Friday, January 4, 2013

Textile Finishing; Flame Resistance Temperature Regulating Heat Reflectant Finishing

Flame Resistance finishing:
Flame resistance finishing is modern process of finishing. The terminology employed in a discussion of flame resistance finishing can be confusing. The following definitions and descriptions are currently accepted, although usage may vary, particularly from country to country.

1. Flame resistance finishing is defined by American Society for Testing and Materials (ASTM) (1998, 23) as “the property of a material whereby flaming combustion is prevented, terminated, or inhibited following application of a flaming or non-flaming source of ignition, with or without the subsequent removal. of the ignition source.” The material that is flame resistant may be a polymer, fiber, or fabric.

2. Use of the terms flame retardant and self-extinguishing is discouraged (ASTM 1998, 23, 40). Flame-retardant treated and flame-retardant treatment are, however, acceptable terms and flame retardant is used in other countries. ASTM does not approve the use of the term self-extinguishing to describe a textile product because it is meaningful only when applied to specific circumstances.

3. A thermally stable material (fiber or polymer) is one that has a high decomposition temperature and is thus inherently flame resistant because of chemical structure (rather than through the presence of added flame-retardant treatments) (Clark and Tesoro 1974).)

Temperature Regulating Finishes
Temperature-regulating fabrics are sensitive to the surrounding temperature or to body heat. Finishes that provide this adaptation include substances called phase change materials (PCMs) (Lennox-Kerr 1998). These substances change from solid to liquid or liquid to solid depending on the temperature. The example we are probably most familiar with is ice changing to water when the temperature rises and then changing back to ice again when cooled. Ice absorbs heat to melt and water gives off heat when it becomes solid. PCMs work the same way but are selected to undergo this phase change around normal skin temperature.

One such finish is polyethylene glycol (PEG), which is applied to fabrics along with a methylol agent such as DMDHEU. The result is a network polymer that is insolubilized on the surface of the fibers. The polymer absorbs and holds heat energy at high temperature, and then releases the stored energy under cooler conditions. The finish is durable to wear and laundering, because it is cross linked on the fabric.

Not only do these finishes help to warm or cool the body, but they also increase the moisture absorbency of fabrics, thereby further enhancing comfort. Other improved properties are resistance to static, wrinkling, abrasion, pilling, and soil. The PEG finish has been used on T-shirts, underwear, socks, activewear, and biomedical products.

In another form, PCMs have been applied to fabrics as microcapsules in coatings, used in nonwoven bonding materials, or included in spinning solutions of manufactured fibers. Outlast Technologies, Inc. produces the microcapsules. Acordis Fibers has produced a version of their Courtelle acrylic fibers with the PCM embedded in them. The fabrics made with these fibers are targeted for outdoor apparel, particularly for cold climates. PCM-containing textile fabrics are expensive because the encapsulation process is technology intensive.

Heat Reflectant Finishes
An increased level of insulation can be provided in garments and draperies by the addition of heat-reflectant finishes. Most of these products are treated with a spray coating of metal and resinous substances. The heat-reflectant material is sprayed onto the surface of a closely woven fabric. The finish is designed to keep heat either on one side or the other side of the fabric. The finish is effective only with radiated heat.

Lining fabrics are usually constructed so that the finish is applied to the inside of the fabric. The finish reflects the body heat back toward the wearer, thus providing added warmth. In protective clothing to be worn under hot conditions, the finish is worn to the outside to deflect heat away from the body.

Draperies may also be treated to provide greater insulation for homes. Treated draperies placed inside windows may serve to keep heat inside the home or to reflect heat outward, preventing it from warming the house. Some of the processes designed to produce heat reflectance use aluminum in the finish, because it provides excellent reflectancy. A variant of this principle is utilized in fabrics coated or laminated with a thin layer of aluminum, foams, resins, or synthetic rubber.

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