Care of Knit Fabric

Care must be taken for Knit Fabrics 
Although there is a great variety in the quality of knitted goods sold, and the performance of any individual knit may differ markedly from that of other knits, some general guidelines for the care of knitted goods can be observed. The problems that consumers seem to encounter most often in the performance of knitted fabrics are in the areas of dimensional stability, snagging, and pilling.

Dimensional Stability
One reason for the popularity of knits for wearing apparel is their comfort. The looped construction of knit fabrics permits the fabric to give with the body as it moves. But the stretchiness of knits also results in lessened dimensional stability. Consumers have complained about shrinkage, stretching, and distortion of knits, although interlock and double knit fabrics are usually more stable and display little or no shrinkage. Similarly, fabrics with weft or warp inserted yarns are more stable. Shrinkage control treatments, heat setting of synthetics, and special resin finishes can provide good dimensional stability for knits. Unfortunately, not all manufacturers provide such treatment for their products. Consumers should check labels for percentage of shrinkage or for other special treatments to judge potential dimensional stability. (About 3 percent shrinkage is one garment size.) If products fail to live up to specified performance standards, items should be returned to the retailer or the manufacturer.

Knits are considered to be easy-care fabrics, and many care labels recommend machine washing. Some labels will also specify that the fabric can be dried in an automatic dryer. In general, however, knits will shrink more in the dryer than if air dried. Knits maintain their shape best if they are dried flat. The weight of a wet knit, hung on a line, may cause the fabric to stretch out of shape. The dimensions of knits usually will be retained best by professional dry cleaning. Hand knits, sweaters of wool or animal hair fiber, and other knits with an open construction may require special hand laundering and blocking (stretching back into shape). Such items should be laid on a sheet of wrapping paper before washing, and the outlines traced. After washing, the garment should be stretched out on the paper to dry. While still damp, the garment should be gently stretched to fit the outline of the original dimensions.

Aside from stretching or shrinking, an additional problem with knitted items is skewing or twisting as the fabric is relaxed during laundering. Side seams of garments may pull to the front or back and hems may hang unevenly. In general, knits made of synthetics will have better resistance to stretching out of shape than will cotton, acetates, and rayons. Blending of synthetics with cottons, acetates, and rayons will improve the resiliency and dimensional stability of knitted fabrics made from these fibers. Price is a good guide-especially for children’s knits.

Mechanical Damage
The loop structure of knitted fabrics makes them especially susceptible to snagging. If a loop catches on another object, it may be pulled up from the fabric surface and a long snag, or pull, of yarn may be formed. If the yarn that has been snagged is not broken, it can be pulled to the back of the fabric. It may be possible to gently stretch the fabric and work the pulled yarn back into place. This is difficult to do with tightly knitted fabric structures. If the yarn has been broken, the snag may produce a hole in the fabric. A few hand stitches with needle and matching thread should be made to secure the yarns so that the hole does not become enlarged during wearing or laundering. Synthetic double knits or knits made from loosely twisted yarns may be subject to pilling. Weaker fibers, such as cotton, rayon, acetate, and wool, generally break off the fabric, but the stronger synthetic fibers cling to the fabric, making an unsightly area on the fabric surface. The use of textured yarns for knitting synthetics decreases the likelihood of pilling. Knits may be damaged by sharp objects puncturing the fabric. If yarns are cut, a hole will result, and further pressure and strain on the fabric may enlarge the open area, as loops are dropped in the interlocking structure.

Effects of Knit Structure on Knitted Fabric Performance

Knit fabrics are most comfortable, durable and make most flexible effect on human body. I am going to describe the effect of knitted structure on knit fabric performance in details. 

Durability Factors 

Strength of knitted fabrics is considered to be less important for durability than it is in woven goods. Knitted fabrics are easily stretched to accommodate changes of shape as a result of stresses imposed in wear and care. When knits are made from resilient fibers and yarns, the ability to stretch and recover from stretching will be enhanced. In comparison to knitted fabrics, woven fabrics are generally firmer and have less elongation. In knits the loops in the structure can be deformed horizontally or vertically, increasing the stretch in both directions. But, as noted earlier, variations in knitting techniques can increase or decrease extensibility of knitted fabrics. Double knit fabrics and warp knit fabrics are usually less extensible than single knit fabrics.A major problem in the durability of knits is the runs that can develop in weft knits when one of the loops is broken. If stronger fibers and yarns are used in these knits, they will be less likely to run. 

Appearance 

Shear ability, discussed in chapter 15, is an important factor in the appearance of textiles. In general, because of the ways in which yarns are combined, woven fabrics have higher shearability than do knitted fabrics. Knitted fabrics have good flexibility and are easily extended. Warp knits do not shear as easily as weft knits. 

These qualities must be taken into account by designers, although they may not be aware of the technical terminology used to describe the fabric properties. For example, a warp knit tricot fabric with low shearability would not be used to make a bias-cut garment in which the intention is to take advantage of high shearability. Instead, the designer would be likely to use a soft, gathered construction where the high flexibility of the fabric would work to good advantage, but where most of the draping would fall in the vertical direction of the fabric. In general, knits wrinkle less than do other fabrics. This is because loosely constructed fabrics generally allow more fiber redistribution and motion. However, knitted fabrics, because of their greater extensibility, are more likely to lose their shape in laundering. The stresses applied in knitting distort the shapes of the loops rather than just stretching the yarns as in weaving. On relaxation, the loops broaden, shrinking the fabric length and increasing the width. As with woven fabrics, the tighter the structure, the higher the shrinkage until the structure becomes so tight that further shrinkage is not possible. Such fabrics may, however, buckle. 

Knitted fabrics tend to have lower cover than do woven fabrics, with weft knits having substantially more porous structures than warp knits, unless the fabric is deliberately made to have an open, lacy construction as in some Raschel knits. Use of thinner or thicker yarns can increase the cover of knitted fabrics. 

Comfort Factors

Knits usually entrap more air than woven fabrics, although the tightness of the knit is a factor as well. Pile or napped knit constructions are especially good for cold weather because the yarns or fibers perpendicular to the surface provide numerous spaces for dead air. This effect is maximized if such fabrics are worn with the napped or pile surface next to the body, or if they are covered with another layer. The flexibility of knits contributes to a feeling of fabric softness. Fibers and yarns used can enhance or detract from the smoothness of knitted fabrics. 

Elongation and Recovery 

The majority of bathing suits for women, and many for men, are tight fitting, with stretch required for getting the garments on and off. Since knits have much higher elongation than woven or nonwoven fabrics, they are the preferred fabric construction for bathing suits that fit tightly to the body. Fibers too play an important role in achieving tightness of fit. Those with lower modulus and high resilience will enhance the stretch and recovery properties of knits. Not only elastomeric fibers but also nylon have low modulus and good recovery. Nylon and spandex are often chosen for swimwear because of these properties. Polyester is not usually used because it has a higher modulus and therefore does not stretch as easily. Knitted fabrics of nylon blended with elastomeric fibers, such as spandex or rubber, will provide the highest amount of stretch. The elastic fibers also have high recovery from stretch. 

Colorfastness 

Bathing suits are exposed to sunshine, chlorine and other chemicals in swimming pools, and salt water in oceans. Fibers and yarns are both important in maintaining the colorfastness of swimming suits that are often made of bright-colored fabrics. Light-fastness of dyed spandex is fair to good, while that of nylon dyed with acid dyes is good. Spandex normally makes up only a small percentage of the fiber content of swimwear fabrics and is often used in core-spun yarns wrapped with nylon. This helps to protect ir from sunlight. Colorfastness of nylon and spandex exposed to pool and salt water is fairly good but these fabrics will show some loss over time. 

Absorbency 

Since bathing suits are worn while swimming in water, the absorbency of the fabric is a consideration. If a material absorbs and retains a significant amount of water, the weight of the suit will increase, affecting its comfort and function. Synthetic fibers have low water regain and are more appropriate for bathing units than the natural fibers that were used many years ago. 

Environmental Resistance 

Light, chlorine, and salt water can also degrade textile fibers. When this occurs, bathing suit fabrics may lose some of their recovery from stretch. Nylon and polyester are more resistant to ultraviolet light and chlorine than spandex. That is another reason why spandex is usually used in small percentages blended with nylon. The use of rubber as an elastomeric fiber in swimwear has decreased because of its susceptibility to degradation by light and other environmental conditions. Because resistance of nylon to degradation by light is higher for fibers that have not been delustered, brighter nylons are usually used in swimwear.

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Pile Weave; Produce woven fabric with Warp Pile and Filling Pile

Pile Weave

Extra sets of warps or fillings are woven over ground yarns of plain or twill weave to form loops. Pile fabrics have been defined as “fabrics(s) with cut or uncut loops which stand up densely on the surface” (Klapper 1967,64). Pile fabrics may be created by weaving or through other construction techniques, such as tufting, knitting, or stitch through. To create the loops that appear on the surface of woven pile fabrics, the weaving process incorporates an extra set of yarns that form the pile. Construction of woven pile fabrics, therefore, represents a complex form of weaving in which there are at least three sets of yarns. 

Woven pile fabrics are divided into two categories depending on whether the extra set of yarns is in the warp direction or the filling direction. Warp pile fabrics have two sets of warp yarns and one set of filling yarns. Filling pile fabrics have two sets of filling yarns. Pile fabrics are woven by one of several methods, depending on whether they are warp pile or filling pile fabrics. 

Warp Pile Fabrics 

Warp pile can be made by the wire method, the double-cloth method, or by slack tension weaving.In the wire method one set of warp yarns and the filling yarn interlace in the usual manner and form the “ground” fabric in either a plain or twill weave. The extra set of warp yarns forms the pile. When the pile yarns are raised by the heddles, the machine inserts a wire across the loom in the filling direction. When the warps are lowered, they loop over the wire to make a raised area. The next several filling yarns are inserted in the usual manner. The wire is then withdrawn, leaving the loop, which is held firmly in place by the other yarns. Frieze, a fabric often used for upholstery, is an example of an uncut, looped pile fabric that can be made by the wire method. If the fabric is to have a cut pile, the wire has a knife blade at the end that cuts the yarns as the wire is withdrawn. 

Velvets may be made in this way. If the fabric is to have an uncut pile, the wire has no cutting edge. The double-cloth method is used for cut pile fabrics. Here, two sets of warps and two sets of fillings are woven simultaneously into a layer of fabric. A third set of warp yarns moves back and forth between the two layers of fabric, holding them together and being held by each fabric. The resultant fabric is cUt apart by a sharp knife, thereby creating two lengths of fabric, each with a cut pile. Velvets and flushes can be made with the double-cloth method. Velvets are usually made of filament yarns. Other nonpile fabrics can be made by the double-cloth method, and are discussed later.Terry cloth is made by the slack tension method. Terry cloth is made with uncut loops. Usually, two sets of warps and one set of filling yarns are used; however, more expensive fabrics may use two sets of yarns in each direction. The ground of the fabric is of warp yarns held under tension, the pile of warp yarns that are allowed to relax. 

Periodically (usually after every three picks), tension is released on the warp pile yarns at the same time as the next three filling yarns are pushed firmly into place. The first two of each three picks are only beaten up part way. The loose warp yarns loop up on the surface to form the terry pile. Loops may remain uncut to form the traditional terry cloth with loops on both sides. 

Sometimes one side is sheared to make an attractive velour face. Such fabrics do not wear as well as uncut loop fabrics. Pile yarns in velour toweling tend to become dislodged more easily, thereby shortening the wear life of the material. Terry pile may appear on one or both sides of the fabric. 

Filling Pile Fabrics 

Filling pile fabrics are woven by the filling pile method. In this method there are two sets of filling yarns and one set of warp yarns. The extra set of filling yarns forms floats that are from four to six yarns in length. The floating yarns are cut at the center of the float, and these ends are brushed up on the surface of the fabric. In some filling pile constructions, the filling yarn that makes the pile is interlaced with the ground one time before it is cut;’ in others, the filling pile interlaces twice. Those fabrics in which there are two interlacings are more durable than when only one interlacing has taken place. Floats for corduroy are placed in lengthwise rows, and floats for velveteen are spaced to produce an overall pile effect. Velveteens are characterized by a uniform, overall pile. The even spacing of corduroy floats produces a strip or wale characteristic of this fabric 

Corduroys are given names according to the numbers of wales. Feathercord corduroy has about 20 to 25 lengthwise wales per inch; fine wale or pinwale corduroy, about 16 to 23 wales; mid, medium, or regular wale corduroy, about 14 wales; wide wale corduroy, about 6 to 10 wales; and broad wale corduroy, about 3 to 5 ribs per inch. Novelty wale corduroys are also produced in which thick and thin wales are arranged in varying patterns. Some corduroy fabrics are now made with 100 percent cotton yarns in the pile filling and polyester and cotton blends in the ground yarns. Other decorative effects can be achieved by cutting floats selectively to vary pattern and texture. Most filling pile fabrics are made from spun yarns.