Chapter 2 - Wool structure and morphology

Abstract

This chapter explores structure and morphology of wool fiber in an attempt to explain characteristic mechanical and chemical properties of the fiber. In the introduction section, generic description of wool as hair of domesticated sheep is discussed. Composite nature of wool fiber viewed as fibril-reinforced matrix, where both fibril and matrix are made of interconnected network of polypeptide chains is introduced. α-keratin, Keratin Intermediate Filament (KIF), and Keratin Associated Protein (KAP) in the structure of wool fiber have been discussed. General chemical composition, amino acid composition, classification of amino acid present in wool fiber in respect of it being acidic, basic hydroxyl containing, sulfur containing and having no reactive group in the side chain, is discussed with the presentation of their respective structures. Amino acid of wool fiber in respect of difference in sulfur content and their molecular mass is taken into consideration in explaining composition of wool. Structure of wool grease and suint are detailed keeping scope of assessment of interfacial adhesion in unscoured wool–polymer composites. Types of secondary bonds or force of attraction present between polypeptide chains of wool fiber such as salt bridge, disulfide bond, isopeptide bond, hydrogen bond, and hydrophobic–hydrophobic interaction and susceptibility of such bonds to different common agents are also explained. Morphology of wool fiber with its different components is also illustrated and introduced. Cuticle and its' sublayers with their dimension, distribution chemistry, and susceptibility have been discussed in brief. Directional interfiber friction typical of wool fiber, arising out of flattened cells of cuticle is also explained in detail. Different types of cortical cells, significance of ortho- and paracortex, and presence of marco- and microfibrils are explained focusing on their difference in relative presence of a keratin, KIF, and KAP. Finally, stress–strain relations of wool fiber are attempted to be explained following two-phase fibril–matrix model proposed. A proposed three-component model is also explained in characterizing wool fiber stiffness.