Molecular structure of wool fibres

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 

Keratin is of amphoteric in nature and is composed of 16 to 18 different a -amino acids. The amino acid residues join together to give a polypeptide chain. There are two types of structure postulated for wool fibre one is folded form of keratin (a - form) [Fig. 1-8] and the other is helical or spiral structure (Fig. 1-9). 

When the fibre is stretched, the coil extends to give p- keratin and on releasing the keratin back into a-form [48]. The amino acid and sequence in wool varies with the variety of wool [49]. The average amino acid contents for major varieties of wool and silk are given in Table 1.8. R represents relatively large side chains which contain amino, carboxyl, sulphide groups and relatively 50% of the weight of wool 

R Amino acid Wool content (g/100 g fibre) Fibrion content (g/100 g fibre) 

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