Fabric Preparation Slide 1

Transcription

1 Slide 1 Fabric Preparation Textile dyeing and finishing is composed of a group of processes used to convert greige textile materials into finished textile products. These processes include: preparation, dyeing or printing and finishing. The general purpose of preparation is to clean the textile and remove various contaminants that may be on the surface or embedded in the textile. It is required for all types of fibers, fabrics, and garments. Other non cleaning processes can also be used in the preparation sequence. Dyeing and textile printing are coloration techniques. Finishing imparts or enhances final performance and appearance properties in the textile product. It includes two distinct types of processing techniques identified as chemical finishing and mechanical finishing. Typically, chemical finishing changes the performance of the textile product, while mechanical finishing changes the appearance. However, these distinctions sometimes overlap or reverse, with chemical finishing changing appearance and mechanical finishing affecting performance.

2 Slide 2 Preparation Definition Preparation is the process of preparing fiber, yarn or fabric for subsequent, including nonapparel, end uses. The primary function of preparation is to remove impurities that will interfere with overall processing through all dyeing and finishing functions. Preparation is required in order to clean or remove impurities from textile materials regardless of the fiber content and construction of the textile. All types of fibers, yarns, fabrics and garments must be cleaned prior to dyeing, printing and finishing. Typical preparation processes include scouring and bleaching. Improper preparation leads to a myriad of poor performance and quality results in the finished textile product. Unfortunately, impurities found on textile materials can vary greatly in their composition, leading to many complexities in the various removal techniques. Companies often contribute to this complexity by poor storage, handling, and housekeeping practices. Removal of impurities can be extremely difficult when the manufacturer has little knowledge of their nature.

3 Slide 3 Preparation Objectives Produce a Substrate that has: Uniform extraction of impurities, such as sizes, seed husks, pectins, waxes, chemicals, catalytic substances, etc. Uniform standards of white Uniformly swollen fibers for transport of dyes and chemicals (absorption) Minimal fiber damage Rapid absorption of water A constant ph Uniform residual moisture content The primary goal of preparation is producing a textile substrate that has rapid and uniform absorption of water. In modern textile dyeing, printing, and finishing, almost all processes, with the exception of the various mechanical finishing techniques, are conducted in water, and some of these mechanical techniques incorporate moisture as a lubricating agent. Because there are no white dyes for textiles, the color of market whites is developed only through bleaching of the textile. Natural fibers normally have some amount of inherent color that must be bleached to produce white. Synthetic fibers often have whitening agents incorporated into their fiber composition and so appear white. However, synthetic textiles are typically bleached for market white products to assure color uniformity and match a standard. Great care must be taken to assure that the preparation processes result in minimal fiber damage. Unfortunately, the fibers cannot self repair or heal this damage. Severe damage results in overall fabric strength loss, even to the point of developing holes. Textile product discoloration or yellowing can also be an indicator of major fiber damage. During and after the preparation processes, the textile material should be maintained at a controllable ph level. Remember that ph represents a scale indicating the acidity and alkalinity of water solutions. The scale is logarithmic and goes from 0 14 with any value near 0 being highly acidic and any value near 14 being highly alkaline. A value of 7 is considered completely neutral and is assigned to distilled water. Control of both bath and textile material ph is extremely important for good dyeing and finishing processes. Preparation of textile materials has often been overlooked as critical to quality. Although materials may appear visually to be clean, it takes precisely controlled testing to determine the quality and effectiveness of the preparation processes. Without proper testing, poor conditions in the material may lie dormant until after dyeing, printing, and finishing, after which the quality defects become apparent and are much more difficult to repair.

4 Slide 4 Problems in Preparation Quality of substrate Lie dormant in fabric and show up during subsequent processes Product quality and the results from preparation processes can be negatively affected by raw material quality. Poor outgoing product quality results from both poor raw material quality and poor preparation. Even under the best of circumstances, consistent results from preparation steps are absolutely necessary for consistent textile product quality.

5 Slide 5 Preparation Processes Singeing Desizing Scouring Bleaching Optical Brighteners Enzyme Processes (cellulosics only) Mercerizing (cotton only) Heatsetting (synthetics only) Spandex Processing Although this list shows the typical preparation processes, the process sequence chosen may include only some of the listed steps and will be selected based on the product s end use requirements, fiber content, yarn type, fabric construction, and any other special circumstances encountered by the manufacturer. Because of the wide range of textile products, no single preparation processing sequence can be used for all products. Each process listed is discussed in detail later in this presentation, but we ll give a brief definition of each here. Singeing is an optional process that can be used on natural fibers, synthetic fibers, or blends to produce a smooth fabric surface and minimum pilling potential. Desizing removes warp sizing and is therefore used only for woven fabrics. It is used with all types of fibers and blends. Scouring is the cleaning process that removes dirt, oil, grease, and any other impurities in the textile material. This process is used for all types of fibers, yarns, fabrics and garments. Bleaching is a chemical process used to destroy any color impurities in the textile substrate. Optical brighteners are fluorescent whitening agents often referred to as colorless dyes. They are normally used along with the bleaching process for market white products. Enzyme processing typically uses cellulase enzymes to remove wild fiber hair or fuzz from the surface of the fabric. These chemicals work only with cellulosic fibers. Mercerization uses solutions of highly concentrated sodium hydroxide to improve cotton properties. Heatsetting is a high temperature process, used only with thermoplastic synthetic fibers, primarily polyester and nylon, to rearrange the internal molecular structure of these fibers to produce very high dimensional stability in the end product. Spandex is a unique fiber with properties similar to natural rubber. Low percentages of spandex are blended with other fibers to produce textiles with a wide variety of stretch properties. Special techniques and conditions are necessary to produce a consistent end product.

6 Slide 6 Singeing Purpose Clean fabric surface Reduce pilling Problems Singer streaks Melt balls Fabric elongation Singeing is an optional process used on yarns or fabrics to produce a clean surface or to reduce pilling of the product. The modern textile singer uses propane or natural gas flames to burn off the fuzzy surface fiber or wild hair. It is often referred to as gassing the fabric and can be used on natural or synthetic fibers. The results of the process, however, will exhibit some variation due to the chemical nature of the fibers. The single most difficult problem with singers is uneven intensity of the gas flames or a clogged gas jet with no flame present. When this happens, a singer steak running the length of the fabric is formed that is often not noticed until after dyeing, where an apparent shade difference in the streak is seen. The surface fuzz in the streak area reflects light differently than in the body of the fabric. The only solution to singer streaks is to singe the fabric again, which may also require re dyeing the fabric. Fabrics containing thermoplastic synthetic fibers should not be singed before dyeing light or pastel shades due to the formation of melt balls during the process. The melted fiber tips dye much more deeply than the normal fiber, so dark colored specks are seen in the dyed fabric. Synthetic fabrics and high synthetic content blends going into pastels should be singed after dyeing as part of the mechanical finishing process. Fabrics for deep shades can be singed before dyeing. Any heat sensitive fiber should be singed with care to prevent damage. Some materials show high elongation during the process due to the high temperature and the tension required to carry the material through the machine.

7 Slide 7 Singeing Diagram This illustration shows several images of a modern singer. The bottom shows the normal view of the outside of the machine as it is operated. The burners cannot be seen, but the observer can see the path of the fabric as it is fed to the machine, passes by the burners and exits at the rear, where it is flat folded into a basket. Singers can be stand alone devices or incorporated as one part of a large continuous fabric preparation range. The drawing on the top left illustrates the action of the burner and its insulating backing materials. Modern singers incorporate sophisticated thermodynamic systems in order to achieve temperature control. The top right shows the burners as they impact the fabric. It can easily be understood why flame intensity must be controlled and flame gaps must be eliminated during the processing to prevent uneven treatment of the fabric across its width. The fabric is moving at speeds between 65 and 300 yards per minute so variability results in linear steaks. The speed at which the cloth travels through the singer depends on fiber content, fabric construction, and fabric weight. In general, the lighter the weight, the faster the speed. If fabric speed is too fast, not enough singeing occurs. If the speed is too slow, the fabric is damaged or destroyed by the flames. The fabric must be cooled rapidly after the singeing process to eliminate the possibility of smoldering sparks igniting the basket of cloth as it is waiting for the next process. Cooling cans filled with circulating cold water are often used for this purpose in stand alone singers. In ranges, the singeing processing is almost always immediately followed by a water bath process such desizing or scouring. The sparks are quenched in the water bath.

8 Slide 8 Singe and Desize Range In a continuous singeing and desize range like the one represented in this diagram, each process is independent, but the cloth flows directly from one process to the next. A range is the most efficient way to prepare fabric because it uses a minimum amount of water, chemicals, energy, and time per yard. However, ranges also have the highest fixed costs, so production quantities must be high enough to justify their purchase and operation. The components of the range illustrated are representative of a typical range and may vary from mill to mill. Here, a brushing process precedes the singer. This is often done to raise any loose fiber so that the surface can be uniformly singed, but it is an optional process. The desizing process is represented by a saturator for applying the correct amount of desize chemicals to the fabric. Remember that the saturator also serves to quench any sparks in the fabric remaining from the singer. Next is a J box, a device that allows the chemicals to dwell in the fabric long enough for proper desizing action to take place. The size can easily be washed away in the subsequent modular washers. The J box is usually steam injected or steam jacketed to keep the temperature of the fabric over 200 degrees Fahrenheit so that the chemical action on the size is rapid and uniform. Once washed, the fabric is dried by passing it over hot stainless steel cans filled with high pressure steam, resulting in uniform and rapid contact drying of the fabric. Ranges can handle fabric in flat open width or in rope form. This equipment illustrated here represents open width processing.

9 Slide 9 Desizing Size is any compound added to warp yarns to give strength and lubrication during weaving. Can be done batch or continuously. Chemicals Used Starch enzyme Polyvinyl alcohol (PVA) or Carboxymethyl Cellulose (CMC) soda, ash, and detergent Factors Affecting Enzyme Action Time Temperature ph Surfactants NOTE: Check for starch; it turns iodine blue Desizing is a process used to remove the size added to the warp yarns of most fabrics during weaving. Knitted fabrics do not have any size on the yarns from which they are constructed, so desizing is not necessary. The size formulations used by most modern weavers are complex mixtures of chemicals that can include products such as film formers, adhesives, lubricants, and preservatives. The goal of desizing is to remove all the chemical components of the size mix from the fabric. This process is much easier for the finisher if the weaver notes the components and amounts in each size formulation, but this information is often not communicated to the finisher. Published test methods help determine the nature of the size formulation, but these are not always exact. Occasionally the finisher must resort to trial and error to determine the chemical composition and amount of size that must be removed. Failure to remove the size from the fabric leads to poor performance in subsequent processing and potential defective finished fabric. To efficiently remove the sizing material, it is necessary to know its chemical nature. For example, starch based sizing materials are not water soluble and require specific enzymes to degrade the size to simple products that can be easily removed. Additionally, corn starch size may require different processing conditions than sizes made from rice, potato, or other vegetable starches. Synthetic materials such as poly(vinyl alcohol) (PVA) or carboxymethyl cellulose (CMC) require no enzymes for removal. They are normally water soluble and are easily removed with proper desizing techniques. Key control factors for any desizing process include time and temperature, bath ph, buffering systems, and the type and amount of surfactant used. Surfactants are often employed as detergents and wetting agents. Once the process is completed, spot checks can indicate any residual sizing material left on the fabric. For example, a spot of iodine solution turns blue in the presence of starch. An experienced operator can decide whether a positive indication of starch requires further action on the fabric, including repeating the desizing process.

10 Slide 10 Scouring Removes dirt, grease, wax, and oil impurities Types of Systems Aqueous (water) Based Solvent Problems Improper scouring causes uneven dyeing, spots, blotches Fastness Yellowing Smoke Redeposition (Polyester) Scouring is the wet finishing process used to remove all but the colored impurities from the fabric, including dirt, oil, grease, and wax. Colored impurities are removed by the bleaching process that will be discussed later. For highest scouring efficiency, the finisher must have a general knowledge of the nature of the impurities on the textile material. Greige fabric storage should minimize the addition of unknown impurities. As a good practice, greige fabric should never be dragged across or stored on the plant or warehouse floor. Scouring is generally done in water baths using surfactants, which are also known as detergents or soaps. Soaps tend to be highly sensitive to hard water, causing them to perform improperly. Detergents are less sensitive to hard water and are typically preferred. Water purity is a major concern for the textile wet processor. Minerals such as calcium and magnesium dissolved in the incoming water cause a condition known as hard water. These minerals interfere with a wide variety of textile wet processing operations. Other materials in the water, such as iron, chlorine, or suspended solids, have the potential to significantly decrease overall finishing performance and quality. Most modern dyeing and finishing companies employ water pretreatment systems to remove or neutralize impurities. Solvent scouring can effectively remove oils, greases, and waxes from a number of textile materials. However, these solvents typically do a poor job of removing water based dirt, sand, and grit. They also pose disposal and indoor air quality problems for the plant. The vast majority of finishers, therefore, use aqueous scouring systems. The use of solvent scouring is generally restricted to the dry cleaning industry for cleaning apparel items that cannot be washed. The overall appearance of the fabric does not change greatly after scouring. Therefore to determine the effectiveness of the scouring process, scoured fabric samples should be tested in the laboratory using extraction and impurity residue measurement procedures. Otherwise, many of the problems resulting from poor scouring are latent and will not be apparent until after some later process such as dyeing. These defects include spots, blotches, yellowing, poor colorfastness, and uneven dyeing. Residual oil, grease, or wax left on the fabric after poor scouring may volatilize in later drying steps to form smoke or blue haze within the plant, creating an indoor air quality problem for company personnel. Some synthetic fibers, especially olefins and polyester, have tenacious attraction for oil based impurities. Special oil removing detergents are often necessary to prevent oily materials from re depositing onto the fabric from the wash bath. The presence of oil impurities can lead to off shade, fabric yellowing, poor colorfastness, blotches, or any number of other fabric defects.

11 Slide 11 Contents of Cotton Fiber A wide variety of natural impurities are found in the raw cotton fiber. The majority of these can be removed easily in a detergent/alkaline scour bath. One of the purposes of the alkali in the bath is to help remove oily materials such as fats and waxes by converting them to water soluble soaps. The nature of the detergent has an impact on the ease of removal of the substances as well. The impurities existing in normal, mechanically cleaned cotton are shown in this slide. The chart does not include any added processing chemicals from fabric manufacture that may be present in significant quantities. Generally, scouring removes most impurities except for those with color. Although these impurities make up only five percent of the total weight of mechanically cleaned cotton fiber, their improper removal can lead to serious quality defects and inconsistent performance in the final finished fabric. Scouring of cotton improves moisture absorbency not only by removing water repellent impurities such as wax, oil, or residual size, but also by rupturing the outer primary wall of the fiber, allowing water to penetrate more easily into the cellulose layer. Following scouring, the cotton will be bleached to remove colored impurities, as well as residual impurities left after scouring. However, bleaching is a destructive and expensive process that should be done only when necessary. Scoured and bleached cotton is essentially pure cellulose with no measurable amount of impurities remaining. It is the cleanest of the clean.

12 Slide 12 Wool Contents This table shows that wool is a much dirtier natural fiber than cotton. Wool is an animal hair fiber that includes impurities from the body of the animal as well as from the animal s environment. In this chart, protein represents the actual wool fiber. Because these percentages are based on the weight of the raw material that is sheared from a sheep, as much as 50% of the weight of the raw fiber is actually some type of impurity. Dirt is defined as the various particulate matter that becomes entangled in the wool during its growth. Suint refers to the salts embedded in the fiber when sheep perspire. Wool grease is composed of lanolin, which is a valuable by product widely used in numerous consumer and industrial products. Plant matter is typically leaf, stick, and stem trash. The high percentage of impurities necessitates that wool be scoured in fiber form before it is processed into yarn and fabric. Wool is highly sensitive to alkali. The alkaline scour conditions utilized for other fibers such as cotton or cotton/synthetic blends could severely damage wool to the point of actually dissolving it. Normal scour conditions for wool would include a mild detergent or soap and a mild alkali such as soda ash, also known as sodium carbonate. The bath temperatures can be hot but are normally well below the boiling point of water. Care must also be taken to have gentle agitation of the wool during scouring. Otherwise, the scales on the fiber surface can entangle during high levels of agitation in a process called felting. This property is an advantage in the wool finishing process known as fulling. Here, thin wool fabrics are run through a hot soapy solution that is being agitated along with mechanical pressure to work the fibers so that they entangle to form a thicker, fuller fabric.

13 Slide 13 Wool Additions for Spinning Moisture Humectant Antistat Some grease is left in (0.5%) After scouring wool to remove the bulk of the impurities, the fiber is spun into yarn and then made into fabric. Wool is then scoured again to remove residual wool grease, which was left in the fiber as a processing lubricant and any added impurities from yarn and fabric manufacturing, such as antistatic agents or humectants. These also have the possibility of interfering with subsequent dyeing or finishing processes.

14 Slide 14 Silk is an animal fiber with similar chemical properties to wool. However, the raw fiber has a much lower impurity content than wool. Silk is coated with a light gummy substance known as sericin that is easily removed in a hot mild detergent or soap bath. Like wool, silk is sensitive to alkali. For both silk and wool, optimum scour conditions occur at a ph of approximately 9.

15 Slide 15 Due to the many different chemical compositions of synthetic fibers, ideal scouring conditions vary greatly. Most synthetic fibers contain processing oils and lubricants, impurities from fabric manufacturing, and spin finish added during fiber extrusion. Some synthetics are cleaned more efficiently with water loving detergents, while others are better cleaned by oil loving detergents.

16 Slide 16 Bleaching Goals Complete removal of non fibrous matter Extraction of colored impurities of indeterminate type Hydrolysis, oxidation and removal of residual size Achievement of requisite degree of whiteness with the least possible damage to the fiber Improved absorbency Bleaching is a process to destroy any inherent color in the fabric as well as remove any residual impurities left in the fabric from the desizing and/or scouring processes. It involves destructive chemical action and should be used only when necessary because of the possibility of severe damage to the fabric. Because there are no white dyes, however, bleaching is the only way to achieve market whites in textile products. White pigments are available, but they do not dye the fabric. Bleaching is also necessary to whiten fabrics so they can be dyed into light and pastel shades or to provide a consistent background for printing. The chemical action of bleaching results not only in removal or destruction of colored impurities but in removal of non fibrous matter, which has the added advantage of improving absorption of the fabric. A major test of the skill of the finisher is achieving the required whiteness while minimizing the damage to the textile fibers and thus to the fabric.

17 Slide 17 Bleaching Problems Leftover Bleach Yellowing (strength loss) Holes Major fabric problems can occur if the bleaching process is out of control or if the chemicals are not properly removed after the process is completed. Any remaining bleach can interfere with dyeing, printing, or chemical finishing. Fabric yellowing often occurs due to over bleaching, defined as either running the process too long or allowing the process to go out of control. Yellowing is a sign of damage to the fiber and can be accompanied by fabric strength loss. Over bleaching can also result in such drastic and irreparable strength loss that the fabric develops holes. Particulate metal contamination in the fabric accelerates bleaching to the point that pinholes develop. Good housekeeping practices help to prevent iron contamination from particulate rust or other types of metals.

18 Slide 18 Bleaching Chemicals Peroxide Hydrogen Peroxide H 2 O 2 Fibers Cotton Silk Wool Jute Some Synthetics Bleach Bath: Peroxide NaOH (ph = )(do not exceed 9.0 with wool) Stabilizer Sequestrant Bleaching is at 95⁰ 100⁰ C Steamer (1 3 minutes), or J Box (1 1.5 hours),or Beck or Jig (1 1.5 hours) Bleaching is at 80⁰ F Pad cold batch (16 to 24 hours) Modern commercial bleaching formulas employ various chemicals that break down in water forming a system based either on peroxide or on chlorine bleaching. The most common type of peroxide or oxygen based system uses hydrogen peroxide, while the most popular type of chlorine bleach is sodium hypochlorite. Both bleaches work by chemical oxidation. The versatility of hydrogen peroxide makes it the most popular bleach. It can be used on a wide range of both natural and synthetic fibers with minimum damage or discoloration to them. It can also be used over a wide temperature range from room temperature to boiling water. Additionally, the concentration of the chemical can be varied over a wide range to allow changing both the time and temperature of the process. Unfortunately, the instability of hydrogen peroxide at bleaching concentrations necessitates that a chemical stabilizer be used in every bleach formulation. Hydrogen peroxide is most stable in alkaline conditions. The exact amount of alkali and ph used typically depends on the fiber being bleached. A sequestrant is added to the bleach bath to tie up any dissolved metals that could lead to fabric strength loss. The specific time and temperature to which the fabric is exposed depend on the equipment available to the manufacturer and the degree of whiteness required for the end product. Times can vary from as little as a few minutes in a continuous steamer to as long as 24 hours in a cold, that is, room temperature, pad batch operation.

19 Slide 19 Peroxide Advantages There is only a slight danger of damage for cellulose, protein, and most synthetic fibers. It is a low price bleaching agent Hydrogen peroxide solutions are stable and easily stored in suitable tanks. Various strength solutions are available for tank truck delivery (70%, 50%, and 35% concentrations). Hydrogen peroxide solutions can be piped to bleaching locations and easily measured for use Hydrogen peroxide produces a durable white fabric suitable for prolonged storage periods. No fumes or corrosion are associated with its use. Solution strengths are easily controlled. Short time reaction periods are possible. Hydrogen peroxide provides flexibility in the ph range of bleaching solutions allowing various alkalies to be chosen for special fabric conditions The versatility of hydrogen peroxide allows its use in various types of processes and equipment Hydrogen peroxide is flexible within the temperature range of fabric treatments. Since water and oxygen are hydrogen peroxide s decomposition products, it requires no after treatment and helps control odors in waste effluent solutions Peroxide has become the most popular of the industrial bleaches for textile materials for the following reasons: It is versatile and can be used on a wide range of fibers with minimum fiber damage as long as the process is properly controlled. It can also be used in various types of batch and continuous processing equipment, at different ph levels, and over a wide temperature range. It produces excellent results even at short processing times. It is easy to use. For example, the chemical is a liquid at room temperature and can easily be diluted to different concentrations and piped to processing equipment from a central chemical mixing location. However, it is a strong oxidizer and care must be taken to ensure that correct mixing procedures are followed. It produces white fabrics that are stable and that can withstand prolonged storage with no appreciable change. Compared to other bleaching chemicals, it is relatively safe to use. It does not release noxious fumes during processing nor does it corrode the metal in the processing equipment. After the process, the chemical decomposes into non polluting waste products of oxygen and water to help the waste water treatment system control objectionable odors while running more efficiently. It is more costly than sodium hypochlorite on a per pound basis, but it does not require a separate final neutralization step which reduces its overall processing cost.

20 Slide 20 Bleaching Chemicals Chlorine Sodium Hypochlorite (NaOCl) Fibers Cotton Bleach Bath Contains: NaOCl Alkali + buffer (ph 9 11) Requires an antichlor treatment to remove residual NaOCl Bleaching is at ⁰ Celsius Sodium hypochlorite is a familiar traditional bleach typically known as chlorine bleach. It is a common household product and is known by many different trade names. For many years, it was the bleach of choice for cotton and other natural cellulose fibers. However, chlorine tends to severely damage protein fibers such as wool and silk. Other bleaching agents were traditionally used for those fibers.

21 Slide 21 Chlorine Advantages and Disadvantages It has a low price. The danger of cellulose degradation is slight if ph and temperature conditions are controlled. Danger to synthetic fibers is great. Chlorine fumes are strong. Chlorine gas is corrosive Stored chlorine solutions are sensitive to sunlight and heat. It can contribute to fabric harshness. Chlorine requires the use of an antichlor treatment. Chlorine bleach is a very strong oxidizer and produces excellent durable whites on cellulose fibers. It also has a lower price per pound than other bleaches. In general, as long as the bleaching process is controlled, fiber damage can be held to a minimum. However, chlorine bleach has a number of serious disadvantages. It can severely damage many synthetic fibers, as well as wool and silk. During processing, the bleach releases dangerous chlorine fumes. The chlorine can attack and degrade the stainless steel equipment used for processing. Additionally, stored bleach solutions can be sensitive to light and heat. Particulate metals such as iron or copper embedded in the fabric catalyze the bleach so that pinholes are formed at the particle locations. Unlike hydrogen peroxide, sodium hypochlorite works in a more narrow range of ph and temperature. It can cause a harsher hand in certain fabrics, and it requires an antichlor treatment after bleaching to neutralize any leftover bleach. The antichlor step requires extra time and chemicals, adding to the overall cost of the process. Finally, the presence of chlorine in the effluent can cause serious problems in the wastewater treatment facility.

22 Slide 22 Bleaching Range The Jemco Bleaching Range is designed for processing tubular knits. Air is injected into the knit tube at the entry points of each range compartment to prevent the knit from developing permanent creases as it is processed through the range. There would be no need to inject air into a woven fabric which is not in tubular form. The infeed mechanism is made up of the fabric roll and the scray, which is a timing device to allow one roll of cloth to be sewn onto the next roll without stopping the flow of goods through the range. A dry J box acts as a timing and tension minimization area prior to the cloth entering into the bleaching compartments themselves. The unique thing about this range is that it can be a scour or a scour/bleach range, depending on how many compartments are connected. Generally, the range consists of a saturation compartment for scour chemicals followed by multiple washing compartments at various temperatures up to the boiling point of water. In the case of a scour/bleach range, the washing compartments are followed immediately by a saturating compartment for the bleaching chemicals and subsequent washing compartments. Alternatively, washing can be done in a separate machine such as a Jet Washer. In all cases, there is enough cloth traversing through the range to require ten to thirty minutes from the time the fabric enters the scour portion of the range until it exits the washing portion. For a scour/bleach range, it may take as long as an hour for fabric to enter the range and exit the final washing compartment. After washing, the moisture from the fabric is extracted to the point where the fabric is damp but not soaking wet when it is taken to the next process.

23 Slide 23 Continuous Open Width Prep Range The illustration represents a typical preparation range. In this schematic, all processes previously described for preparation are accomplished one right after the other. The fabric is processed in a flat, open width form to avoid the development of creases and wrinkles that can lead to permanent defects. Guiding devices maintain uniform width without putting excessive stress or strain on the fabric as it is passing through the range. This type of equipment is used for woven fabrics only because of their ability to withstand the inevitable stress of the process. Knits would distort and exhibit excessive amounts of shrinkage if they were processed through a range of this nature. In the diagram, the singeing process is followed immediately by desizing, scouring, and finally bleaching. Various steamer designs are illustrated. Steamers give thermal energy and dwell time to the fabric while it is impregnated with chemicals. In each of the wet processes, the chemicals typically dwell for ten to thirty minutes before being removed by washing and the fabric then proceeding to the next compartment. Various types of washing systems can be used effectively to remove the degradation products resulting from each process. Once all processes have been completed, the fabric is dried by passing over a series of steam filled cylinders known as dry cans. The fabric is then flat folded into a basket or rolled up on an A frame and taken to the next process. A range of this type has a running speed of 90 to120 yards per minute. There should be enough fabric in each steamer at any one time so that it takes ten to twenty minutes for a point on the fabric to enter the steamer, pass through and exit or, in other words, to accomplish proper dwell time.

24 Slide 24 Optical Brightening Agents (OBAs) Fluorescent Whitening Agents (FWAs) Definition: Colorless organic compounds that absorb invisible ultraviolet light and re emit the energy in the lower end (blue) of the visible spectrum. (fluorescence) Guide Lines for Use Each optical brightener has an affinity for specific fibers Anionics Cotton, Wool, Nylon Cationics Acrylics, Polyester Nonionics All synthetics They vary in fastness to light and washing They are not a substitute for bleaching Usually applied to market whites Some are resistant to specific bleaching agents and can be applied during bleaching Optical brightening agents are compounds that exhibit fluorescent properties and have affinity to many different textile fibers. These unique materials can absorb invisible ultraviolet energy and re emit this energy as visible light, typically blue to blue green wavelengths of light. They are highly beneficial for market white fabrics because their fluorescence makes the fabric look brighter, and their blue cast negates yellow cast in the fabric. Thus, the brightening agents make these white fabrics look brighter and whiter. These compounds are used in the textile finishing industry and as additives in most home and commercial laundry detergent formulations. Although they exhibit their greatest benefit on white fabrics, detergent manufacturers have found that they make many pastel and bright colored fabrics look brighter and cleaner after laundering. Unfortunately, these home applied brighteners have very limited fastness to light and laundering. Different types of optical brighteners are available for the textile finisher. Anionic types, which have a negative charge when immersed in water, are used for cotton, wool, and nylon fibers. Cationic types have a positive charge when immersed in water and are used for acrylics and some types of polyesters. Nonionic types have no charge and are used for most synthetic fibers. Optical brighteners can vary widely in their washing durability and fastness to light. Those applied by a textile finisher usually exhibit superior fastness properties to those applied in home laundering of textile products. Some industrial brighteners can even be somewhat resistant to bleaching and can be applied during the bleaching process. Optical brighteners are sometimes referred to as colorless dyes, which in strictly technical terms is a misnomer. Dyes by definition cannot be colorless. However, optical brighteners do exhibit certain properties similar to dyes, and they are applied to fabric in a similar manner to dyes. Brighteners are often used as an additive to the bleaching procedure, but they should never be considered a substitute for the process because they cannot destroy colored impurities in the fabric.

25 Slide 25 Absorption Emission Spectrum This graph represents the phenomenon of fluorescence. Using the electromagnetic energy scale of wavelength in nanometers, the diagram shows the absorption of ultraviolet energy in the 275 to 375 nanometer region, followed by the emission of this energy as visible light in the 425 to 525 nanometer region. Note that the peak of the emission energy is in nanometers, which is blue to blue green energy. The specific optical brightener illustrated would be excellent for market whites due to the nature of this emission spectrum. The visible light emitted by this compound would help cancel any yellowish cast on the white fabric. Other optical brighteners could show slightly different peak energies and locations in the UV and visible regions. Several specialty dyes also exhibit this type of behavior. These dyes are some of the brightest on the market, especially in high UV conditions such as sunlight.

26 Slide 26 Examples of Optical Brightening Fabric A qualitative assessment of the presence of an optical brightener on a fabric can be accomplished by viewing the fabric under a UV light source, or black light. Optical brighteners will cause the fabric to glow, generally with a bluish cast, under a black light, as observed in the photograph. Compare the two fabrics at the bottom of the picture and predict which of the two has been treated with an optical brightener. The fabric on the left has been treated. Now observe the two t shirts at the top. The neck ribbing on the left shirt has not received an optical brightener, while the body of the shirt has. The situation is reversed in the shirt on the right.

27 Slide 27 Mercerization Definition: Mercerization is the treatment of cotton with a strong caustic solution. This is performed on yarn or fabric, both woven and knits. Tension may or may not be used. Purposes Improves absorption, increase in dye affinity and yield Improves breaking strength (improved up to 20%) Improves dimensional stability Improves chemical reactivity Improves fabric smoothness Covers immature cotton fibers Increases Luster Mercerization is one the oldest chemical finishing treatments for cotton textile fabrics. It was invented by an English chemist named John Mercer in 1857 who discovered that when cotton was treated with a concentrated sodium hydroxide solution, a number of fiber property changes occurred. The technology has been developed and refined so that today this quality improvement process is successful on both woven and knit fabrics. To achieve the full benefits of mercerization, the fabric or yarn must be treated while under controlled tension, but it is also possible to use a low or non tension process to develop a measurable of amount of elasticity or stretch not found in untreated cotton. While it is possible to mercerize other cellulosic fibers, it is essentially a cotton only process. No other cellulosic fiber shows the overall quality improvement that cotton exhibits. For other cellulosics, the cost of the process outweighs the benefits gained. The process does not work at all on non cellulosic fibers. Other finishing processes exist that use caustic soda, but these do not yield the same type of results as the mercerization process. The process typically involves treating a fabric or yarn with a concentrated solution of sodium hydroxide, also known as caustic soda, at room temperature. The chemical penetrates the cotton fiber, causing it to swell rapidly. If the material is held under tension, the swelling action causes the convolutions of the fiber to smooth out or disappear, known as deconvolution. The mercerized fiber rearranges from a flat, twisted ribbon shape to a round, smoother rod shape. The combination of these effects results in a fabric with a smoother, more consistent surface appearance. An additional benefit of the rounder fiber shape is a noticeable increase in fabric luster. In fact, the mercerization process can be repeated several times to give the fabric an almost silk like luster. Additionally, the swelling action causes the cellulose molecules to rearrange to produce a more open internal structure, leading to a fabric with improved moisture absorption properties, increased dye or color yields, and improved chemical reactivity. These improvements result not only in a higher quality end product but in reduced operating costs for the dyeing and finishing plant. In standard textile processing, dyes are generally the most expensive chemicals used. After mercerization, many operations report as much as a 40% savings in dye use. In other words, the same shade can be obtained on mercerized cotton fabric using 40% less dye than on the same fabric that was not mercerized. Depending on the product mix and variety of shades produced by the company, these dye cost savings alone can offset the cost of the mercerization process. Another positive result of the process is an increase in the brightness of the final dye shade. Keeping all other factors equal, the dyed shades on mercerized cotton are the brightest shades possible for this type of textile product. Based on marketing research, this improvement in color brightness is of primary importance to the textile consumer. Colorfastness of the final dyed product may also improve on mercerized material; however, colorfastness of various dyes on cotton is a very complex situation, and improved results may not be seen with every dye formulation. Chemical finishes often show improved results and performance on mercerized fabrics. In some cases, a lower amount of finish can be used, but these savings are not as great as those realized with the dyeing process. Mercerization increases the tensile strength of the cotton fiber by as much as 20%. Increased fiber strength leads to increased yarn and fabric strength, resulting in lighter weight fabrics with increased durability and wearing properties.

28 One of the most perplexing problems associated with cotton processing is the presence of immature fibers in the final fabric. Immature fibers are caused by drying of the cotton fiber on the plant before development of the secondary wall, resulting in a weak, thin fiber with little cellulose. Every bale of cotton produced will contain some immature fibers. Good agriculture and harvesting practices help minimize the total amount of immature fibers present but cannot totally eliminate them. The immature fibers are carried through the yarn and fabric manufacturing processes, ending up as part of the final greige fabric. Because they have little or no cellulose, these fibers will not dye and are seen as white or very light specks in the dyed fabric. Weak, immature fibers can also lead to a variety of yarn and fabric defects, including an increased pilling tendency. Mercerization is the finishing process that is most effective for eliminating the negative effects of immature fibers. The swelling action of the caustic soda on what little cellulose is present in the immature fibers causes them to swell so that they can accept dye. Immature fibers that contain essentially no cellulose are dissolved and washed away by the process. The mercerized fabric now dyes more evenly and uniform with no light specks. The finished fabric exhibits markedly reduced pilling tendency as well.

29 Slide 28 The cotton fibers in the photomicrograph on the left are not mercerized and exhibit the inconsistent kidney bean shape, with an easily distinguished lumen in the center of the fiber. After mercerization, the fibers show much more consistency in shape. They do not exhibit the kidney bean shape but appear to be essentially round. In many of these mercerized fibers, the lumen has partially or completely disappeared. The swelling action of the caustic soda on the cellulose, along with the controlled tension applied during the process, results in the collapse of the lumen. The process yields fibers with more structural uniformity, resulting in improved dyeing results and increased fiber tensile strength. After one mercerization process, there may still be variability in the fiber shapes, and not all fibers will show a fully collapsed lumen. Repeating the process yields increased uniformity in fiber shape and smoothness. Some manufacturers mercerize fabrics as many as five times to obtain maximum fiber uniformity, consistency, smoothness, and strength.

30 Slide 29 The photograph illustrates the appearance effects of mercerization on a woven cotton fabric. The fabric on the right was mercerized before dyeing, resulting in a more lustrous appearance and a deeper, brighter shade of red than the fabric on the left. Note the small, white specks of un dyed fibers marked by the arrows. The specks are caused by the presence of immature cotton fibers that did not take up the dye molecules. These specks are not observed in the mercerized fabric.

31 Slide 30 As explained in an earlier slide, an immature fiber has little or no development of cellulose in its secondary wall, and it therefore has no regions for accepting dye molecules. Mercerization will minimize the effects of immature cotton either by swelling and enlarging the small amount of cellulose present or by dissolving and removing those immature fibers with no cellulose at all.

32 Slide 31 Mercerization Procedure Pad 22 25% NaOH at 100% wpu Dwell for seconds Stretch to greige width Wash to 3% NaOH and release Acid sour, rinse, and dry The modern mercerization process typically saturates the cotton yarn or fabric with a 22 to 25% sodium hydroxide solution with a dwell time of 30 to 40 seconds while the material is held under tension. The caustic is then thoroughly washed from the fabric. It is usually necessary to neutralize residual caustic in the fabric with an acid sour. The finisher should take care to minimize the formation of insoluble salts in the textile from the neutralization step. The textile material is then heavily rinsed to remove residual impurities and finally dried. In the specific case of double merceriziation of certain popular knit textile products currently available on the market, the typical processing sequence is to prepare and mercerize the yarn, dye the yarn in the required shades, knit the dyed yarn into fabric and then mercerize the knitted fabric. These two mercerizing steps produce knitted cotton fabrics with deep, bright pattern colors with very high luster that are popular in women s garments and men s and women s golf shirts. For solid shades, it is also possible to knit cotton yarns into fabric, prepare and mercerize, dye, and then mercerize a second time, producing deep, bright solid colors with high luster.

33 Slide 32 Open Width Mecerization The schematic is of an open width fabric mercerizing range, used for woven or knitted fabrics. The fabric is held open and flat under consistent tension. Control of fabric width and tension is important for developing the optimum conditions for mercerization. The fabric must be handled with great care to avoid wrinkle and crease formation that could be permanently set into the fabric during mercerization. The fabric is first saturated with the mercerization chemicals, and then immersed several times in the bath. Multiple immersions have been found to be the most mechanically efficient way to allow thorough chemical penetration of the fabric at processing speeds of yards per minute or higher. Next, the fabric passes through rolls to squeeze out excess chemicals and while leaving the proper amount, an important step for consistent results from lot to lot. The exact pressure used by the squeeze rolls depends on fabric weight and fabric construction parameters. Experience has shown that it is not necessary to have fabric width control in the saturation bath because the mercerization chemicals do not swell the cotton fibers instantaneously. Sufficient tension is generated at this stage by the lengthwise movement of the fabric. At normal processing speeds, the fabric proceeds to the clip or pin tenter before massive fiber swelling occurs. The tenter is a frame that holds two continuous circular chains that can be driven independently. The width between the chains can be varied during processing to accommodate numerous fabric types and to maintain consistent fabric tension to ensure optimum mercerization results. Tenter frame speed is adjusted to allow the chemicals sufficient dwell time to swell the cotton fibers. Counter flow washers are mounted over the top of the frame to wash out the mercerization chemicals as the process is completed. These high efficiency washers work by reusing water flowing in the opposite direction to the fabric movement. The cleanest water is introduced to the fabric through the last washer. This used water is then captured and introduced to the fabric again through the next to the last washer. This operation is repeated through each subsequent washer so that the dirtiest water is used in the first washer. By this time, the waste water has a high concentration of the mercerizing chemicals. It is then sent to the chemical recovery and waste water disposal system. Sodium hydroxide, or caustic soda, is a toxic chemical in wastewater, so it must be removed or neutralized to prevent severe environmental pollution or damage. Secondly, this chemical is too expensive to discard in the high quantities used for the normal production mercerizing range. It is more cost effective to recover and reuse the chemical. The cost savings realized from the recovered caustic can easily offset the cost of the recovery system. However, as much as 10% of the original caustic soda can remain in the final wastewater and must be neutralized prior to disposal. The clean, mercerized fabric may be held in a wet or dry condition prior to the next processing step, depending on the production setup of the finisher.