past ten years, remarkable results have been achieved. Some varieties have achieved no PVA sizing, but in some hard-to-hit varieties, PVA slurry is not completely sized, and its overall technology Development is still a long way to go. To solve the difficulty of desizing of PVA slurry and environmental pollution, there are two technical routes: First, the use of PVA enzyme, but its high cost, and PVA decomposition enzymes are not yet industrialized; Second, the development of alternative PVA slurry, which This method is more realistic now. Jiangnan University has developed multiple modified starch slurries with a combination of cationic groups and acetate esters, which has made good progress in replacing PVA slurries and improving the sizing effect, and laid the foundation for desizing of biological enzymes.
In the future, the focus should be on the enhancement of high-performance, multi-dimensional and highly modified starch, ternary and multi-component polyacrylate ester slurries, compounding and synergistic mechanisms, and the development of high-toughening, high-plasticizing slurry additives to achieve complete replacement of PVA slurries.
Bioenzyme pretreatment
The pretreatment of cotton fabric bio-enzymes has the following advantages: It saves a lot of process water, energy consumption, chemical raw materials, etc., while reducing the waste water treatment costs, so the production cost is not higher than the traditional process; significantly reduce the amount of wastewater discharge and discharge of wastewater The content of salt, AOX, dyes, chemicals, etc., the COD value of wastewater is significantly reduced; due to the avoidance of the damage of fibers caused by chemicals such as strong alkalis, oxidants, etc., the fabric has a good hand, appearance, physical and mechanical properties and dyeing properties, etc. Significantly improved.
The traditional high temperature and strong alkali dyeing and finishing of cotton fabrics have the following problems. Large water consumption: 10,000 meters of cotton fabrics need to consume 300 tons of water; high energy consumption: the process temperature of 95 ~ 100 °C, accounting for 45% of the entire process energy consumption; wastewater treatment is difficult: pH> 11, COD> 3000mg / L, BOD/COD<0.2; fiber damage; equipment is easily damaged.
Obstacles to industrial application: PVA-containing pulp fabrics hinder the popularization and application of starch enzyme desizing. Low-quality cotton (such as carded cotton) has high impurity content, especially cottonseed hulls, and has a long production time.
The future needs to be further studied: PVA alternative pulp sizing fabric enzyme desizing process; high-performance enzyme preparation technology based on multi-enzyme functional complex; cottonseed husk enzymatic removal technology; enzymatic decoction cold-reactor technology and continuous steam at medium temperature Technology; focus on industrial application of biological enzyme pretreatment technology promotion.
Bio-enzyme pre-treatment technology has significant energy-saving and emission-reducing effects: Take the traditional fiber (cotton fabric) dyeing and pre-processing as an example, biological pre-treatment and traditional chemical treatment process: wastewater discharge is reduced by 50% to 60%, COD value of wastewater is decreased 1/3 to 1/2, the pH value of the wastewater reaches the direct discharge requirement, saving 1/2 staining time, 2/3 reduction in steam consumption, 1/2 reduction in power consumption, and 1/3 to 1/2 reduction in overall cost.
Low-temperature bleaching technology
The conventional bleaching of cotton fabrics is performed at 98~100°C, which has high energy consumption during processing and large fiber damage. Low-temperature bleaching can now be reduced to 80°C. The low-temperature bleaching technology of natural fiber based on cationic bleach activators developed by Jiangnan University: The activator has good water solubility and reacts quickly with hydrogen peroxide to form a cationic activated hydrogen peroxide system, which has good directness to cellulose and can be neutral. Bleaching (pH7), there is no need for large amounts of water after bleaching, and no special treatment is required for the discharged wastewater after bleaching. In particular, the bleaching temperature can be reduced to 50° C., resulting in significant energy savings and no significant damage to cotton fibers.
Ultrasonic low temperature washing technology
Washing is an essential 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 processes require 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 pretreatment, or removing floating color and impurities after dyeing or printing. All must be washed with high-temperature water 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 water consumption for printing and dyeing, respectively.
Ultrasonic low-temperature water cleaning principle developed by Jiangnan University: The high-frequency oscillation signal emitted by the ultrasonic generator is transmitted to the medium through transducer conversion to high-frequency mechanical oscillation, which causes the water cleaning liquid to flow and generate tens of thousands of tiny bubbles. . The microbubbles present in the liquid oscillate under the action of the sound field. When the sound pressure reaches a certain value, the bubbles rapidly grow and then abruptly close. When the bubbles close, a shock wave is generated and thousands of atmospheric pressures are generated around the cavitation effect. ), to destroy insoluble dirt and disperse them in the cleaning solution, so as to achieve the purpose of cleaning the surface of the material.
Through the effective combination of ultrasonic devices and printing and dyeing equipment, developed ultrasonic dyeing and washing machine, is currently mainly used in dyeing and finishing all types of washing: such as back, boiled, washed after bleaching, washing after dyeing, printing after washing and so on.
Jiangnan University, jointly with Jiangsu Hongqi Printing and Dyeing Machinery Co., Ltd. and Wuxi South Acoustics Engineering Co., Ltd., jointly developed the first domestic ultrasonic printing and dyeing washing machine with independent intellectual property rights. It has three integrated technologies: "smart multi-frequency constant power ultrasonic device", "high-efficiency ultrasonic washing unit for printing and dyeing" and "ultrasonic washing technology".
From November 18, 2011 to December 20, 2011, Shaoxing Haishen Printing and Dyeing Garment Co., Ltd. tried the ultrasonic dyeing and washing machine and tested the ultrasonic washing effect. Compared with the conventional washing effect, the following conclusions were obtained: 21 detected The washing effect of the batch printing product found that the fastness of the ultrasonic washing of 95% of batch products and the two times of conventional washing was equivalent or even improved. Since June 2010, Changzhou Printing and Dyeing Machinery Testing Center (Changzhou Bayang Textile Co., Ltd.) has used two sets of ultrasonic washing devices for actual production. The results showed that the friction and soaping fastness of fabric after ultrasonic washing were all better than those of conventional washed fabrics, and the product quality was stable. Ultrasonic water washing eliminates steam heating and brings greater economic benefits.
Ultrafine coating dyeing technology
The 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 used as a dye-accelerating agent in the dyeing bath, the dye utilization rate is low, and the dyeing water is used. Wastewater has large emission, high chroma, and high salt content. In particular, different fibers require different dyes and dyeing processes. The process is complex and the dyeing quality is not easy to control. The ultrafine paint preparation technology with a particle size of about 200 nm developed by Jiangnan University and the ultrafine paint dyeing technology based on pre-/simultaneous modification of fiber cations. Compared with the conventional coating dyeing, due to the ultra-fine pigment, the color strength, gloss and hiding power are significantly improved. The K/S value of the fabric after dyeing with the ultrafine coating is obviously increased and the fabric color is deeper, which can significantly save the amount of coating. The use of ultra-fine paint dyeing, only need to be carried out at room temperature, energy saving, saving dye materials, water-saving, and the process is simple, the process is short (at the time of 1/3), 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 options, the optimization of the environment with light pollution, and the economy of energy saving and consumption reduction.
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