Finishing

Finishing encompasses chemical or mechanical treatments performed on fiber,yarn, or fabric to improve appearance, texture, or performance. Mechanical finishes can involve brushing, ironing or other physical treatments used to increase the luster and feel of textiles. Application of chemical finishes to textiles can impart a variety of properties ranging from decreasing static cling to increasing flame resistance. The most common chemical finishes are those that ease fabric care, such as the permanent-press, soil-release, and stain- resistant finishes. Chemical finishes are usually followed by drying, curing, and cooling steps. Application of chemical finishes are often done in conjunction with mechanical finishing steps (Snowden-Swan, 1995). Selected mechanical and chemical finishing techniques are described below.

Chemical Treatments

Optical finishes

Optical finishes added to either brighten or deluster the textile.

Absorbent and soil release finishes

These finishes that alter surface tension and other properties to increase water absorbency or improve soil release.

Softeners and abrasion-resistant finishes

Softeners and abrasion-resistant finishes are added to improve feel or to increase the ability of the textile to resist abrasion and tearing.

Physical stabilization and crease-resistant finishes

These finishes, which may include formaldehyde-based resin finishes, stabilize cellulosic fibers to laundering and shrinkage, imparting permanent press properties to fabrics (ATMI, 1997b).

Fabrication

Finished cloth is fabricated into a variety of apparel and household and industrial products. The simpler of these products, such as bags, sheets, towels, blankets, and draperies, often are produced by the textile mills themselves. Apparel and more complex housewares are usually fabricated by the cutting trades. Before cutting, fabrics must be carefully laid out. Accuracy in cutting the lay fabric is important since any defects created at this point may be carried through other operations and end up in the final product. For simple household and industrial products, sewing is relatively straightforward. The product may then be pressed to flatten the fabric and create crisp edges.

Mechanical Treatments

Heatsetting

Heatsetting is a dry process used to stabilize and impart textural properties to synthetic fabrics and fabrics containing high concentrations of synthetics. When manmade fibers are heatset, the cloth maintains its shape and size in subsequent finishing operations and is - stabilized in the form in which it is held during heatsetting (e.g., smooth, creased, uneven). Textural properties may include interesting and durable surface effects such as pleating, creasing, puckering, and embossing. Heatsetting can also give cloth resistance to wrinkling during wear and ease-of-care properties attributed to improvements in resiliency and in elasticity. Pollution outputs may include volatile components of spin finishes if heatsetting is performed before scouring and bleaching processes. These components are introduced to the fabrics during the manufacture of synthetic fibers, when proprietary spin finishes are applied to provide lubrication and impart special properties, such as antistatic, to the fiber.

Brushing and napping

Brushing and napping decrease the luster of fabrics by roughening or raising the fiber surface and change the feel or texture of the fabric (ATMI, 1997b). These processes involve the use of wires or brushes that pull individual fibers.

Softening

Calendering, or ironing, can be used to reduce surface friction between individual fibers, thereby softening the fabric structure and increasing its sheen. In calendering, the fabric passes through two or more rolls. Typically, one roll is made of chilled steel, while the other is made of a softer material like cotton fibers. The steel roll may also be heated using gas or steam. Once goods pass through the machine they are wound up at the back of the machine.

Optical finishing

Luster can be added to yarns by flattening or smoothing the surfaces under pressure. This can be achieved by beating the fabric surface or passing the fabric between calendering rolls. The luster can be further increased if the rolls are scribed with closely spaced lines.

Shearing

Shearing is a process that removes surface fibers by passing the fabric over a cutting blade.

Compacting

Compacting, which includes the Sanforizing process, compresses the fabric structure to reduce stresses in the fabric. The Sanforizing process reduces residual shrinkage of fabrics after repeated laundering (Wingate, 1979). The fabric and backing blanket are fed between a roller and a curved braking shoe, with the blanket under tension. The tension on the blanket is released after the fabric and blanket pass the braking shoe. Compacting reduces the potential for excessive shrinkage during laundering.