PREPARATORY TREATMENTS OF FABRIC

chemical composition of the fibre. Chemical bleaching is typically accomplishe by oxidization, destroying color by the applying of atomic number 8, or by reduction, removing color by chemical change. Cotton and different plastic fibres area unit sometimes treated with heated alcalescent chemical element peroxide; wool and different animal fibres area unit subjected to such acidic reducing agents as gaseous sulfur dioxide or to such gently alcalescent oxidizing agents as hydrogen peroxide. Synthetic fibres, after they need bleaching, is also treate with either oxidizing or reducing agents, relying upon their chemical composition. Cottons area unit often worn and bleached by a nonstop system.

Mercerization
Mercerization is a process apply to cotton, and sometimes to cotton blends, to increase luster, improve strength, and enhance dye affinity—thereby improving the overall appearance of the fabric. Manufacturers can apply this process either at the yarn stage or the fabric stage. It involves immersing the cotton under tension in a solution of caustic soda (sodium hydroxide), and then neutralizing it with an acid rinse.The treatment produces permanent swelling of the fibre.
DRYING

Textile processing uses water at various stages, which accumulates in the materials and must eventually be remove. Since evaporation through heat is expensive, the initial drying stage relies on mechanical methods to remove as much moisture as possible. These methods include centrifuges and continuous systems that use vacuum suction rolls.

To remove the remaining moisture, the fabric passes through heated dryers. Different types of dryers operate by either: festooning the relaxed fabric in loops through the chamber, holding the selvages taut on a frame as the fabric travels, or passing the material over a series of hot cylinders.

Because overdrying can lead to a harsh fabric feel (or “hand”), manufacturers must carefully control temperature, humidity, and drying time.

Treatments enhancing appearance embrace such processes as off your guard and cutting off, brushing, singeing, beetling, decating, tentering, calendering or pressing, moiréing, embossing, creping, glazing, polishing, and optical brightening.

Napping and cutting off

Napping is a process apply to woolens, cottons, spun silks, and spun rayons—both woven and nonwoven—to create a soft, velvety surface. The fabric passes over revolving cylinders covered with fine wires that lift short, loose fibers (typically from the weft) to the surface, forming a nap. This treatment enhances warmth and is commonly use on woolens, worsteds, and blankets.

Brushing

Brushing, done with bristle-covered rollers, removes loose threads and fiber ends from smooth-surfaced fabrics. It is also use to raise a nap on knits and woven fabrics, typically after shearing to eliminate detache fibers and refine the surface.

Singeing (Gassing)

Singeing removes protruding fibers, yarn ends, and fuzz to create a smooth surface. The fabric or yarn is pass rapidly over a gas flame or heat copper plates, which burns off unwant fibers without damaging the material. A dampening step follows to extinguish any smoldering. Singeing is apply to both yarns and fabrics.

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Beetling

Beetling, primarily used on linen and linen-like cotton fabrics, produces a flat, lustrous surface and reduces porosity. In this process, dampen fabric is wrapp around an iron cylinder and pound with heavy wooden mallets in a special machine.

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Decating

Decating is use on woolens, worsteds, synthetics, and blend or knit fabrics to set the weave, develop luster, improve softness, and stabilize dimensions. It involves applying heat and pressure. Wet decating produces a soft bloom by steaming the fabric under tension as it passes over perforated cylinders. It is especially useful for double knits to give a crisp hand and reduce shrinkage.

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Tentering, Crabbing, and Heat-Setting

These processes set the warp and weft at right angles and stretch the fabric to its final dimensions.

• Tentering uses a frame with pins or clips to hold the selvages taut as the fabric moves through a heated chamber, straightening the weave and removing wrinkles.

• Crabbing is use specifically on wet wool fabrics.

• Heat-setting applies to synthetic fibers and helps fix pleats, creases, or textured effects permanently.

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Calendering

Calendering involves applying heat and pressure by passing the fabric between heated rollers to create a smooth, glossy surface. This technique is commonly use on cotton, linen, silk, and various synthetic fabrics.

For pile fabrics like velveteen, manufacturers use steaming instead of pressing to preserve the raised surface and avoid flattening the pile.

When apply to wool, the process is known as pressing. It involves steaming and compressing the fabric using heated metal plates to produce a smooth, finished appearance.

• Calendering is usually not permanent unless combined with resins or applied to thermoplastics like acetate.

Variations:

• Moiré: A wavy or “watered” effect from engraved rollers. Permanent on acetates and resin-treated rayons.

• Embossing: Creates raised patterns by pressing the fabric between heated, engraved rollers. Modern methods allow permanent embossing.

• Glazing: Produces a stiff, shiny surface using starch, shellac, or resin followed by hot rollers. Resins now make this finish more permanent.

• Ciré: A wax application followed by hot calendering to give rayons and silks a high, metallic gloss. Acetates can achieve this without added wax due to their thermoplastic nature.

• Polishing: A milder finish that imparts shine without excessive stiffness, often achieved through mercerization and friction rollers.

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Creping

Crepe effects may be produce by finishing techniques.

• One temporary method involves steaming the fabric as it passes between hot, patterned rollers, creating puckered textures.

• A more permanent method uses caustic soda (NaOH). A patterneresist paste is apply, and the fabric is immersed in the solution. The treated areas shrink, while untreated areas pucker.

  • If appliin stripes, the effect is called plissé.

  • A full-surface design results in blister crepe.

Optical Brightening

Optical brighteners (or bleaches) enhance the whiteness and brightness of fabrics by reflecting more blue light. These fluorescent compounds absorb UV light and emit visible light, giving textiles a “brighter-than-white” look. Though they may fade over time, users can reapply them during washing.