Wet process engineering (WPE) is one of the major trends in textile techniques that refers to the technique of textile chemical processes and applied science. The other three streams in textile engineering are yarn engineering, fabric engineering and apparel engineering.
The wet process is usually carried out on the assembly of interlaced, filament, and/or yarn fibers having a substrate surface (planar) in relation to its thickness, and sufficient mechanical strength to provide a cohesive structure. In other words, the wet process is done on the fabric produced. This flow process is involved or carried out in an aqueous stage and is thus called a wet process which typically includes pre-treatment, dyeing, printing and completion.
All these stages require aqueous media made by water. A large amount of water is required in this process per day. It is estimated that on average, nearly 100 liters of water is used to process only 1 kg of textile goods. Water can have different qualities and attributes. Not all water can be used in the textile process, it certainly has some properties, quality, color & amp; attribute for use in textile processes. This is why water is a major concern in wet process engineering.
Video Wet processing engineering
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Much of the water used in the textile industry comes from deep well water found 800Ã, ft below the surface. A major problem related to the use of water in textile processes is the hardness of water caused by the presence of dissolved salts of metals including calcium and magnesium. Iron, aluminum and copper salts can also contribute to the hardness, but the effect is much less. Using hard water in the wet process can cause problems such as scale formation in the boiler, reaction with soap and detergent, reactions with dyes and problems due to Iron.
Water hardness can be removed by boiling process, calcification process, sodalime process, base exchange process or synthetic ion exchange process. Recently some companies have started harvesting rainwater for use in the wet process because it is less likely to cause problems related to water hardness.
Maps Wet processing engineering
Pretreatment
Wet process engineering is the most significant division in textile preparation and processing. This is a major flow in textile engineering under the part of textile chemical processing techniques and applied sciences. Textile manufacturing covers everything from fiber to garment; covering with yarn, fabric, dyeing cloth, printing, finishing, garment or apparel manufacturing. There are many variable processes available at the spinning stage and fabric formation coupled with the complexity of the finishing and coloring process for the production of a wide range of products.
In Bangladesh, textile manufacturing is the main industry. In this industry, the wet process plays an important role in the field of pre-treatment, dyeing, printing and finishing of both fabric and clothing. But the color in the fiber stage or yarn stage is also included in the wet processing division.
All this flow process is performed in an aqueous or aqueous media. The main process of this section includes:
- Singeing
- Turn on
- Scrub
- Bleaching
- Maintenance
- Coloring
- Finishing
Singeing
The scorching process is performed for the purpose of removing loose furry fibers protruding from the fabric surface, providing a smooth, flat and clean face. Singeing is an important process for textile goods or materials to be worn mercerizing, coloring and printing to get the best results from these processes.
The cloth passes the brush to raise the fiber, then passes the plate heated by a gas fire. When done for cotton-containing fabrics, this results in increased wetability, better dyeing characteristics, reflective refinement, no "blurry" appearance, smoother surfaces, better clarity in printing, improved visibility of fabric structure, reduced pilling and reduced contamination through the removal of feathers and fibers.
Singeing machines can consist of three types: scorching plate, singing roller, or gas singing. Gas burns are widely used in the textile industry. In singing gas, the flame comes to direct contact to the fabric and burns the protruding fibers. Here, the high flame and speed of the fabric are the main concern to minimize fabric damage.
Singeing is only done in woven fabric. But in the case of knit fabrics, the same singing process is known as biopolishing in which enzymes are used to remove protruding fibers.
Singeing is a mechanical process by which hair, loose fibers are removed from the surface of textile materials either by heating or burning to make the material smooth and shiny.
Uses: Equal to bio-polishing without point 5.
Desizing
Desizing is the process of removing the sizing material from the fabric, which is applied to increase the strength of the yarn that can withstand friction looms. Unfiltered fabrics are very rigid and cause difficulties in their treatment with different solutions in the subsequent process.
After the burning operation, the sizing material is removed by making it dissolve in water and washing it with warm water. Desizing can be done by hydrolytic method (steep rot, steep acid, enzymatic steep) or oxidative methods (chlorine, chloride, bromite, hydrogen peroxide)
Depending on the size of the material that has been used, the fabric may be immersed in dilute acid and then rinsed, or the enzyme can be used to break down the sizing material. Enzymes are applied in the desizing process if starch is used as a sizing agent. Carboxymethyl cellulose (CMC) and Poly vinyl alcohol (PVA) are often used as sizing agents.
Scouring
Scouring is a chemical washing process done on cotton cloth to remove natural impurities and non-fibrous impurities (eg seed scraps) from the fibers and dirt or impurities added. Scouring is usually carried in iron vessels called kiers. The fabric is boiled in alkali, which forms a soap with free fatty acids (saponification). A kier is usually closed, so the sodium hydroxide solution can be boiled under pressure, excluding oxygen which will lower the cellulose in the fiber. If proper reagents are used, scrubbing will also remove the size of the fabric although desizing often precedes the polisher and is considered a separate process known as fabric preparation. Preparation and scouring is a prerequisite for most other finishing processes. At this stage even the most natural white cotton fibers are yellowish, and bleaching, the next process, is required.
The three main processes involved in grinding are saponification, emulsification and detergency.
The main chemical reagents used in cotton scrubbing are sodium hydroxide which convert fats and oils into soap, dissolves mineral substances and converts pectose and pectin into soluble salts.
Other scrubbing chemicals are detergents which are emulsifying agent and remove dust particles and dirt from fabric.
Because the damage can cause the cotton substrate by sodium hydroxide. Because of this, and to reduce the alkali content in the waste, Bio-scouring is introduced in the scrubbing process in which biological agents are used, such as enzymes.
Bleaching
Bleaching improves whiteness by eliminating natural staining and traces of dirt from cotton; the required level of bleaching is determined by the whiteness and absorption required. As a vegetable fiber, cotton will be bleached using an oxidizing agent, such as dilute sodium hypochlorite or dilute hydrogen peroxide. If the fabric is deeply dyed, the lower bleaching rate may be acceptable. However, for white sheets and medical applications, the highest level of whiteness and absorption is essential.
Reductive bleaching is also done, using sodium hydrosulphite. Fibers such as polyamides, polyacrylates and polyacetates can be bleached using reductive bleaching technology.
After polishing and bleaching, the optical brightening agent (OBA), is applied to make the textile material appear whiter. OBA is available in various colors like blue, purple and red.
Mercerizing
Mercerizing is a treatment for cotton and yarn fabric that gives the cloth or yarn a sparkling appearance and strengthens it. This process is applied to cellulosic materials such as cotton or hemp. Another possibility is mercerizing as long as the fabric is treated with a solution of sodium hydroxide causing swelling of the fibers. This results in increased affinity, strength and dye. The cotton is dircerized under tension, and all the alkali must be washed before the tension is released or the shrinkage will occur. Mercerizing can occur directly on the greige fabric, or after bleaching.
Immersion
Dyeing is the process of adding color to textile products such as fibers, yarns, and fabrics. Dyeing is usually done in a special solution containing dyes and certain chemicals. After immersion, the dye molecule has a chemical bond that is not cut with fiber molecules. Temperature and time control are two key factors in immersion. There are mainly two classes of dyes, natural and man-made.
Coloring solution
The dye solution, also known as dipping or spinning, is the process of adding pigments or dyes that do not dissolve into the spinning solution before the solution is extruded through the spinneret. Only artificial fibers can be dipped. It is used for hard-dipped fibers, such as olefin fibers, and for dyeing fibers for end use which require excellent colorfastness properties. Because the color pigment becomes part of the fiber, the dyed-solvent material has excellent color to light, wash, crocking, sweat, and bleach. Dyeing at the solution stage is more expensive, because the equipment must be thoroughly cleaned every time a different color is produced. Thus, the resulting colors and nuances are limited. In addition, it is difficult to stock inventory for each color. Decisions about color should be made very early in the manufacturing process. So, this dyeing stage is usually not used for clothing.
The filament fibers produced using the wet spinning method can be dyed while the fibers are still in the clotting tub. The penetration dye at this stage is high, because the fiber is still soft. This method is known as gel immersion.
Fiber dyeing
Stock dyeing, top dyeing, and tow dyeing are used to dye fibers at various stages of the manufacturing process before fiber is spun into yarn. The names refer to the stage where the fiber was when dyed. All three fall into the broad category of fiber immersion.
Stock immersion is raw fiber dyeing, also called stock, before being aligned, mixed, and spun into yarn.
Upper immersion is a dirty dyeing of wool fibers after combed to straighten and remove short fibers. The wool fiber at this stage is known as the top. Upper immersion is preferred for woolen wool because the dye should not be discarded on the short fibers removed during the combing process.
Immersion dyeing is dyeing of filament fibers before being cut into short staple fibers. The filament fibers at this stage are known as tow.
The dye penetration is excellent in fiber staining, therefore the amount of dye used to color at this stage is also higher. Fiber dyeing is relatively more expensive than yarns, fabrics, and dyeing products. Decisions on color selection should be made at the beginning of the manufacturing process. Fiber dyeing is commonly used for dyeing wool and other fibers used to produce yarn of two or more colors. Fibers for tweed and fabrics with a "heather" look are often dyed fibers.
Yarn dyeing
Yarn dyeing adds color to the yarn stage. The skein, package, beam, and dyeing methods are used to color the yarn.
In dyeing skein, the yarn is wrapped in a scroll or skein and then dyed. The yarn has good dye penetration, but the process is slow and relatively more expensive.
In dyeing yarn thread that has been perforated on hollow reel dipped in pressure tank. The process is relatively faster, but the uniformity of the dye may not be as good as the skein dye.
In the beam blocking of the hollow weft beams are used instead of the reels used in packet immersion.
Room immersion is used to produce yarn with many colors.
In general, yarn dye provides adequate color absorption and penetration for most materials. Thick and deeply twisted threads may not have good dye penetration. This process is usually used when different colored threads are used in fabric construction (eg plaques, checks, colorful fabrics).
Fabric dye
Fabric dyeing, also known as dyeing a piece, is dyeing the fabric after it is made. This is the most economical and most common method for coloring solid colored fabrics. Decisions about color can be done after the fabric has been produced. As such, it is perfect for quick response orders. Dye penetration may not be good on thicker fabrics, so yarn dyeing is sometimes used to dye thick fabrics in solid colors. Different types of dyeing machines are used for dyeing a piece. The selection of equipment is based on factors such as dye and fabric characteristics, cost, and end use as desired.
Union immersion
Union immersion is a "dyeing method of fabric containing two or more types of fibers or yarns into the same color so as to achieve the appearance of solid colored fabrics". Fabrics can be dyed using a single or multiple step process. Union immersion is used to dye solid color mixtures and combination fabrics commonly used for clothing and home furnishings.
Cross immersion
Cross immersion is "blender or combination dyeing method for two or more colors by using dyes with different affinity for different fibers". The cross-immersion process can be used to create heather effects, and plaid, check, or striped cloth. Cross-dyed fabrics may be mistaken for fibers or yarn-dyed materials because the fabric is not a solid color, a characteristic that is considered typical of dyed fabrics. It is impossible to visually distinguish between the dyed fabric and the dyed one on the fiber or yarn. An example is a cross-dyeing of blue woolen wool with polyester pin stripes. When dyed, the wool yarn is dyed blue, while the polyester yarn remains white.
Cross-dyeing is commonly used with cut or dyed fabric. However, the same concept applies to yarn dyeing and products. For example, silk fabrics embroidered with white threads can be embroidered before dyeing and dyed products when orders are placed.
Dip the product
The dyeing of products, also known as clothing dyeing, is the process of dyeing products such as socks, sweaters, and carpets after they are manufactured. This immersion stage is suitable when all components color the same color (including yarn). This method is used to color thin socks because it is knitted using a tubular knitting machine and then sewn before immersion. Tufted carpets, with the exception of carpets produced using a dyed fiber solution, are often dyed after they are tufted. This method is not suitable for clothing with many components such as coatings, zippers, and sewing threads, as each component can be colored differently. The exception is a dye with pigment jeans for a "vintage" look. In staining, color is used, whereas in other treatments such as acid leaching and stone washing, chemical or mechanical processes are used. After garment construction, these products are given a "faded" or "used" look with finishing methods as opposed to immersion.
Coloring at this stage is ideal for quick response. Many T-shirts, sweaters, and other types of casual wear are dyed products for the maximum response to fashion demand for certain popular colors. Thousands of clothes are built from ready-to-dye fabrics (PFD), and then dyed to the best-selling colors.
Dye type
The acid dye is a water-soluble anionic dye applied to fibers such as silk, wool, nylon and acrylic fibers modified by washing with neutral acid dyes. The attachment of the fibers is given, at least in part, to the formation of salts between the anionic groups in the dyestuff and the cationic groups in the fibers. Acid dyes are not substantive to cellulose fibers.
The basic dye is a water-soluble cation dye that is mainly applied to acrylic fibers, but found some used for wool and silk. Usually acetic acid is added to the dyed rinse to help the absorption of the dye into the fibers.
Immediate or substantive dyeing is usually performed on a neutral or slightly basic bed, at or near the boiling point, with the addition of sodium chloride, sodium sulphate or sodium carbonate. Direct dyes are used on cotton, paper, leather, wool, silk and nylon.
The mordant dye requires mordan, which increases the dye resistance to water, light and sweat. The mordan choice is very important because different mordans can change the final color significantly. The most natural dye is the mordan dye and therefore there is a large literary base that describes the immersion technique. The most important mordant dyes are synthetic dyes, or chrome dyes, used for wool; It consists of 30% dye used for wool, and is very useful for black and dark blue. The mordant, potassium dichromate, is applied as a treatment afterwards. Many mordans, especially those included in the heavy metal category, can be harmful to health and should be very careful about using them.
The dye dye is basically insoluble in water and is not able to color the fibers directly. However, the reduction of an alkaline liquid produces a water-soluble alkali metal salt of the dye, which, in this leuco form, has an affinity for the textile fibers. The subsequent oxidation reformed the insoluble native dye. The color of the denim is due to indigo, the original vat dye.
Reactive dyes use chromophores attached to substituents that are able to react directly with the fiber substrate. A covalent bond that attaches reactive dyes to natural fibers makes it one of the most permanent dyes. "Cold" reactive dyes, such as Procion MX, Cibacron F, and Drimarene K, are very easy to use because the dye can be applied at room temperature. Reactive dyes are by far the best choice for dyeing cotton and other cellulose fibers at home or in art studios.
Dissolution of the dye was originally developed for dyeing cellulose acetate, and not soluble in water. The dye is finely ground in the presence of a dispersing agent and sold as a paste, or dried by spray and sold as a powder. Its main use is to dye polyester but they can also be used to color nylon, cellulose triacetate, and acrylic fiber. In some cases, a dipping temperature of 130 Â ° C is required, and pressurized dip is used. The very fine particle size provides a large surface area that helps dissolution to allow fiber absorption. The level of immersion can be significantly affected by the choice of dispersant used during the milling.
Azoic immersion is a technique in which insoluble azo dyes are produced directly to or within the fiber. This is achieved by treating fibers with diazoic components and coupling. With appropriate adjustment of the dyebath conditions, the two components react to produce the required insoluble azo dyes. This dyeing technique is unique, because the final color is controlled by the choice of diazoic components and coupling. This method of dyeing cotton is declining due to the toxic nature of the chemical used.
The sulfur dye is a two part "developed" dye that is used to dye cotton with a dark color. Initial baths impart yellow or faded yellow colors, These are after treated with sulfur compounds in place to produce the dark black we know with socks for example. Sulfur Black 1 is the largest sales dye by volume.
Textile printing is referred to as local staining. It is a color application in the form of pastes or inks to the fabric surface, in a predetermined pattern. Printing designs on dyed fabrics is also possible. On properly printed fabrics, the color is tied to the fibers, so that the wash-resistant and friction-resistant. Textile printing is concerned with immersion but, while in coloring the entire fabric is uniformly covered with one color, in one or more color printing is applied only in certain parts, and in sharply defined patterns. In printing, wooden beams, stencils, carved plates, rollers, or silkscreens can be used to place color on the fabric. The dye used in the printing contains thickened dye to prevent the color spread by the capillary appeal beyond the boundaries of the pattern or design.
Finishing
Finishing textiles is a term used for a series of processes where all greige, dipped, printed and certain greige fabrics are worn before they are placed in the market. The purpose of textile finishing is to make textile items in line with the purpose or the final use and/or improve the fabrication of the fabric.
Finishing on the fabric is done for aesthetic and functional purposes to improve the quality and appearance of the fabric. Fabrics can receive substantial added value by applying one or more finishing processes. The finishing process includes
- Cultivation
- Sign up
- Resilience folds
- Charge
- Soften
- Stiffening
- Water disapproval
- Moth proofing
- Cleaning with mushrooms
- Flame retard
- Anti-static
- land barrier
Calendering is an operation performed on the fabric to enhance the aesthetics. Fabric passes through a series of calendar rollers by wrapping; the face in contact with the roller alternately from one roll to the next roll. An ordinary calendar consists of a series of hard and soft (tenacious) bowls placed in a definite order. Soft rollers can be compressed with cotton or wool paper, linen paper or hemp paper. Hard metal bowls are cold iron or cast iron or steel. The calendar may consist of 3, 5, 6, 7, and 10 rolls. The roller sequence is that no two hard rollers touch each other. Pressure can be applied by combined levers and weights, or hydraulic pressure can be used as an alternative. The pressure and heat applied in calendering depends on the type of finishing required.
The purpose of calendering is to upgrade the hand fabric and to provide a smooth, delicate touch to the fabric, to press the fabric and reduce its thickness, to increase fabric opacity, to reduce fabric air permeability by altering porosity, to provide different degrees of luster, and to reduce thread slippage.
Raising
An important and oldest textile finishing is brushing or raising. Using this process a wide range of fabrics including blankets, flannel fabrics and industrial fabrics can be manufactured. The lifting process consists of lifting from the body of a fiber layer cloth that protrudes from a surface called a "pile". The formation of the pile on the fabric produces a "noble" handle and may also subdue the weave or the pattern and color of the fabric.
There are different types of lifting machines; Teasel machine and wire-card machine. The speed of a wire-card milling machine varies from 12-15 meters per minute, which is 20-30% higher than lifting the teasel. That is why wire cable milling machines are widely used.
Resilience fold
The formation of folds on woven or knitted fabrics comprising cellulose while washing or folding are the main disadvantages of cotton fabrics. The molecular chains of cotton fibers are bonded to each other by weak hydrogen bonds. During washing or folding, the hydrogen bonds break easily and after drying the new hydrogen bonds form with the chain in their new position and the folds become stable. If crosslinking between the polymer chains can be introduced with crosslinking chemicals, it strengthens the cotton fibers and prevents the permanent displacement of the polymer chains when the fiber is emphasized. It is therefore much more difficult to fold to form or to shrink fabrics on washing.
In the cotton layer removed from the wrinkles, the following steps are followed
- Padding the material with a solution containing the condensation polymer precursor and the corresponding polymerization catalyst.
- Drying and pickling in the stenter frame to form cross links between polymer chains and adjacent polymer chains.
The catalyst allows the reaction to be carried out at a temperature range of 130-180 degrees normally used in the textile industry and within the usual curing time (within 3 minutes, maximum).
The three main classes of catalysts are commonly used today.
- Ammonium salt, eg. Ammonium chloride, sulfate and nitrate.
- Metal salt eg. Magnesium chloride, Zinc nitrate, Zinc chloride.
- Mixture of catalyst, e.g. magnesium chloride with the addition of organic and inorganic acids or acid donors.
The purpose of the additive is to offset or offset some or all of the adverse effects of crosslinking agents. So the softening and smoothing agent is applied not only to improve the grip, but also to compensate as much as possible for loss of tear strength and abrasion resistance. Each final resin recipe contains surfactants as emulsifiers, wetting agents and stabilizers. this surface active agent is required to ensure that the wet cloth is fast and thorough during the padding and stable components in the liquor.
References
Source of the article : Wikipedia
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