87—THE EFFECT OF HEATING WOOL CONTAINING ALKALI

Abstract

The yellow discoloration produced by drying wool containing alkali at elevated temperatures has been shown to be dependent on the the time and temperature of drying and the presence of strong alkali. The presence of mild alkali, such as sodium carbonate, in the wool in amounts likely to occur in industrial processing was found to produce no yellowing additional to that produced by drying wool free of alkali under the same drying conditions. The discoloration was shown to be sensitive to pH changes, being partly discharged by acid. It faded quite rapidly on standing in air and could be readily bleached with a mild oxidative treatment. Attempts to minimize the yellowing by the addition of oxidizing or reducing agents to the alkali, or by chemical modification of the wool, have proved unsuccessful. Preliminary investigations into the mechanism of wool yellowing suggest that, under mild conditions, the discoloration results from cystine breakdown, but, under conditions which produce more intensive discoloration, other amino-acid residues such as tyrosine may also contribute.