Studies in Wool Yellowing

Abstract

When wool which has been yellowed by irradiation with a fluorescent sunlamp is bleached with hydrogen peroxide, its susceptibility to subsequent photochemical yellow ing is increased. In addition, its strength is diminished and three successive irradiations and peroxide bleachings reduce the tensile strength to a quarter of its original value. Bleaching with peroxide followed by hydrosulfite causes losses of strength and chemical changes similar to those produced by peroxide alone. On the other hand, susceptibility to yellowing by heating dry or in pH 8 buffer is not increased by previous heating and peroxide bleaching nor is there any appreciable loss in strength. Saturation of the peroxide solution with sodium chloride reduces its bleaching action but has little effect on the fall in tensile strength during repeated alternate uv yellowing and bleaching. Impregnation of wool with thiourea and formaldehyde to retard uv yellowing confers some protection against loss in strength but also diminishes the bleaching effect of peroxide. The concentration of thiol plus disulfide groups is progressively lowered by the successive bleachings, regardless of the method used for yellowing. The concentration of "apparent thiol" groups is increased sharply by each uv treatment, and to a small extent by dry heating, but not by heating in pH 8 buffer.