Fibre Blends; Properties of fiber Blended Yarns

Fibre Blends 

Fibre Blending is the process of mixing fibers together. As noted earlier, it can take place at any of several points during the preparation of a yarn. The purposes of blending are (1) the thorough intermixing of fibers and/or (2) combining fibers with different properties to produce yarns with characteristics that cannot be obtained by using one type of fiber alone. Self blending of bales of the same fiber is done routinely in processing natural fibers because the fibers may vary from bale to bale. In this type of blending, the mixing of as many bales as possible is done early in the processes preparatory to spinning so that the subsequent steps can help to mix the fiber still more completely. For the same reasons, even when two or more different fiber types are combined, blending is done as early as possible. Carding helps to break up fiber clusters and intermix fibers more thoroughly. However, if the fibers being blended require different techniques for opening, cleaning, and carding, as with polyester and cotton, then slivers can be blended. For blended yarns of different fibers, the blend level is the percentage by weight of each fiber. Blending is not limited to staple-length fibers. Filament fibers of different generic types can be combined into a single yarn. This can be done either by extruding these fibers side by side, during drawing, or during texturing. As described earlier, a blended yarn can be core spun with one fiber at the center and a different fiber as the covering or be wrapped with one fiber making up the central section and another the wrapping yarn. As yarn spinning and texturing technologies grow more sophisticated, we expand the possibilities of combining several different fibers into one yarn. Multiple-input texturing machines can produce specialty yarn blends. 

It should be noted that fabrics woven from two or more yarns each made of different fibers are not considered blends. These fabrics are, instead called combination fabrics. They do not behave in the same way as those fabrics in which, the fibers are more intimately blended and may require special care procedures. Regrettably, the Textile Fibers Products Identification Act (TFPIA) labeling requirements do not distinguish between blended fabrics and combination fabrics when fiber percentage contents of fabrics are given. 

Properties of Blended Yarns 

Fibers with different characteristics, blended into a yarn, can each contribute desirable properties to the final textile material. The ultimate performance is an average of the properties of the component fibers. For example, a fabric of 50 percent cotton and 50 percent polyester would have an absorbency intermediate between that of cotton or polyester. In some cases, however, the observed fabric property is not determined simply by the relative amounts of each fiber in the blend. In blends of nylon with cotton, the tenacity of the blended yarn initially decreases with increasing amounts of nylon because of differences in the breaking elongation of the two fibers. At the breaking elongation of the cotton fibers, the nylon fibers are not assuming their share of the stress, leaving the cotton to bear the load. 

The stage at which blending occurs also affects the properties of the fabrics. In general, the more intimate the mixing of fibers in the blends, the better the resulting properties. Yarns blended at the fiber stage exhibit a more effective averaging of properties than ply-blended yarns. Even though considerable study and evaluation have been made of optimum fiber proportions required to achieve desired results in blends, no certain conclusions have been reached. It is clear that extremely small proportions of fibers have no appreciable influence on performance, although they may have some effect on appearance.

Modern spinning method; Ultra Modern method of manufacturing yarn.

OTHER METHODS OF MANUFACTURING YARNS 

In addition to ring and open-end spinning, techniques that insert true twist into yarn, there are other types of yarn construction. Three of those that have some current commercial application are described in the following sections: false-twist, or self-twist, spinning; yarn wrapping; and splitting or slitting films made from synthetic polymers. The viability of these processes for commercial purposes varies. 

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Air-Jet Spinning 

Air Jet spinning is a ultra modern spinning or yarn manufacturing method The Murata Company, a Japanese firm, has commercialized an air-jet spinning machine that functions as follows. A largely untwisted sliver is fed into the machine. Two nozzles, each forcing an air jet against the sliver from opposite directions, cause fibers from the outer layer of the sliver to wrap around the interior fibers, thereby forming the yarn. 

Hollow Spindle Spinning 

Hollow spindle spinning is another modern yarn manufacturing process. In hollow spindle spinning, a sliver of core fibers is fed through a hollow spindle where it is wrapped by a filament yarn unwinding from the spindle. An interesting application of the technique has been in the manufacture of towels and other fabrics, in which the wrapped yarns are used in the pile. In this instance, the wrapping yarn is made from soluble polyvinyl alcohol (PVA) fibers. After the fabric has been put through the finishing processes, these yarns dissolve, leaving a soft, all-cotton twist less and absorbent yarn in the pile 

Core Spinning 

Core spinning is also a special spinning for yarn manufacturing. Core-spun yarns are usually made with a continuous filament core surrounded by twisted fibers or other yarns. Recently, core spun yarns with a staple core of one fiber and an outer sheath of another fiber have been produced by an adaptation of ring spinning. Two rovings, one of polyester and one of cotton, are fed through drafting rollers and then pass through separate channels before being wound on the spindle. The channel for the cotton sheath is longer, ensuring that it will wrap around the polyester core as the twist is inserted. Fabrics from staple core yarns are more durable and have more easy-care features than those of 100 percent cotton yarns. 

Making Yarns from Films 

Recently, various new techniques have emerged that allow yarns to be formed directly from synthetic polymers without the formation of fibers or the twisting of fibers into yarns. These processes include the formation of yarns by the split-film and slit-film processes. Slit-film yarns could be classified as monofilaments. Yarns made by the split-film process do not fit neatly into the categories of staple or filament yarns. 

Split Films 

In the creation of yarns by the split-film technique, a sheet of polymer is formed. The formed sheet is drawn in the lengthwise direction. Through drawing, the molecules in the polymer are oriented in the direction of the draw, causing the film to be strengthened in the lengthwise direction and weakened in the crosswise direction. This causes a breakdown of the film into a mass of interconnected fibers, most of which are aligned in the direction of the drawing, but some of which also connect in the crosswise direction. The process is known as fibrillation. 

The fibrillated materials can be twisted into strings or twines or other coarse, yarn like materials. The usefulness of split-film yarns is limited because the yarns created are coarse. Olefins are made into split-film yarns for use in making bags, sacks, ropes, and other industrial products. 

Slit Films 

Slit films are made by cutting film into narrow, ribbon like sections. Depending upon the process used for cutting and drawing the film, the tapes may display some degree of fibrillation, like that described for split films. When tapes are made that do not fibrillate, they are flatter and are more suitable for certain uses. Flat tapes are used as warp yarns in weaving and can be made into carpet backings that will be very stable, remaining flat and even. All types of tape yarns are used in making wall coverings, packaging materials, carpet backing, and as a replacement for jute in bags and sacks. 

Lurex@, a flat, ribbon like yarn with a metallic appearance, is a slit film yarn that is often used to add decorative touches to apparel or-household textiles. Lurex@ is made from single or multiple layers of polyester film. Multi-layered types are made by placing a layer of aluminum foil between two layers of polyester film. 

Monoply types are cut from metallized polyester film, protected by a clear or colored resin coating. The natural color of Lurex@ is silver. Other colors are produced by adding pigments to the lacquer coating or to the bonding adhesive. The width of these yarns ranges from 0.069 to 0.010 inch. 

Ply Yarns 

Ply yarns are made from two or more single yarns that are twisted together. Ply yarns are much more expensive than single yarns but are nevertheless often produced to achieve certain benefits. Ply yarns made from identical single yarns are more regular in diameter and are stronger. Ply yarns are often made to achieve particular decorative effects. 

In general, the steps involved in creating ply yarns include: 

1. Winding single yarns and clearing any flaws. 

2. Placing the required number of component yarns alongside each other, in place, ready for supplying to the machine 

3. Insertion of twist to form the ply yarn by any of a number of different machines 

4. Winding the finished yarn on a cone or package for delivery to the customer 

A number of different machines are used in making ply yarns, which may also be referred to as folded yarns. Ring-folding machines, for example, operate on the same principle as ringspinning machines except that instead of a roving being fed to the traveler, the single yarns to be combined are both fed together for twisting.

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Yarn construction; Basic yarn manufacturing process

YARN CONSTRUCTION 

Basic Yarn Manufacturing Processes:
Carding –– Combing –– drafting –– twisting –– winding. 

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As the fibers pass through these processes, they are successively formed into: lap, sliver, roving and finally yarn.
The manufacturing operation in which these stages occurred
(1)Lap to card sliver by the lading process
(2)Card Sliver to Cone sliver by combing process.
(3)Shiver to roving by the drafting, or drawing out process
(4)Roving to yarn by further drafting and twisting process.
(5)Yarn reeled on bobbins, spools or cones by the winding process. 

(1) Bending, Ending, Opening and Cleaning: 
(i) The cotton arrives at the mill in large bales weighing about 500 pounds / 225 kg. The compressed mass of raw fibers must be removed from the bales, blended, opened & cleaned.
(ii) Opening is necessary in order to loosen hard lumps of fibers & disentangle them.
(iii) Cleaning is required to remove trash – such as dirt, leaves, burrs, seeds, etc.
(iv) Blending is necessary to obtain uniformity of fiber quality.
(v) Blending: Mechanical bale pickers pluck thin, even layers of the matted fiber from each of a predetermined number of bales in turn and deposit them on Hooper. The fiber is mixed & passed to an opener.
(vi) Opening: As the mass of fiber passes through the openers, cylinders with protruding fingers open up the lumps & free the trash. The number & kind of cylinder, or beaters, employed depend upon the type of cotton that is being processed.
(vii) Cleaning: As the cotton is opened, trash falls through a series of grid bars. When the cotton emerges from the opener, it still contains small tuffs with about 2/3rd of trash.
(vii) This may be conveyed as a lap, which is loosely entangled mass about 1" thick and about 40" wide. Or it may be fed by chute directly to the card for further cleaning and fiber separation.

Blending

Opening and Cleaning

(2) Carding: 

(i) This is the process of arranging the fibers in a parallel fashion. This is necessary for all staple fibers; otherwise, it would be impossible to produce fine yarns from what is originally a tangled mass.
(ii) Before the raw stock can be made into yarn, the remaining impurities must be removed, the fibers must be disentangled, and they must be straightened.
(iii) The lap is passed through a beater section and drawn on a rapidly revolving cylinder covered with very fine hooks or wire brushes.
(iv) A moving belt of wire brushes slowly moves concentrically above this cylinder. As the cylinder rotate, the cotton is pulled by the cylinder through the small gap under the brushes, the teasing action remove the remaining trash, disentangles the fibers and arranges them in a relatively parallel manner in the form of a thin web.
(v) This web is drawn through a funnel – Shaped device that molds it into a round ropelike mass called the card sliver (about thickness of a broom stick).

Carding

(3) Combing: 
(i) In this operation, fine-toothed combs continue straightening the fibers until they are arranged with such high degree of parallelism that the short fibers called ‘noils’ are combed out and completely separated.
(ii) This procedure is not done when processing man-made staple fibers because they are cut into predetermined uniform length.
(iii) This operation eliminate, as much as 25% of the original card sliver, thus almost one-fourth of the raw cotton becomes waste.
(iv) The combing process forms a comb sliver made of the longest fibers, which, in then, produces a smoother & more even yarn. 

Combing

(4) Drafting / Drawing 

(i) The draw frame has several pairs of rollers, each advance set of which revolves at a progressively faster speed.
(ii) This action pulls the staple lengthwise over each other, thereby producing longer & thinner slivers.
(iii) After several stages of drawing out, the condensed sliver is taken to the slubber, where rollers similar to those in the drawing frame draw out the cotton further.
(iv) The slubbing is passed to the spindles, where it is given its first twist & is then wound on bobbins.

Drawing

(5) Roving: 
(i) Roving is the final product of several drawing out-operation.
(ii) These bobbins are placed on the roving frame, where further drawing out and twisting take place until the cotton stock is about the diameter of a pencil lead
(iii) To this point, only enough twist has been given the stock to hold the fibers together.
(iv) Roving has no tensile strength, it will break apart easily with any slight pull. 

Roving

(6) Spinning: 
(i) The ring spinning frame complete the manufacture of yarn
• By drawing out the roving
• By inserting twist
• By winding the yarn on bobbins.
(ii) Ring Spinning draws; twist s& winds in one continuous process. The traveler carries the yarn as it slides around the ring, thus inserting the twist.