Hard fibres

Zinc Chloride.—This material is recovered by systematic washing of hard fibre. The diluted liquor has a density of from 16 to 20°B6., and is concentrated to from GS to 72°B6. in a double-effect evaporator which has a capacity of from 1.3 to 1.8 gal. per square foot, with a steam pressure of from 5 to 20 lb. and a vacuum of 27... 

Greenville Textile Club, Greenville, S. C. Ray W. Bayne, president D. W. Stevenson, secretary. Hard Fibres Association, 425 West 25th St., New York, N. Y. Chester P. Smith, president R. S. 

Natural fibres can be subdivided into plant, animal, and mineral fibres. All plant fibres (cotton, jute, flax, hemp, etc.) are made of cellulose animal fibres are made of protein (wool, silk, hair). Based upon their origin, plant fibres are subdivided into bast and hard fibres. Bast fibres are derived fix)m the stems or stalks of plants hemp, jute, ramie, and flax, for example, belong to this category. Hard fibres, on the other hand, are derived from leaves, leaf sheaths, or fruit sisal and coconut belong to this category ... 

Leaf or hard fibres These fibres are most commonly used as reinforcing agents in polymers. They can be extracted for instance from sisal, henequen, abaca or pineapple. 

Nature in its abundance offers us a lot of material that can be called fibrous fibres are found in plant leaves, fraits, seed covers and stalk. Fibres from these plants can be considered to be totally renewable and biodegradable. Bast fibres are soft, woody fibres obtained from stems of dicotyledonous plants (flowering plants with net-veined leaves). Such fibres, usually characterized by fineness and flexibility, are also known as soft fibres, distinguishing them from the coarser, less flexible fibres of the leaf, or hard , fibre group. This chapter will discuss bast fibres from flax, hemp, jute, ramie, kenaf and abaca. 

Table 2.17 shows recent distribution of the global production of abaca, according to the Abaca Growers Corporation of Ecuador (CADE), whose production represents 42% of the national total the Philippines has never lost its predominant place in the global produchon of abaca. Abaca in Ecuador is processed with special equipment that separates the raw material and fibre in contrast, in the Philippines the process is shh performed manually, resulting in a lower yield and quality. The quality of the abaca plant in Ecuador is 12.5% (1.1% hard fibre and 11.4% soft fibre or bagasse). 

Hard fibres (also termed leaf and structural fibres) are larger and stiffer than bast fibres, hence the name. They grow throughout the leaves or stem of monocotyledonous plants and like the bast fibres they give rigidity to the plant and also transport water and plant food from one part of the plant to another. 

Sisal (Agave sisalana) is the most important species of hard fibre and is used for natural geotextiles as well as other industrial products. It is grown in Java, Africa and Haiti and accounts for about 1.5% of the world total natural fibre production. The leaves are harvested and subjected to a decortication process in which the epidermis and pulp are scraped from the fibre whilst simultaneously being washed. The resulting fibre mass is then dried and baled. 

Cellulosic fibres from vegetable sources other than cotton and wood are used in a variety of textile and industrial products. These fibres are mostly obtained either from the leaves of tropical plants or from the stems of reed-like plants. Leaf fibres are generally stiff ( hard fibres ) and are used mostly for cordage. Stem fibres (also known as bast fibres) are usually finer ( soft fibres ) and find use in textile applications. The cellulose content of these materials is usually in the range 70—90% (on dry weight). The more important commercial products and their principal usage are shown below. 

Leaf fibres are usually obtained from the leaves or leaf stalks of monocotyledonous plants. Leaf fibres are often known as hard fibres because they are less flexible and coarser than bast fibre. Sisal, abaca and henequen are most important fibres of this group. These are part of the plant s transportation system the cells are small and are bound together by pectins. They cannot be isolated by retting but are extracted by scraping pulp from the fibres by a knife, either manually or mechanically, in a technical process called decortication. 

The generic thermosets are the epoxies and the polyesters (both widely used as matrix materials for fibre-reinforced polymers) and the formaldehyde-based plastics (widely used for moulding and hard surfacing). Other formaldehyde plastics, which now replace bakelite, are ureaformaldehyde (used for electrical fittings) and melamine-formaldehyde (used for tableware). 

Compared with nylon 66 fibres, the polyurethane fibres (known as Perlon U) have a tensile strength at the higher end of the range quoted for nylon 66, they are less prone to discolouration in air, are more resistant to acid conditions and they have a lower moisture absorption. On the debit side they are less easy to dye, are hard, wiry and harsh to handle and have too low a softening point for many applications. They are currently of little importance but have found some use in bristles, filler cloths, sieves and a few other miscellaneous applications. 

One partieular form of thermoplastic polyurethane elastomers is the elastic fibre known as spandex fibre. Like the usual thermoplastic rubbers these materials consist of hard and soft segments but to qualify for the term spandex by the US Federal Trade Commission the polymer used should contain at least 85% of segmented polyurethane. The first commercial material of this type was introduced by Du Pont in 1958 (Lycra). Several other similar materials have since been introduced including Dorlastan (Bayer), Spanzelle (Courtaulds) and Vyrene (US Rubber). 

It has been shown that the anisotropy depends on the orientation of the diagonals of indentation relative to the axial direction 14). At least two well defined hardness values for draw ratios A. > 8 emerge. One value (maximum) can be derived from the indentation diagonal parallel to the fibre axis. The second one (minimum) is deduced from the diagonal perpendicular to it. The former value is, in fact, not a physical measure of hardness but responds to an instant elastic recovery of the fibrous network in the draw direction. The latter value defines the plastic component of the oriented material. 

Complete C-fibre inhibitions can be produced under normal conditions but opiates do not always produce a complete analgesia in some clinical situations, especially when the pain arises from nerve damage. Reasons for this are suspected to be excessive NMDA-mediated activity which is hard to inhibit and the mobilisation of cholecysto-kinin in the spinal cord which can act as a physiological antagonist of opiate actions. The idea that pre-emptive analgesia aids post-operative pain relief by preventing the pain-induced activation of these systems is becoming popular. 

In contrast to the Pt catalysts discussed above, Ni based catalysts (i.e., also when supported on ZrO usually form coke at such a rapid rate that most fixed bed reactors are completely blocked after a few minutes time on stream (see Fig. 8) [16], The coke formed with the Ni catalysts is filamentous. The Ni particle remaining at the tip of the filament hardly deactivates as the coke formed on its surface seems to be transported through the metal particle into the carbon fibre, but the drastic increase in volume causes reactor plugging and prevents use of the still active catalyst (see Fig. 8). The TEM photographs indicate that the carbon filaments have similar diameters to those of the Ni particles. 

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