Cortex, wool

The cortex comprises the main bulk and determines many mechanical properties of wool fibers (see Fig. 1). Cortical cells are long, polyhedral, and... 

Wool fibers have a very complex morphological stmcture. They can be considered as biological composite materials, in which the various regions are both chemically and physically different (87). Fine wool fibers contain two types of cell those of the internal cortex and those of the external cuticle. 

Cortexes, in wool fibers, 11 173 Cortisone, production of, 11 10 Corundum, 1 1 2 345t color, 7 328... 

The hair shaft (Figure 6.1) comprises three main structures (1) the outer cuticle responsible for the main optical and frictional properties of the fiber (2) the cortex, responsible for the bulk fiber mechanical properties such as strength and flexibility and (3) the porous medulla, which is more prominent in gray hair, but otherwise may or may not be present. Cuticle thickness varies markedly between species. Though much of our understanding of hair structural biology is derived from the study of wool, this homologous... 

External hair of animals, generally called wool, was spun into yam and woven into fabrics. Like silk, wool is essentially protein it is composed of various amino acids, a majority of which are keratin. (Unfortunately, the keratin contains sulfur, which attracts certain insects that thrive on wool and contribute to the scarcity of historic woolen fabrics.) The outstanding morphological characteristic of wool fiber is its external scales that overlap in one direction toward the tip of the fiber. The scales can be chemically, mechanically, and temporally damaged and can disappear as the wool deteriorates. Outside of the scales is a membranous layer, the epicuticle inside them is the bulk of the wool fiber, the cortex, which consists of millions of double-pointed, needle-like cells neatly laid... 

The amount of protein extracted from wool or hair with thioglycolate at pH 10 can be increased by pretreatment with concentrated sulfuric acid (Lustig and Kondritzer, 1945). Some fractionation of the protein extracted from the cortex was achieved by Lustig et al. (1945). 

It has been shown by De Deurwaerder et al. (1964) that a protein fraction rich in glycine, tyrosine, tryptophan, and phenylalanine can be extracted from wool with a solntion of tris(diethylaminomethyl)phosphine in formamide. Examination with the electron microscope showed that this material was derived mainly from the membrane complex between the cuticular cells the microfibrillar texture of the cortex appeared to be intact. 

The histological structure of wool fibre comprises consisting three layers the scaly covering layer (cuticle), the fibrous fibrillar layer (cortex) and medullary layer (medulla). Fig. 1 - 5 shows the diagarm of wool fibre showing fibre morphology... 

An important component of cuticle is 18 - methyl - eicosanoic acid [40]. Fatty acid is bound to a protein matrix, forming a layer in the epicuticle [41,42], and this layer is referred to as F - layer [43]. The F - layer can be removed by treatment with alcoholic alkaline chlorine solution in order to enhance wettability. The cuticle and epicuticle control the rate of diffusion of dyes and other molecules onto the fibre [44]. The cortex, however, controls the bulk properties of wool and has a bilateral structure composed of two types of cells referred to as ortho and para [45,46]. The cortical cells of both are enclosed by membranes of at least three distinct layers within which the microfibrils fit. Cells of intermediate appearance and reactivity designated meso - cortical have also been reported [47]. Cortical cells on the ortho side are denti-cuticle and thin, those on the para side are polygonal and thick [47]. Fig. 1-7 illustrates the bilateral structure which is responsible for the crimp of the... 

The natural colour of animal fibre is closely related to the character of environment in which the animal lives [19]. Wool lots completely free of dark fibres do not exist [20]. In animal (and human) hair two kinds of pigments occur, namely eumelanin (responsible for black, dark brown and grey colours and commonly referred to as melanin) and pheomelanin (present in yellow, reddish-brown and red hair). Both are thought to be formed by different mechanisms and chemically differed [21]. Eumelanin is formed by enzymatic (tyrosinase) oxidation of tyrosine and polymerisation of several oxidation product [22]. Pheomelanin occurs in form of discrete grannules. Melanin grannules can occur in the cortex or in the cuticle. 

The two major morphological parts in the structure of wool are cuticle and cortex. The epi-cuticle of wool fibres surrounds each cuticle, it consists of approximately one-quarter fatty acid and three-quarters protein by mass. The hydrophobic epiCLiticle acts as a barrier to dyes which enter the wool fibre between cuticle cells through the highly cross-linked cell membrane complex (CMC). Enzyme from the liquor can diffuse into the interior of the fibre and hydrolyse parts of the endocuticle and proteins in the cell membrane complex, completely damaging the fibre if not controlled. In contrast, the catalytic action of enzyme on cotton is confined to the surface and the amorphous region only. 

Animal fibers are made from proteins and the long molecules are built from some 20 or so different types of amino acid molecule. The proportion and arrangement of these different units determine the structure of the protein molecule and the nature of the protein itself. Wool cells come in two different types the para cortex and the ortho cortex, which lie on opposite sides of the fiber and grow at slightly different rates. This causes a three-dimensional corkscrew pattern of coiled springs, giving wool high elasticity and a memory that allows the fibers to recover and resume normal dimensions. 

The wool fibre is complex in structure and composed essentially of three tissues, the cuticle, the cortex and the medulla. Each of these, however, is further subdivided by tissue differentiation. A purely diagrammatic illustration of the structure of a non-medullate fibre is shown in Fig. 5.5. 

In spite of its capacity to absorb moisture in the form of vapour, it is extremely diffieult to wet wool out in cold water. This is because the vapour ean penetrate to the cortex where it is retained, but in the liquid phase water must pass through the epithelial scales which offer considerable re-sistanee. In order to wet wool out the temperature of the water must be raised to 60°C (HOT) or, alternatively, a wetting agent must be used. The absorption of water vapour is accompanied by the liberation of considerable quantities of heat as illustrated by the following figures (AiEsaNDER AND Hudson, Wool, its Chemistry and Physics, 1st edn.), see Table 5.3. 

The Pauly test consists essentially of treating wool with diazotized sul-phanilic acid which couples with the tyrosine and histidine residues to form a brown-coloured product. These residues are found only in the cortex and, are absent from the cuticle so that the degree of staining is a measure of the breakdown of the scales. A modification of the Pauly test was recommended by Rimington J. Text. Inst., 1930, 21t, 237). The reagents required are ... 

These four structures, except for the medulla, are in all animal hairs. Figure 1-4 contains scanning electron micrographs of four mammalian species taken at different magnifications. These micrographs clearly demonstrate the cuticle scale structure of a cat whisker, a wool fiber, a human hair, and a horsetail hair. The cross sections of the horsetail hair also reveal the cortex and the porous multiple channels or units of the medulla characteristic of thick hairs, but generally absent from fine animal hairs. 

A portion of the undermembrane of Figure 1-21 is also epicuticle. The cystine-rich proteins of the cuticle belong to the group of proteins called keratin-associated proteins. Although structurally different, keratin-associated proteins are also found in the matrix of the cortex. See the section that discusses keratin-associated proteins in Chapter 2. For more details of the intercellular structures, see Figure 1-23. Thus, the cuticle of human hair is a laminar structure similar to the cuticle of wool liber, and the different layers of the cuticle have been described for merino wool [64] and for human hair [58, 65, 66, 67], Figures 1-23 and 1-24 illustrate the... 

Figure 1-29. Schematic of a wool fiber, illustrating orthocortex and paracortex regions of the cortex in relation to crimp.

Current evidence suggests that crimp frequency in wool is determined by the relative proportion of the three types of cortical cells, their location in the fiber cortex, and the protein composition of the matrix of the orthocortical cells [84]. 

For large metal complex dyes (>650Da), Feeder et al. [62] have demonstrated that intercellular diffusion of these materials occurs into wool fiber. Certain alcohols, such as butanols, are considered nonswelling solvents and have been shown by Jurdana and Leaver [63] not to penetrate into the cortex of wool but to penetrate readily into the cortex of human hair via the intercellular regions. 

Similar isoelectric points for hair and wool fiber are to be expected because chemical compositions of the cuticle are similar and because both fibers show similar dye-staining characteristics. Cuticle from both fibers stains more readily with cationic dyes than with anionic dyes [96], whereas the cortex stains readily to anionic dyes [121]. 

TEM studies of thin transverse fiber sections show that the cortical structure of cashmere is considerably different from that of fine wool [296,311,320]. Australian and Chinese cash-mere fibers display both bilateral symmetry and random cell arrangements, not only in cashmere fibers from different samples but also in fibers from the same fleece [296,311], whereas fine wool fiber exhibits bilateral asymmetry only. The variation in cortical structure among fibers from the same cashmere fleece suggests that different mechanisms may be involved in fiber formation. Cashmere cortex is composed predominantly of ortholike and mesolike cells, whereas fine wool is composed predominantly of ortho- and paracortical cells arranged bilaterally. Because of the variations observed, many transverse sections need to be examined before definitive statements can be made about the physical structure of fiber from a given cashmere sample. 

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