Keratin fibres

Maxwell, J.M. and Huson, M.G., Scanning probe microscopy examination of the surface properties of keratin fibres, Micron, 36, 127-136, 2005. 

Allen, A. K., Ellis, J., and Rivett, D. E. (1991). The presence of glycoproteins in the cell membrane complex of a variety of keratin fibres. Biochim. Biophys. Acta 1074, 331-333. 

Other molecules, though, are more complex. The classical experiments were made with keratin. The keratin fibre can, when... 

Protein fibres are grouped into animal fibres (wool and other animal hairs, known also as a-keratin fibres) and insect fibres (silk, a fibroin fibre). Both... 

The amino acid amounts difler in a-keratin fibres from silk, as revealed by data in Table 9.6.2. 

The peptide arrangement in protein fibre has been investigated since the first half of the twentieth century. Astbury used X-rays to demonstrate the nature of a crystalline phase in hair. The X-ray dilfraction pattern of animal hairs shows a meridian reflection at 0.51 mn and an equatorial reflection at 0.98 nm. Interpreting these results Pauling et al. proposed the a-helix structure to give account of the secondary structure of the keratin fibre, shown in Figure 9.6.5. 

Thus, the a-keratin fibre is the best example of a natural composite system, having a complex dual structure at all levels. 

Keratin fibres are available almost everywhere in the world. Wool, produced by sheep, is by far the most widely used keratin fibre, while shatoosh produces the most expensive one and is found only on the high peaks of Himalaya. 

Among all keratin fibre producers, the sheep is the most important one. Economically the sheep is a fibre factory without wastes. The by-products of the factory are defined from the point of view of the down processing industry. For example, the textile industry regards milk and meat (lamb) as secondary products. 

Jurdana LE, Ghiggino KP, Leaver IH, and Cole-Clarke P (1995) Application of FT-IR step-scan photoacoustic phase modulation methods to keratin fibres. Applied Spectroscopy 49 361-366. 

The section ends with some comments on fracture of biological fibres. These fibres are characterised by a hierarchical structural design with length scales ranging from molecular to macroscopic. Clearly, detailed quantitative models for prediction of tensile strength of biological fibres are far from being available. However, some trends in connection with cellulose and keratin fibres are briefly discussed. 

Wool, hair and other animal fibres have a hierarchical microstruclure and no reliable model has been developed for prediction of the failure stress of lhe.se fibres which encompasses all the relevant length scales. Three models are available to explain the tensile properties of a-keratin fibres all deal with a system of parallel microfibrils embedded in a proteinaceous matrix at a scale of 10 nm. In 1959, Feughelman laid the foundations of stmctural interpretation of the stress-strain curve with his two-phase model of microfibrils imbedded in a matrix, a model that was improved in 1994 (Feughelman, 1994). In the same year, Wortmann and Zahn (1994) proposed another version of the microfibril model. The third model, the Chapman and Hearle model (Hearle, 1967 Chapman, 1969) is based on the mechanics of stress transfer in a composite system consisting of microfibrils, which undergo an a p transition, in parallel with an elastomeric amorphous matrix. The Wortmann and Zahn model does not explicitly mention breakage of fibres, but it is implicit that this must be triggered... 

Chapman, B.M. (1969) A mechanical model for wool and other keratin fibres. Textile Re.i. J 39 1102-1109. 

Feughelman, M. (1959) Two-phase structure for keratin fibres. Textile Res. J., 29 223-228. 

Barone, J.R. and Schmidt, W.F. 2005. Polyethylene reinforced with keratin fibres obtained from chicken feathers. Compos. Sci. Technol. 65 173-181. 

D. M. Lewis and J. A. Rippon (ed.). The Coloration of Wool and other Keratin Fibres, John Wiley Sons Ltd, Chichester, 2013, in... 

Aldehyde-releasing agents, particularly those which release formaldehyde, find application in a number of processes as preservatives, such as in cutting-oil emulsions and latexes [325]. Formaldehyde may be applied to natural keratin fibres in the leather and textile industry to prevent problems of anthrax contamination [341], in paints as preservatives [342] and in the construction industry as toxic washes to prevent microbial growth on large surface areas [343] or as additives in concrete itself [344]. Formaldehyde has long been used as a preservative for natural history specimens in, for example, museums, to prevent biodeterioration and maintain the structure of organs and tissues [345]. 

Vacuolated cells may also be present along the axis of coarser a-keratin fibres, forming the medulla. These cells generally constitute only a small percentage of the mass of hair and are believed to contribute negligibly to the mechanical properties of human hair fibres. Physically, the medulla forms the empty space of the fibre [4, 7],... 

Like all polymeric structures, keratin fibres consist of long, tightly bound molecular chains held together in many different ways from covalent bonds to weaker interactions such as hydrogen bonds, Coloumbic interactions, van der Walls interactions and, when water is present, hydrophobic bonds. Hair reactivity is complex and depends not only on the presence of reactive groups in the fibre, but also on their availability. The latter is significantly affected by fibre morphology and molecular structure [2]. Hair is mostly proteinaceous in nature, while structural hpids and other materials represent only a minor fraction of its constituents. 

Feughelman M (1997) Mechanical properties and structure of alpha-keratin fibres. UNSW Press, Sidney... 

Pille L, Church JS, Gilbert RG (1998) Adsorption of amino-functional polymer particles onto keratin fibres. J Colloid Interface Sci 198(2) 368-377... 

Keratins are products of epithelial cells. They occur in the outer skin layer (epidermis), and in some skin structures (fur, horns and hooves). The main group are the so-called a-keratins, based on a right-handed polypeptide with an a-helical structure and molecular weight of 10-50 kDa, stabilised by disulfide bridges and hydrogen bonds. Three polypeptides form left-handed helices called protofibrils and 11 protofibrils (two inside and nine outside) create microfibrils. Several hundred microfibrils create macrofibrils that finally form the keratin fibre (e.g. hairs and wool fibres). 

Figure 7. Cross-section of a Merino wool fiber showing the structure at progressive magnifications (Produced by 77. Roe from a drawing by Dr. RDB Fraser, in Freughelman, M, Mechanical Properties and Structure of Alpha-keratin Fibres. University of South Wales Press, Sydney, Australia, 1997).

Speakman, J.B. In Fibre Science, Chapter 16, Survey of the Chemistry of Keratin Fibres, Preston, J.M., Ed. The Textile Institute Manchester, 1953, pp. 331-367. 

Zahn, H. In Occassional Publication, The Macrofibril of Keratin Fibres, European Fine Fibre Network, No.4,1996, pp. 3-14. 

Hong, C. K. and Wool, R. P. (2005) Development of a bio-based composite material from soybean oil and keratin fibres. J. Appl. Polym. ScL, 95, 1524-1538. 

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