42—THE YELLOWING OF WOOL BY HEAT AND ALKALI

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Abstract
An investigation into the nature of the chemical changes occurring when wool containing alkali is heated has indicated that the amino acids cystine, tryptophan, threonine, arginine, and lysine are modified and that some main-chain breakdown also occurs. Under neutral conditions, modification is mainly restricted to tryptophan and the free amino groups of lysine. By relating the extent of yellowing to the corresponding amino-acid breakdown of normal and chemically modified wools, it has been shown that the mechanisms of alkali-yellowing and heat-yellowing are quite different. Under moist alkaline conditions, there appears to be a correlation between cystine breakdown and yellowing. On the other hand, yellowing by heat in the absence of alkali appears to involve interaction between amino and carboxyl groups, although tryptophan may contribute to a limited extent.

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