Fiber length, pulp

Fibrillated Fibers. Instead of extmding cellulose acetate into a continuous fiber, discrete, pulp-like agglomerates of fine, individual fibrils, called fibrets or fibrids, can be produced by rapid precipitation with an attenuating coagulation fluid. The individual fibers have diameters of 0.5 to 5.0 ]lni and lengths of 20 to 200 )Jm (Fig. 10). The surface area of the fibrillated fibers are about 20 m /g, about 60—80 times that of standard textile fibers. These materials are very hydrophilic an 85% moisture content has the appearance of a dry soHd (72). One appHcation is in a paper stmcture where their fine fiber size and branched stmcture allows mechanical entrapment of small particles. The fibers can also be loaded with particles to enhance some desired performance such as enhanced opacity for papers. When filled with metal particles it was suggested they be used as a radar screen in aerial warfare (73). 

The long leaf fibers contribute strength to the leaves of certain nonwoody, monocotyledonous plants. They extend longitudinally the hiU length of the leaf and are buried in tissues of a parenchymatous nature. The fibers found nearest the leaf surface are the strongest. The fibers are separated from the pulp tissue by scraping because there is Htde bonding between fiber and pulp this operation is called decortication. Leaf fiber strands are also multiceUed in stmcture. 

Practically any natural plant can be utilized as a source of papermaking fibers, but there is considerable variation in the quality of paper realized from alternate plant sources. Factors such as fiber length, content of non-fibrous components such as parenchyma tissue, contaminants such as silica, etc. greatly influence the quality of the final sheet. Procurement of sufficient quantities of the raw material and seasonal fluctuations in supply can also pose problems. It is also necessary to use alternate pulping equipment to handle the plant materials since the material tends to mat down in the digester making it difficult to get uniform circulation of the cooking chemicals. 

In preparing compositions use is made of organic and mineral fillers. The most important organic filler is bleached wood pulp. The pulp fiber length depends on the type of wood thus, pulp produced from beech has 1 mm-long fibers, whilst that obtained from conifers -3 mm-long fibers. 

Fi bGI" PropsrtiGS. Most commercially available fibers are now available in a variety of forms, inclnding continnons filament yams of different deniers, staple products of various lengths, pulp, paper products, and some nonwoven fabrics. Physical and chemical properties have most often been determined for the yam products, with the understanding that these properties would usually apply to the other forms as well. While there is some variation in properties among the various deniers, it is usually not large. Representative properties of the major types of commercial yam are shown in Tables 4 and 5. These properties are taken from the catalogs published by each manufactin-er (53,54). Test methods are described in Table 6. 

For pulp manufacture, the PPTA yarn is chopped into short fibers, which are then suspended in water. The suspension passes through a refiner mill similar to the kind used in paper manufacture from wood pulp. In the mill aramid fibers are chopped even further, whereby the cutting action of the rotors gives rise to a random distribution of fiber length. At the same time, some crystalline domains partially detach themselves from the main... 

Figure 3. Tensile Strength of Polypropylene-High Legnin Thermomechanical Pulp Composites vs. Filler Concentrations for Various Fiber Lengths.

Thermomechanical Pulp Composites vs. Filler Concentrations for Various Fiber Lengths. 

Fiber length is an important property of the pulp. The strength properties of the pulp are generally enhanced by longer fibers, up... 

The latest results of a controlled crystallization of macromolecules are the polymer fibrids which are a completely new modification of synthetic polymers as far as the micro- and macro-structure is concerned. They exist of small fibers having a length of up to some millimeters, which are highly oriented, and which have a macro-morphology similar to that of cellulose pulp. 

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