FIBRES for Fabrics

FIBRES for Fabrics

Post 368 ⇒   by Gautam Shah 

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A fibre is a flexible linear entity with very small section compared to its length. Fibres are of natural plant or animal origin, or synthetic products. Fibres are used for spinning into yarn, forming threads and ropes. Yarns are used for weaving or knitting into fabrics. Fibres of plant origin, like cotton is pure cellulose and used for production of paper and other cellulosic compounds. Fibres are massed (without any weaving) to form padding materials, filter media, blankets and mattresses. Fibres and their products are also used as reinforcements and as the fillers in formation of composites.

Polyester Texturized Yarn

A fiber is characterized by its length which is as much as 100 times its diameter or width (10 µm -width of cotton fibre). Fibres do not have consistent section along its length. Fibres of natural origin (and synthetic fibres that has been cut) are short, called staples, whereas silk and synthetics are long length fibres, called filaments. To spin fibres into a yarn, the lengths should be minimum 5 mm. A typical yarn could have more than 30 fibres. To spin a yarn fibres must have flexibility, texture, cohesiveness, elasticity, fineness, uniformity, durability, luster and sufficient strength for spin-twisting. A variable cross section gives (longitudinal structural elements -fibrils) textural effect to the fabric. Fibres that cannot be split longitudinally are called elementary, and when several such elementary fibres join longitudinally to form conjugated fibres. The length of the fiber affects the appearance of the yarn and the quality of the fabric. It is easy to produce a smooth yarn from a filament compared to staples, which require greater amount of the twist. Yarns made from the filament have greater luster, but yarns made from staple fibres have a dull appearance.

Cotton fibre under scanner

The quality of a fabric is largely related to the physical characteristics of the fiber such as:

Colour: Colour of the natural fibres varies; however darker shades can be lightened by bleaching and than a uniform colour can be applied.

Luster: Luster is the amount of light reflected by the fiber. It is both a desirable and undesirable property, depending on the type of use-conditions. Man-made fibres generally have a high luster, which can be reduced or de-lustered by incorporating titanium dioxide in the manufacturing process.

Silk from cocoon is a fine filament fibre -several of these spun into yarn – dyed -ready for weaving as hanks

Shape: Shape relates to the shape of the cross section of the fiber. In case of man-made fibres, it is very uniform (unless further processed by ‘texturizing’) over the length, compared to a variable cross section of natural fibres. Cross sectional shape affects the appearance, feel, surface texture, body, covering power and luster. Round sectional fibres have soft, smooth and slippery feel, high luster, poor covering, and close packing. Dog bone shaped and flat section fibres have a harsher, less smooth handle, good covering and high luster (except cotton). Fibres with multiple lobes in cross section have high covering power, silk like feel, high luster and sometimes soft subdued sheen. Hollow fibres are made by dissolving the inner core material and have high bulk but low weight, fluffy. Such fibres are insulative and absorbent.

Hand spun llama yarn

Surface contour: Surface contour of the fiber in length is smooth, rough or uneven. Wool is covered with small scales that make the fiber cling together, cotton has twisted surface, that reflects the light unevenly and imparts a dull appearance. Manufacturing characteristics and irregularities appear on man-made fibres.

Magnified fibers of (a) silk (b) wool (c) cotton

Crimp: Crimp is an undulating physical structure. Wool has a natural three-dimensional crimp. Most man made fibres are either produced with a crimp or texturized. Fabrics produced from crimped fibres have increased bulk, cohesiveness, warmth, false absorption and better resiliency.

Jute

Types of Fibres and Yarns: Fibres are spun into yarn. Yarns are uninterrupted threads of textile fibres that are ready to be turned into fabrics. Natural fibres originating from natural sources are: Plant (cellulosic), animal (protein). Manufactured, synthetic, or man-made fibres originate from chemical sources or could also be from regenerated or recycled sources.

Aramid Fibers

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FABRIC TEXTURIZING

Post 163   by Gautam Shah ➔

Yarns for special textural effects

Fabric manufacturing involves texturizing processes at several stages, like, Fibre production, Spinning, Post spinning, Weaving, and Post weaving treatments. These entirely dissimilar processes, at different stages, are designed to achieve specific results. The processes are temporary as well as permanent are mechanical, heat setting, chemical and radiation treatments. Few processes are also used to relax the material and recover from texturizing effects. Some of the texturizing processes are very ancient, used since prehistoric times. Many of the texturizing processes are universal and are used with other materials such as leather, wood, paper, paints, hairdressing and foods.

Texturizing of YARN creates products of many different characteristics from same basic raw materials. Texturizing processes make yarns increase elasticity, surface textures, cross section features, warmth and absorbency; while reducing the transparency, slipperiness, and the possibility of piling (formation of small fibre tangles on a fabric surface). The texturizing includes selective or spot stretching or shrinking, heat setting, chemical fixing, napping, sue-ding, singeing, spot fusing, spot burning, spot dissolving, flocking, embroidery, pile forming, etc.

Mansestr

Corduroy fabric

Texturized yarn is the formation of crimp, loops, coils, or crinkles in filaments. Such changes in the physical form of a fibre affect the behaviour and hand of fabrics made from them. Hand, or handle, is a general term for the characteristics perceived by the sense of touch when a fabric is held in the hand, such as drapability, softness, elasticity, coolness or warmth, stiffness, roughness, and resilience. For continuous yarns the fibre producer may provide primary texturing treatments, followed by a secondary treatment by an intermediate processor. The textile producer treats it further, before or after the weaving. Textured yarns are synthetic filament yarns that are made bulky or stretchy by heating or other techniques. In yarns used for weaving, the warp, or lengthwise, yarns are usually made stronger, more tightly twisted, smoother, and more even, than the filling, or crosswise, weft yarns. For abraded yarns, the surfaces are roughened or cut at various intervals and given added twist, producing a hairy effect. These create air spaces in the yarns, imparting absorbency and improving ventilation. Crimping imparts waviness similar to the natural crimp of wool fibre. Curling, produces curls or loops at various intervals. Coiling adds sections that become stretchable. Such changes are set mainly set by heat application, but occasionally with chemicals. Bulk yarns are often produced by the false twist method, a continuous process in which the filament yarn is twisted and set, and then untwisted and heated again to either stabilize or destroy the twist. The stuffing box technique is often applied to materials like Nylon, where the filament is compressed in a heated tube, imparting a zigzag crimp. In the knit-de-knit process, a synthetic yarn is knitted, heat is applied to set the loops formed by knitting, and the yarn is then unravelled and lightly twisted, thus producing the desired texture in the completed fabric.

Stretchable fabrics

Texturizing of FABRICS endows the textile new physical properties, such as bulk, feel, absorbency, and patterns. Texturizing processes which were once designed for man-made fibres, are now also applied to natural and mix fibres.

Singeing is a process to produce a smooth surface finish on fabrics made from staple fibres. The fabrics are rapidly passed over a heated copper plate or above a gas flame to burn ends of protruding fibres. Filament yarns do not require singeing, as there are no short fiber ends to project onto the surface of the fabric. A process similar to this but lighter in effect is Ironing, which removes creases from a fabric or garment.

Felt sheets

Napped and Sueded fabrics have fiber ends brushed-up onto the surface of the fabric. Napping and sueding are applied to woven or knitted goods. Term pile is often used to refer to the fiber ends that appear on the surface of the cloth. Sueding develops a very low pile on the surface of the fabric that looks and feels like a suede leather. An abrasive material like a sandpaper, is rubbed over a fabric surface to achieve the finish. Napped fabrics are used for clothing and household textiles in which warmth is desired. Fabrics that have some component of thermoplastics or are resin treated are napped to emboss various types of textures. Embossed designs provide surface texture at a lower cost than do woven designs. Blankets, sleep wear, coating fabrics, sweaters etc. are from napped fabrics. Flocking has short fibres with glue printed on the fabric, wholly or selectively (to form patterns).

Beetling is a finish used on linen and fabrics that resemble linen. The fabric revolves slowly over a wooden drum and is pounded with wooden block hammers. The pounding flattens the fabric to make the weave appear more closely woven. The process increases the lustre, smoothness, and absorbency of the fabric.

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