Environmental Friendly Sizing, Dyeing And Finishing, Energy Saving And Emission Reduction

In recent years, with the increasing production of grey cloth, printing and dyeing cloth and the increasing requirements for environmental protection, the wastewater discharge standard of the textile industry has become higher and higher.

According to experts, the COD value of pre-treatment wastewater in the printing and dyeing industry accounts for 40%~60% of the total COD discharge in the printing and dyeing industry, and the high COD value of pre-treatment wastewater is mainly caused by hard to degrade PVA and other slurry. Therefore, solving the environmental protection of textile sizing and reducing the COD value of desizing waste liquid are the common goals of cotton textile industry and printing and dyeing industry.

　　 Environmentally friendly sizing is needed for development

Textile sizing is an indispensable key link in the whole weaving process, and the sizing effect plays a decisive role in the production efficiency of weaving. In order to ensure the smooth progress of weaving, it is necessary to size the yarn to enhance its strength, improve its abrasion resistance and reduce its hairiness. However, after the warp and weft yarns are interwoven on the loom to form a fabric, the size attached to the yarn will complete its mission, and the dyeing and finishing of the subsequent yarn will become an obstacle. Because desizing must be done before dyeing and finishing, and it must be removed completely. According to the national wastewater discharge standard, the desizing waste liquid should be biodegradable and recyclable, so it is very important to ensure the environmental protection of textile sizing and energy saving and emission reduction of dyeing and finishing.

　　 PVA slurry cannot meet environmental requirements

Polyvinyl alcohol (PVA) is a kind of high molecular compound with excellent film-forming property. Before the 1970s, because PVA had very low BOD (biochemical oxygen demand), its harm to the environment did not attract people's attention, so the market of PVA for textile sizing continued to expand. However, with the continuous improvement of people's requirements for environmental protection, PVA was first listed as a pollutant in the United States in 1978, because it is stable to acids, alkalis and general microorganisms and is not easy to be decomposed.

　　 Promote environmental protection sizing and be responsible for the environment

Although PVA has excellent sizing performance, its biodegradability is poor and cannot meet the environmental requirements. It is an indisputable consensus that environmental friendly sizing must be used instead of PVA sizing. In terms of textile sizing, China's cotton textile industry has also been actively promoting environmentally friendly sizing technology.

In 2008, the Cotton Textile Association and the Printing and Dyeing Association jointly carried out the publicity and promotion activities of not using PVA sizing, and evaluated the environment of grey fabric desizing waste liquid. Through the rebate rate CODcr、BOD5、 Comprehensive evaluation of biodegradability (BOD/COD), ammonia nitrogen content, phosphorus content and other indicators, the Cotton Textile Association and the Printing, Dyeing and Dyeing Association jointly recommended 10 excellent first class PVA free sizing products, and recommended 9 excellent PVA free sizing products; Ten PVA free sizing applications are recommended. This year, the Cotton Textile Association and the Printing and Dyeing Association will continue to carry out the activity of "recommending PVA free sizing products". These activities carried out in recent years have effectively promoted the process of replacing PVA sizing, and at the same time, they have received positive response and strong support from textile enterprises, size production enterprises, experts and scholars.

In view of the effect of promoting the substitution of PVA sizing over the past few years, PVA sizing can be completely avoided on ordinary cotton products with medium and fine counts. For polyester cotton products and pure cotton products with high counts, high density and high tightness, the amount of PVA is gradually reduced, and the effect of using less PVA has also been achieved. Printing and dyeing enterprises are also actively using PVA free grey fabrics to promote PVA free sizing.

From the development of more than ten years, it is not easy to replace PVA with environmentally friendly slurry. Various market factors, technical factors, social responsibility and benefit factors, policies, laws and regulations, etc. are influencing the process of application of environmentally friendly slurry.

Specifically, first, the product grade of yarn and fabric is improved, and the sizing requirements and technical difficulties are increased; Second, the environmental protection requirements are getting higher and higher, and the requirements on whether the slurry contains phosphorus or how much, and whether it is easy to be biodegradable are very high; Third, the requirements for cleaner and energy-saving processes in size production, sizing production, weaving production, dyeing and finishing production are becoming higher and higher; Fourth, the R&D capability of sizing agent is weak, and there are few substitutes with stable and mature performance that can be comparable to PVA sizing performance, high cost performance ratio; Fifthly, enterprises pursue different social responsibilities and corporate benefits, so they are vulnerable to the impact of the decline in PVA prices and give up PVA free sizing; Sixth, the driving force of the market is insufficient. There is not much demand for PVA free sizing grey cloth from downstream printing and dyeing enterprises, and PVA free sizing is still in a passive state of less demand. The above factors slow down the sizing process of completely replacing PVA, but obvious results have been achieved in reducing the use of PVA. {page_break}

　　 Upstream and downstream should work together to promote PVA free sizing

Now, when studying the production process of textile sizing, the engineers of textile sizing have changed their previous concept of only looking at weaving and ignoring the requirements of dyeing, finishing and desizing, and have taken the environmental protection and energy saving of dyeing, finishing and desizing as one of the important factors in selecting sizing materials and formulas.

Sizing shall meet the requirements of weaveability. The quality of sizing is the key factor to ensure the weaveability. The purpose of sizing is to ensure that the size is evenly adhered to the inside and outside of the yarn, so that the yarn is wear-resistant, smooth, and flexible to adapt to the tension changes and strength requirements of high-speed weaving.

The slurry that is easy to degrade and has little environmental pollution is preferred. The main slurry must meet the environmental protection requirements, and the environmental protection of other auxiliary slurry must be considered to ensure the environmental protection requirements of the overall slurry formula. The main slurry with BOD5/CODcr ≥ 0.3 should be selected, and the biological treatment of wastewater is better; Such as high-performance modified starch, degradable polyacrylic size, etc., and main size without or with low phosphorus content.

The grey cloth without PVA sizing provides necessary guarantee conditions for improving the quality of dyeing and finishing. At present, people have higher and higher requirements for the quality, color, feel and functionality of fabric products. In order to meet these requirements, the pretreatment quality of dyeing and finishing is the key link, so the problem of PVA desizing is also highlighted. If PVA grey fabric is desized, it will appear dim color and depth differences; Unsmooth desizing will affect the durability of functional finishing, and the finishing effect of ironproof, waterproof and oil proof.

PVA free sizing is also a prerequisite for the use of biochemical dyeing and finishing process. Biochemical dyeing and finishing process can not only effectively reduce processing procedures, shorten processing time, reduce energy consumption and water consumption, but also greatly reduce processing costs. The application of biotechnology can bring hope for the printing and dyeing industry to achieve cleaner production. However, the precondition of application is that PVA cannot be included. Therefore, PVA free sizing has become an urgent problem to be solved for improving the quality of dyeing and finishing and applying biotechnology.

Some experts have proposed that the textile industry can take measures to solve the environmental pollution problem caused by PVA size by developing commercial PVA degrading enzymes and desizing process, or promoting oxidation desizing process to replace the existing alkali desizing process.

The measures for not using PVA are: developing degradable environmentally friendly size such as high-performance deeply modified starch, developing natural polymer size, high-performance and easily degradable polyacrylic size, and low viscosity modified PVA; Optimize the slurry formula and study the environment-friendly formula with few components and multiple functions; Use advanced spinning technology to improve yarn quality, and use advanced sizing technology to reduce sizing amount; The application of PVA recycling technology can not completely abandon PVA sizing at present, reduce the environmental pollution of PVA, and recycling PVA is an effective measure.

The promotion of PVA free sizing, especially the R&D and promotion of key technologies for textile sizing, needs the encouragement and support of national policies. The cotton textile industry and the printing and dyeing industry will also work together to achieve environmentally friendly sizing of every meter of cloth and reduce the COD value of every ton of desizing waste liquid.