Type 4 fibers

In integrated photoelasticity it is impossible to achieve a complete reconstruction of stresses in samples by only illuminating a system of parallel planes and using equilibrium equations of the elasticity theory. Theory of the fictitious temperature field allows one to formulate a boundary-value problem which permits to determine all components of the stress tensor field in some cases. If the stress gradient in the axial direction is smooth enough, then perturbation method can be used for the solution of the inverse problem. As an example, distribution of stresses in a bow tie type fiber preforms is shown in Fig. 2 [2]. 

Figure 2 Stress distribution in a bow tie type fiber preform.

Other elastomeric-type fibers iaclude the biconstituents, which usually combine a polyamide or polyester with a segmented polyurethane-based fiber. These two constituents ate melt-extmded simultaneously through the same spinneret hole and may be arranged either side by side or ia an eccentric sheath—cote configuration. As these fibers ate drawn, a differential shrinkage of the two components develops to produce a hehcal fiber configuration with elastic properties. An appHed tensile force pulls out the helix and is resisted by the elastomeric component. Kanebo Ltd. has iatroduced a nylon—spandex sheath—cote biconstituent fiber for hosiery with the trade name Sidetia (6). 

It has been shown that keratin [9008-18-8] and not ceUulose-type fibers, are dyed. It is speculated that a lead—sulfur—keratin complex is formed. The color penetrates the hair fiber to a limited extent, forming a ring around the outside edge and imparting a lifeless appearance. Once developed, the color cannot be removed. The shades are limited yeUows or light browns. Appealing mainly to men, the products are often called color restorers because of the... 

HoUow-fiber membranes, therefore, may be divided into two categories (/) open hoUow fibers (Eigs. 2a and 2b) where a gas or Hquid permeates across the fiber waU, while flow of the lumen medium gas or Hquid is not restricted, and (2) loaded fibers (Eig. 2c) where the lumen is flUed with an immobilized soHd, Hquid, or gas. The open hoUow fiber has two basic geometries the first is a loop of fiber or a closed bundle contained ia a pressurized vessel. Gas or Hquid passes through the smaU diameter fiber waU and exits via the open fiber ends. In the second type, fibers are open at both ends. The feed fluid can be circulated on the inside or outside of the relatively large diameter fibers. These so-caUed large capiUary (spaghetti) fibers are used in microfUtration, ultrafUtration (qv), pervaporation, and some low pressure (<1035 kPa = 10 atm) gas appHcations. 

Economic Aspects and Uses. The principal producers in the United States are U.S. Borax and Chemical Corp., North American Chemicals Co., and American Borate Corp. Their combined aimual capacity in 1989 was reported to be 735,000 metric tons of equivalent boron oxide [1303-86-2], B2O2 (20). Of this toimage, 50% is exported. About 30% of boron compounds are used in glass fiber insulation. Another 30% is used in other type fibers and borosihcate glasses. Boron is also used in soaps and detergents, fire retardants, and agriculture (see Boron compounds). 

A possible adjunct to the laminate design procedure is a specific laminate failure criterion that is based on the maximum strain criterion. In such a criterion, all lamina failure modes are ignored except for fiber failure. That is, matrix cracking is regarded as unimportant. The criterion is exercised by finding the strains in the fiber directions of each layer. When these strains exceed the fiber failure strain in a particular type of layer, then that layer is deemed to have failed. Obviously, more laminae of that fiber orientation are needed to successfully resist the applied load. That is, this criterion allows us to preserve the identity of the failing lamina or laminae so that more laminae of that type (fiber orientation) can be added to the laminate to achieve a positive margin of safety. 

The myoflbers of muscle are not homogenous but can be categorized into red and white on the basis of ATPase activity ( ). Not only the functional properties but also the composition of the two fiber types varies widely. Red fibers, for example, have considerably more myoglobin and lipid than do white type fibers. 

The aim of the analysis of cannabinoids in plants is to discriminate between the phenotypes (drug-type/fiber-type). Quantification of cannabinoids in plant material is needed if it will be used in medicinal appHcations, e.g., in C. sativa extracts. The ratio between A9-THC and CBN can be used for the determination of the age of stored marijuana samples [84]. 

Fiber-type Fiber-type WeA >50 Fiber-type 70[Pg.137]

Other innovations include PLE, MAE (see Section 1.3.1), and solid-phase microextraction (SPME). SPME is a sampling method applied to GC, HPLC, and CE. It is based on adsorbent- or adsorbent-type fibers and lends itself well to miniaturization. ... 

Adhesion on HLORIN -type fibers, has been studied as a function of five process factors. The names of factors, with their variation levels, are shown in Table 2.32. Matrix 23 of full factorial experiment has been used in constructing random balance matrix. The design matrix by the method of random balance with experimental results is shown in Table 2.33. Note that each design point was repeated 20 to 50 times due to high non reproducibility of the system. 

The next series of reports based on use of bark for wet process hardboard were published over a 7-year span from 1950-1956 by Anderson and Runckel. In the first report (22), the results included laboratory boards made from Douglas-fir slabwood containing bark, which varied between 15 and 45% of the total furnish. Bending tests indicated adequate strengths were obtained, and addition of bark enhanced moisture resistance of the boards. Acceptable boards also were made when white fir and western hemlock barks made up a portion of the furnish. No binder was added to the Asplund-type fiber. 

It was, however, observed that such systems under appropriate conditions of concentration, solvent, molecular weight, temperature, etc. form a liquid crystalline solution. Perhaps a little digression is in order here to say a few words about liquid crystals. A liquid crystal has a structure intermediate between a three-dimensionally ordered crystal and a disordered isotropic liquid. There are two main classes of liquid crystals lyotropic and thermotropic. Lyotropic liquid crystals are obtained from low viscosity polymer solutions in a critical concentration range while thermotropic liquid crystals are obtained from polymer melts where a low viscosity phase forms over a certain temperature range. Aromatic polyamides and aramid type fibers are lyotropic liquid crystal polymers. These polymers have a melting point that is high and close to their decomposition temperature. One must therefore spin these from a solution in an appropriate solvent such as sulfuric acid. Aromatic polyesters, on the other hand, are thermotropic liquid crystal polymers. These can be injection molded, extruded or melt spun. 

Crystalline oxide fibers represent an important dass of ceramic fibers mainly because of their superior oxidation resistance, being oxides. We describe the processing, structure, and properties of oxide fibers, mainly alumina and some alumina+silica-type fibers. 

Many other alumina or alumina-silica-type fibers are available. Most of these are made by the sol-gel process. Sumitomo Chemical company produces a fiber that is a mixture of alumina and silica. The flow diagram of this process is shown in Fig. 6.8. Starting from an organoaluminum (polyaluminoxanes or a mixture of polyaluminoxanes and one or more kinds of Si containing compounds), a pre-... 

Figure 6.26 Tensile strength and modulus of Nicalon type fibers as a function of temperature and oxygen content (after Okamura etal, 1993).

As pointed out above, boron fiber is also a composite fiber like any other CVD-type fiber. During fracture, cracks frequently originate at pre-existing defects located at the boron/core interface or at the surface. Commonly, a radial crack originates at the boron/core interface and leads to a brittle fracture. 

This book is about materials in fibrous form, precisely what the title says. Perhaps the only thing that needs to be emphasized is that the materials aspects of fibers are highlighted. The main focus is on the triad of processing, microstructure, and properties of materials in a fibrous form. I have kept the mathematics to the bare minimum necessary. More emphasis is placed on physical and chemical insights. Although all kinds of fibers are touched upon, there is a distinct tilt toward synthetic, nonapparel-type fibers. This is understandable inasmuch as the second half of the twentieth century has seen tremendous research and development activity in this area of high performance fibers, mainly for use as a reinforcement in a variety of matrix materials. 

The spun fibers were cross-linked (cured) by air oxidation and pyrolyzed to give silicon-carbide-type fibers. Yajima et al. (7) reported further that heteroatoms such as titanium could be incorporated into the polymers and ceramic fibers to enhance their stability (equation 3). 

Gas-phase curing of polymer fibers with trichlorosilane followed by pyrolysis gave high-nitrogen, low-carbon, silicon-nitride-type fibers. 

---