Phototendering of wool sensitized by naturally occurring polyphenolic dyes

A number of naturally occurring polyphenolics have been used since antiquity to dye wool. These colourants, originally extracted from plants and insects, can be fixed to wool fibres by a metal ion mordant with the free carboxylic acid and sulphydryl groups present in wool protein providing the necessary metal ion binding sites. Wool undergoes a variety of chemical reactions induced by exposure to UV radiation which eventually manifest themselves as changes in the tensile strength and elasticity of the fibre (phototendering). It is expected that UV-absorbing dyes applied to wool fibres provide some photoprotection to the fibres by partially screening them from this damaging radiation. However, it was found that when mordanted by some metal ions, the natural polyphenolic dyes madder, alizarin and weld which contains the flavonoid, luteolin, exacerbate phototendering compared with undyed wool or fibres which had been treated with the mordant metal ions alone. Several metal ions used as mordants since antiquity such as ferric, cupric, stannic and aluminium have different effects on the rates of this phototendering of dyed wool fabric. (C) 2004 Elsevier B.V. All rights reserved.