Environmentally friendly sizing promotes energy saving and emission reduction in dyeing and finishing industry

In recent years, with the increasing production of grey cloths and printing and dyeing fabrics and the increasing requirements for environmental protection, the sewage discharge standards of the textile industry are also getting higher and higher. According to experts, the COD value of the pre-treatment wastewater in the printing and dyeing industry accounts for 40% to 60% of the total COD emissions of the printing and dyeing industry, and the main cause of the high COD value of the pretreatment wastewater is the refractory 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 pursued by the cotton textile industry and the printing and dyeing industry.

Environmentally friendly sizing is a development need

Textile sizing is an indispensable key link in the whole weaving process. The advantages and disadvantages of sizing effect play a decisive role in the production efficiency of weaving. In order to ensure the smooth progress of the weaving, the yarn must be sizing, the yarn strength is enhanced, the wear resistance is improved, and the hairiness is reduced. However, after the warp and weft yarns are interwoven on the loom to form a fabric, the slurry adhering to the yarn completes the mission, and the dyeing and finishing of the subsequent lane becomes an obstacle. Because it must be desizing before dyeing and finishing, and must be removed. According to the national standards for wastewater discharge, the desizing waste liquid should be degradable and recyclable, thus ensuring the environmental protection of textile sizing, and it is very important for energy saving and emission reduction of dyeing and finishing.

PVA slurry can not meet environmental requirements

Polyvinyl alcohol (PVA) is a polymer compound excellent in film formability, and it is one of the best film forming properties in conventional pastes. Before the 1970s, because PVA had a very low BOD (biochemical oxygen demand), its environmental hazard did not attract people's attention, so the market for PVA for textile sizing is expanding. However, with the continuous improvement of environmental protection requirements, 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 easily decomposed.

Promoting environmentally friendly sizing is responsible for the environment

Although PVA has excellent sizing performance, its biodegradability is poor, it can not meet environmental protection requirements, and it is an indisputable consensus to replace PVA sizing with environmentally friendly slurry. China's cotton textile industry has been actively promoting and promoting environmental sizing technology in textile sizing. In 2008, the Cotton Textile Association and the Printing and Dyeing Association jointly launched a publicity and promotion campaign without PVA sizing, and evaluated the desizing waste liquid environment of the grey fabric. Through the comprehensive evaluation of the net rate, CODcr, BOD5, biodegradability (BOD/COD), ammonia nitrogen content, phosphorus content and other indicators, the Cotton Textile Association and the Printing and Dyeing and Printing Association jointly recommended 10 first-class products without PVA sizing. 9 excellent products without PVA sizing; 10 PVA-free sizing applications were recommended. This year, the Cotton Textile Association and the Printing and Dyeing Association will continue to carry out the activities of “recommended PVA-free sizing products”. These activities carried out in recent years have effectively promoted the process of replacing PVA sizing, and also received positive response and strong support from the majority of textile enterprises and slurry manufacturers and experts and scholars.

In the past few years, from the effect of promoting the replacement of PVA sizing, PVA sizing can be completely avoided in pure cotton and fine-branched ordinary products. For polyester-cotton products and pure cotton high-density and high-density products, the amount of PVA is gradually reduced. Less use has also achieved results. Printing and dyeing companies are also actively using grey cloth without PVA sizing to boost the sizing without PVA.

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 and legal and regulatory factors are affecting the process of applying environmentally friendly slurry. Specific analysis, first, the product grade of yarn and fabric is improved, the requirements of sizing and technical difficulty are increased; second, the environmental protection requirements are getting higher and higher, and whether the slurry contains phosphorus or content, whether it is easy to biodegrade, etc. Third, the process of slurry production, sizing production, weaving production, dyeing and finishing production is more and more clean and energy-saving; fourth is the ability of slurry research and development is weak, comparable to PVA sizing performance, excellent cost performance, performance There are fewer stable and mature alternatives; the fifth is that enterprises have different pursuits of social responsibility and corporate benefits, so they are vulnerable to the fall in PVA prices, and they give up no PVA sizing; sixth, the market's driving force is insufficient, and 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 with less demand. The above factors make the process of completely replacing PVA sizing slow, but it has achieved obvious results in the less use of PVA.

Upstream and downstream should join forces to promote PVA-free sizing

Nowadays, when studying the textile sizing production process, the textile sizing engineers have changed the concept that only weaving, regardless of dyeing and finishing requirements, has been used. The environmental protection and energy saving of dyeing and finishing desizing have been regarded as important for selecting the slurry and formula. One of the factors.

Sizing should meet the weavability requirements. The quality of sizing is the key factor to ensure the weavability. The purpose of sizing is to uniformly adhere the slurry to the inside and outside of the yarn, so that the yarn is wear-resistant and smooth, and it must have a certain flexibility to adapt to high speed. Tension changes and strength requirements for weaving.

A slurry which is easily degraded and has little environmental pollution is preferred. The main slurry must meet environmental protection requirements, and the environmental protection of other auxiliary slurry must be considered to ensure the environmental requirements of the overall slurry formulation. To select BOS5/CODcr≥0.3 bulk slurry, the wastewater has better biological treatment; such as high-performance modified starch, degradable polyacrylic acid slurry, etc., and no phosphorus or low phosphorus content bulk slurry.

The grey cloth without PVA sizing provides the necessary guarantee conditions for improving the quality of dyeing and finishing. At present, people are increasingly demanding the quality, color, feel and functionality of fabric products. To achieve these requirements, the pre-treatment quality of dyeing and finishing is a key link, so the problem of PVA desizing is also highlighted. Come out, if the gray fabric of PVA is not cleaned by desizing, there will be dim shade and depth difference; the unslurrying will affect the durability of functional finishing, and it is free from ironing, waterproof and oil proofing.

PVA-free sizing is also a prerequisite for the use 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 the energy consumption and water consumption, but also greatly reduce the processing cost. The application of biotechnology can bring hope to the clean production of the printing and dyeing industry. However, the precondition for the application is that it cannot contain PVA. Therefore, the sizing without PVA has become an urgent problem to improve the quality of dyeing and finishing and to apply biotechnology.

Some experts have suggested that the environmental pollution problem brought by PVA slurry, the textile industry can currently take countermeasures to develop commercial PVA degrading enzyme and its desizing process, or promote the oxidation desizing process to replace the current alkali desizing process. The measures for not using PVA are: developing degradable environmentally friendly slurry such as high-performance deep-modified starch, developing natural polymer slurry, high-performance and easily degradable polyacrylic acid slurry, low-viscosity modified PVA; optimizing slurry formulation, Research on environmentally-friendly formulas with few components and versatility; use advanced spinning technology to improve yarn quality, apply advanced sizing technology, reduce sizing amount; PVA recycling and recycling technology application, can not completely abandon PVA at present In the case of sizing, reducing the pollution of the PVA to the environment, recycling PVA is an effective measure.

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 environmentally friendly pulp and reduce the COD value per ton of desizing waste.