Microfiber is defined as a staple fiber or filaments of linear density approximately 1 dtex or less, and above 0.3 dtex. Although acrylic, viscose and polypropylene are available for the production of microfibers, polyester and polyamide are the main source. The fabrics made from them can be 100% microfiber or in blends with wool, cotton or viscose. Microfibers are half the diameter of a fine silk fiber, one-third the diameter of cotton, one-quarter the diameter of fine wool, and one hundred times finer than human hair. In order to be classified as a microfiber, the fiber must be less than 1 dtex in width. Fabrics made of microfibers are generally lightweight, resist wrinkling, have a luxurious drape on the body, retain shape, and resist pilling. They are also relatively strong and durable in relation to other fabrics of similar weight, and they are more breathable and more comfortable to wear. Fabrics made of microfibers show lower heat conductance and therefore higher thermal insulation properties. Microfiber fibers exhibit a warmer feeling than conventional fabrics depending on pressure, which may be due to the difference in the fiber and fabric surface in contact with the human skin.
The first ‘micro-denier’ products were introduced by Japanese fiber manufacturing companies during the 1970s. The production of microfibers followed in Europe during the 1980s and since the 1990s by American manufacturers. Toray was the first company in the world to introduce microfibers, followed by Teijin, Hoechst, ICI, DuPont, and others. Recently Toray has introduced an ultra-fine polyester microfiber with a linear density of filament of about 0.05 dtex. This may be called the finest synthetic fiber so far produced commercially. At present, polyester and nylon are generally used for manufacturing microfibers. However, ‘micro-denier’ versions of rayon and acrylic products are on the horizon.
Three conventional spinning methods, i.e. melt spinning, dry spinning, and wet spinning can be used to manufacture microfibers. However for producing microfibers by these methods, the polymerization process, polymer spinning and drawing conditions have to be selected and executed very carefully. The technology involved in the extrusion of microfibers is more sophisticated and costly than that of conventional deniers as microfibers are delicate products that require great attention in handling during textile mill processing.
Microfiber spinning is now possible by many major fiber producers on their existing equipment, however economical production of high quality microfibers will require significant changes in future machine design and operation. Generally speaking, there are two techniques to produce microfibers:
•direct spinning (conventional POY spinning), and
•bi-component process (segment and island-in-sea type).
Different procedures have been presented and employed to produce microfibers:
1.Dissolved type
2.Split type
3.Direct spun type
4.Super-drawing technique
5.Sheath-core spinning method
6.Flash-spinning method
7.Solution flash-spinning
8.Emulsion-spinning method
9.Jet-spinning method
10.Centrifugal-spinning method
11.Turbulent forming method
12.Conjugate-spinning method.
Microfibers are specified by their remarkable properties such as luster, pleasant softness and handle, good drapability, bulk and outstanding surface properties. Woven fabric was produced from a 0.1 dtex UFF hollow microfiber combined with a single hollow staple fiber. This product offers a sense of warmth, dry handle, softness, bulk, good recovery, and is lightweight. Microfibers have high strength properties, are very soft, have luxurious hand with a silken or suede touch, extreme drapability, ultra-fine linear density (less than 0.1 dtex/f) and are finer than the most delicate silk. They are shrink resistant, washable, dry-cleanable, non-electrostatic and are hypoallergenic, therefore they do not create problems for those suffering from allergies. Anti-microbial agents help to protect the wearers from the dangers of the bacteria that cause odor and mildew. Microfibers are super-absorbent, absorbing over seven times their weight in water and they dry in one-third of the time of ordinary fibers. They insulate well against wind, rain and cold and furthermore are environmentally friendly.
The higher absorption surface of microfibers results in a dyeing rate four times higher than that of normal fibers. Therefore, to reach the same depth of shade they require more dyestuff than standard fibers, which can cause unevenness in the dyeing. Their larger external surface means an increase in the number of threads exposed to light which, on destruction of dye, is expressed as the lower light fastness rating. Because of the fineness, the total surface area of microfiber yarn or fabric is much bigger than ordinary fibers. Therefore the quantity of required size needed to be applied on microfilament warp yarns is higher. Since microfibers have very small interstitches, with consequent difficulties of size accessibility and diffusibility, desizing becomes quite difficult and costly. The most useful machine for microfiber fabric processing is a Jet dyeing machine, as it allows the fabric to develop a desirable bulk. The difficulty in processing microfibers can be overcome by proper selection of dyestuffs, using appropriate dyeing machinery (air jet type) and choosing suitable processing parameters. Proper dye selection eliminates problems regarding build-up and fastness properties. Staple microfibers offer difficulty in carding, but the emerising effect, which imparts a slightly napped, peach-like surface and a pleasant soft handle, has grown in importance for microfiber fabrics. The emerising treatment must always be carried out before pre-setting to prevent an uneven surface.
