Fibers requirements

The studies all concluded that rayon required less energy to make than polyester but there was Httie agreement on the magnitude of the difference. The wet-spun ceUulosic fibers required more energy than melt-spun polyester for the fiber-making step, but they had no monomer energy requirement. 

RO membrane performance in the utility industry is a function of two major factors the membrane material and the configuration of the membrane module. Most utility applications use either spiral-wound or hollow-fiber elements. Hollow-fiber elements are particularly prone to fouling and, once fouled, are hard to clean. Thus, applications that employ these fibers require a great deal of pretreatment to remove all suspended and colloidal material in the feed stream. Spiral-wound modules (refer to Figure 50), due to their relative resistance to fouling, have a broader range of applications. A major advantage of the hollow-fiber modules, however, is the fact that they can pack 5000 ft of surface area in a 1 ft volume, while a spiral wound module can only contain 300 ftVff. 

Monofilament fibers require special attention to ensure a uniform open space between the filaments. 

Simple equipment with provision for wide selection of accurate ratios of carriage-to-mandrel speeds. Powerful machine and many spools of fiber required for large mandrel. 

Two fibers are presently produced by CVD on a commercial scale boron and silicon carbide. The production of these two fibers requires a monofilament starter core capable of being heated resistively such as a tungsten or graphite fiber. I l The deposition apparatus is shown schematically in Fig. 19.1. 

Bico fibers have been available for at least 30 years, but only recently have they developed widespread applications. Bico production equipment is relatively more complex and expensive, and so the fibers require higher selling prices. As these fibers become more common in specialty markets, production cost is decreasing, so that they are now beginning to find uses in commodity applications. 

In the case of HI variants, linker histones selectively bind ADPr homopolymers over competitor DNA [223]. Furthermore, Hit displays a high degree of affinity for the ADPr subunits even in the presence of salt [223]. Interestingly, this testis specific variant interacts with DNA the least tightly, and has been implicated in fiber decondensation [25,226,227]. This result suggests that potential interactions between HI molecules and ADPr are specific and not just the bi-product of electrostatic attractions. In this regard, specificity for the ADPr subunits may facilitate removal of HI from chromatosomal DNA, and initiate an unraveling of the 30 nm fiber required for DNA activation or repair. Unfortunately, the... 

Zig-zag fiber morphology persists at later stages of digestion and is attributed to retention of the globular domain of LH in fiber The three-dimensional organization of nucleosomes in extended (low ionic strength) chromatin fibers requires the globular domain of LHs and either the tails of LH or the N-terminal tails of H3... 

Fig. 1. The two competing classes of models for the 30-nm fiber can be distributed into (a) solenoid models and (b) crossed-linker models. For both fiber types the side and the top view are shown. Two nucleosomes that are directly connected via DNA linker are shaded in grey. In the solenoid these nucleosomes are located on the same side of the fiber requiring the linker to be bent. In the crossed-linker case they sit on opposite sides of the fiber and are connected via a straight linker.

The computational description of a large biomolecular complex such as the chromatin fiber requires techniques that are difierent from the widely applied molecular dynamics methods used to simulate biopolymers at atomic resolution. 

Extraction of Surfactant. The influence of surfactant on the physical properties of the fiber require its removal prior to the establishment of the reverse osmosis rejection membrane. Surfactant is removed in a pressure extraction apparatus by the recirculation of hot aqueous alcohol. Surfactant is removed to concentrations less than 2% on the weight of dry fiber. 

Interpenetrated Mall Matrix. Ion-exchange hollow libers can be produced by polymerizing an ionic monomer within (he porous wall matrix of a hollow fiber. Requirements of such a fabrication are th the monomers should not dissolve or plastici/c die polymer from which the fibers arc made. f2i the heat generated during the polymerization and contraction prior to the formation of new interpenetrating polymer should be minimized and ( ) the polymerization should not occur within the lumen (and hence cause plugging of the fiber). One drawback of such fibers is brittleness. 

Cellulose fibers require careful pretreatment before dyeing. Direct dyes are especially sensitive to differences in fiber affinity. Pretreatment involves desizing, bleaching, possibly subsequent mercerization and increasing the wettability. 

The process of raising the caterpillars, harvesting the cocoons, and obtaining the silk fibers requires much hand labog meaning that items made of silk are quite expensive relative to those made of other... 

Limitations Solids collect around and at potted ends of fibers Requires air scour to clean Cannot perform true recycle High pressure drop limits fiber length Requires significant filtration for pretreatment... 

The preservation of textiles made from man-made fibers requires attention to similar factors as textiles made from natural fibers—i.e., temperature, humidity, light conditions, and air purity. In some instances, preservation should be easier. Synthetic fibers and cellulose derivative fibers, for example, would be less prone to insect damage than natural fibers. As in the case of the natural fibers, there are well-established techniques for determining the type and extent of damage that has occurred to man-made fibers during use. This will assist in determining cleaning and preservation techniques. 

On the demand side, by the year 2000, the paper industry s fiber requirement is expected to more than double. Structural wood products will continue to expand, but at a somewhat slower rate. Many sources predict a substantial increase in the volume of wood used as fuel for domestic and commercial purposes. Total demand will force the utilization of some more expensive timber sources, thus adding to the average cost. The indicated increase in the real price of fiber reflects these developments. 

Creep of fibers also occurs much more rapidly than happens in bulk materials, in part because of the much smaller grain sizes present in the fibers. Creep and creep rupture test techniques for composites are described elsewhere in this volume (Chapter 4 Weiderhom and Fuller) but performing such tests on small diameter fibers requires somewhat different apparatus.57 To date, only a small number of fiber compositions have been characterized.58... 

Of all of these five parameters, the perimeter has proven to be the least variable with growing conditions and is essentially an invariant property with respect to genetic variety. For this reason perimeter has become recognized by many as inherent or intrinsic fiber fineness. Because of the irregularity of cotton fiber cross sections it is very difficult to measure a real diameter (this would presuppose that the fiber was circular in cross section). Similarly, cross-sectional area, mass per unit length, and specific fiber surface are dependent on maturity and thus are not real independent variables that we desire. However, from the standpoint of the spinner, the most important of the possible fineness parameters listed above is mass per unit length. A knowledge of this parameter allows the selection of fibers based on the minimum numbers of fibers required to spin a certain size yarn, i.e., the finer the yarn, the finer the fiber required. 

In order to determine 4, we now consider a simple model of a fiber of length / embedded in a polymer matrix (see Fig. 15.20b). The tensile stress on the fiber required to produce fiber debonding and pullout is determined in a first approximation by balancing the tensile and shear forces,... 

Table 6 lists the three principal natural fibers. But of the three fibers only asbestos is a true natural fiber. Glass and aluminum silicate fibers require human intervention in their processing, and might be better considered man-made fibers. 

Mertens, D. R. (1997). Creating a system for meeting the fiber requirements of dairy cows. /. Dairy Sci. 80, 1463-1481. 

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