1) Raw fabric preparation: Raw fabric preparation includes raw fabric inspection, flipping (batch, box, printing), and sewing. The purpose of raw fabric inspection is to check the quality of the grey fabric and promptly solve any problems found. The inspection content includes two items: physical indicators and appearance defects. The former includes the length, amplitude, weight, density and strength of warp and weft yarns of the original fabric, while the latter includes defects such as spinning, weaving, various stains and damages. Usually, around 10% of the total amount is sampled. After the inspection of the raw fabric, it must be divided into batches and boxes, and printed on the fabric head, indicating the variety, processing technology, batch number, box number, release date, and flipper code for easy management. To ensure continuous batch processing, the original fabric must be sewn together.

2) Singing: The purpose of singeing is to burn off the fuzz on the fabric surface, making it smooth and beautiful, and preventing uneven dyeing and printing defects caused by the presence of the fuzz during dyeing and printing. Fabric singeing refers to the process of quickly passing a fabric through a high-temperature flame or rubbing it against a hot metal surface. At this time, the fuzz on the fabric surface quickly heats up and burns, while the fabric body is relatively tight and heats up slowly. Before reaching the ignition point, it has already left the flame or hot metal surface, thus achieving the goal of burning off the fuzz without operating the fabric.

3) Desizing: Textile factories often size warp yarns to improve strength and wear resistance for smooth weaving. The size on the grey fabric not only affects the water absorption performance of the fabric, but also affects the quality of the dyeing and finishing products, and increases the consumption of dyeing and chemical drugs. Therefore, the size should be removed before cooking, which is called desizing. The sizing material on cotton fabrics can be removed from the fabric by methods such as alkali desizing, enzyme desizing, acid desizing, and oxidant desizing. Alkali desizing causes the size to swell and reduce its adhesion to fibers, which are then washed and removed from the fabric. Enzymes, acids, and oxidants degrade starch, increase its solubility in water, and remove it after washing. Due to the significant damage caused by acids and oxidants to cotton fibers, they are rarely used alone and are often used in combination with enzyme desizing and alkali desizing

4) Cooking: When cotton fibers grow, they are accompanied by natural impurities (pectin, waxy substances, nitrogen-containing substances, etc.). After desizing the cotton fabric, most of the size and some natural impurities have been removed, but there is still a small amount of size and most of the natural impurities remaining on the fabric. The presence of these impurities makes the surface of cotton fabric yellow and has poor permeability. At the same time, the presence of cottonseed husks greatly affects the appearance quality of cotton cloth. Therefore, it is necessary to boil the fabric in high-temperature concentrated alkaline solution for a long time to remove residual impurities. Cooking is the use of caustic soda and other cooking aids to undergo chemical degradation reactions or emulsification, swelling, etc. with pectin, waxy substances, nitrogen-containing substances, and cottonseed shells. After washing with water, impurities are removed from the fabric

5) Bleaching: After scouring, cotton fabric may not have a clean and white appearance due to the presence of natural pigments on the fibers, which can affect the brightness of the color when used for dyeing or printing. The purpose of bleaching is to remove pigments and impart necessary and stable whiteness to the fabric, while the fibers themselves are not significantly damaged. The commonly used bleaching methods for cotton fabrics include sodium nitrite method, hydrogen peroxide method, and sodium chlorite method. The pH value of the sodium hypochlorite bleaching solution is about 10, and it is carried out at room temperature. The equipment is simple, the operation is convenient, and the cost is low. However, it causes significant damage to the strength of the fabric and has a low whiteness. The pH value of the hydrogen peroxide bleaching solution is 10. When bleached at high temperatures, the bleached fabric has a high and stable whiteness, good hand feel, and can also remove pulp and natural impurities. The disadvantage is high equipment requirements and high costs. Under appropriate conditions, combined with caustic soda, desizing, scouring, and bleaching can be completed in one go. The pH value of sodium chlorite bleaching solution is between 4 and 4.5, which is carried out at high temperatures. It has the advantages of good whiteness and minimal fiber damage. However, during bleaching, toxic gases are easily generated, polluting the environment, and corroding equipment. The equipment needs to be made of special metal materials, so its application is limited to some extent. After bleaching with sodium hypochlorite and sodium chlorite, dechlorination is necessary to prevent damage to the fabric due to the presence of residual chlorine during the process

6) Dyeing and dyeing is a relatively complex process, and the dyeing process for fabrics of different qualities varies. Some cotton, polyester cotton, hemp cotton, woolen fabrics, silk products, chemical fiber products, blended products, and so on can be dyed with pad or roll dyeing, while others must be dyed with high temperature and pressure. Some only need to be dyed once, while others need to be colored multiple times. There are different processes for using different dyes, just taking basic cotton fabrics as an example: although dyeing can be done through a rolling mill, it is also the most difficult process because the color control of dyeing is not only known, but also involves many unknown things, such as the stability of dyes at different temperatures, steam control, rolling pressure control, etc., which are all very delicate activities. The dyed long car is divided into two parts, front car dyeing and rear car fixing The dyeing method varies depending on the type of dye used. Dyes generally include reactive dyes, silene, vulcanization, and coatings. Each of them has its own advantages and disadvantages, and generally depends on the required color. They cannot be replaced with each other. Among them, silene has the best color fastness, but it is expensive and not suitable for dyeing deep colors. Light colors are not bright enough. In addition to increasing the cost of dyeing deep colors, it is also difficult to control dark colors compared to reactive dyes, It is prone to phenomena such as fabric surface flowers. The active color fastness is worse than that of Shilin, but dyeing light colors is more beautiful, and dark colors are easier to control, resulting in lower costs. Sulfurization is the worst, and the color fastness is not very good, and AZO prohibition is not yet up to standard. However, there is a liquid vulcanization (also known as water vulcanization) that prohibits AZO, which can meet the standard, but the price is close to Shilin, and dyeing is not easy to control and cannot be popularized. Only a few people pursue its fading effect and use it. Coatings are not comparable, It has severe color fading and is the best choice for clothing to pursue a fading effect after washing. It can be flexibly applied with Shilin or Active Primer to achieve different washing effects (usually Shilin or Active Primer, coating cover color, can solve the problem of white spots in single dye coatings, and the cost increases accordingly) The dyeing front wheels of active, shilin, and vulcanized dyes are basically the same, but the difference is that one set of infrared pre baked, two sets or not, and the rear wheels are completely different. Active dyes use salt and soda ash for fixation, shilin uses hydrogen peroxide for reduction fixation (hence shilin is also known as reducing dyes), and vulcanized dyes require high-temperature cooking for fixation, and the water temperature must be above 95 degrees Celsius After dyeing the coating, it is determined whether to bake and fix the color according to the fading requirements of the color fastness. The baking temperature is around 195-210 degrees Celsius. Dyeing cannot be 100% good, and it is inevitable to trim and peel the color. Minor adjustments such as shallow coating and deep washing with soda ash.

7) Mercerization: Mercerization refers to the process of treating cotton fabrics with a concentrated caustic soda solution at room temperature or low temperature, under tension in both warp and weft directions, to improve fabric properties. After mercerization, cotton fabric undergoes natural twisting and disappearance due to fiber swelling, resulting in an elliptical cross-section that exhibits a more regular reversal of light, thus enhancing its luster. The increase of intangible fixed area of fibers increases the dye uptake rate during dyeing. The increase in orientation increases the strength of the fabric while also having a shaping effect. After mercerizing, it is necessary to use methods such as flushing and suction to remove alkali, steam box to remove alkali, or flat washing to remove alkali thoroughly until the fabric is neutral. Dyeing and dyeing is the process of combining dyes with fibers physically or chemically, or using chemical methods to generate pigments on the fibers, to give the entire textile a certain color. Dyeing is carried out under certain conditions such as temperature, time, pH value, and required dyeing aids. The dyed product should have uniform color and good dyeing fastness. The dyeing methods of fabrics mainly include dip dyeing and pad dyeing. Dip dyeing is a method of immersing a fabric in a dye solution and gradually allowing the dye to be applied to the fabric. It is suitable for small batch and multi variety dyeing. Rope dyeing and roll dyeing belong to this category. Pad dyeing is a dyeing method that first immerses the fabric in the dye solution, then passes the fabric through a roller to evenly roll the dye solution into the interior of the fabric, and then undergoes steam or hot melt treatment. It is suitable for dyeing large batches of fabrics

8) Post finishing is a textile technology project that endows clothing fabrics with wearability and aesthetics. The following are the common types of textile finishing at present: the main equipment includes: singeing machine, desizing machine, mercerizing machine, liquid ammonia machine, shaping machine, pre-shrinking machine, calendering machine, washing machine, sanding machine, scratching machine, coating machine, etc.

Main functions: 1. Polishing 2. Calendering or embossing 3. Embossing or embossing 4. Flocking and transfer hot stamping. 5. Coating (a, dry coating; b, wet coating; c, transfer coating, also known as centrifugal paper coating) 6. PVC rolling and embossing treatment 7. Composite (a, TPU film coating PTFE film coating; b, fabric composite) 8. Washing, grinding, inkjet, and color fixing treatment. 9. Waterproof, windproof, and fluffy resistant treatment. 10. Anti static treatment 11, flame retardant treatment 12, UV protection treatment 13, brushed, ground, anti pilling treatment 14, wrinkling and foaming treatment 15, stretching and shaping, soft pre shrinking, and other textile finishing processes play an extremely important role in developing fabrics with special functions, endowing fabrics with special functions, and improving wearing effects.

With the progress of technology, new processes and materials for post processing will continue to emerge. Dyed fabric - Color fastness is the most important indicator of dyed fabric.

The ability of printed and dyed textiles to withstand external influences and maintain their original color, also known as color fastness. After dyeing and printing, textile fabrics sometimes undergo other processes, such as shrinking of wool fabrics and heat setting of synthetic fiber textiles; During consumption, it is necessary to come into contact with the atmosphere, sweat stains, and withstand external effects such as washing, friction, and ironing. These can cause varying degrees of fading and discoloration of printed and dyed textiles.

The main processes that affect the dyeing fastness of printed and dyed textile fabrics are shrinkage, carbonization, chlorine bleaching, sublimation, etc. The dyeing fastness of dyes or pigments on textile fabrics is related to their chemical structure, concentration and state on the fibers, and the properties of the fibers. The testing methods for various dyeing fastness are formulated by simulating various consumption or process conditions.

The International Organization for Standardization (ISO) has developed international standards and testing and evaluation methods for various color fastness based on the standards established by the Dyeing and Chemical Societies (SDC and AATCC) in the United Kingdom and the United States, as well as the European Association for Color Fastness (ECE) and other organizations (see Textile Standards).

China also has national standards for major color fastness, such as:

① Light fastness, also known as light fastness, is divided into 8 levels, with level 1 being the least light resistant and level 8 being the best. At all levels, there is a reference sample of blue wool fabric dyed with specified dyes at the specified concentration, called the blue standard sample. During the experiment, the sample and 8 blue standard samples are exposed to sunlight under specified conditions for a considerable period of time, and then compared with the blue standard sample to evaluate the level of light fastness of the sample. Due to the long duration of the sun exposure test and the limitations of climate change, artificial light sources are generally used, with xenon lamps and carbon arc lamps commonly used. The spectral energy distribution of xenon lamps is relatively close to that of sunlight.

② Color fastness to washing can be divided into two types: fading and staining. The specified gray standard sample is used to evaluate it in five levels, and the color difference of each level is divided into geometric levels. During the experiment, the sample and white cloth are overlapped and sewn together, washed under specified conditions, and then dried. Separate the sample from the white cloth, and evaluate the fading fastness using a gray fading sample card based on the color difference before and after washing the sample. Level 1 has the maximum color difference, and level 5 has no color difference visually. Compare the staining of white cloth with the gray staining sample card to evaluate the color fastness of the sample to the staining of white cloth. Level 1 staining is the most severe, and level 5 visual inspection shows no staining. There are four testing temperatures for washing fastness: 95 ℃, 60 ℃, 50 ℃, and 40 ℃, depending on the usage requirements of printed and dyed textiles.

③ The rubbing fastness is also classified into 5 levels. During the test, the sample is rubbed with dry and wet white cloth according to the specified conditions, and the degree of staining on the white cloth is compared and evaluated with the gray staining sample card. The result obtained by rubbing dry white cloth is dry rubbing fastness; The result obtained by rubbing wet white cloth is wet rubbing fastness. Other color fastness tests can be conducted according to specified conditions, and the test results can be compared with the gray fading sample card or gray staining sample card to evaluate the grade.

Characteristics and Hazards of Printing and Dyeing Wastewater

The daily discharge of printing and dyeing wastewater in China is (300-400) × 104t is one of the major polluters in various industries. Printing and dyeing wastewater

Mainly composed of desizing wastewater, cooking wastewater, bleaching wastewater, mercerizing wastewater, dyeing wastewater, and printing wastewater, wastewater is discharged from all four processes of printing and dyeing processing. During the pre-treatment stage (including desizing, cooking, bleaching, mercerizing, etc.), desizing wastewater, cooking wastewater, bleaching wastewater, and mercerizing wastewater are discharged. Dyeing wastewater is discharged from the dyeing process, while printing wastewater and soap wastewater are discharged from the printing process, The sorting process discharges the sorting wastewater.

The commonly referred to printing and dyeing wastewater is a mixture of various types of wastewater or a comprehensive wastewater other than bleaching wastewater. The water quality of printing and dyeing wastewater varies depending on the type of fiber used and processing technology, and the pollutant components vary greatly. Printing and dyeing wastewater generally has the characteristics of high pollutant concentration, multiple types, toxic and harmful components, and high chromaticity. Generally, the pH value of printing and dyeing wastewater is 6-10, CODCr is 400-1000mg/L, BOD5 is 100-400mg/L, SS is 100-200mg/L, and the chromaticity is 100-400 times. But when the printing and dyeing process, the types of fibers used, and the processing technology change, the wastewater quality will have a significant change.

In recent years, due to the development of chemical fiber fabrics, the rise of imitation silk, and the advancement of dyeing and finishing technology, a large number of difficult to degrade organic compounds such as PVA size, alkali hydrolysates of artificial silk (mainly phthalates), and new additives have entered printing and dyeing wastewater. The CODCr concentration has also increased from hundreds of mg/L to over 2000-3000mg/L, BOD5 has increased to over 800mg/L, and the pH value has reached 11.5-12, This reduces the CODCr removal rate of the original biological treatment system from 70% to around 50%, or even lower.

The drainage situation of each printing and dyeing process is generally as follows:

(1) Desizing wastewater: The amount of water is small, but the concentration of pollutants is high, which contains various sizes, size decomposition products, fiber chips, starch alkali, and various additives. The wastewater is alkaline with a pH value of around 12. The desizing wastewater mainly composed of starch (such as cotton fabric) has high COD and BOD values and good biodegradability. The desizing wastewater mainly composed of polyvinyl alcohol (PVA) for sizing (such as polyester cotton warp yarn) has high COD and low BOD, and the biodegradability of the wastewater is poor.

(2) Cooking wastewater: It has a large amount of water and a high concentration of pollutants, including cellulose, citric acid, wax, oil, alkali, surfactants, nitrogen compounds, etc. The wastewater is strongly alkaline, with high water temperature and a brown color.

(3) Bleaching wastewater: The amount of water is large, but the pollution is relatively light, which contains residual bleaching agents, small amounts of acetic acid, oxalic acid, sodium thiosulfate, etc.

(4) Mercerizing wastewater: It has a high alkali content, with a NaOH content of 3% -5%. Most printing and dyeing factories recover NaOH through evaporation and concentration, so mercerizing wastewater is generally rarely discharged. After multiple repeated uses of the process, the final discharged wastewater still shows strong alkalinity, with high BOD, COD, and SS.

(5) Dyeing wastewater: The amount of water is relatively large, and the water quality varies depending on the dyes used. It contains slurries, dyes, additives, surfactants, etc., and is generally strongly alkaline,