Fiber property

Physical Properties. Relationships between fiber properties and their textile usefulness are in many cases quite obvious. Since fibers are frequently subjected to elevated temperatures, it is necessary that they have high melting or degradation points. It is also necessary that other fiber properties be relatively constant as a function of temperature over a useful temperature range. 

The predominant cellulose ester fiber is cellulose acetate, a partially acetylated cellulose, also called acetate or secondary acetate. It is widely used in textiles because of its attractive economics, bright color, styling versatiUty, and other favorable aesthetic properties. However, its largest commercial appHcation is as the fibrous material in cigarette filters, where its smoke removal properties and contribution to taste make it the standard for the cigarette industry. Cellulose triacetate fiber, also known as primary cellulose acetate, is an almost completely acetylated cellulose. Although it has fiber properties that are different, and in many ways better than cellulose acetate, it is of lower commercial significance primarily because of environmental considerations in fiber preparation. 

The heated polymer solution emerges as filaments from the spinneret into a column of warm air. Instantaneous loss of solvent from the surface of the filament causes a soHd skin to form over the stiU-Hquid interior. As the filament is heated by the warm air, more solvent evaporates. More than 80% of the solvent can be removed during a brief residence time of less than 1 s in the hot air column. The air column or cabinet height is 2—8 m, depending on the extent of drying required and the extmsion speed. The air flow may be concurrent or countercurrent to the direction of fiber movement. The fiber properties are contingent on the solvent-removal rate, and precise air flow and temperature control are necessary. 

Quench. Attempts have been made to model this nonisotherma1 process (32—35), but the complexity of the actual system makes quench design an art. Arrangements include straight-through, and outside-in and inside-out radial patterns (36). The optimum configuration depends on spinneret size, hole pattern, filament size, quench-chamber dimensions, take-up rate, and desired physical properties. Process continuity and final fiber properties are governed by the temperature profile and extension rate. 

Other Properties. Polyester fibers have good resistance to uv radiation although prolonged exposure weakens the fibers (47,51). PET is not affected by iasects or microorganisms and can be designed to kill bacteria by the iacorporation of antimicrobial agents (19). The oleophilic surface of PET fibers attracts and holds oils. Other PET fiber properties can be found ia the Hterature (47,49). 

Terephthahc acid (TA) or dimethyl terephthalate [120-61 -6] (DMT) reacts with ethyleae glycol (2G) to form bis(2-hydroxyethyl) terephthalate [959-26-2] (BHET) which is coadeasatioa polymerized to PET with the elimination of 2G. Moltea polymer is extmded through a die (spinneret) forming filaments that are solidified by air cooling. Combinations of stress, strain, and thermal treatments are appHed to the filaments to orient and crystallize the molecular chains. These steps develop the fiber properties required for specific uses. The two general physical forms of PET fibers are continuous filament and cut staple. 

Thermal Resistance and Flammability. Thermal analysis of PVA filament yam shows an endothermic curve that starts rising at around 220°C the endothermic peak (melting point) is 240°C, varying afitde depending on manufacture conditions. When exposed to temperatures exceeding 220°C, the fiber properties change irreversibly. 

The bulk properties of regenerated cellulose are the properties of Cellulose II which is created from Cellulose I by alkaline expansion of the crystal stmcture (97,101) (see Cellulose). The key textile fiber properties for the most important current varieties of regenerated cellulose are shown in Table 2. Fiber densities vary between 1.53 and 1.50. 

Properties. Fiber property comparisons for the different products are given in Table 1. 

A selection of fiber property data is given ia Table 2 as an illustration of the range of fiber properties available commercially for use ia manufacturiag nonwoven fabrics. In general, fiber diameters range from 5 to >40 p.m for natural fibers, and from less than 10 p.m (microdenier) to as high as needed for manufactured fibers. 

One of the limitations of the curtain/slot draw process is that the amount of fiber attenuation is constrained due to the short distance generally allowed between the spinnerette and the venturi slot and the use of relatively low pressure air for drawing so as not to induce high turbulence in the area of the laydown. In practical terms this has made the process difficult to adapt for the production of polyester fabrics which inherently require much higher fiber acceleration to attain the desired polyester fiber properties. 

To accommodate the various uses in 100% form and in blends, the tenacities and elongations of the nylon staple offerings range from 0.3 to 0.6 N /tex (3—7 g/den) and from 50 to 100% elongation. Most other fiber properties of nylon staple differ tittle from those of the continuous filament property characteristics of nylon-6 and nylon-6,6 are similar (see Polyamides, general). 

Effect of Fiber Properties. Acid dyes are attracted to the accessible amine ends of the nylon chains located in the amorphous regions of the fiber. Acid dye affinity of nylon can be adjusted by a dding excess diamine or diacid to the polymer salt or by changing the molecular weight in polymerization. A light acid-dyeable nylon-6,6 is spun with 15—20 amine ends, expressed in terms of gram equivalents per 10 g of polymer. A medium or... 

Qiana, introduced by Du Pont in 1968 but later withdrawn from the market, was made from bis(4-aminocyclohexyl)methane and dodecanedioic acid. This diamine exists in several cis—trans and trans—trans isomeric forms that influence fiber properties such as shrinkage. The product offered silk-like hand and luster, dimensional stabiUty, and wrinkle resistance similar to polyester. The yam melted at 280°C, had a high wet glass-transition temperature of - 85° C and a density of 1.03 g/cm, the last was lower than that of nylon-6 and nylon-6,6. Qiana requited a carrier for effective dyeing (see Dye carriers). 

Fiber. High molecular weight linear PPS is weU-suited for fiber applications. The inherent properties of PPS (flame resistance, chemical resistance, and thermal stability) make PPS fiber highly desirable ia textile applications (128). PPS fiber has been designated by the U.S. Federal Trade Commission as a new generic class of materials called sulfar. Typical fiber properties are listed ia Table 7 (see High performance fibers). 

In order to achieve the desired fiber properties, the two monomers were copolymerized so the final product was a block copolymer of the ABA type, where A was pure polyglycoHde and B, a random copolymer of mostly poly (trimethylene carbonate). The selected composition was about 30—40% poly (trimethylene carbonate). This suture reportedly has exceUent flexibiHty and superior in vivo tensile strength retention compared to polyglycoHde. It has been absorbed without adverse reaction ia about seven months (43). MetaboHsm studies show that the route of excretion for the trimethylene carbonate moiety is somewhat different from the glycolate moiety. Most of the glycolate is excreted by urine whereas most of the carbonate is excreted by expired CO2 and uriae. 

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