What is textile wet processing? Describe the textile wet process.

Textile wet processing

Textile wet processing is one of the major streams in textile engineering and refers to textile chemical processing and applied science. It is usually done on the manufactured assembly of interlacing fibers, filaments, or yarns having a substantial surface area in relation to its thickness, and adequate mechanical strength to give it a cohesive structure. An alternative way to say, the wet process is done on manufactured fabric. The processes of this stream are carried out in an aqueous stage and thus it is called a wet process which usually covers pretreatment, dyeing, printing, and finishing. All of these stages are required an aqueous medium that is created by water. A massive amount of water is required in these processes per day. It is estimated that, on average, almost 100-110 liter of water is used to process only 1 kg of textile goods. Water can be of various qualities and attributes. Not all water can be used in textile processing, it must have certain properties, quality, color, and properties for use in textile processes. That is why water is concerned with wet processing.

Water for wet processing

Most water used in the textile industry is from deep well water which is observed 800ft beneath the surface level. The main hassle which is concerned with the usage of water in textile processes is water hardness resulting from the presence of soluble salts of metals which include calcium and magnesium. Iron, aluminum, and copper salts may also make contributions to the hardness, however, their results are much less. Using difficult water within the wet process can motive problems consisting of the formation of scale in boilers, reactions with soap and detergents, reactions with dyes, and issues due to Iron.

Water hardness may be removed with the aid of the boiling procedure, liming process, soda-lime method, Base Exchange system, or artificial ion exchange procedure. Recently some groups have started harvesting rainwater to be used in wet procedures as its miles are much less probably to reason the issues related to water hardness.

Pretreatment of wet processing

Wet processing is the most important section in textile preparation and processing. It is a major branch of textile engineering under the Department of Textile Chemical Processing and Applied Sciences. Textile production covers everything from fiber to clothing; there are many variable processes that are found with the complexity of finishing and dyeing processes in a wide range of product production stages, including cutting, fabrication, fabric dyeing, printing, finishing, garment, or garment production.

In the textile industry, wet processing plays a vital role in the area of pre-treatment, dyeing, printing, and finishing of both fabrics and apparel. Coloration in the fiber stage or yarn stage is also included in the wet processing division.

All the processes of this section are carried out in an aqueous medium. The main processes of this section are bellows-

a.    Singeing process

Singeing is a procedure that is performed for the purpose of removing loose hairy fibers scattered from the surface of the fabric, giving it a smooth, even, and clean appearance. This is a necessary process for products or textile materials that will suffer from mercerizing, dyeing, and printing to get the best results from these processes.

In this process, first, the fabric goes over the brush to increase the fibers, then goes over a plate heated by the flame of gas. When done on cotton fabrics, it results in reduced durability, better dyeing properties, improved reflection, no frosty appearance, a smoother surface, better printing precision, improved visibility of the fabric structure, less peeling, and reduced contamination resulting in fluff and debris removal.

Singeing machines can be of three types: plate sizing, roller sizing, or gas sizing. Gas singeing is broadly used in the textile industry. When the gas singeing, a flame comes in direct contact with the fabric and burns the expanding fiber. Here, the flame height and fabric speed are the main concerns to reduce fabric damage.

Singeing is done only on woven fabric. In the case of woven fabrics, however, a similar process to singeing is known as bio-polishing where the enzyme is used to remove protruding fibers.

b.    Desizing process

It is the process of removing sizing materials from the fabric or garments which are applied in order to increase the strength of the yarn which can withstand the friction of the loom. The fabric which has not been desized, it is very stiff and causes difficulty in its treatment with a different solution in subsequent processes.

After the singeing operation, the sizing material is removed by making it water-soluble and washing it with warm water. Desizing may be done by the hydrolytic method or the oxidative method.

Depending on the sizing materials which one has been used, the cloth may be steeped in dilute acid and then rinsed, or enzymes may be used to break down the sizing material. Enzymes are used in the desizing process if starch is applied as sizing materials. Carboxymethyl cellulose (CMC) and Polyvinyl alcohol (PVA) are often used as sizing materials.

c.    Scouring process

Scouring is a chemical washing technique that is carried out on cotton fabric to remove natural wax and fibrous impurities from fibers and any added soil or dirt. It is usually carried in iron containers called coir. The fabric is boiled in an alkali, which makes soap with free fatty acids. Kier is usually closed, so a solution of sodium hydroxide can be boiled under pressure by excluding oxygen which reduces the cellulose of the fiber. If appropriate reagents are used, the scoring will also remove the shape from the fabric although de-sizing is often done before shaking and this is considered a separate process is known as fabric preparation. Preparation and scouring are other prerequisites for other finishing processes. At this stage even very naturally white cotton fibers are yellow in color and bleaching, the next process is necessary. The three main processes involved in this scouring are saponification, emulsification, and detergency.

The main chemical reaction used in cotton wool is sodium hydroxide which converts saponifiable fats and oils into soaps dissolve minerals and convert pectose and pectin to their soluble mass. Another scouring chemical is detergent that is an emulsifying agent and removes dust and dirt particles from the fabric. Since sodium hydroxide can cause damage to the cotton substrate. Because of this, and to reduce the alkaline component in the flowing matter, bio-scouring is introduced in a scouring process where biological agents are used, such as an enzyme.

d.    Bleaching process

Bleaching is the next process of scouring, where natural color removed and textiles get permanent white. Bleach improves whiteness by removing natural coloration and remaining trace impurities from the cotton. The power of bleaching necessary is determined by the required whiteness and absorbency. Cotton being a cellulose fiber will be bleached using an oxidizing agent, such as dilute sodium hypochlorite or dilute hydrogen peroxide. When the fabric is to be dyed a deep shade, then lower levels of bleaching are acceptable. However, for white bedsheets and medical applications, the highest levels of whiteness and absorbency are essential. Reductive bleaching is also carried out, using sodium hydrosulfite. Fibers like polyamide, polyacrylics, and polyacetates can be bleached using reductive bleaching technology. After scouring and bleaching, optical brightening agents (OBA), are used to make the textile material appear whiter. These OBAs are available in different tints such as blue, violet, and red.

e.    Mercerization process

Mercerization is a process by which cotton fabrics and threads shine like silk and strengthen them. The process is applied to cellulosic materials such as cotton or flax. The process is accomplished by a solution of 55–65 ° twaddle sodium hydroxide. More likely Mercerizing is the swelling of the fibers during which the fabric is treated with a sodium hydroxide solution. The result is improved luster, strength, and pigmentation. Cotton is synthetic in excitation and all alkalis must be washed off before the tension is expressed or compressed. Mercerizing can occur directly on gray cloth or after bleaching.

f.     Dyeing process

Dyeing is the process of adding color to textile products like fibers, yarns, and fabrics. It is normally done in a special solution containing dyes and particular chemical material. After dyeing, dye molecules have an uncut chemical bond with fiber molecules. Temperature and time control are two key factors in dyeing. There are mainly two classes of dye, natural and man-made. There are various types of dyeing as follows-

Solution dyeing

Solution dyeing is also called dope or spun dyeing, is the process of adding pigments or insoluble dyes to the spinning solution before the solution is extruded through the spinneret. Only manufactured fibers can be solution-dyed. It is used for difficult-to-dye fibers such as olefin fibers, and for dyeing fibers for end uses that require excellent colorfastness properties. Because the color pigments become a part of the fiber, solution-dyed materials have excellent colorfastness to light, washing, rubbing, perspiration, and bleach. Dyeing at the solution stage is more expensive since the equipment has to be cleaned thoroughly each time a different color is produced. Thus, the variety of colors and shades produced is limited. In addition, it is difficult to stock the inventory for each color. Decisions regarding color have to be made very early in the manufacturing process. Thus, this stage of dyeing is usually not used for apparel fabrics. 

Gel dyeing

Filament fibers that are produced using the wet spinning method can be dyed while the fibers are still in the coagulating bath. The dye penetration at this stage is high as the fibers are still soft. This method is known as gel dyeing.

Fiber dyeing

There are many types of dyeing is done for fiber dyeing. The names refer to the stage at which the fiber is when it is dyed. All three are included under the broad category of fiber dyeing.

Stock dyeing is dyeing raw fibers, also called stock, before they are aligned, blended, and spun into yarns.

Top dyeing is dyeing worsted wool fibers after they have been combed to straighten and remove the short fibers. The wool fiber at this stage is known as the top. Top dyeing is preferred for worsted wools as the dye does not have to be wasted on the short fibers that are removed during the combing process.

Tow dyeing is dyeing filament fibers before they are cut into short staple fibers. The filament fibers at this stage are known as tow.

The dye penetration is excellent in fiber dyeing, therefore the amount of dye used to dye at this stage is also higher. Fiber dyeing is comparatively more costly than yarn, fabric, and product dyeing. The decision regarding the selection of colors has to be made early in the manufacturing process. Fiber dyeing is typically used to dye wool and other fibers that are used to produce yarns with two or more colors. Fibers for tweeds and fabrics with a “heather” look are often fiber dyed.

Yarn dyeing

There are many forms of yarn dyeing. Common forms are the package form and the hanks form. Cotton yarns are mostly dyed in package form, and acrylic or wool yarn is dyed in hank form. In the continuous filament industry, polyester or polyamide yarns are always dyed at package form, while viscose rayon yarns are partly dyed at hank form because of technology.

Fabric dyeing

It is also called piece dyeing, is dyeing fabric after it has been constructed. It is economical and the most common method of dyeing solid-colored fabrics. The decision regarding color can be made after the fabric has been manufactured. Thus, it is suitable for quick response orders. Dye penetration may not be good in thicker fabrics, so yarn dyeing is sometimes used to dye thick fabrics in solid colors. Various types of dyeing machines are used for piece dyeing. The selection of the equipment is based on factors such as dye and fabric characteristics, cost, and the intended end-use.

Union dyeing

It is "a method of dyeing where a fabric containing two or more types of fibers or yarns to the same shade so as to achieve the appearance of a solid-colored fabric". Fabrics can be dyed using a single or multiple step process. Union dyeing is used to dye solid colored blends and combination fabrics commonly used for apparel and home furnishings.

Cross dyeing

Cross dyeing is “a method of dyeing blend or combination fabrics to two or more shades by the use of dyes with different affinities for the different fibers”. The cross dyeing process can be used to create heather effects, and plaid, check, or striped fabrics. Cross dyed fabrics may be mistaken for fiber or yarn-dyed materials as the fabric is not a solid color, a characteristic considered typical of piece-dyed fabrics. It is not possible to visually differentiate between cross-dyed fabrics and those dyed at the fiber or yarn stage. An example is cross dyeing blue worsted wool fabric with polyester pinstripes. When dyed, the wool yarns are dyed blue, whereas the polyester yarns remain white.

Cross dyeing is commonly used with pieces of fabric dyed materials. However, the same concept is applicable to yarn and product dyeing. For example, silk fabric embroidered with white yarn can be embroidered prior to dyeing and product dyed when an order is placed.

Garments dyeing

Garments dyeing is also known as product dyeing, is the process of dyeing products such as hosiery, sweaters, and carpet after they have been produced. This stage of dyeing is suitable when all components dye the same shade. This method is used to dye sheer hosiery since it is knitted using tubular knitting machines and then stitched prior to dyeing. Tufted carpets, with the exception of carpets produced using solution-dyed fibers, are often dyed after they have been tufted. This method is not suitable for apparel with many components such as lining, zippers, and sewing thread, as each component may dye differently. The exception is tinting jeans with pigments for a “vintage” look. In tinting, color is used, whereas in other treatments such as acid-wash and stone-wash, chemical or mechanical processes are used. After garment construction, these products are given the "faded" or "used" look by finishing methods as opposed to dying.

Dyeing at this stage is ideal for a quick response. Many t-shirts, sweaters, and other types of casual clothing are product dyed for maximum response to fashion’s demand for certain popular colors. Thousands of garments are constructed from prepared-for-dye fabric and then dyed to colors that sell best.

Printing process

Textile printing is referred to as localized dyeing. It is the application of color in the form of a paste or ink to the surface of a fabric, in a predetermined pattern. Printing designs onto already dyed fabric is also possible. In properly printed fabrics the color is bonded with the fiber, so as to resist washing and friction. Textile printing is related to dyeing but, whereas in dyeing proper the whole fabric is uniformly covered with one color, in printing one or more colors are applied to it in certain parts only, and in sharply defined patterns. In printing, wooden blocks, stencils, engraved plates, rollers, or silkscreens can be used to place colors on the fabric. Colorants used in printing contain dyes thickened to prevent the color from spreading by capillary attraction beyond the limits of the pattern or design.

Finishing process

Textile finishing is the term used for a series of processes to which all bleached, dyed, printed, and certain grey fabrics are subjected before they put on the market. The object of textile finishing is to render textile goods fit for their purpose or end-use and/or improve the serviceability of the fabric.

Finishing on fabric is carried out for both aesthetic and functional purposes to improve the quality and look of a fabric. Fabric may receive considerable added value by applying one or more finishing processes. Finishing processes are below-

Raising finishing

A raising card is used to raise cloth. It is the technique used to produce the nap of cloth. Originally, only woolen cloth was raised, but now flannelette and other cotton fabrics are also raised. Raising is one of the last steps in the finishing process for cloth. It teases out the ends of the fibers in the cloth to produce a nap. The raising was first using the dried fruit pod of a teasel plant, then technology moved on and raising cards were created. A raising card is a brush with metal bristles, similar to hand cards, and to the original teasel pod. The process was mechanized during the industrial revolution, and the raising machine looks and works much like the large carding machines, in that it has a large main roller with several small ones positioned around it. The small ones rotate quickly, in either the same direction or opposite of that of the cloth. After the raising process, the nap is uneven. In order to gain an even surface, the nap is then sheared, or cut, to the desired height. There are two types of raising machine; Teasel machine and Card-wire machine. The speed of the card-wire raising machine varies from 12-15 yards per minute, which is 20-30% higher than that of teasel-raising. That is why the card-wire raising machine is widely used.

Calendaring

Calendaring is a finishing process used to smooth, coat, or thin a material. With textiles, the fabric is passed through calender rollers at high temperatures and pressures. It is used on fabrics such as moiré to produce its watered effect and also on cambric and some types of sateens. In preparation for calendaring, the fabric is folded lengthwise with the front side, or face, inside, and stitched together along the edges. The fabric can be folded together at full width, however, this is not done as often as it is more difficult. The fabric is then run through rollers that polish the surface and make the fabric smoother and more lustrous. High temperatures and pressure are used as well. Fabrics that go through the calendaring process feel thin, glossy, and papery. The wash durability of a calendared finish on thermoplastic fibers like polyester is higher than on cellulose fibers such as cotton. On blended fabrics such as Polyester/Cotton, the durability depends largely on the proportion of synthetic fiber component present as well as the amount and type of finishing additives used and the machinery and process conditions employed.

Crease resistance

Crease formation in woven or knitted fabric composed of cellulose during washing or folding is the main drawback of cotton fabrics. The molecular chains of the cotton fibers are attached to each other by weak hydrogen bonds. During washing or folding, the hydrogen bonds break easily, and after drying new hydrogen bonds form with the chains in their new position and the crease is stabilized. If crosslinks between the polymer chains can be introduced by cross-linking chemicals, then it reinforces the cotton fibers and prevents the permanent displacement of the polymer chains when the fibers are stressed. It is therefore much more difficult for creases to form or for the fabric to shrink on washing.

Softening process

The fibers at the fabric surface are squashed and frayed, and this condition hardens while drying the laundry in the air, giving the laundry a harsh feel. Adding a liquid fabric softener to the final rinse results in the laundry that feels softer. Fabric softeners are usually either in the form of a liquid, which is added to the washing machine during the rinse cycle; or as a dryer sheet which is added to the moist laundry at the beginning of the dryer cycle. Liquid fabric softeners can be added manually during the rinse cycle or automatically if the machine has a dispenser designed for this purpose.

Fabric softeners coat the surface of a fabric with chemical compounds that are electrically charged, causing threads to "stand up" from the surface and thereby imparting a softer and fluffier texture. Cationic softeners bind by electrostatic attraction to the negatively charged groups on the surface of the fibers and neutralize their charge. The long aliphatic chains then line up towards the outside of the fiber, imparting lubricity.

Fabric softeners impart antistatic properties to fabrics and thus prevent the build-up of electrostatic charges on synthetic fibers, which in turn eliminates fabric cling during handling and wearing, crackling noises, and dust attraction. Also, fabric softeners make fabrics easier to iron and help reduce wrinkles in garments. In addition, they reduce drying times so that energy is saved when softened laundry is tumble-dried. Last but not least, they can also impart a pleasant fragrance to the laundry.

Water-repellent process

Water-repellent coatings are basically just a step up from water-resistant coatings. If a device is labeled as water-repellent it actually possesses the properties in which to, you guessed it, repel water from it, making it hydrophobic. A water-repellent device stands a very high chance of being coated with some form of thin-film nanotechnology, whether that is on the inside, outside, or both, and has a much better chance of standing up to water than your average device. Many companies claim water-repellency, but the term is heavily debated because a durable water-repellent is rare and because of all the questions and unpredictable elements associated with it.

Fire-retardant process

Fire-retardant fabrics are textiles that are more resistant to fire than others through chemical treatment or manufactured fireproof fibers. The term fire-retardant as applied to organic (i.e., containing carbon) materials, is intended to refer to reduced fire hazard, as all will burn under certain circumstances. The tests used specified in building codes, such as NFPA 701, are more correctly flame resistance tests, which test a fabric's ability to resist ignition with the flame size and duration in the test conditions.

When a fabric is designated as inherently fire-retardant, permanently fire-retardant, or durably fire-retardant, the flame retardancy will last for the life of the fabric as it has been woven into the fabric fiber itself. The drapery can be laundered or dry-cleaned as recommended by the drapery manufacturer. In the case of fabrics that are designated as fire-retardants that have been topically treated with chemicals the flame retardancy of the fabric will dissipate over time, particularly with repeated cleaning. As these chemicals are soluble in liquids-either water or dry cleaning fluid, these fabrics must be dry-cleaned with a non-liquid cleaning agent. The flame retardants work by coating the flammable fabrics with a mineral-based barrier, preventing a fire from reaching the fibers.