Studies in Wool Yellowing Part XIX: Improved Stability of Fluorescent-Brightened Fabrics to Simulated Sunlight

Abstract

The effects of modifications of thiourea-formaldehyde treatment of bleached and unbleached wool fabrics have been studied with regard to the protection against uv radiation damage. Pretreatment of bleached fabric with stannous chloride improves the shrink resistance of the wool but causes some yellowing. Pretreatment with aluminum sulfate does not affect the color of the wool and improves the setting and insectproofing properties. Aluminum sulfate also acts as a mordant for the fluorescent brightening agent. A comparison of reducing agents used during the application of brightening agent shows that sodium formaldehyde sulfoxylate is slightly superior to zinc formalde hyde sulfoxylate when wet wool is exposed to uv radiation. The concentration of formaldehyde has an important influence on the protection conferred by thiourea- formaldehyde during short reaction times. Application of high concentrations of fluorescent brightener, followed by thiourea-formaldehyde, improves both the initial appearance and the light fastness of the fabric. The additional fluorescence masks small changes in shade of the underlying fabric, as revealed by yellowness index measurements.