Chemical Finishing Slide 1

Transcription

1 Slide 1 Chemical Finishing As the name implies, finishing processes are the last steps in the manufacture of a textile fabric. The final properties and the conformity to desired fabric specifications are determined in finishing so the finisher is generally responsible for the final fabric width, weight, count, shrinkage and other properties contributing to the fabric quality. Finishing adds value to the fabric by enhancing existing desirable properties or by imparting new properties. Finishing can improve the appearance or the functionality of the fabric or both. The same starting fabric can be given vastly different properties, depending on the finishing steps it undergoes. Knowledge of the fundamentals of the various finishing processes will lead to a better understanding of the fabric properties that can be achieved as well as the limitations and variables of the finishing processes. Examples of properties that can be enhanced by finishing are hand, appearance, wrinkle resistance, water and oil repellency, and comfort, to name just a few. These properties can be affected by the application of chemicals to the fabric, by mechanical manipulation of the fabric or by a combination of the two. Finishing processes can include both chemical and mechanical aspects, but this section will concentrate on chemical finishing, or processes in which the principle agent of change to the fabric is chemical in nature.

2 Slide 2 Finishing Definition: Any operation (other than preparation or dyeing) in the manufacture of textiles that improves the appearance and/or imparts useful characteristics to the fabric. May give same basic fabric multiple uses for market versatility. Can be broken down into two categories: Chemical Finishing Mechanical Finishing Finishing is defined as any textile operation other than preparation or dyeing that improves the appearance or usefulness of a fabric. In fact, some processes that are usually classified as preparation steps can also be done as finishing steps. Heat setting of synthetics and mercerization of cotton are examples of these. Finishing steps are generally done after the fabric has been dyed, so the effect of finishing on the final fabric shade must be taken into account. Two categories of finishing are chemical finishing and mechanical finishing. Individual processes are categorized as one of these two types based on the major factor causing the change in the fabric. For example, many mechanical finishing processes require steam or moisture, which can be considered as chemicals, to lubricate the fabric, but mechanical action is the primary cause of the fabric enhancement. Conversely, many chemical finishing processes require machinery and mechanical action for application of the chemical agent, but they are classified as chemical finishing processes because the chemical is the primary cause of the change. Most chemical finishes use water as the solvent for application of the finishing chemicals.

3 Slide 3 Processes, Applicators and Reactors Processes Application of Finish Solution Evaporation of Solvent or Water (drying) Heating to Activate Chemicals (curing) Padders Applicators Padders Vacuum Extractors Kiss and Engraved Roll Applicators Foam Spray Reactors (Drying and/or Curing) Dry Cans Roller Ovens Loop Ovens Tenter Frames Examples of chemical finishes are those that improve wrinkle resistance, softness, water and oil resistance, stain release and resistance, and flame resistance. The various classifications of chemical finishes will be examined individually, but the general procedure for applying any chemical finish is to expose the fabric to a solution, generally aqueous, of the active chemical followed by uniform drying to remove the solvent and then curing of the active chemical by exposure to high temperatures. During the curing step, a chemical reaction is usually taking place. This reaction can bind the finishing chemical to the fabric or bind it to itself to form a network structure that promotes durability of the finish. Various methods exist to apply finish to fabric, examples of which are listed here. Subsequent slides will illustrate the equipment and procedures. Depending on the compatibility of the finishing chemicals and auxiliaries, more than one type of finish can be applied in the same step. For example, softeners are often included in the formulations of other finishing chemicals such as durable press agents. Padders, or squeeze rolls, are often used to apply chemicals to fabric. In padding, the fabric passes through a trough containing the finishing solution and then through squeeze rolls to remove excess solution before going to drying and curing. An alternative to padder rolls for removing excess liquid would be vacuum extractors. A lower, more efficient use of water in the chemical application procedure can be achieved with various application methods, including kiss roll applicators, foam application and sprayers. Finally, the reactors listed represent processes to expose the fabric to heat for drying and/or curing. Drying cans are a series of heated cans that the fabric is threaded through to allow fabric to can contact from can to can. Roller ovens contain a series of stationary rollers enclosed in a heated chamber through which the fabric is threaded. A loop oven is similar to a roller oven except that the fabric is looped over rollers that can move, thus minimizing tension on the fabric during drying. A tenter frame is probably the most commonly used, workhorse machine for drying and curing in a textile finishing operation. In discussing any type of drying equipment for textiles, it is important to know that the fabric itself, and not just the equipment providing the heat, must reach the appropriate temperature and remain at that temperature for a sufficient time for drying or curing to occur. A more detailed look at some of the equipment used for chemical finishing follows.

4 Slide 4 This is a side view of a single dip, single nip padder configuration, which is the most common type. The dip refers to immersion of the fabric in a trough or pan containing the finishing chemical solution, and the nip refers to the point of contact of the fabric between the two squeeze rolls. The squeeze rolls are sometimes called a mangle. One of the rolls can be rubber and the other metal, and the pressure between the rolls determines percent wet pick up. Percent wet pick up (%WPU) can also be influenced by fabric construction and the nature of the fiber itself. For example, with a hydrophobic fiber like polyester, most of the finish solution will be located in the spaces between fibers and yarns, whereas a hydrophilic fiber like cotton will actually absorb the solution into the fibers. Percent wet pick up is defined as the weight of liquid picked up by the fabric after padding expressed as a percentage of the original dry fabric weight. For example, if the initial dry weight of the fabric was 100 pounds, and the fabric weighed 190 pounds after padding, the %WPU would be 90%. Typical values for %WPU are between 75% and 100%. If the pressure on the squeeze rolls is too low, the solution can puddle up on the fabric, resulting in uneven drying and migration of the finish. The amount of active finishing chemical on the fabric after padding is a product of the %WPU and the concentration of the chemical in the pad bath. A typical concentration value is 10%. Recall from the Dyeing Module that the chemical concentration in the bath should remain constant during the process because the fabric is picking up the solution from the pan rather than preferentially absorbing the chemical. If the fabric has been properly scoured and bleached during preparation, it should have uniform absorption of solution in the trough. It may be possible to save water and drying costs by increasing the concentration of active chemicals in the pad bath, thus requiring a lower value for wet pick up, but doing so decreases the likelihood of uniform coverage over the fabric. Thus, the proper settings are a balancing act between energy efficiency and product quality.

5 Slide 5 Vertical Padder Animation The animation shows fabric running through a single dip single nip padder configuration. Note the vertical arrangement of the two padder rolls.

6 Slide 6 Horizontal Configuration The padder rolls can also be configured horizontally, as seen in this animation. The padder configuration is optional and depends on such factors as available space and the tendency of the fabric to wrinkle. The more popular setup is the vertical padder configuration because it provides a better view of the fabric by the operator at the nip point than the horizontal configuration.

7 Slide 7 Double Dip Double Nip Padder For thicker fabrics that are difficult to wet out or pile fabrics such as carpet, it may be necessary to use a three roll padder configuration to improve wetting and penetration of the finishing chemicals. This is called double nip, double dip and is illustrated in this slide. The fabric is immersed in the solution, padded, immersed again in the same solution, and padded a second time. In most cases, the fabric is dry before the initial immersion, which is called wet on dry finishing. However, the fabric can be wet, or undried, prior to finishing, and this is called wet on wet finishing.

8 Slide 8 Padder Video This video represents the points previously described of a padding machine. Note that this is a single dip, single nip with a vertical roll configuration pad.

9 Slide 9 Open Type Vacuum Slot Vacuum slots are a means of removing excess water from the fabric and are used in many applications. They are typically used in conjunction with padding, either before, to control the moisture level in wet on wet finishing, or after, to remove excess water in order to increase drying speeds. They allow application of finishing chemicals from a higher bath concentration by lowering wet pick up. For example, a padded fabric with 80% wet pick up passes over a vacuum slot that removes excess water from spaces between the fibers to give a 50% WPU. The slot removes water but may remove the finishing chemicals as well. Removal of the water allows a shorter drying time, thus increasing production in addition to saving energy. Vacuum efficiency is measured by the discharge coefficient. As the value for the discharge coefficient increases, more water is extracted from the fabric. The discharge coefficient is affected by the shape of the slot orifice. In cases where the fabric width does not cover the entire slot, automatic seals cover the portion of the slot not covered by fabric to insure maximum vacuum efficiency. An additional advantage in using vacuum slots is removal of lint from the surface of the fabric that could interfere with subsequent operations, for example, printing.

10 Slide 10 Herringbone Design The open type vacuum slots work well with woven or stable knit fabrics, but they subject some knitted fabrics or spandex containing stretch fabrics to too much tension. Knitted fabrics should be subjected to minimal tension during all stages of processing. Consequently, most knitted fabrics should be held in a slack configuration as they are processed. The slack in the knitted fabric could be pulled into an open vacuum slot. The herringbone design pictured is advantageous for knitted or stretch fabrics because it prevents suction from pulling the fabric into the vacuum slot, while still allowing the removal of excess water.

11 Slide 11 Kiss Roll Animation The animation shows a method for applying finish to one side only of a fabric. In this method, the kiss roll revolves through the chemical bath and transfers the finishing chemicals to the fabric as it passes across the top of the roll. The fabric is not ever immersed in the bath. The wet pick up on the fabric is determined by the speed of roller rotation, the speed of the moving fabric and the viscosity of the solution. Two small guide rolls on the top side of the fabric hold it against the kiss roll, which is rotating in the same direction that the fabric is moving. Moisture sensors on either side of the kiss roll can monitor fabric wet pick up by adjusting the fabric and roll speeds accordingly. A typical use for the kiss roll is the application of backing to upholstery fabric. The amount of finish applied cannot be precisely controlled by the kiss roll applicator, but the method is suitable for finishes such as latex backing that are not very costly and are desired on only one side of the fabric.

12 Slide 12 Engraved Rollers A second type of roller application is an engraved metal roll. The setup is similar to a kiss roll in that the roll revolves through the finishing solution to transfer it to the fabric. However, the roll is engraved with a pattern that transfers finish to the fabric in the pattern areas only. A pressurized backing or squeeze roll, usually rubber, is necessary to promote transfer of finish from the engraved roll to the fabric. A doctor blade is positioned between the chemical bath and the point of contact between engraved roll and fabric to remove liquid from the roller surface, leaving it in the engraved depressions only. The top rubber roll forces the fabric down into the pattern areas where the finish chemicals wick into the fabric. Wet pick up is determined by the depth of the engravings on the roller rather than by the fabric speed, and the amount of solid chemical applied is therefore controlled by the depth of engraving and the concentration of solids in the bath. Care must be taken to keep the engraved roll free of lint, so this method is not typically used with cotton fabrics.

13 Slide 13 Foam Applicator Knife Another energy efficient way to apply chemical finishes to textiles by minimizing water consumption is by using foam rather than liquid to deliver the active chemicals. Foam is a collection of air bubbles created by beating or whipping a liquid, and it can, therefore, be considered as a liquid diluted by air. Pure water does not foam unless a surfactant, or foaming agent, is added. The density of the foam can be described by a number called the blow ratio, which is the ratio of the volume of foam to the volume of the original liquid. Lower density foams (higher blow ratio) have larger bubbles than higher density foams. The stability of the foam is dependent on the strength of the liquid walls of the bubbles. Foam stability is described by the term persistence, which is defined as the time it takes a foam to revert back to a liquid. Foam persistence can be increased by adding a thickener or a water soluble polymer that will increase the viscosity of the liquid. Foams for textile finishing applications can be categorized, depending on their stability, as either persistent or metastable. These two types of foams require different types of application equipment. Persistent foams are applied by knife or horizontal roll coaters, while metastable foams require equipment that can generate and apply the foam simultaneously. The illustration shown is a knife coater applying a persistent, or stable, foam to one side of a fabric in a setup that is open to the atmosphere. The foam must therefore be stable with a low tendency to evaporate. The add on of foam is controlled by the distance, or gap, between the knife blade and the fabric surface. After metering of the foam by the knife, the fabric passes between squeeze rolls or a vacuum slot to break the bubbles in the foam and cause penetration of the liquid into the fabric.

14 Slide 14 Foam Applicator Horizontal Roll A variation of the knife coater is the horizontal pad pictured in this animation. This setup requires a stable foam that will not evaporate. An advantage to the horizontal pad is its ability to coat both sides of the fabric in one step. Banks of foam are located in the crevices between fabric and rollers as the fabric moves downward. The gap between roller and fabric meters the foam onto the fabric and breaks the bubbles in the foam.

15 Slide 15 Foam Applicator Unstable Foam A metastable foam requires application equipment that will both generate and apply the foam from an enclosed chamber. The foam breaks upon contact with the fabric and begins to penetrate. Wet pick up is controlled by the feed rate of liquid into the foam generator and by the fabric speed. A system of this type could be designed with two finishing heads that would allow finishing of one or both sides of the fabric as it passes through the machinery.

16 Slide 16 Sprayer A sprayer is another way to apply chemical finishes by using lower amounts of water than conventional padding, provided that the chemical mix is compatible with this type of application and does not lead to clogging or blockage of the nozzles. The animation shows two rows of nozzles spraying finish across the width of the fabric, one row for each side of the fabric. The machinery can be configured to spray one or both sides of the fabric. Note that the nozzles and the spray streams are spaced across the fabric so as to give uniform, complete coverage of the fabric surface without an overlap of the streams, which would result in a double application of the finish. For one sided applications of finish to fabric, the penetration of the solution depends on the amount of solution applied, or wet pick up, and the absorptive nature of the fiber. Cotton fabrics would absorb the solution into the fibers, thereby minimizing migration to the other side of the fabric. For polyester or other hydrophobic fibers, the finish would not be absorbed and would penetrate through the fabric by capillary action. For a cotton fabric, a wet pick up of at least 40% would be needed in order for the finish to completely penetrate the fabric. In cases where it is desirable to concentrate the finish on one side of the fabric, a lower wet pick up could be utilized.

17 Slide 17 Open Width Tenter Frame The next few slides illustrate equipment utilized for drying and curing of finished fabric. Drying of fabric is influenced by the temperature and relative humidity of the surrounding air and the flow of air over the fabric in addition to the fabric s construction and fiber composition. Water will evaporate rapidly from a fabric once it has reached its boiling point, but it is important to remember that the temperature of the fabric will not exceed the boiling point of water until all water is removed. Thus, the higher temperatures usually necessary for curing can not be reached until the fabric is completely dry. During drying and curing steps, it is important to monitor the temperature of the fabric itself in addition to the temperature of the surrounding air. Drying must occur evenly to prevent migration and uneven distribution of the finishing chemicals. The tenter frame, pictured here, is considered the workhorse machine for drying, heating setting and curing fabrics in a textile wet processing facility. It processes the fabric in open width form. In the illustration, the fabric moves from right to left. A gantry aligns the fabric for proper entry with no bow or skew introduced. The fabric then passes under a walkway that allows operator access. The fabric is introduced to a moving chain on each side that carries clips and pins for gripping the fabric on its selvages. Sensors on the machine allow for proper width adjustment. Clips are generally utilized for woven fabrics and pins for knitted fabrics. The fabric can be overfed, or fed more quickly than the chain is moving, to allow for pre shrinkage, or it can be stretched to increase yardage yield. Too much tension during drying can lead to stiffness and distortion of the fabric. Overfeeding introduces ripples in the fabric that allow for lengthwise shrinkage during drying, which can prevent later shrinkage during consumer use. After the fabric is gripped on both sides, it moves through the sequential heating zones, which can be heated by steam, natural gas, propane or oil. The temperature in each zone can be set independently to provide the necessary drying and curing conditions for the particular fabric being processed. The temperature profile for the fabric will also be affected by its speed through the frame. A profile of the actual fabric temperature and the dwell time at various temperatures is an important indicator of whether the tenter frame settings will produce proper drying, curing, or other desired effects on the fabric. In summary, drying and curing can be done as separate processes or they can be done as consecutive steps of the same process, but no curing can occur until the fabric is completely dried. Control of process variables during drying and curing can affect surface sheen, stability, shrinkage and stiffness of the finished fabric.

18 Slide 18 Tenter Frame Video This video is of an actual tenter frame in production, which illustrates the points just discussed.

19 Slide 19 Can Dryers Schematic Pictured in this diagram is a side view of a can dryer, in which fabric in open width form is threaded and runs continuously around a series of stacked stainless steel heated drums, allowing direct contact with the heated surfaces. The arrangement of the cans allows alternating contact with the face and back surfaces of the fabric. The number of cans in the arrangement is determined by the type of fabric being dried. The drums can be heated by steam, hot oil, electricity or gas, with steam being the most prevalent source of heat. Can dryers are used for woven fabrics only because they would subject knitted fabrics to too much tension. The tension is parallel to the warp direction; there is no width control on the can dryer setup. Friction between the can surface and the fabric holds the fabric in place in the width direction, and care must be taken not to impart and set creases, wrinkles or folds in the fabric during the process. Can dryers can be used in tandem with other equipment. For example, a fabric may be dried on a can dryer followed by curing on a tenter frame.

20 Slide 20 Loop Dryer Animation Shown is an animation of a loop oven, in which the fabric falls in long loops between rollers, also called sticks, that slowly move from the entrance end to the exit end of the enclosed, heated oven. The sticks are attached on each end to a chain that propels them across the chamber. At the same time, the rollers can freely revolve to prevent stick marks caused by contact of the fabric with the hot metal stick. New fabric loops are continuously being formed on the entry side as dried loops are removed from the exit end. The loops are dried by hot air circulating through the chamber. This type of dryer is for woven fabrics only because the weight of the hanging loops would stretch and elongate a knitted fabric.

21 Slide 21 Properties That Can Be Enhanced Durable Press Softness Stiffness Water Resistance Oil Resistance Stain Release Stain Resistance Flame Resistance Pilling Resistance Antimicrobial Comfort Wicking Absorbency Temperature Adaptability Antistatic Whiteness (optical brighteners) Let s examine the different types of chemical finishes and the fabric properties they impart or enhance. This slide summarizes some typical properties affected by finishes that will be covered in more detail in subsequent slides. Brief descriptions of the finishes to be covered are as follows: Durable press finishes are added to cellulosic fabrics such as cotton or rayon to impart wrinkle resistance and dimensional stability. Softeners are included in almost all finish formulations to impart a softer hand or to counteract the stiffening effects of some types of finishes. Hand builders are chemicals added to stiffen a fabric. Water resistant chemicals allow fabric to resist wetting by water while still allowing air and water vapor to penetrate. Oil resistant chemicals resist wetting by oils. Stain resistant chemicals cause the fabric to resist oily stains. Stain release chemicals make hydrophobic fabrics easier to launder by making the fabric surface more hydrophilic in order to release oily stains. Flame retardants lower the tendency of a fabric to burn. Pilling resistant treatments remove surface fibers from a fabric, which tend to entangle and form pill balls. Antimicrobials inhibit the growth of bacteria in a fabric. Comfort finishes promote wicking and absorbency, factors that can enhance comfort. Other types of comfort finishes can store and release thermal energy in active wear for heating and cooling effects. Antistatic chemicals prevent, reduce or dissipate static charges in fabric. Optical brighteners are added to enhance the whiteness and brightness of market white goods.

22 Slide 22 For the most part, consumers prefer a smooth, wrinkle free appearance in garments and other textile products. The resistance to wrinkling of a textile product is dependent on many fiber, yarn and fabric factors. One of the primary factors affecting wrinkling is the fiber s chemical composition and, specifically, its ability to absorb moisture. A hydrophilic fiber such as cotton can absorb moisture, disrupting hydrogen bonding between hydroxyl groups and providing lubrication between the cellulose polymer chains. The cellulose chains can then move past each other and form new hydrogen bonds in the new, wrinkled configuration. The new intermolecular bonds give stability to the wrinkled fabric. This process works in reverse when ironing cotton fabrics using steam. The moisture from the steam stabilizes the cotton fabric in a flat configuration. Because of the moisture absorption factor, durable press finishes are used on cotton, rayon and other cellulosic fabrics but are not useful or effective on synthetic fabrics like nylon and polyester. These synthetic fabrics can be stabilized against wrinkling and shrinkage by heat setting. Construction factors that affect wrinkling tendency are fiber fineness, yarn twist and fabric construction. In general, any physical factors that impart stress to the polymer chains in a fiber will increase the fabric s propensity to wrinkle. Coarser fibers promote a higher tendency to wrinkle because they have a greater bending radius of curvature than finer fibers, which puts more stress on the internal polymer chains. A higher twist level in spun yarns also puts more stress on the polymer chains, resulting in a higher wrinkling tendency, all other factors being equal. In general, knitted fabrics show a lower tendency to wrinkle than woven fabrics because the yarns and fibers in knits have greater freedom of movement and lower stress. Based on this same reasoning, a loosely woven fabric would show a lower tendency to wrinkle than a tightly woven fabric.

23 Slide 23 Overview Low Level (2 4%) Gives dimensional stability and shrink resistance to cotton and rayon Most cotton knits are given a resin treatment to set the loops and stabilize the fabric. High Level (Crease Recovery) (6 8%) Gives smooth drying properties, but drastically reduces tensile strength and abrasion resistance. Losses may be countered by blending with polyester. All important resins are formaldehyde derivatives. The principle of durable press finishing is to treat cellulosic fabric with a resin that reacts with the polymer chains to form cross links between chains, thereby stabilizing the chains and preventing their movement and slippage when the fabric is exposed to moisture. Through the years, this type of treatment has been referred to as wash and wear, crease resistant, wrinkle resistant or easy care, but durable press is the term used most often today. In addition to wrinkle resistance and dimensional stability, another effect that can be achieved with durable press finishes is the setting of permanent creases into fabric by treatment with the finish before creasing, followed by drying, creasing and then curing of the finish with the fabric in the creased state. The cross linking reaction does not occur until the high temperatures associated with curing are reached. The stabilizing effects of durable press finishes are also associated with the non desirable side effects of stiffening, weakening, and decrease in abrasion resistance of the fabric. Tear strength in particular is adversely affected because it is a function of both fiber strength and fabric stiffness. The first durable press finishes were used in the 1930 s. From the beginning, the chemistry of these resin finishes has been based on the crosslinking of cellulose chains with formaldehyde containing compounds, but the compounds have evolved through the years to minimize their tendency to release free formaldehyde during and after reaction with cellulose. The first permanent press creases were marketed in 1961 by the Koret Company. In the early days of permanent press, consumers sometimes found that their pants cuffs fell off after wear and laundering, but they were willing to endure the side effects of weakened fabrics in order to be freed from the task of ironing! In time, the strength durability of permanent press fabric was improved by blending polyester, a strong fiber unaffected by the resin treatment, with the cotton. A blend of 65% cotton and 35% polyester was found to be optimum. The properties achieved by treatment of a fabric with a resin finish depend on the amount of resin added. The amount is usually expressed as a percentage based on the weight of the fabric. A lower level of finish, 2 to 4 %, gives dimensional stability and shrink resistance, while a higher level of 6 to 8 % is required to give wrinkle resistance and crease recovery. If too much resin is added to the fabric, the strength loss and stiffness effects will be unacceptable.

24 Slide 24 Properties vs. Degree of Crosslinking Good Properties: Shrinkage control Shape retention No Iron (smoothness) Wrinkle Resistance Bad Properties: Tensile and tear losses Loss in abrasion resistance The degree of cross linking is determined by the amount of resin added to the fabric and the curing conditions, and it indicates how many links have formed between the cellulose chains, thereby immobilizing them. Remember that this type of treatment is effective for cellulose only. The presence of cross links improves shrinkage resistance, shape retention, wrinkle resistance and crease recovery in the fabric but also leads to fabric stiffening and a decrease in tensile strength, tear strength, and abrasion resistance. It is, therefore, critical to use just enough resin to achieve the desired effects and to monitor application, drying, and curing conditions so as not to over cure the treated fabric. To further counteract the negative effects of the resin, a softening chemical is usually incorporated into the resin formulation. Softeners will be discussed in more detail in later slides. Other properties that may be adversely affected by resin treatment are fabric absorbency, dyed fabric shade appearance and washfastness and soil retention.

25 Slide 25 Properties Factors Dependent On: Reagent Concentration Time and temperature of cure Catalyst to resin ratio Catalyst type Typical Formulation: Resin Catalyst Wetting Agent Softener Other This list summarizes factors that determine the degree of cross linking in a resin treated fabric. The time and temperature of cure should be selected based on the resin used. A catalyst is a chemical that causes the curing reaction to occur without reacting itself. Many of the catalyst systems are acidic so care must be taken to minimize damage of the cellulose by the catalyst. The typical formulation shown in this slide contains the durable press resin, a catalyst to cause the curing reaction to occur, a wetting agent to promote penetration of the formulation into the fabric and a softener to counteract the stiffening effects of the resin. The formulation would typically be applied to the fabric by padding, followed by drying and curing. The dominant resin for durable press finishing is known is DMDHEU, which stands for dimethylol dihydroxyethylene urea. The properties of DMDHEU include low free formaldehyde release, good shelf life, durability to home laundering of the finished goods, and a low degree of cross linking until a temperature exceeding 130 C is reached in processing. This last property allows fabrics to be treated with the chemical and then stored for over six months for delayed cure applications.

26 Slide 26 Various test methods exist for evaluating the effectiveness of durable press finishes on fabrics. Many of the methods are published by the American Association of Textile Chemists and Colorists (AATCC). Pictured are standard replicas for evaluating laundered fabrics for smoothness appearance according to AATCC Test Method 124, which gives specific directions for laundering and evaluation. Based on comparison to these standards, a laundered fabric would be assigned a rating from 1, indicating an extremely wrinkled appearance, to 5, indicating a very smooth appearance. Similar methods exist to aid in evaluation of such properties as seam smoothness, crease retention and dimensional stability or resistance to shrinkage.

27 Slide 27 Improve Hand Purpose of Softeners Improve Tear and Abrasion Improve Sewing Improve Appearance Softeners are chemicals that are added to fabrics to improve hand, drape, tear resistance and abrasion resistance. Softeners are included in almost all finishing formulations to improve the aforementioned properties and to counteract the stiffening effects of other finishes such as resins. In fact, most consumers use softeners in home laundering applications by applying a liquid softener to the rinse cycle or by using a dryer sheet. Softeners act as lubricants on the fiber, thereby improving its surface smoothness and ability to slide past other fibers. Lubrication lowers the coefficient of friction between fibers and other materials they contact. The lubricating effects of a softener also improve the sewability of a fabric by preventing needle cuts caused by friction between the needle and the yarns. Friction causes the sewing needle to become hot, leading to sewing thread breaks as well as yarn breaks in the fabric.

28 Slide 28 Softener Selection The physical state of the softener/lubricant will govern the corresponding hand of the fabric. Low viscosity lubricants are responsible for soft, pliable, silky feel, while solid waxes provide low coefficient of friction without changing the fabric s hand. The softener material s initial color and/or propensity to develop color when heated or aged must be considered when selecting the class of material to use. The softener material s smoke point may cause processing problems. Fabric odors may be caused by certain classes of softener materials. Softeners can alter the shade of the fabric. Some react with the dye to change its lightfastness properties, while some will cause the shade to become darker (the same phenomenon that makes wet fabric look darker). Softeners can be responsible for poor crockfastness by dissolving surface dye. Some dissolved dye may migrate onto adjacent light colored yarns, causing them to be stained. Softeners are typically fats, oils or waxes. The wide variety of softeners provides many choices of chemical composition and properties. Many times, the same chemicals that serve to soften a fabric can also serve as surfactants or water repellents. The choice of softener should be based on the fabric properties desired and on the compatibility of the softener with other chemicals in the finish formulation. For example, the viscosity of a softener can vary from that of a liquid to a semi solid material. Lower viscosity softeners provide a soft, silky feel and good drape, while a waxy solid is better for improving sewing, tear strength and abrasion properties. Another consideration would be the tendency of the softener to yellow when heated, thus changing the shade of the fabric. Softeners can also darken the shade simply by their application, or they can affect the lightfastness properties of the dyes. The smoke point of the softener is the temperature at which it volatizes, and the softener chosen should possess a smoke point higher than the highest temperature to which the fabric is expected to be exposed during processing. Smoke from oils and waxes can condense and redeposit on the fabric, causing spots. Fabric odors are a particular problem with fat based softeners, which can become rancid. Certain softeners can also adversely affect crockfastness, particularly of disperse dyes, by dissolving surface dyes. In cases of patterned or striped designs in which light and dark fabric areas are adjacent, the softener can cause migration of surface dye from darker to lighter areas, causing a staining effect.

29 Slide 29 Chemical Types Anionics Sulfonated oils and waxes Extensive use on fabrics to be mechanically finished Good re wetting properties Limited durability Cationics Aminoamides, imidazolines, fatty amines, and ammonium salts Impart very soft hand May change dye shade and affect soil removal Nonionics Silicones and other chemical types Preferred for white goods Expensive Softeners are classified as anionic, cationic or nonionic, depending on the electrical charge of the softening agent s molecular structure. Anionic softeners are negatively charged and are known for their rewetting potential. Because of this, a primary use of anionic softeners is on towel fabrics. They are also used as lubricants in fabrics to be mechanically finished by napping or shearing. Anionic softeners are not used on apparel fabrics when a soft, silky hand is of primary importance, and they have limited durability to laundering and dry cleaning. Anionics will not exhaust from a bath into fibers; they are applied to a fabric by physical deposition with a padder and are generally used on cellulosic fibers. The chemical composition of most anionic softeners is sulfonated oils, waxes or fatty esters. Cationic softeners are widely used on apparel goods to give a soft, silky hand on most all types of fabrics. They are positively charged compounds based on nitrogen containing chemical structures. The nitrogen atoms in the compounds become positively charged under proper application conditions. These compounds can be aminoamides, imidazolines, fatty amines or quaternary ammonium salts. In addition to being the most commonly used type of softener used in combination with other finishes, cationic softeners are also the type used by consumers in home laundry applications. They can exhaust from dye baths and can impart a soft fabric hand at very low add on levels, making them an efficient softener. Exhaustion can generally be improved under acidic conditions. Other benefits of using cationic softeners are reduced fabric stiffness, improved tear and abrasion resistance, compatibility with resin finishes and usefulness as a lubricant for the mechanical finishing processes of napping and sueding. Possible disadvantages of cationic softeners are their incompatibility with anionic auxiliary chemicals, potential for yellowing if overheated, retention of chlorine from bleach baths, inhibition of soil release and production of unwanted water repellency. Nonionic softeners have no electrical charge and can be silicone based compounds, ethylene oxides or hydrocarbons. Advantages of this category include chemical compatibility with other finishes, stability to heat and light, and effectiveness in improving wrinkle resistance, sewability, and tear and abrasion resistance. They produce a slick, silky hand and are used on white goods because they have a low tendency to yellow. However, silicone softeners are expensive, and they convey water repellency, which makes them unsuitable as towel softeners.

30 Slide 30 Hand Builders Overview Definition: Chemicals applied to a fabric to impart stiffness, weight or stability. Examples Lace stiffness and shape retention Denim stiffness or weight Hand builders are chemical treatments that cause a fabric to become stiffer or bulkier. Reasons for imparting stiffness to a fabric include providing a better appearance to the consumer in stores, as in starched shirts, improving cutting and sewing of the fabric, stabilizing a limp fabric, adding weight and providing product behavior that the consumer has come to know and expect. An example of the last category would be denim jeans, which the consumer expects to be stiff at the time of purchase.

31 Slide 31 Nondurable Builders Types of Hand Builders Starch Carboxymethycellulose (CMC) Polyvinyl Alcohol (PVA) Durable Thermosetting Builders Melamine/Formaldehyde Urea/Formaldehyde Durable Thermoplastic Builders Vinyl polymers Add weight and stiffness, but can be designed to proper stiffness Give luster Improve handling and sewing characteristics Hand builders can be classified as durable or non durable. Non durable hand builders are removed by washing or dry cleaning and are the type used to stiffen denim jeans and other consumer products. The chemicals used for this purpose are generally the same ones used in warp size applications for weaving: starch, carboxymethyl cellulose or poly(vinyl alcohol). Durable hand builders are more permanent and are added to fabrics to prevent limpness, add weight, and improve toughness and abrasion resistance. Thermosetting resins such as melamine and urea or thermoplastic vinyl polymers provide options for durable hand builder applications. The choice and chemical structure of the hand builder depends upon the properties and degree of stiffness desired. The cost and ease of application are also considered.

32 Slide 32 Water Repellent Finishes Overview The ability of a fabric to resist wetting by water is dependent on the chemical nature of the fibers, the porosity of the fabric structure, and the force behind the impacting water spray. Water repellency indicates the ability of the fabric to resist wetting, in contrast to waterproof, which indicates that the fabric is impermeable to water, even under hydrostatic pressure. Waterproof fabrics are usually coated to fill in the pores between yarns and fibers and are impervious to air as well as water, whereas water repellent fabrics have been treated to make the fiber surfaces more hydrophobic and water resistant, but they are still breathable. The wettability of a fabric surface can be gauged by observing a droplet of water placed on the fabric. If the fabric is not water resistant, the water droplet will spread over the surface and will disappear as it is absorbed by the fibers. On a water resistant fabric, the droplet will not spread and will appear as the rounded beads illustrated in the photograph. The droplet can be characterized by its contact angle, which is the angle measured from the fabric surface through the droplet to a line drawn tangent to the droplet from the outer point of contact between water and fabric. A droplet that completely wets the fabric would have a contact angle of zero. A higher contact angle (up to 180 degrees) indicates better water resistance. Water repellent chemicals change the surface chemistry of the fibers in a fabric by making the surface more hydrophobic, lowering the surface energy and causing a higher contact angle between water droplets and fabric surface. Certain water repellent treatments that impart very low surface energy to the fiber surfaces can impart oil repellency as well. Listed are several categories of water repellent chemicals. In order from least to most expensive, they are waxed based repellents, silicones and fluorocarbons. Durability to repeated laundering increases with cost of the finish. In considering the cost of a treatment, it is important to consider not only the cost per pound of the chemical, but the amount of the chemical required to achieve the desired properties. Sometimes a small amount of an expensive finish can be more cost effective than a large application of a cheaper finish to achieve the same degree of water repellency. Silicone water repellents impart resistance to water but not to oily liquids, whereas fluorocarbon treatments can impart both water and oil repellency. Water repellent finishes can be applied by padding, spraying or exhaustion techniques.

33 Slide 33 Standard Spray Test Several standard test methods exist to test the water resistant and repellency properties of a fabric. One is AATCC Test Method 22, which evaluates the appearance of a fabric mounted on an embroidery hoop at an angle and subjected to a spray of 250 milliliters of water from above, simulating rain falling on the fabric. A fabric with good water repellency would be given a rating of 100, indicating that no wetting of the fabric surface at all occurred, and all the water droplets beaded up and rolled off the surface. A fabric which exhibits complete wetting would be given a rating of zero. Another method to measure water resistance, known as the rain test, involves backing a vertically mounted fabric with a piece of dry blotter paper whose initial weight has been recorded. Water is sprayed sideways onto the fabric, after which the blotter paper is reweighed to determine the amount of water that has penetrated the fabric. These are but two of several AATCC methods for measuring water repellency.

34 Slide 34 The table illustrates the relationship between cost and durability for the three primary types of water repellent finishes. As stated earlier, durability generally increases with cost, but it is also important to choose the finish that gives the properties desired for the fabric in the most cost effective manner. A finish with a high cost per pound may need only a small add on to be effective, whereas a cheaper finish may require a large amount. All three types of water repellents work by lowering the surface energy of the fabric, causing water drops to form beads and not spread. All can be applied in conjunction with durable press finishes. Wax based repellents have the lowest cost and durability. Waxes melt, penetrate and coat the fabric with a thin waxy layer that provides repellency, but the layer can easily be abraded away. Silicone water repellents are much more durable than waxes to washing and dry cleaning. They form a sheath of finish around the fibers that is more abrasion resistant than wax, and the finishes can give a soft, pliable fabric hand. However, if the sheath of finishing cracks, durability will be lost. Silicone finishes impart water, but not oil, repellency. A disadvantage to silicones is their potential to absorb hydrophilic substances during dry cleaning and laundering that reduce water repellency. One use of silicones is to make upholstered furniture repellent to water borne stains. Fluorochemical repellents lower the surface energy of fabric to an even greater degree than silicones and, therefore, impart both water and oil repellency. They are the most expensive of the three categories, but wax is sometimes added to the formulation to lower the cost. Fluorochemical finishes are durable to laundering and dry cleaning and are often used to give water and oily stain repellency to upholstery fabrics and carpets. They are also used in polyester/cotton rainwear fabrics. By coating the individual fibers, the fluorochemical finish gives water repellency to the fabric while allowing it to retain its breathability.

35 Slide 35 Stain Finishes Definitions Soiling overall contamination or discoloration of a textile material by waterborne or oil borne stains, dry particulate matter, oil, or grease. Staining localized soiling of a textile material. Stain repellency the ability of a fabric to withstand penetration by liquid soils under static conditions; that is, conditions under which the liquid is not forced into the fabric by external sources other than capillary forces and the weight of the liquid drop. Stain resistance the degree to which a treated fabric, stained under dynamic conditions, can be returned to its original state by wiping or blotting of the fabric surface. Stain or soil release the ability of a fabric to be cleaned by laundering. Staining behavior that is inherent in a fabric can be altered by the application of chemical finishes. The terminology related to fabric staining can sometimes be confusing or misused, so some of the more commonly used terms are defined. The first distinction is between the terms soiling and staining. Soiling refers to the overall dirtying or discoloration of a fabric, whereas staining indicates localized soiling. A staining example would be a drop of salad dressing or spaghetti sauce on a shirt. A stain is considered more problematic than soiling because of its conspicuousness. A second important distinction to make is between stain resistance and stain release. Stain resistance causes fabric to resist penetration by a staining liquid so that the stain can be removed by wiping or blotting. Stain resistance and stain repellency have similar meanings. Conversely, a fabric with good stain release properties will allow stains to be removed by laundering. Good stain resistant properties are important for upholstery fabrics, carpet, and other fabrics that can not be laundered or dry cleaned, whereas stain release properties are more important for apparel fabrics that can be washed. Stain release can be a particular problem with hydrophobic fibers such as polyester. The chemical nature of the polyester is similar to that of oily stains and soils, so the stain does not want to leave the polyester to go into an aqueous laundry bath. Stain release properties are imparted to polyester by making fiber surfaces more hydrophilic. Stain resistant properties are typically imparted by lowering the surface energy of the fabric, which is the same mechanism used for imparting water repellency.

36 Slide 36 Finishes for Stain Resistance Fluorocarbons impart very low surface energy to fabric surfaces and thus provide both water and oil repellency. Silicone water repellents resist water borne stains only. Fluorocarbons are necessary to resist oily stains. Used on upholstery, floor coverings, and other products typically not laundered or dry cleaned. Allow the consumer time to wipe away the spill before it penetrates into the fabric. An effective stain resistant treatment will produce an upholstery or carpet fabric that allows the consumer time to wipe away water or oil borne liquid stains before they can penetrate into the fabric. The finishing agent forms a protective film around the fibers that causes beading of the liquid stain droplets, allowing them to be wiped or blotted away. A relatively small amount of the finishing agent can impart stain resistance, but it must be applied correctly and uniformly. The same type of chemicals that are used for water repellency applications, fluorocarbons and silicones, are used for stain resistance applications. Fluorocarbons are required to give resistance to both water and oily stains. One example of a situation where even fluorocarbon finishes can be ineffective to prevent stains is the case of a spill on nylon carpet of Kool Aid or other drinks colored with food colorings that are essentially acid dyes. Recall from the Dyeing module that acid dyes are used on nylon, and their good fastness properties are derived from the dye forming a strong ionic bond with the fiber. Therefore, Kool Aid stains can actually dye the carpet. Prevention of this type of stain requires a finish called a stain blocker that gives a negative charge on the nylon fiber to repel the food coloring acid dyes. Again, the finish gives the consumer time to wipe away the stain before it penetrates. The stain blockers are typically sulfonated aromatic aldehyde resins.