In recent years, with the annual increase in the production of grey cloths and printing cloths and the increasing demand for environmental protection, the sewage discharge standards in the textile industry have also become higher and higher. According to experts, the COD value of the pre-treatment waste water in the printing and dyeing industry accounts for about 40% to 60% of the total COD emissions in the printing and dyeing industry. The main reason for the high COD value of the pre-treatment waste water is the hard-degradable PVA paste. Therefore, solving the environmental protection of textile sizing and reducing the COD value of desizing waste liquid are the common goals pursued by the cotton textile industry and the printing and dyeing industry.
Environmental sizing is a development need
Textile sizing is an indispensable step in the entire weaving process. The quality of sizing plays a decisive role in the production efficiency of weaving. In order to ensure the smooth progress of the weaving, the yarn must be sizing to make the yarn stronger, the wear resistance improved and the hairiness reduced. However, after the warp and weft yarns are interwoven on the loom to form a fabric, the slurry attached to the yarn accomplishes its mission and becomes an obstacle to the subsequent dyeing and finishing. Because it must be desizing before dyeing and finishing, and it must be removed. According to the national standards for wastewater discharge, desizing waste liquid should be degradable and can be recycled. Therefore, the environmental protection of textile sizing is ensured, and energy saving and emission reduction of dyeing and finishing are very important.
PVA slurry cannot meet environmental requirements
Polyvinyl alcohol (PVA) is a high molecular compound with good film forming properties. It is the best film-forming property in commonly used pastes. Before the 1970s, because PVA had a very low BOD (Biochemical Oxygen Demand), its harm to the environment did not attract people's attention. Therefore, the market for PVA used in textile sizing continues to expand. However, with the continuous improvement of people's environmental protection requirements, PVA was first listed by the United States as a contaminant in 1978, because it was stable to acids, alkalis, and microorganisms in general and was not easily decomposed.
Promoting environmental protection sizing is responsible for the environment
Although PVA has excellent sizing properties, its biodegradability is poor and cannot meet environmental requirements. It is an indisputable consensus that green slurry must be used instead of PVA sizing. In the aspect of textile sizing, the Chinese cotton textile industry has also been actively promoting publicity and promotion of environmental protection sizing technology. In 2008, the Cotton Textile Association and the Printing and Dyeing Association jointly carried out promotional campaigns that did not use PVA sizing, and evaluated the desizing and waste liquid environment of grey fabrics. Through the comprehensive evaluation of the indicators such as the rate of rejection, CODcr, BOD5, biodegradability (BOD/COD), ammonia nitrogen content, and phosphorus content, the Cotton Textile Association and the Printing and Dyeing and Printing and Dyeing Association jointly recommended 10 outstanding first-class products without PVA sizing. Nine outstanding products without PVA sizing; 10 PVA-free sizing applications are recommended. This year, the Cotton Spinning Association and the Printing and Dyeing Association will continue to carry out the "Recommended PVA-free sizing products" campaign. These activities carried out in recent years have effectively promoted the process of replacing PVA with sizing. At the same time, they have also received positive responses and strong support from textile companies and slurry manufacturers and experts and scholars.
In the past few years, from the perspective of advancing the effect of replacing PVA sizing, pure PVA can be used without sizing at all in fine-grade ordinary products. The use of PVA in polyester-cotton products and high-strength, high-density and high-tightness cotton products is gradually reduced. Using less has also achieved results. Printing and dyeing companies are also actively adopting grey fabrics without PVA sizing to boost PVA-free sizing.
From the development of more than ten years, it is not easy to replace PVA with environmentally friendly pulp. Various market factors, technological factors, social responsibility and benefit factors, policies and laws and regulations affect the application of environmental protection slurry. Specific analysis, first, the yarn and fabric products improve the grade, sizing requirements and technical difficulties increase; Second, the environmental protection requirements are getting higher and higher, the slurry is the content of phosphorus or how much, easy to biodegradable and other requirements are high Third, the slurry production, sizing production, weaving production, dyeing and finishing processes, such as the cleanliness and energy-saving requirements are getting higher and higher; Fourth, the slurry development capability is weak, can be comparable with the PVA sizing performance, cost-effective, performance There are few stable and mature substitute products; Fifth, companies are different from the pursuit of social responsibility and corporate efficiency, so they are vulnerable to the decline of PVA prices, but they also give up the non-PVA sizing; Sixth, the market's impetus is insufficient, the downstream printing and dyeing companies seek no There is not much demand for PVA sizing fabrics, and no PVA sizing is still in a passive situation where there is less demand. The above factors make the process of completely replacing the PVA sizing slow, but it has also achieved significant results in the use of PVA.
Upstream and downstream should join forces to promote PVA-free sizing
Now when we study textile sizing production technology, textile sizing engineers have changed the notion that we only looked at weaving regardless of dyeing and desizing requirements. We have already made environmental protection and energy saving of dyeing and finishing processing desizing as an important choice for selecting pulp and formula. One of the factors.
Sizing must meet weavability requirements. The quality of sizing is a key factor in ensuring weavability. The purpose of sizing is to uniformly adhere the sizing to the inside and outside of the yarn, making the yarn wear-resistant, smooth, and also have a certain degree of flexibility to accommodate high speeds. Weave tension changes and strength requirements.
Preferred is a slurry that is easily degradable and less polluting to the environment. The main slurry must meet the environmental protection requirements, but also consider the environmental protection of other auxiliary slurries in order to ensure the environmental protection requirements of the overall slurry formula. To select the main slurry with BOD5/CODcr≥0.3, the biological treatment of wastewater is better, such as high-performance modified starch, degradable polyacrylic acid slurry, etc., without phosphorus or low phosphorus content of the main slurry.
The PVA-free sizing fabric provides the necessary guarantee conditions for improving the quality of the dyeing and finishing process. At present, people have higher and higher requirements on the quality, color, feel and functionality of fabric products. To achieve these requirements, the quality of the pretreatment of dyeing and finishing is the key link, and the problem of PVA desizing is not obvious. Come out, if the PVA fabric is not clean due to desizing, there will be differences in the color shade and depth of the dyeing; the lack of a desized pulp will affect the durability of the functional finishing, avoid ironing, waterproofing, and oil-repelling finishing effects.
PVA-free sizing is also a prerequisite for the application of biochemical dyeing and finishing processes. The biochemical dyeing and finishing process can not only effectively reduce the processing steps, shorten the processing time, reduce energy consumption and water consumption, but also greatly reduce the processing cost. The application of biotechnology can bring hope for the clean production of the printing and dyeing industry. However, the prerequisite for the application is that it cannot contain PVA. Therefore, PVA-free sizing has become an urgent problem to solve in order to improve the quality of dyeing and finishing processes and to apply biotechnology.
Some experts have pointed out that for the environmental pollution caused by PVA slurry, the textile industry can currently take measures to develop commercial PVA degrading enzymes and its desizing process, or to implement an oxidative desizing process instead of the current alkaline desizing process. For PVA-free measures, develop degradable environmental-friendly slurries such as high-performance deep-modified starches, develop natural polymer slurries, high-performance and easily-degradable polyacrylic slurries, and modified low-viscosity PVA; optimize slurry formulations, Studying less-component, multi-functional environmental protection formulas; using advanced spinning technology to improve yarn quality, applying advanced sizing technology, and reducing the amount of sizing; the application of PVA recycling recycling technology cannot fully abandon PVA at present. In the case of sizing, reducing PVA pollution to the environment and recycling PVA are effective measures.
The implementation of PVA-free sizing, especially the development and application of key technologies for textile sizing requires the encouragement and support of national policies. The cotton spinning industry and the printing and dyeing industry will also work together to achieve a good green pulp for each meter and reduce the COD value per ton of desizing waste liquid.