Fiber microfibers

Du Pont first introduced microfibers in 1989. Microfibers have diameters that are less than typical fibers they are about half the diameter of fine silk fiber, one-quarter the diameter of fine wool, and one hundred times finer than human hair. Denier, the weight in grams of 9,000-meter length of a fiber, is the term used to define the diameter or fineness of a fiber. Microfibers have a denier that is 0.9 denier or less. In comparison, nylon stockings are knit from 10- to 15- denier fiber. 

Nanofibers are generally produced from polymers which deviate from the conventional fiber-forming type of materials, and so it may be apprehended that the scope of use of these nanofibers may be far beyond the use of standard fibers, microfibers or fibrous materials. The bottom-up method modifies the fibers at a molecular or supramolecular level of fragmentation and transforms them into a polymer/polymer blend before the formation of fibers, which gives them new, specific properties favorable from a practical point of view. Nanocellulose fibers possess optimized product properties and target-directed development, quantification of eco-efficiency and sustainability factors. 

Overall, cellulose I is mainly responsible for the mechanical properties of reinforced polymer composites due to its high elastic modulus and crystallinity. The elastic modulus of perfect cellulose crystals has been calculated and estimated between 130 GPa to 250 GPa, whereas the tensile strength is approximately between 0.8 GPa to 10 GPa [28]. In previous studies cellulose has already been processed into films, gels, fibers, microfibers, nanofibers and nanocrystals for different applications [29-32]. Actually, cellulose fiber is the bundle of microfibrils comprising nanocrystalline domains linking through amorphous domains [33]. 

Natural cellulose, a polysaccharide, is a linear natural polymer of fS-(l — 4)-d-glucopyranose possessing abundant surface hydroxyl groups that form abundant inter- and intramolecular hydrogen bonds (Figure 2.16). The polymer chains accumulate into elementary fibrils (diameter 1.5-3.5 nm), and bundle to microfibrils (nanofibers, diameter tens to hundreds of nanometers), further form randomly interconnected hierarchical networks of microfibrillar fibers (microfibers, diameter in the micrometer scale or larger), resrdting in the familiar bulk cellulose... 

Typical textile fibers have linear densities in the range of 0.33—1.66 tex (3 to 15 den). Fibers in the 0.33—0.66 tex (3—6 den) range are generally used in nonwoven materials as well as in woven and knitted fabrics for use in apparel. Coarser fibers are generally used in carpets, upholstery, and certain industrial textiles. A recent development in fiber technology is the category of microfibers, with linear densities <0.11 tex (1 den) and as low as 0.01 tex. These fibers, when properly spun into yams and subsequendy woven into fabrics, can produce textile fabrics that have excellent drape and softness properties as well as improved color clarity (16). 

The tendency of the strong, highly crystalline fibers to fibnUate, ie, to develop a hairy surface on wet-abrasion has, for the textile appUcations, been minimized by process changes both in fiber production and fabric manufacture. However, for nonwoven or speciaUty paper appUcations, this property can aUow potential users to develop ceUulosic microfibers during processing. 

Significant improvement in the fiber stmctuie of leather is finally achieved by using microfibers as fine as 0.001—0.0001 tex (0.01—0.001 den). With this microfiber, a man-made grain leather Sofrina (Kuraray Co., Ltd.) with a thin surface layer (Fig. 7), and a man-made suede Suedemark (Kuraray Co., Ltd.) with a fine nap (Fig. 8) were first developed for clothing, and have expanded their uses. Ultrasuede (Toray Industries, Inc.) also uses microfibers with a rather thick fineness of 0.01 tex (0.1 den). Contemporary (1995) man-made leathers employ microfibers of not mote than 0.03 tex (0.3 den) to obtain excellent properties and appearance resembling leather. 

Man-Made Leathers. These materials contain a nonwoven fabric which is impregnated with a polyurethane to improve fiexibiHty, processibiHty, and conformabiHty (Fig. 9). Advanced man-made leathers contain microfibers as fine as 0.03 tex (0.3 den) or less to imitate coUagen fiber bundles, thereby attaining the soft feel and appearance essential for soft leather use. Polyurethane in the substrate is usually provided with porous stmcture by poromeric technology. The coating layer is also porous in the two-layer type man-made leathers (5—10). 

Fig. 10. Formation of fibers used in Kuraray man-made leather (a) porous fiber, and (b) a bundle of microfibers.

Fig. 11. (a) Cross-sectional view of substrate with porous fibers and polyurethane sponge, (b) Cross-sectional view of substrate with bundle of microfibers... 

This dynamic increase in production was accompanied by the qualitative development of PET fibers, which manifested itself in the widening of assortment of the fibers being produced (e.g., staple microfibers and filament yarns of the POY, MOY, FOY, and HOY type) and in the manufacture of second-generation fibers on... 

Microfiber glass fleece mats are typically produced from a blend of 20 - 30 percent glass microfibers <1 //m in diameter, with the balance of the glass fibers thicker (3 - 10 //m) and longer (cf. Fig. 1), on a specialized paper machine (Fou-drinier), since this is the only way of achieving the desired tensile strength without binder. The material is supplied in roll form, even though it is normally not processed into pockets, which are not required due to the absence of free electrolyte. The classification here as a leaf separator should be seen in this sense. 

These generally defined requirements are met quite comprehensively by microfiber glass fleeces. These are blends of C-glass fibers of various diameter, which are processed in the usual way on a Foudrinier paper machine into a voluminous glass mat. The blending ratio gains special importance since cost aspects have to be balanced against technical properties. The... 

Absorptive microfiber glassmat separators (100% glass fibers ) ... 

Glass fiber boards are manufactured from glass microfibers with a diameter of less than 1pm, by pressing into plates [44]. The heat treatment at 500 °C after the pressing ensures the stability of the shape. The boards have a low compressibility (about 5 percent). This will be obtained by adjusting the density of the boards to 0.3gem-3. ... 

The decrease in the fiber diameter of fabric resulted in a decrease in porosity and pore size, but an increase in fiber density and mechanical strength. The microfiber fabric made of PCLA (1 1 mole ratio) was elastomeric with a low Young s modulus and an almost linear stress-strain relationship under the maximal stain (500%) in this measurement. 

Multilayer deposition of halloysite is possible not only on large solid surfaces but also on soft biological surfaces such as wood or cotton cellulose microfibers (Figure 14.18). This coating allows a drastic increase in the porosity of the fibers and materials made from them (paper and textile). 

Kopelman et al.73 have prepared fiber optic sensors that are selective for nitric oxide and do not respond to most potential interferents. Both micro-and nanosensors have been prepared, and their response is fast (<1 s), reversible, and linear up to 1 mM concentrations of nitric oxide. The respective "chemistry" at the fiber tip was contacted with the sample, light was guided to the sample through the microfiber, and emitted light was collected by a microscope (without the use of fibers, however). 

Sumetsky, M. Dulashko, Y., Sensing an optical fiber surface by a microfiber with angstrom accuracy, In Optical Fiber Communication conference, Anaheim, 2006... 

A PET microfiber is loosely defined as one with a decitex (see Section 5 earlier) per filament less than one. This translates to a fiber diameter of 10 xm or less. In fabric form, such fibers provide a very soft hand and a non-shiny appearance. They can also make moisture-repellant fabrics without sacrificing comfort or air porosity, ideal for sportswear. The larger fiber surface area also can be useful for filtration applications. 

The islands-in-the-sea approach uses bico technology to extrude filaments that contain a multiplicity of small fibrils encased in a soluble matrix. After fiber processing and fabric formation, the matrix is dissolved away to leave behind the microfibers. Fibers with sub-micron diameters can be produced. The process is expensive, but luxurious fabrics and nonwoven materials such as Ultrasuede are made in this way. 

Figure 12.18 Bicomponent fibers before being separated into microfibers...

Microfibers allow a fabric to be woven that is lightweight and strong. They can be tightly woven so that wind, rain, and cold do not easily penetrate. Rainwear manufacturers use microfibers for this reason. They also have the ability to allow perspiration to pass through them. Thus, so-called microfiber athletic-wear is becoming more commonplace. Microfibers are also very flexible because the small fibers can easily slide back and forth on one another. The first fabric made from microfiber was Ultrasuede in which short polyester microfibers were imbedded into a PU base. Today microfibers are made mainly from polyesters, nylon, acrylic, and rayon fibers. 

In 1970, Miyoshi Okamoto, a scientist from Toray Industries, created the first microfiber. A few months later his colleague Toyohiko Hikota developed a process that allowed the production of fabric that was later trademarked as Ultrasuede . Ultrasuede was produced from such thin PET polyester fibers that a pound of them laid end-to-end would reach from the earth to the moon and back. Ultrasuede is soft and supple, resistant to stains and discoloration, and machine-washable and dry-cleanable. 

Microfibers are also made by simple extrusion through a spinneret with a smaller hole than normally employed for fiber production. The third method involves spinning a bi-component fiber and using a solution to split the fiber into smaller pieces. Initially, bi-component fibers in the range of 2-4 denier are spun and then split into microfibers. If a 32-segment pie of nylon-polyester fiber is used, the final fineness is on the order of 0.1 denier. Brushing and other techniques can be used to enhance the effects. Hollow fibers are also being used... 

The care of microfiber products is similar to that of the normal fiber materials made from the same polymer. One caution is heat sensitivity. Because the fibers are so fine, heat penetrates easily causing them to scorch or glaze more quickly than normal fibers if too much heat is applied or heat is applied over too long a period. Typically, microfibers are wrinkle-resistant, but if ironing is done, it should be accomplished using lower temperatures and only as directed. 

Microfibers are simply fibers that are much thinner than typical fibers. They may be derived from any fiber-producing material that is suitably treated to give thin fibers. 

Figure 12.7 Photographs of electrospun fiber mats embedded with 1 (a) before and (b) after 254-nm UV irradiation (1 mW/cm ) for 3 min. (c) Scanning electron microscopy image of the microfibers containing polymerized 1. (c) Photographs of the polydiacetylene-embedded electrospun fiber mats prepared with various diacetylene monomers after exposure to organic solvent. Reprinted fi om Yoon et al. (2007). Copyright 2007 American Chemical Society. (See color insert.)...

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