Protein Fibre Surface Modification

Many natural fibres, including wool, cashmere and silk, are protein-based materials; the dry weight of wool is almost entirely derived from proteins (Maclaren & Milligan 1981). As such, they possess an inherent structural and chemical heterogeneity not found in synthetic polymers. Although typically less heterogeneous than biological fibres, the rapidly emerging range of commercially available protein-based biomaterials also contain a wide range of functionality derived from their constituent primary and secondary protein structure. The response of fibres to processes such as dyeing and finishing treatments correlates directly to their structural and chemical properties, and this is particularly true for surface treatments. Due to its barrier function in the fibre, modification of the surface has a profound impact on processing and performance. Keratinous fibres such as wool and cashmere have an outer lipid layer which results in a hydrophobic surface. Recently a range of innovative and novel fibre surface technologies has been developed, many of which involve altering surface properties by the removal of the lipid layer, which exposes a proteinaceous surface with a variety of reactive chemical moieties. Treatments that can be covalently bound to fibre surface components, rather than simply physically applied to the surface, offer the potential for superior durability. The surface modification of proteinaceous fibres has a long history. These include plasma applications, which expose and generate functional groups on the protein surface, etching into the surface of the cuticle scales, to improve properties such as surface wettability, dyeability, shrink-resistance and felting-resistance. Chemical approaches utilised include ozone treatments, which cause oxidation of the surface and altered ionic balance, leading to a more plastic and reactive fibre surface and shrinkage control; chlorination, which improves sorption characteristics and reduces shrinkage; hydrogen peroxide treatment; and acid anhydride acetylation of silk and wool, which improves the textile response to dyeing, shrink resist, and setting treatments. Enzymatic treatments have been utilised to decuticulate the surface and improve properties such as shrink resistance. More recent developments include reaction of functional chemical agents or branched molecules to exposed reactive groups on the fibre surface, enabling the attachment of covalently-bound smart treatments, or the amplification of reactive groups for increased functionality. This chapter outlines developments in the area of targeted surface modification of proteinbased fibres and textiles, including summarising applications and future directions. It is not