Since hot water is an expensive raw material and environmental pollution laws regulate discharge water, it is important to reduce the amount of water consumed by these operations. One way to reduce water consumption is by Counterflow Washing. Water flow through the wash boxes counter to the flow of the fabric Fresh water is fed to the exit compartment to insure that the fabric exits through the cleanest water. The water from the last box is pumped to the preceding wash box which in turn is pumped to the one preceding it. The water from the entry box is dumped into the drain since it is the most heavily contaminated wash water. This technique saves on water consumption since only the most heavily contaminated water is discharged, cleaner water is reused until it becomes heavily contaminated IIL. REFERENCES
Since hot water is an expensive raw material and environmental pollution laws regulate discharge water, it is important to reduce the amount of water consumed by these operations. One way to reduce water consumption is by Counterflow Washing. Water flow through the wash boxes counter to the flow of the fabric. Fresh water is fed to the exit compartment to insure that the fabric exits through the cleanest water. The water from the last box is pumped to the preceding wash box which in turn is pumped to the one preceding it. The water from the entry box is dumped into the drain since it is the most heavily contaminated wash water. This technique saves on water consumption since only the most heavily contaminated water is discharged, cleaner water is reused until it becomes heavily contaminated. III. REFERENCES 12
CHAPTER 2 CHEMISTRY OF YARN AND FABRIC PREPARATION . YARN PREPARATION A. Warp size In the production of woven fabrics, warp yarns are sized with a protective coating to improve weaving efficiency. Movement of the warp yarn through the heddles and mechanical actions during insertion of filling creates a great deal of brasive stresses on these yarns. Unprotected, the warp yarns cannot withstand the rigors of weaving. They will break causing machine to stop and thus be responsible for loss of productivity. Weaving efficiencies are vastly improved when the warp is properly sized. Size or Sizing is defined as the composition of matter applied to the warp yarn for weaving protection. Size usually consists of a water soluble, film forming macromolecule and a lubricant 1. Requirement of a Good Size The qualities required of a good size depends, in the main, on what type of yarn is in the warp. For example, fine count spun yarns require more protection than do plied yarns or course count spun yarns a Spun Yarns Spun yarns require that size contribute to yarn strength and that the protruding fiber ends be glued down to make it less hairy. To do this, the sizing solution must have a high viscosity to prevent penetration into the yarn. Optimum protection is afforded when most of the size remains on the yarn surface to coat the yarn and glue down the protruding hairs
CHAPTER 2 CHEMISTRY OF YARN AND FABRIC PREPARATION I. YARN PREPARATION A. Warp Size In the production of woven fabrics, warp yarns are sized with a protective coating to improve weaving efficiency. Movement of the warp yarn through the heddles and mechanical actions during insertion of filling creates a great deal of abrasive stresses on these yarns. Unprotected, the warp yarns cannot withstand the rigors of weaving. They will break causing machine to stop and thus be responsible for loss of productivity. Weaving efficiencies are vastly improved when the warp is properly sized. Size or Sizing is defined as the composition of matter applied to the warp yarn for weaving protection. Size usually consists of a water soluble, filmforming macromolecule and a lubricant. 1. Requirement of a Good Size The qualities required of a good size depends, in the main, on what type of yarn is in the warp. For example, fine count spun yarns require more protection than do plied yarns or course count spun yarns. a. Spun Yarns Spun yarns require that size contribute to yarn strength and that the protruding fiber ends be glued down to make it less hairy. To do this, the sizing solution must have a high viscosity to prevent penetration into the yarn. Optimum protection is afforded when most of the size remains on the yarn surface to coat the yarn and glue down the protruding hairs. 13
b. Continuous filament yarns These yarns are strong to begin with. The main purpose of the size is to tie all of the filaments together. Stray filaments are easily broken; however, as part of a single, large bundle, the yarn is strong and abrasion resistant. Viscosity needs to be low so that the solution penetrates into the yarn bundle. Also the better the adhesion between the size and the fiber, the better is the protection c. General Requirements of a Good Size Tensile Strength s Abrasion resistant a Inexpensive m Good adhesion m Flexible ■ Extensible a Not support bacteria Easily removed IL. FABRIC PREPARATION A. Warp size and desizing For woven fabrics, warp size constitutes the major impurity that must be removed in fabric preparation. This section introduces the materials often used warp sizes and the chemistry needed to remove them Sources of Sizing Compounds The following list summarizes the materials that can be used as warp sizes Some of the base materials are used either alone or as additives to impart desirable properties to other bases. When designing the desizing step, it is important to know what base size was used. Each film-former has its own optimum conditions for effective removal. a knowledge of the chemistry of the film-formers will make it easier for one to grasp how to best desize specific fabrics s Starches s Flours Polyvinyl alcohol m Dextrine s Gums s Polyacrylic Acid m Glue n Gelatins Carboxymethyl Cellulose Synthetic Polymers and Co-polymers Of the bases listed above, starch and polyvinyl alcohol are the polymers most often used when sizing spun yarns. Synthetic polymers work best on filament yarns These polymers at times are blended with starch to improve starch's adhesion to synthetic fibers
b. Continuous Filament Yarns These yarns are strong to begin with. The main purpose of the size is to tie all of the filaments together. Stray filaments are easily broken; however, as part of a single, large bundle, the yarn is strong and abrasion resistant. Viscosity needs to be low so that the solution penetrates into the yarn bundle. Also the better the adhesion between the size and the fiber, the better is the protection. c. General Requirements of a Good Size II. FABRIC PREPARATION A. Warp Size and Desizing For woven fabrics, warp size constitutes the major impurity that must be removed in fabric preparation. This section introduces the materials often used as warp sizes and the chemistry needed to remove them. 1. Sources of Sizing Compounds The following list summarizes the materials that can be used as warp sizes. Some of the base materials are used either alone or as additives to impart desirable properties to other bases. When designing the desizing step, it is important to know what base size was used. Each film-former has its own optimum conditions for effective removal. A knowledge of the chemistry of the film-formers will make it easier for one to grasp how to best desize specific fabrics. Of the bases listed above, starch and polyvinyl alcohol are the polymers most often used when sizing spun yarns. Synthetic polymers work best on filament yarns. These polymers at times are blended with starch to improve starch's adhesion to synthetic fibers. 14
Ⅲ. STARCH Historically, starches and flours have been the film-formers of choice for textile sizing. The key difference between flours and starches is the gummy substance gluten, starches are flours which have had the gluten removed. Nature produces a wide variety of starches as a white granular substance found in seeds, roots and stem piths of growing plants. Flours or meal is leached with water (to remove the gluten) leaving the white, free-flowing granule which has limited solubility in cold water A. Sources of starches used as textile size Listed below are the natural sources of starch used as textile size a Potato(farina) ■ Tapioca( cassava) a Sago ■ Wheat R i a Sweet Potato ■ Yucca B. Chemical constitution Starch polymers are carbohydrates composed of repeating anhydroglucose units linked together by an alpha glucosidic linkage. The structure contains two secondary hydroxyls at the- 2, 3-positions and a primary hydroxyl at the 6-position The alpha linkage is an acetal formed by the linkage of the hydroxyl at the -1 position with the -4 position of another. This gives rise to a linear polymer called Amylose. Branching can occur when an acetal linkage between the -1- position of one ring forms with the -6-position of another. Highly branched polymers are called Amylopectin. The differences between amy lose and amylopectin are d Amylose is a linear polymer, molecular weight range 100,000 to 300,000, found in the interior of the starch granule and accounts for 19 to 26% of the weight. It is soluble in hot water; however, when the solution is cooled, it will form strong hy drogen bond between adjacent chains making it difficult to re-solubilize a Amylopectin is the major component of starch and comprises the outer sheath of the granule. a highly branched, high Mw polymer (1. 6M), less water soluble than amylose
III. STARCH Historically, starches and flours have been the film-formers of choice for textile sizing. The key difference between flours and starches is the gummy substance gluten, starches are flours which have had the gluten removed. Nature produces a wide variety of starches as a white granular substance found in seeds, roots and stem piths of growing plants. Flours or meal is leached with water (to remove the gluten) leaving the white, free-flowing granule which has limited solubility in cold water. A. Sources of Starches Used as Textile Size Listed below are the natural sources of starch used as textile size: B. Chemical Constitution Starch polymers are carbohydrates composed of repeating anhydroglucose units linked together by an alpha glucosidic linkage. The structure contains two secondary hydroxyls at the -2,3- positions and a primary hydroxyl at the -6- position. The alpha linkage is an acetal formed by the linkage of the hydroxyl at the -1- position with the -4- position of another. This gives rise to a linear polymer called Amylose. Branching can occur when an acetal linkage between the -1- position of one ring forms with the -6- position of another. Highly branched polymers are called Amylopectin. The differences between amylose and amylopectin are: Amylose is a linear polymer, molecular weight range 100,000 to 300,000, found in the interior of the starch granule and accounts for 19 to 26% of the weight. It is soluble in hot water; however, when the solution is cooled, it will form strong hydrogen bond between adjacent chains making it difficult to re-solubilize. Amylopectin is the major component of starch and comprises the outer sheath of the granule. A highly branched, high MW polymer (1.6M), less water soluble than amylose. 15
Figure ll Chemical structure of Amylose and amylopectin Amylose Amylopectin C. Starch Solutions Natural starches are not very soluble in cold water. Cooking is necessary to get the starch granules to form a homogenous solution. Typically the starch granules are stirred in cold water and kept suspended by high speed mixing. As the temperature is raised, water penetrates through the amylopectin membrane solubilizing amylose. The granules swell as more and more water diffuses in enlarging to many time their original dimensions. The viscosity of the solution increases as the granules swell, reaching a maximum at the point where the swollen granules are crowding against each other. Prolonged heating and mechanica shearing cause the swollen granule membrane to rupture allowing the solubilized amylose to spill into the bulk of the solution. At this point the viscosity begins to fall off finds a stabilized level and remains there the starch solution can be considered as solubilized amylose molecules intermingled with ruptured swollen fragments ofthe amylopectin membrane 1. Retrograding The solution will remain fluid as long as it is stirred and kept hot. However if the solution becomes concentrated by evaporation of water, and/or should the
Figure 11. Chemical Structure of Amylose and Amylopectin C. Starch Solutions Natural starches are not very soluble in cold water. Cooking is necessary to get the starch granules to form a homogenous solution. Typically the starch granules are stirred in cold water and kept suspended by high speed mixing. As the temperature is raised, water penetrates through the amylopectin membrane solubilizing amylose. The granules swell as more and more water diffuses in enlarging to many time their original dimensions. The viscosity of the solution increases as the granules swell, reaching a maximum at the point where the swollen granules are crowding against each other. Prolonged heating and mechanical shearing cause the swollen granule membrane to rupture allowing the solubilized amylose to spill into the bulk of the solution. At this point the viscosity begins to fall off, finds a stabilized level and remains there. The starch solution can be considered as solubilized amylose molecules intermingled with ruptured swollen fragments of the amylopectin membrane. 1. Retrograding The solution will remain fluid as long as it is stirred and kept hot. However if the solution becomes concentrated by evaporation of water, and/or should the 16