Multifilament fibers

Recently, Caster et al. described the surface modification of multifilament fibers such as nylon or Kevlar [70]. Coating techniques using preformed ROMP-based polymers and process contact metathesis polymerization (CMP), initially described by Grubbs et al. [71], were both used. The latter involves a procedure where the initiator is physisorbed onto the surface of a substrate and fed with a ROMP-active monomer that finally encapsulates the substrate. These modified fibers showed improved adhesion to natural rubber elastomers. 

Chemical Vapor Infiltration (CVI). Recall from Section 3.4.2 that CVI is primarily nsed to create ceramic matrix composites, CMCs. Fabrication of CMCs by CVI involves a sequence of steps, the first of which is to prepare a preform of the desired shape and fiber architecture. This is commonly accomplished by layup onto a shaped form of layers from multifilament fibers using some of the techniques previously described, such as filament winding. 

The multifilament fiber (10-20 xm diameter) as commercially produced consists of a mixture of /3-SiC, free carbon and SiOj. The properties of this fiber are summarized in Table 6.5. The properties of Nicalon start to degrade at temperatures above about 600°C because of the thermodynamic instability of composition and microstructure. A ceramic grade of Nicalon, called Hi Nicalon, having low oxygen content is also available Yet another version of a multifilament silicon carbide fiber is Tyranno, produced by Ube Industries, Japan. This is made by pyrolysis of poly (titano carbosilanes) and contains between 1.5 and 4wt% titanium. 

Another silicon carbide multifilament fiber, made via a polymeric precursor by Dow Corning Corp., US A, is called Sylramia According to the manufacturer, this textile grade silicon carbide fiber has a nanocrystalline, stoichiometric... 

Excellent results have been obtained with commercial oligomeric HALS (e.g. 146,147,160,161a) in stabilizing multifilaments, fibers, and thin foils from PP [9]. 

Available forms Extrusion and molding powders, aqueous dispersion, film, multifilament fiber. 

In the following section (Sect. 5) an overview will be given over thin SiC fibers characterized by small diameters of one to few tens of a micrometer and produced via the polymer route (in most cases). This kind of fiber is applied as rovings consisting of some hundred up to more than a thousand single filaments, so-called multifilament fibers, which may be woven and is predominantly used for reinforcing brittle matrices (ceramics and glasses). 

Cai J, Zhang LN, Zhou JP, Qi HS, Chen H, Kondo T, Chen XM, Chu B (2007) Multifilament fibers based on dissolution of cellulose in NaOHAirea aqueous solution structure and properties. Adv Mater 19 821-825... 

The three major constituents of any continuous fiber ceramic matrix composite are the reinforcing fibers, the matrix and a fiber-matrix interphase, usually included as a coating on the fibers. HiPerCompTM composites can be processed with various monofilament and multifilament fibers, such as the SCS family of monofilament SiC from Specialty Materials, Inc. CG-Nicalon and Hi-Nicalon Type S from Nippon Carbon Company Tyranno ZE , Tyranno ZMl and Tyranno S A from Ube Industries and Sylramic fiber from COl Ceramics. However, the composites described in this paper all utilize Hi-Nicalon SiC fiber from Nippon Carbon Company. A companion paper, in this book, by Jim DiCarlo [11] from NASA gives the properties of slurry cast composites reinforced with Sylramic and Sylramic-iBN fibers. 

FIGURE 4. Schematic of the set up used for fabrication of small diameter, multifilament fiber tow reinforced ceramic composites. (Reprinted, from reference 26, with kind permission from Elsevier). 

Conductive yams can be either based on nonmetaUic conductive materials, such as carbon fibers, or metallic materials, as metal fibers. Such yams can include a set of metal filaments, for example, stainless steel filaments, which can be twisted around each other. By twisting a fine metal wire around a multifilament fiber, the electrical conductivity of the yam is achieved with an improvanent of the mechanical stability (Fig. 4.3B and C). 

Fibers of fluoroplastics have been made and oriented to impart strength to themf ] and enhance their load-bearing capability at elevated temperatures. Perfluoroplastics can be spun into multifilament fibers by extrusion. Vita, et have reported fabrica-... 

Fig. 1. Schematic drawings of five types of geotextile fibers (a) monofilament, (b) multifilament, (c) staple fibers, (d) staple yam, and (e) sHt film.

Surgical sutures are sterile, flexible strands used to close wounds or to tie off tubular structures such as blood vessels. Made of natural or synthetic fiber and usually attached to a needle, they are available ia monofilament or multifilament forms. Sutures are classified by the United States Pharmacopeia (USP) (1) as either absorbable or nonabsorbable. The USP also categorizes sutures according to size (diameter) and Hsts certain performance requirements. Sutures are regulated by the Food and Dmg Administration (FDA) as medical devices under the Food, Dmg, and Cosmetics (FDC) Act of 1938, the Medical Device Act of 1976, and the Medical Device Reporting regulation of 1995. 

All these weaves may be made from any textile fiber, natural or synthetic. They may be woven from spun staple yarns, multifilament continuous yarns, or monofilament yarns. The performance of the filter cloth depends on the weave and the type of yarn. 

Fabrication of drug-containing fibers is a natural progression when one considers the extensive history of lactide/glycolides in suture applications. The lactide/glycolide polymers are easily melt-spun into mono- or multifilament products at relatively low temperatures. 

Bundle Preparation. Packages of multifileiment yarns are backwound to prepare bundles necessary for the manufacture of a reverse osmosis module. A proprietary winder for this operation has been designed and constructed at Albany International Research Co. This device is capable of helically winding multifilament yarns into bundles around a mandrel. This is done in a manner such that the resulting bundle has uniform cylindrical dimensions and uniform fiber density. This minimizes channeling and optimizes exposure of membrane surface area. 

Many Quantro II membranes varying incrementally in composition have been under test for 18 months at Albany International Research Co. Tests are performed on experimental samples of fiber. Approximately 16 inches of multifilament yarn are typically subjected to various feeds and conditions. Such a yarn sample is embedded in epoxy which is sealed into a pressure system. Several test facilities are in operation to provide various feeds and conditions. 

Research effort at Albany International Research Co. has developed unit processes necessary for pilot scale production of several species of reverse osmosis hollow fiber composite membranes. These processes include spin-dope preparation, a proprietary apparatus for dry-jet wet-spinning of microporous polysul-fone hollow fibers, coating of these fibers with a variety of permselective materials, bundle winding using multifilament yarns and module assembly. Modules of the membrane identified as Quantro II are in field trial against brackish and seawater feeds. Brackish water rejections of 94+% at a flux of 5-7 gfd at 400 psi have been measured. Seawater rejections of 99+% at 1-2 gfd at 1000 psi have been measured. Membrane use requires sealing of some portion of the fiber bundle for installation in a pressure shell. Much effort has been devoted to identification of potting materials which exhibit satisfactory adhesion to the fiber while... 

The polymer was extruded at 240 C to produce 28-strand multifilament yarn. The yam was hot-stretched and fiber tensile strengths in the range 3-6 g/den (1-2 dpf) could be obtained. The yam was placed on braider bobbins on a 12-carrier machine with 7-ply core. The braid was made with 51 picks per inch and hot-stretched 25% at215 F. 

A variation on this approach used multifilament coextrusion, so-called microfabrication by coextrusion (MFCX) . A limitation of the single-filament process is the size of the filament. The rheological properties of the polymer/ ceramic blends make spinning fibers smaller than 250 pm very difficult. Additionally, spooling fine-diameter fibers is quite challenging. The MFCX is shown schematically in Fig. 1.3. The setup is the same as that used to spin fibers except that the spinneret is replaced with an extrusion die with a diameter between 1 mm and 6 mm. Two separate extrusion steps are used. In the first step, coarse primary filaments are extruded from the feedrod (Fig. 

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