Materials fibrous

Paper production is mainly based on fibrous raw material which may consist of primary or secondary fibers. Primary fibers are obtained directly from plant raw materials, mainly from wood and annual non-wood plants. Industrially, mostly thinnings and sawmill wastes are used. Secondary fibers are produced from recovered paper. Rags are used only in very small amounts. Synthetic and mineral fibers do not play an important role. 

Copyright 2006 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 3-527-30997-7 

Before the invention of the mechanical and chemical pulping processes in the 19th century, rags (used textiles) tvere the only raw fiber source. The development of the worldwide use of fibrous raw material since 1980 is shown in Table 2.1. In the next ten years, the world-wide consumption of pulp fibers is expected to be 46% for chemical pulp, 10% for mechanical pulp and 44% for recycled paper pulp. 

Chemical pulp is produced by chemical pulping of vegetable raw materials such as not only hardwood and softwood, but also from straw from different kinds of cereals, bagasse, reed, or esparto grass, and from other annual non-wood plants. 

During chemical pulping, the most of the lignin is removed from the raw material. The yield of the pulp is therefore only 45 to 55%. Two main industrial processes of chemical pulping are used  

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Fibrous composites Fibrous glass Fibrous materials Ficam... 

The beater additive process starts with a very dilute aqueous slurry of fibrous nitrocellulose, kraft process woodpulp, and a stabilizer such as diphenylamine in a felting tank. A solution of resin such as poly(vinyl acetate) is added to the slurry of these components. The next step, felting, involves use of a fine metal screen in the shape of the inner dimensions of the final molded part. The screen is lowered into the slurry. A vacuum is appHed which causes the fibrous materials to be deposited on the form. The form is pulled out after a required thickness of felt is deposited, and the wet, low density felt removed from the form. The felt is then molded in a matched metal mold by the appHcation of heat and pressure which serves to remove moisture, set the resin, and press the fibers into near final shape (180—182). 

Fibers are used ia the manufacture of a wide range of products that can generically be referred to as fibrous materials. The properties of such materials are dependent on the properties of the fibers themselves and on the geometric arrangement of the component fibers ia the stmcture. 

This brief overview of the types of fibrous materials is intended to indicate the broad range of materials that can be produced from fibers. Since the properties of fibrous materials depend both on the properties of the fibers themselves and on the spatial arrangement of the fibers in the assembly, a given type of fiber may be used in many different end products, and similarly a given end product can be produced from different fiber types. 

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. 

Physical testing appHcations and methods for fibrous materials are reviewed in the Hterature (101—103) and are generally appHcable to polyester fibers. Microscopic analyses by optical or scanning electron microscopy are useful for evaluating fiber parameters including size, shape, uniformity, and surface characteristics. Computerized image analysis is often used to quantify and evaluate these parameters for quaUty control. 

P. S. Tung and S. Jayaraman, in T. L. Vigo and A. F. Turbak, eds., High-Tech Fibrous Materials, American Chemical Society, Washington, D.C., 1991, Chapt. 4. 

Laminates ate a special form of composite material or reinforced plastic because the continuous reinforcing ply of fibrous material imparts significant strength in the x—j plane. The strength along the axis results from interlaminar bonding of resins. Very few fibers ate oriented in the direction, so it tends to be the weak link in this type of composite. 

Albumen has the largest number of acid and basic groups. It is the most soluble of the proteins present in a hide. The albumen is not a fibrous material, however, and therefore has no value in the leather. Keratin is the protein of the hair and the outermost surface of the hide. Unless the hair is desired for the final product it is removed by chemical and/or physical means. The elastin has Htde acid- or base-binding capacity and is the least soluble of the proteins present. The lack of reactivity of the elastin is a detriment for most leather manufacture. The presence of elastin in the leather greatly limits the softness of the leather. 

Similar to pure polyglycoHc acid and pure polylactic acid, the 90 10 glycolide lactide copolymer is also weakened by gamma irradiation. The normal in vivo absorption time of about 70 days for fibrous material can be decreased to less than about 28 days by simple exposure to gamma radiation in excess of 50 kGy (5 Mrads) (35). 

Fibrous materials may be naturally occurring or synthetically manufactured by thermal or chemical processes (Fig. 1) (see Fibers, survey). Refractory fibers are generally used in industrial appHcations at temperatures between 1000°C and 2800°C. These fibers may be oxides or nonoxides, vitreous or polycrystalline, and may be produced as whiskers, continuous filaments, or loose wool products. 

Oxide and nonoxide refractory fibers have become essential materials for use in modem high temperature industrial processes and advanced commercial appHcations. Future process improvements, cost reductions, and performance enhancements are expected to expand the uses and markets for these specialized fibrous materials. 

Other Inks. The alkan olamine titanates, such as TYZOR TE, when mixed with a coloring agent used to print fibrous materials such as cotton, wool, or silk, promote adhesion of the dye molecule to the fiber, thus minimizing bleeding of the printed design (511). 

Fig. 3. Relationship of moisture content and relative humidity to specific resistance of polymeric, fibrous materials.

The replacement of asbestos fibers by other fibrous materials has raised similar health issues in relation to substitute materials. However, since lung cancer has a latency period of approximately 25 years, and since the fiber exposure levels in contemporary industries is far lower than those which prevailed half a century ago, the epidemiological data on most substitutes is insufficient. A possible exception is slag fibers for which several studies on worker populations are available over extended periods (44) some results show a substantial increase in lung cancer occurrence. Consequentiy, the toxicity of asbestos substitute fibers remains a subject of active investigation. 

A stronger separator is one made of sausage casiag material (ESC), a regenerated cellulose similar to cellophane but including some fibrous material. ESC is usually extmded ia tubes and electrodes are iaserted iato each ead of the tube. The tube is folded to form the so-called U wrap. 

Expression Dewaterings of Fibrous Materials. Fibrous materials are frequently dewatered in belt-filter, screw, disk, and roU presses and in batch pot and cage presses. Table 1 Hsts appHcations of screw, roU, and pot presses. Screw and high pressure belt presses are continuous and have replaced batch pot and cage presses in most appHcations. Traditionally, however, batch presses have been used for squee2ing cocoa butter from cocoa beans, which require pressures up to 41 MPa (6000 psi) (39). A description of many types of batch presses is included in Reference 40. 

Moderate and High Temperature [over 2°C (36°F)] Cellular or fibrous materials are normaUy used. See Fig. 11-68 for nominal... 

The turbo-tray dryer can handle materials from thick slurries [1 million (N s)/m (100,000 cP) and over] to fine powders. It is not suitable for fibrous materials which mat or for doughy or tacky materials. Thin slurries can often be handled by recycle of dry product. Filter-press cakes are granulated before feeding. Thixotropic materials are red directly from a rotary filter by scoring the cake as it leaves the drum. Pastes can be extruded onto the top shelf and subjected to a hot blast of air to make them firm and free-ffowing after one revolution. 

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